rudist-bearing carbonate platforms of the Mediterranean Tethys and

Transcription

Late Cretaceous (Campanian–Maastrichtian)
rudist-bearing carbonate platforms
of the Mediterranean Tethys and
the Arabian Plate
Dissertation zur Erlangung des akademischen Grades eines
Doktors der Naturwissenschaften
an der Fakultät für Geowissenschaften der Ruhr-Universität Bochum
vorgelegt von Malte Schlüter
aus Unna
Bochum, Oktober 2008
Die vorliegende Arbeit wurde von der Fakultät für Geowissenschaften der Ruhr-Universität
Bochum als Dissertation zur Erlangung des Grades eines Doktors der Naturwissenschaften
(Dr. rer. nat.) anerkannt.
Erster Gutachter:
Prof. Dr. J. Mutterlose
Zweiter Gutachter:
Prof. Dr. T. Steuber
fachfremder Gutachter:
Prof. Dr. J. Schreuer
Tag der Disputation: 2. Dezember 2008
Erklärung
Hiermit erkläre ich, dass die vorliegende Dissertation in dieser oder ähnlicher Form bei keiner
anderen Fakultät oder Hochschule eingereicht wurde. Ich versichere, die Arbeit selbständig
angefertigt, sowie keine anderen als die angegebenen Hilfsmittel und Quellen verwendet zu
haben.
Bochum, Oktober 2008
Malte Schlüter
Table of contents
Table of contents
Abstract ................................................................................................................................ III
Kurzfassung........................................................................................................................... V
1. Introduction
1
1.1 Cretaceous carbonate platforms .............................................................................. 1
1.2 Purpose of the thesis................................................................................................ 5
1.3 Organisation of the thesis........................................................................................ 5
References ........................................................................................................................ 6
2. Chronostratigraphy of Campanian–Maastrichtian platform carbonates
and rudist associations of Salento (Apulia, Italy)
10
Abstract .......................................................................................................................... 10
2.1 Introduction ........................................................................................................... 10
2.2 The Apulian carbonate platform in Salento .......................................................... 12
2.3 Material and methods ............................................................................................ 14
2.3.1 Field methods ............................................................................................ 14
2.3.2 Laboratory methods................................................................................... 14
2.3.3 Description and biostratigraphy of localities studied................................ 15
2.3.4 Strontium-isotope stratigraphy.................................................................. 21
2.3.4.1 Elemental composition............................................................... 21
2.3.4.2 Sr ratio and derived ages ............................................................ 25
2.4 Taxonomy of large-sized, canaliculate recumbent rudists .................................... 26
2.5 Discussion ............................................................................................................. 29
2.6 Conclusions ........................................................................................................... 31
Acknowledgements ........................................................................................................ 31
Appendix. List of taxa mentioned in the text ................................................................. 31
References ...................................................................................................................... 34
3. Evolution of a Maastrichtian–Paleocene tropical shallow-water
carbonate platform (Qalhat, NE Oman)
39
Abstract .......................................................................................................................... 39
3.1 Introduction ........................................................................................................... 39
3.2 Regional geotectonic setting and previous studies................................................ 40
3.3.1 Field methods ............................................................................................ 42
3.3.2 Laboratory methods................................................................................... 44
3.4 Results ................................................................................................................... 44
3.4.1 Lithology and microfacies......................................................................... 44
3.4.2 Biostratigraphy .......................................................................................... 49
3.4.3 Strontium-isotope stratigraphy.................................................................. 52
3.4.4 Stable isotopes........................................................................................... 53
I
Table of contents
3.5
Discussion ............................................................................................................. 54
3.5.1 Completeness of the sedimentary record across the K/P boundary .......... 54
3.5.2 Environmental change across the K/P boundary....................................... 56
3.5.3 Sea-level change........................................................................................ 58
3.6 Conclusions ........................................................................................................... 58
References ...................................................................................................................... 59
4. Rudist-bearing carbonate platforms of the latest Cretaceous (Campanian–
Maastrichtian) – strontium-isotope stratigraphy and rudist provincialism
66
Abstract .......................................................................................................................... 66
4.1 Introduction ........................................................................................................... 67
4.2 Latest Cretaceous carbonate platforms ................................................................. 67
4.4 Regional pattern and stratigraphy of shallow-water carbonate platforms............. 70
4.5 Provincialism of rudists......................................................................................... 77
4.6 Global change and demise of rudist-bearing platforms ........................................ 81
4.7 Conclusions ........................................................................................................... 85
Appendix ........................................................................................................................ 85
References ...................................................................................................................... 88
5. Conclusions and perspectives
5.1
5.2
95
Conclusions ........................................................................................................... 95
Perspectives ........................................................................................................... 96
Acknowledgements .............................................................................................................. 98
Curriculum Vitae.................................................................................................................. 99
II
Abstract
Abstract
The history of the demise of Late Cretaceous rudist-bearing carbonate platforms is rather
imprecisely constrained, due to the low biostratigraphical resolution of shallow-water
sediments which is mainly based on long ranging taxa of benthic foraminifers and
calcareous algae. Therefore the precise chronology of the demise of the characteristic
rudist associations remains uncertain. The correlation of the rudist extinction patterns and
the decline of Late Cretaceous shallow-water carbonate platforms is still poorly
understood, as is the casual linkage of both trends. This lack of knowledge is closely linked
to the rarity of observations from sections which show a continuous sedimentary record
covering the Cretaceous–Paleogene boundary.
This thesis presents data from three different regions along the former Late Cretaceous
Tethys. The different outcrops are located in S Italy (Apulia, Salento peninsula), SE
Turkey (region of Malatya, Adıyaman and Hatay) and in NE Oman (Qalhat). Every single
region made their contribution to decipher the Campanian–Maastrichtian history of the
rudist associations and of the shallow-water carbonate platforms.
One of the major methods used during this thesis was strontium isotope stratigraphy
(SIS) which improves the precision of biostratigraphy and supplies numerical ages. By
using SIS it is therefore possible to calibrate the range of the characteristic rudist
associations to chronostratigraphy and to obtain a high resolution stratigraphical
framework. The SIS data thus improve the understanding of the timing and pattern of the
demise of the rudists, their accompanying biota and it consequently elucidates the
development of shallow-water carbonate platforms.
The Late Cretaceous rudist-bearing limestones of the Salento peninsula (S Italy) were
deposited on an isolated carbonate platform throughout the Santonian to latest
Maastrichtian. The limestone deposits are characterized by highly diverse rudist
associations and show an erosional unconformity at their top. The provincialism of the
Late Cretaceous rudists is highlighted here by the new rudist taxa related to the genera
Sabinia and Pseudosabinia.
The rudist associations from Turkey, which are characterized by species-rich localities,
can be divided into two different paleobiogeographic groups. Group one is of AfroArabian Plate origin while the other one is of European Plate origin. The
chronostratigraphical age of various rudist-bearing limestones has been revised from the
Maastrichtian to the mid-Campanian due to numerical ages yielded by SIS.
III
Abstract
The paleotropical shallow-marine section of Qalhat (NE Oman) shows a continuous
sedimentation throughout the Maastrichtian into the Danian / Selandian. The shallow-water
biota
change
from
typical
Late
Cretaceous
associations
of
rudists
and larger benthic foraminifers to an assemblage dominated by dasycladaleans, codiaceans,
and red algae. This change of the major carbonate producers documents the healthy
conditions for shallow-water organisms throughout the Maastrichtian–Danian / Selandian.
All three studied regions document that the rudist associations of the Tethys range into
the latest Maastrichtian, they are moderate to high divers with partly high abundances (S
Italy, SE Turkey). All of the three observed tropical carbonate platforms show a
Campanian–Maastrichtian limestone sedimentation which can be regarded as healthy, until
cut by erosion or sealed by complicated geotectonic history, respectively. The case study
of the Qalhat section (Oman) proves that some carbonate platforms had a high potential to
survive even beyond the Cretaceous–Paleogene boundary. The development of the Late
Cretaceous geotectonic conditions however finally caused the decline of the shallow-water
carbonate platforms and influenced therefore the evolution of the rudists.
The demise of the rudists has been caused by a casual chain of various factors. The loss
of shallow-water habitat is suggested to be the initial factor, followed by increasing
endemism of many taxa which finally results in the extinction of the rudist bivalves at the
Cretaceous–Paleogene boundary.
IV
Kurzfassung
Kurzfassung
Der Untergang der oberkretazischen Karbonatplattformen ist aufgrund der geringen
Auflösung der Biostratigraphie von Flachwasserkarbonaten, die sich größtenteils auf Taxa
mit langen Reichweiten bezieht, bislang nur wenig bekannt. Eine präzise Chronologie des
Niedergangs der charakteristischen Rudisten, die zu den heterodonten Muscheln gehören,
wurde daher bislang noch nicht erreicht. Auch ist immer noch unklar, ob ein kausaler
Zusammenhang zwischen dem Aussterben der Rudisten und dem Untergang der tropischen
Flachwasser-Karbonatplattformen besteht. Verstärkt wird diese Problematik durch einen
Mangel an untersuchten oberkretazischen Karbonatplattformen, die eine durchgehende
Sedimentation bis in das untere Paläogen aufweisen können.
Im Rahmen der Dissertation wurden drei Regionen entlang der ehemaligen Tethys
untersucht, die die rudistenführenden Karbonatabfolgen des Campan, Maastricht und
Paläogen erschließen. Die unterschiedlichen Lokalitäten befinden sich in Süditalien
(Apulien, Salento Halbinsel), im Südosten der Türkei (in den Regionen um Malatya,
Adıyaman und Hatay), sowie im Nordosten des Omans (Qalhat). Jede einzelne Region
liefert dabei einen wichtigen Beitrag um die Geschichte der Rudisten und der
Karbonatplattformen zu klären.
Die Strontium Isotopen Stratigraphie (SIS) ist eine Methode die im Rahmen der
Dissertation verwendet wurde und die wesentlich zur Klärung des Problems beigetragen
hat. Mit Hilfe der SIS kann, durch das Ableiten von numerischen Altern, die Präzision der
Biostratigraphie nachhaltig verbessert und präzisiert werden. Mit den jeweiligen Altern
können dann wiederum die Reichweiten charakteristischer Rudistenassoziationen kalibriert
und ein hochauflösendes startigraphisches Muster erstellt werden. Somit verhilft
letztendlich die SIS zu einer präzisen Charakterisierung von Entwicklung und Niedergang
der tropischen Karbonatplattformen in der hohen Oberkreide.
Die rudistenführenden Kalksteine von Apulien wurden auf einer isolierten
Karbonatplattform abgelagert und haben ein Santon bis Maastricht Alter. Die Karbonate
weisen eine hohe Rudisten Diversität auf, dessen Ende im oberen Maastricht durch einen
Auftauchhorizont gekennzeichnet ist. Der verstärkte Endemismus der oberkretazischen
Rudisten wird auf der Apulischen Karbonatplattform durch die Entdeckung einer neuen
Gattung, die eine enge Verwandtschaft zu den Gattungen Sabina und Pseudosabinia
aufweist, verdeutlicht.
V
Kurzfassung
Die türkischen Rudisten-Vergesellschaftungen sind durch eine zum Teil hohe
Abundanz gekennzeichnet und können in zwei verschiedene paläobiogeographische
Gruppen unterteilt werden. Die eine Gruppe ist der ehemaligen Afro-Arabischen Platte zu
zuordnen, während die andere Gruppe zur Europäischen Platte gezählt wird. Die
chronostratigraphischen
Altersangaben
der
verschiedenen
rudistenführenden
Kalksteinformationen beider Gruppen konnten mit Hilfe der SIS im Rahmen dieser Arbeit
korrigiert werden. Dadurch sind viele ehemalige Maastricht Lokalitäten nun dem mittleren
Campan zu zuordnen.
Die kontinuierliche Sedimentation des Oman-Profils wird von Flachwasser-Karbonaten
dominiert, die vom Maastricht bis ins Dan / Selandium reichen. Dabei wird die typische
oberkretazische Flachwasser-Flora und Fauna, die größtenteils aus Rudisten und
Großforaminiferen besteht von einer Vergesellschaft abgelöst die sich hauptsächlich aus
Grünalgen (Dasycladaceen, Codiaceen) und Rotalgen zusammensetzt. Der Wechsel der
Hauptkarbonatproduzenten bei gleichbleibender Karbonatproduktion ist dabei ein Hinweis
wie gut die Lebensbedingungen für Organismen der Flachwasserbereiche am Übergang
vom Mesozoikum zum Paläogen hin waren.
Die Untersuchungen der vorliegenden Arbeit zeigen, dass die vornehmlich hoch
diversen Rudisten Assoziationen der tropischen Tethys bis in das obere Maastricht reichen.
Die geotektonische Entwicklung der Oberkreide führte allerdings zur Reduzierung der
Flachwasser-Karbonatplattformen
und
beeinflusste
somit
auch
unweigerlich
die
Entwicklung der Rudisten. Der Niedergang der Rudisten ist letztendlich auf eine kausale
Verkettung verschiedener Faktoren zurück zuführen. Der Rückgang des bevorzugten
Lebensraum der Rudisten ist der initiale Faktor und das verstärkte endemische Auftreten
verschiedener Rudistengattungen führte schließlich zum endgültigen Aussterben an der
Kreide–Paläogen Grenze.
VI
Chapter 1 ◦ Introduction
1. Introduction
1.1 Cretaceous carbonate platforms
The Cretaceous period, is well known as an episode of global change and the
reorganization of its plate-tectonics and biology, but also because of the mass extinction at
the Cretaceous–Paleogene boundary (K/P; Skelton, 2003). The break-up of the two supercontinents Laurasia and Gondwana started at the beginning of the Jurassic and marks the
initial opening of the Atlantic Ocean both in the southern high-latitudes and in the northern
hemisphere. Consequently the stepwise increasing spreading-rate of the mid-Atlantic ocean
ridges causing a global sea-level rise (Miller et al., 2005). The shift continued well into the
Cretaceous, which can be viewed as a period of major transgression with the highest global
sea-level recorded throughout the Phanerozoic (Miller et al., 2005). Accordingly this
pattern led to an increasing growth of global shelf areas (Walker et al., 2002). This
development of increasing shallow-marine carbonate platforms was supported by the
emergence of numerous microcontinents in the Tethys (Skelton, 2003).
An early classification of carbonate platforms was made by Wilson (1975) followed by
Schlager (1981), Read (1982), Tucker and Wright (1990), Bosence (2005), and other
authors (refer to Schlager (2005) for more references). The carbonate platforms of the
tropical realm are constructed by various benthic organisms and can be mainly classified
by their geotectonic position (Fig. 1.1): a) as a part of the shelf with almost horizontal
bedding of the platform deposits and a topographical relief at the edge formed by reef or
reef-like bioconstructions (rimmed shelf), b) as a part of the shelf with a distinct
declination of a more or less steep slope towards the open sea (ramp) or c) in an isolated
position within the ocean e.g. top of an atoll (isolated platform; Tucker and Wright, 1990).
Figure 1.1: Basic classification of different types of carbonate platforms after Tucker and Wright (1990).
Vertical and horizontal sizes of the platforms are not scaled, but average estimated dimensions are indicated
in the figure.
1
The water depth of the shallow-marine platforms is predominantly less than 100m and the
living conditions of the benthic biota are therefore especially constrained by variations of
sea-level, sun light and nutrient input.
The main biota of the shallow-water benthic community, responsible for the
precipitation of the carbonate material can be mainly assigned to invertebrate organisms
(corals, foraminifers, mollusks) and calcareous algae (dasycladalean, codiaceans, red
algae). The tropical carbonate shelves of the earliest Cretaceous up to the latest Early
Cretaceous were dominated by the chlorozoan-chloralgal biota (Carannante et al., 1995)
with only minor mollusks and foraminifers. In the Late Cretaceous the rudists became
together with larger benthic foraminifers the dominant shallow-water carbonate producers
(Steuber, 2002). Those benthic communities are best described as foraminifer-mollusc
assemblages (‘foramol’; Carannante et al., 1995). The Late Cretaceous evolution of the
foramol assemblages is characterized by three phases of decline and subsequent recovery
with a final peak of rudist diversity in the Campanian - early Maastrichtian (Scott, 1995;
Steuber and Löser, 2000). The rudists are known as gregarious sediment-dwellers of
different shallow-water settings and although their biostromes can not be titled as original
reefs (Gili et al., 1995) they replaced the corals from the edge positions of rimmed shelves
and thrived also at restricted parts of the inner platforms or even at isolated carbonate
platforms (Skelton and Wright, 1987; Schlüter et al., 2008).
The rudists belong to the group of heterodont bivalves (Hippuritoidea) and are often
first noticed by the extraordinary structure and geometry of their shells. Early primitive
forms of the rudists appeared at the Late Jurassic and can be assigned to the family of the
Diceratidae, closely followed by forms of the Requiinidae (Kauffmann and Johnson,
1988). These early rudists were fixed to the substrate with the left valve (normal), while
most of the following taxa are attached with the right one (inverse). The first ‘inverse’
rudists appeared at the earliest Cretaceous (Berriasian: Caprotinidae, Monopleuridae) and
evolved throughout the complete Cretaceous period (Hauterive: Radiolitidae; Apt:
Caprinidae; Cenoman: Hippuritidae) until they got extinct at the K/P boundary
(Kauffmann and Johnson, 1988). Skelton and Gili (1991) defined three paleoecological
morphotypes of rudist bivalves which emphasize the relationship of the shell geometry and
their preferred habitat (Fig. 1.2). The early forms, i.e. Diceratidae and Requiinidae can be
mainly included in the morpho-group of the ‘clingers’. These morphotypes are attached
and encrusted on the surface of the solid substrate and preferred an environmental regime
with variable water turbulences ranging from calm to moderate
2
Figure 1.2: Three morphotypes of the rudist bivalves after Skelton and Gili (1991). The clingers are
encrusted to the ground, whereas the recumbents are maximizing their complete shells and are not permanent
fixed. The elevators are sticking in the sediment and show a distinct vertical growth. The sizes of the rudists
are variable and range from a few cm to several tenth of cm. Arrows indicating the growth directions.
(Steuber and Löser, 2000). The second morpho-group of the ‘recumbents’ (Fig. 1.2) are
represented by many taxa of the Caprinidae. They have often a sickle-shaped shell due to
the extension of their relative shell diameter (Gili et al., 1995) and lying directly on the
substrate surface in high-energy current regimes (Steuber and Löser, 2000). The third
morphotype, dominated by Hippuritidae and Radiolitidae, is assigned to the ‘elevators’
(Fig. 1.2). These forms had a dominant vertical shell growth and the elevated constructions
leads to the assumption that they could cope with high-accumulation rates of the
surrounding sediments (Steuber and Löser, 2000). Some taxa of the Radiolitidae show a
variable shell growth, which implies the potential attachment to different kinds of
substrate, and thus implies that they could live in different kinds of environment (Steuber
and Löser, 2002).
The rudist bivalves show not only a broad variability of the shape of their shells, but
also of the preferred mineralogy of the CaCO3 modifications used for their shell
constructions. The rudist shells consist of three different carbonate layers. The outer shell
layer is made of calcite (low-Mg calcite), whereas the inner ones consist of aragonite. The
various amount of the preferred shell material (outer calcite layer vs. inner aragonite
layers) is also assumed to reflect the change of the seawater chemistry, including the
Mg/Ca ratio (Steuber and Rauch, 2005). The domination of the ‘aragonite-favored’ rudists
range from the Hauterivian to the Cenomanian, while the ‘calcite forms’ dominate from the
Turonian to the end of the Maastrichtian (Steuber, 2002). Biotic low-Mg calcite is
identified as the most stable calcite variation with respect to diagenetic influence (Al-Aasm
and Veizer, 1986). Therefore the outer shell layer of the rudists is also the preferred
material for the strontium-isotope stratigraphy (SIS) of the Cretaceous time, approved for
many rudist-bearing carbonates along the Tethys (Steuber, 2001, 2003; Steuber et al.,
3
2005). The profound knowledge of the variations of the marine strontium isotope ratio
throughout the complete Phanerozoic (Veizer et al., 1999) and of the Late Cretaceous
(McArthur and Howarth, 2004) improves the potential of the SIS for global
chemostratigraphical correlations (McArthur et al., 2000). Especially on inner-platform
environments, the SIS can be used to improve the precision of the biostratigraphy by
deriving numerical ages.
The general trends of expanding shelf-areas were brought to an end by the regressive
trend of the Campanian and Maastrichtian stages. The features of this episode of global
relative sea-level fall can be observed at different shallow-water carbonate platforms along
the Tethys (Fig. 1.3), where elements of karstification or discontinuity surfaces are
common and their chronological appearance confirmed by SIS (Steuber et al., 2005;
Schlüter et al., 2008). In other regions of the tropical realm, including the Caribbean
(Mitchell, 2006), the shallow-water platforms are strongly influenced by the changing
environmental and geotectonical conditions. The environmental change affected the
benthic communities of the shallow-marine tropical regions, due to their sensitivity to sealevel changes and to other significant changes of the platform conditions.
Figure 1.3: Paleogeographical map of the latest Cretaceous with distribution of the tropical shallow-water
carbonate platforms.
The reaction of the rudist associations culminate in an increasing provincialism in different
regions of the Tethys (Philip, 1998). The demise of most of the characteristic benthic
groups of the tropical shallow-marine regions, including the extinction of the rudists at the
4
K/P boundary was finally caused by the geotectonical changes of the end of the Cretaceous
period.
1.2 Purpose of the present thesis
The present thesis concentrates basically on stratigraphical and paleontological issues and
gives an approach which is mainly based on geochemical, sedimentological and
taxonomical methods. To obtain a higher precision of the chronostratigraphy of the rudist
associations and to better understand the fate of shallow-marine carbonate platforms at the
end of the Cretaceous time the present thesis addresses the following objectives:
•
To examine and describe Late Cretaceous platform carbonates located at different
paleogeographical positions along the Mediterranean and Arabian parts of the
Tethys (Italy, SE Turkey and NE Oman).
•
To analyse characteristic rudist associations of the studied carbonate platforms with
respect to the timing and pattern of their paleogeographical distribution,
development and taxonomic composition.
•
To improve the stratigraphical framework of the tropical platform carbonates by
supplying numerical ages based on SIS.
•
To evaluate the degree of interlinking of rudist associations and shallow-marine
1.3 Organisation of the thesis
The thesis is subdivided into five chapters. Chapter one gives a brief introduction into the
main features characterising the Cretaceous shallow-marine carbonate platforms and their
major carbonate producers. Chapter two to four are three individual manuscripts published
in or ready to submit to international scientific journals. To obtain a uniform appearance of
style these chapters have been slightly adapted to the overall layout of the present thesis.
In Chapter 1 (Introduction) the background informations of the different objectives
mentioned throughout the thesis are summarized. Here I concentrate on the environment of
the Cretaceous carbonate platforms and describe broadly how the major shallow-water
biota developed throughout the Late Cretaceous environmental change.
Chapter 2 (“Chronostratigraphy of Campanian–Maastrichtian platform carbonates and
rudist associations of Salento (Apulia, Italy)”, by M. Schlüter, T. Steuber and M. Parente,
was
published
2008
in
Cretaceous
Research
29,
100-114;
doi:
10.1016/j.cretres.2007.04.005). This paper deals with intra-oceanic limestones and species5
rich rudist associations of the Apulian carbonate platform (SE Italy). Their
chronostratigraphical distribution ranges from the Turonian to the Late Maastrichtian
determined with the help of SIS and leads to new consolidated findings of the regional
stratigraphy of Apulia and to a new rudist taxa related to the genera Sabinia and
Pseudosabinia.
The main purpose of Chapter 3 (“Evolution of a Maastrichtian–Paleocene tropical
shallow-water carbonate platform (Qalhat, NE Oman)”, by M. Schlüter, T. Steuber, M.
Parente and J. Mutterlose, was published 2008 in Facies: doi: 10.1007/s10347-008-01508). It includes the observation, description and interpretation of a tropical rudist-bearing
carbonate platform existing continuously from the Late Maastrichtian to the early
Paleocene (Danian–Selandian). The obvious change of major carbonate producers from
larger foraminifers and rudist bivalves to calcareous algae reflects the global pattern of the
expanding new modern-type of shallow-water carbonate producers.
Chapter 4 (“Rudist-bearing carbonate platforms of the latest Cretaceous”, in
preparation), by M. Schlüter, T. Steuber, M. Parente and J. Mutterlose, is focused on the
global development and environmental change of rudist-bearing latest Cretaceous
carbonate platforms. A key point is the question of the timing and pattern of the Late
Cretaceous platform demise. Likewise the question whether the extinction of the rudists at
the end of the Cretaceous is casual related to the decreasing carbonate platforms or not will
be discussed.
The results and interpretations of the different sections of the present thesis are
discussed and summarized in Chapter 5 (Conclusions and perspectives). Within the last
chapter I will also give an outlook based on the results and conclusions of the thesis and
furthermore I will encourage the discussion of the issues of future studies.
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7
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Skelton, P.W., Gili, E., 1991. Palaeoecological classification of rudist morphotypes. In:
Sladić-Trifunović, M. (Ed.), 1st International Conference on Rudists. Serbian
Geological Society, Special Publication 2, 265-287.
Skelton, P.W., Wright, V.P., 1987. A Caribbean rudist bivalve in Oman: island-hopping
across the Pacific in the Late Cretaceous. Palaeontology 30, 505–529.
Steuber, T., 2001. Strontium isotope stratigraphy of Turonian-Campanian Gosau-type
rudist formatios in the Norhern Calcareous and Central Alps (Austria and
Germany). Cretaceous Research 22, 429–441.
Steuber, T., 2002. Plate tectonic control on the evolution of Cretaceous platform-carbonate
production. Geology 30, 259–262.
Steuber, T., 2003. Strontium isotope stratigraphy of Cretaceous hippuritid rudist bivalves:
rates of morphological change and heterochronic evolution. Palaeogeography,
Palaeoclimatology, Palaeoecology 200, 221–243.
Steuber, T., Korbar, T., Jelaska, V., Gušić, I., 2005. Strontium-isotope stratigraphy of
Upper Cretaceous platform carbonates of the island of Brać (Adriatic Sea,
Croatia): implications for global correlation of platform evolution and
biostratigraphy. Cretaceous Research 26, 741–756.
Steuber, T. ,Löser, H., 2000. Species richness and abundance patterns of Tethyan
Cretaceous rudist bivalves (Mollusca: Hippuritacea) in the central-eastern
Mediterranean and Middle East, analysed from a palaeontological database.
Steuber, T., Rauch, M., 2005. Evolution of the Mg/Ca ratio of Cretaceous seawater Implications from the composition of biological low-Mg calcite. Marine Geology
217, 199–213.
Tucker M.E., Wright V.P., 1990. Carbonate sedimentology. Blackwell Scientific
Publications, 482 pp.
Veizer, J., Ala, D., Azmy, K., Bruckschen, P., Buhl, D., Bruhn, F., Carden, G.A.F., Diener,
A., Ebneth, S., Godderis Y., Jasper, T., Korte, C., Pawellek, F., Podlaha O.G.,
Strauss, H., 1999.
87
Sr/86Sr, δ13C and δ18O evolution of Phanerozoic seawater.
Chemical Geology 161, 59–88.
8
Walker, L.J., Wilkinson, B.H., Ivany, L.C., 2002. Continental drift and Phanerozoic
carbonate accumulation in shallow-shelf and deep-marine settings. The Journal of
Geology 110, 75–87.
Wilson, J.L., 1975. Carbonate Facies in Geologic History. Springer, 471 pp.
9
Chapter 2 ◦ Chronostratigraphy of Campanian–Maastrichtian platform carbonates
2. Chronostratigraphy
of
Campanian–Maastrichtian
platform
carbonates and rudist associations of Salento (Apulia, Italy)
Malte Schlüter1, Thomas Steuber2, Mariano Parente3
1
Institut für Geologie, Mineralogie und Geophysik, Ruhr-Universität, 44801 Bochum, Germany
2
The Petroleum Institute, P.O. Box 2533, Abu Dhabi, UAE
3
Dipartimento di Scienze della Terra, Università Federico II, 80138 Napoli, Italy
(published in Cretaceous Research 29, 100–114; doi:10.1016/j.cretres.2007.04.005)
Abstract
Late Cretaceous platform carbonates from the Salento peninsula (south Italy) were studied
by strontium-isotope stratigraphy to improve their chronostratigraphy. Forty-three samples
from nine localities were collected and the numerical ages were derived from fifteen
geochemically well-preserved samples of rudist shells that were analyzed for
87
Sr/86Sr
values. Strontium isotope stratigraphy yielded new ages for the base of the Ciolo
Limestone. The oldest successions studied in Salento are 85.9 Ma (+/- 0.6) old and
assigned to the Melissano Limestone. The youngest Cretaceous limestones observed at the
Ciolo Limestone type locality (Ciolo cove) are 66.4 Ma (+/- 1.5), and the base of this
formation is older than 72.8 Ma (+/- 0.4). Karstic cavities observed at the Cava Cocumola
in the mid-Campanian S. Cesarea Limestone are tentatively interpreted to be linked to an
intra-Campanian emersion event which is related to a sea-level lowstand inferred also on
the island of Brač (Adriatic coast of Croatia) and in the Boreal realm at 75–77 Ma. A new
large recumbent rudist similar to Sabinia and Pseudosabinia is observed in the Ciolo and
S. Cesarea Limestone and appears to be characteristic for the Apulian platform carbonates.
Rudist associations from the S. Cesarea Limestone and the overlying Ciolo Limestone are
remarkably similar, although they range over a time interval of more than 12 My.
Keywords: Apulian carbonate platform; upper Cretaceous; strontium-isotope stratigraphy;
rudist bivalves
2.1 Introduction
Much progress has been made in deciphering the general evolutionary pattern of the
Cretaceous Tethyan intra-oceanic carbonate platforms (Vlahović et al., 2005). However, in
many regions the Late Cretaceous evolution of the rudist-dominated platforms still lacks a
precise stratigraphical framework so that the patterns and causes of the demise of these
10
characteristic marine ecosystems can only be evaluated tentatively (Steuber et al., 2007).
Stratigraphical ranges of rudist bivalves are not well constrained, and the Campanian–
Maastrichtian biostratigraphy of carbonate platforms relies largely on relatively longranging benthic foraminifera. These are abundant only in open platform facies so that the
stratigraphical subdivision of the volumetrically dominant, more restricted inner platform
deposits is particularly challenging. Due to these general problems with biostratigraphy, a
global correlation of Late Cretaceous Tethyan carbonate platforms with deposits from
higher latitudes or the deep sea has not yet been established. In the present contribution, we
address these problems by deriving numerical ages from the
87
Sr/86Sr values of well-
preserved biological calcite.
The strontium isotope ratio (87Sr/86Sr) of biological carbonates is increasingly used to
derive numerical ages when biostratigraphy is difficult to apply. Strontium in seawater has
a long residence time (4*106 years) with respect to the mixing time of the ocean (1*103
years) so that its distribution and isotopic composition in seawater is homogeneous at a
given time, but varies significantly with time (Veizer, 1989; McArthur, 1994). The
precipitation of biological carbonates involves no relevant fractionation of strontium
isotopes so that the Sr-isotope ratio of geochemically well-preserved fossils reflects the
isotopic composition of ancient seawater.
Increasing precision of the reconstructed variations of the
87
Sr/86Sr value of seawater
with time has significantly improved the potential for such correlations (McArthur et al.,
2001). An important advantage of the method is the potential for global
chronostratigraphical correlation, without the limits and problems related to faunal
provincialism or the absence of age-diagnostic fossils in many deposits (McArthur, 1994;
Veizer et al., 1997). The method has proven to be successful in Upper Cretaceous
carbonate-platform deposits, and particularly in deposits from restricted inner platforms
(Steuber, 2001, 2003a, b; Steuber et al., 2005). Some characteristics of the latest
Maastrichtian rudist associations of Salento have been discussed in a previous paper
(Steuber et al., 2007), and we contribute further details about the morphology and
taxonomy of canaliculate recumbent rudists, which are abundant in the late Campanian–
Maastrichtian limestones of Salento.
2.2 The Apulian carbonate platform in Salento
The Apulian platform is a characteristic example of Tethyan intra-oceanic carbonate
platforms without significant siliciclastic intercalations. Shallow water carbonate11
sedimentation started in the Late Triassic and persisted during the Mesozoic, interrupted by
relatively short periods of non-deposition, resulting in the accumulation of a pile of
carbonates up to 6000 m thick (Puglia 1 well , Ricchetti et al., 1992). The Cretaceous
deposits that belong to the former Apulian platform crop out in the SE of Italy (Fig. 2.1),
from the Gargano Peninsula along the Adriatic coast to S. Maria di Leuca in Salento.
These Upper Cretaceous deposits are characterized by prolific rudist associations (Cestari
and Sartorio, 1995). Locally, the Cretaceous succession is overlain by Cenozoic deposits,
characteristically
divided
by
a
sharp
sedimentary
unconformity.
Figure 2.1: Localities studied. 1, Cava Cocumola,
Cava Longo; 2, Vitigliano, Cava Soframa, Cava
Due; 3, Torre Tiggiano; 4, Ciolo Cove. Map of
Salento modified after Laviano (1996a).
The Upper Cretaceous is the only outcropping part of the Mesozoic of the Salento
Peninsula (Parente, 1994) and has been intensively studied in terms of stratigraphy
(Bosellini et al., 1999) and paleontology (Laviano, 1996a, b; Parente, 1997).
The first studies at the beginning of the 20th century focused on Miocene successions
lying on the top of Cretaceous deposits. Among others, Dainelli (1901, 1905) discussed
various sections of Paleogene and Cretaceous deposits. Luperto (1962) reported Late Creta
12
ceous and Paleogene foraminifera. At this time the main aspect of research in the Salento
region was the second edition of the Geological Map of Italy (Luperto, 1962; Largaiolli et
al., 1966; Nardin and Rossi, 1966; Martinis, 1967; Rossi, 1969). Bosellini and Russo
(1992) delineated four different units based on sequence stratigraphy. Their lowest unit is
the Cretaceous Melissano Limestone largely following the definition of Martinis (1967).
The three other units are of Paleogene age. For more details on the history of geological
studies in the Salento area see Parente (1994).
The most recent stratigraphical classification of the Upper Cretaceous (Fig. 2.2) is from
Bosellini and Parente (1994): accordingly, the Melissano Limestone is the lowermost unit
and underlies the mid Campanian–lower Maastrichtian S. Cesarea Limestone. The
uppermost unit of the Cretaceous successions is the Ciolo Limestone which has an
uppermost Maastrichtian age at its type locality (Steuber et al., 2007).
Figure 2.2: Numerical ages of localities studied and comparison with previous stratigraphical schemes.
Bosellini et al. (1999) provide a detailed geologic map of the eastern coastline of the
Salento peninsula. Numerous localities in Salento are known from the intensive studies of
their rudist-associations (Sladić-Trifunović and Campobasso, 1980; Cestari and Sirna,
1989; Laviano, 1996a). The stratigraphic ranges of the different rudist taxa are, however,
13
not well constrained, and a precise chronology of platform evolution at the end of the
Cretaceous is not yet established. Field studies of the Campanian–Maastrichtian rudist
associations also revealed that a conspicuous group of large-size canaliculate rudist occurs
abundantly and has not yet been described in detail.
2.3 Material and methods
2.3.1 Field methods
The exposed limestones were analyzed in the field with respect to their fossil content,
lithological features and rudist assemblages. The first visual screening for suitable material
for strontium-isotope stratigraphy (SIS) took place at the outcrop, focussing on apparently
unaltered, compact calcite shells of hippuritid and radiolitid rudists, or other bivalves.
Forty-three rock samples from nine different localities (Fig. 2.1) between Porto Badisco
and S. Maria de Leuca were analyzed for microfacies and age-diagnostic microfossils.
2.3.2 Laboratory methods
Selected shell material was analyzed for its chemical composition (Sr, Mn, Fe, and Mg
concentrations) and, after geochemical screening for diagenetic alteration, splits of suitable
samples were analyzed for their
87
Sr/86Sr values. The samples for the Sr-isotope
measurements and analysis of elemental concentration were drilled from polished surfaces
of rock samples or thin section counterparts with a tungsten drill bit. Each sample was
taken from a single, well-defined object, such as a rudist shell or other larger bioclast.
For the analysis of Sr, Mn, Fe, and Mg concentrations by inductively coupled plasmaatomic emission spectrometry (ICP-AES), about 1 mg of sample powder was dissolved in
1 ml 1.25 N HCl and then diluted with 5 ml of distilled water. Detection limits for the
prepared solutions were 6 ppm Sr, 16 ppm Mn, 32 ppm Fe, and 1 ppm Mg. Only samples
that had potentially preserved their original Cretaceous seawater Sr-isotope value, i.e.
samples with low Mn and Fe concentrations, and high Sr concentrations above 1000 ppm
(McArthur, 1994; Steuber, 2003b) were selected for dating by Sr-isotope analysis
(Tab. 2.1).
For Sr-isotope analysis, strontium was separated with standard ion-exchange methods
and loaded on a rhenium filament. The 87Sr/86Sr ratio was measured by thermal ionisation
mass-spectrometry (Finnigan MAT 262) in dynamic mode. Analytical precision (2 s.e.) of
87
Sr/86Sr values was +/- 8 x 10-6 as indicated by the repeated preparation and measurement
14
of standard material that was run together with the samples: USGS EN-1 (mean value =
0.709148; 2 s.e. = 8 x 10-6; n = 3).
2.3.3 Description and biostratigraphy of localities studied
The Cretaceous successions studied are exposed along the eastern part of Salento from
Otranto in the north to S. Maria di Leuca in the south. The localities visited are quarries
except for Torre Tiggiano and Ciolo, which are a road-cutting section and a natural coastal
outcrop respectively (Fig. 2.1). The Late Cretaceous carbonates are all overlain
unconformably by Paleogene sediments but the unconformity itself is only exposed in
Cava Soframa, Cava Due, Cava Vitigliano and at Ciolo.
Table 2.1: Results of elemental and strontium isotope analysis, and numerical ages derived from
87
Sr/86Sr
values
Locality
Sample
Sr [ppm]
Cava Soframa
CS - 1a
1424
CS - 2c
1631
CS - 3b
1527
CS - 4a
1662
Cava Due
CC - 1b
1683
Torre Tiggiano
TG - b
1650
Cava Longo
CL - 2a
1672
Cava Cocumula
CO - 16a
1391
CO - S2
1415
CO - S1
1233
CO - 4
1202
Cava Vitigliano
PO - 1/2
451
PO - 1/4
270
PO - 3/2
1544
Ciolo*
Cl - 1/1
1273
Cl - 1/2
1199
Cl - 1/3
1375
Cl - 1/M
237
87
Sr / 86Sr
Mg [ppm] Mn [ppm] Fe [ppm]
+/- 2s.e.(x 10-6 )
Age
1103
1142
1685
1149
bdl
bdl
bdl
bdl
113
214
122
116
0.707769
0.707761
0.707779
0.707767
6
7
7
6
1697
bdl
141
0.707786
7
68.1 (+/- 0.9)
1877
bdl
99
0.707419
7
85.9 (+/- 0.6)
1435
bdl
125
0.707685
6
72.8 (+/- 0.4)
1162
2067
1444
1736
bdl
bdl
bdl
bdl
93
bdl
bdl
bdl
0.707580
0.707569
0.707574
0.707575
7
7
7
14
77.2 (+/- 0.6)
77.4 (+/- 1.0)
2563
2562
2125
bdl
bdl
bdl
bdl
bdl
88
0.707633
0.707676
0.707591
7
7
7
--------------76.6 (+/- 0.6)
2768
2783
1767
3465
n.n.
n.n.
n.n.
n.n.
n.n.
n.n.
n.n.
n.n.
0.707813
0.707828
0.707794
0.707933
7
7
7
7
69.6 (+/-1.0)
69.1 (+/-1.3)
77.6 (+/- 0.8)
66.4 (+/- 1.5)
--------
Cava Soframa: samples CS - 1a, CS - 2c and CS - 3b, CS - 4a are from the same stratigraphic horizon.
Cava Cocumula: samples CO - S2 and CO - S1 are from the same stratigraphic horizon.
Ciolo: samples Cl - 1/1, Cl - 1/2 and Cl 1/3 are from the same stratigraphic horizon.
* values attained by T.Steuber et al. (2007)
Torre Tiggiano. The road-cutting section next to Torre Tiggiano (39°53’48N, 18°23’25E)
is located on the coast road from Castro to Ciolo at kilometre 36.9, but is not the same
locality described under that name by Parente (1994). The fine-grained, laminated
15
limestone with stromatactis structures formed in a restricted environment of the inner
platform. Rudists are relatively rare, and we identified Biradiolites angulosus. The
limestones cropping out next to Torre Tiggiano have been mapped as the Ciolo Lst.
(Bosellini et al., 1999), but B. angulosus indicates a Late Turonian–Coniacian age (Cestari
and Sartorio, 1995). Moreover, the inner platform peritidal facies of this outcrop recalls
more the Melissano Lst. rather than the Ciolo Lst., which is characterised by high-energy
shelf margin facies. We collected samples from compact rudist shells for geochemical
analysis.
Cava Cocumola. At Cava Cocumola (40°03’22N, 18°25’49E), bioclastic wackestones,
packstones and rudist-rich rudstones have been quarried. The only paper discussing Cava
Cocumola is from Laviano (1996a), who reported shelf margin deposits and presented a
section from the southern wall of the quarry. The eastern, western, and southern faces of
the quarry studied by us contain the same microfossils: Accordiella conica, Dicyclina
schlumbergeri,
Moncharmontia
apenninica,
Rotorbinella
scarsellai,
Stensioeina
surrentina, Decastronema sp., Cuneolina sp., Dictyopsella sp., Rotalia sp., Scandonea sp.,
and a common unidentified uniserial lituolid (Figs. 2.3–2.4). Thaumatoporella
parvovesiculifera was also recorded. According to biostratigraphy, the age of these
limestones cannot be constrained more precisely than Coniacian–Maastrichtian, because of
long ranges of the identified foraminifera.
At the eastern face of the quarry, very large rudists such as Favus antei, Pironaea
polystyla and Joufia reticulata are abundant. Shell fragments of the new taxon of
canaliculate recumbent rudist are up to one metre long and have a diameter of 20 cm.
The southern and western walls of the quarry expose a system of karstic cavities with a
fine-grained limestone infilling (Fig. 2.5). Cavities consist of three to four different
generations and their size varies from cm- to metre-scale. The main layer filling the bottom
of the cavity structure is pink-coloured laminated wackestone with calcispheres, overlain
by a thin layer of sparry calcite. Both layers are overlain by a greenish marlstone, only a
few tens of centimetres thick. The limestone that encloses the cavity structures was
deposited under shallow-water conditions, probably in the peritidal zone, as indicated by
stromatactis-type solution cavities. This complex cavity system structure is interpreted to
be related to a subaerial exposure surface above, which is not exposed in the quarry. When
the area was flooded again, these karstic cavities were filled with fine-grained open marine
sediments with calcispheres .
16
Quarry N of Vitigliano. This quarry has been frequently studied because of the superb
preservation of rudists (Cestari and Sirna, 1987; Guarnieri et al., 1990; Laviano and
Skelton, 1992; Laviano, 1996a, b). Swinburne (1990) provided Sr-isotope data from this
locality and determined a Late Campanian age. The microfauna consists of Raadshovenia
salentina, Murciella cuvillieri, Pseudochubbina bruni, Pseudosiderolites vidali and
Orbitoides media(?) (De Castro, 1990; Guarnieri et al., 1990).
Figure 2.3: a–e, Cava Longo (sample CL4); f–h, l, Cava Longo (sample CL3); i–k, Cava Cocumola (sample
COS1). a, ? Sulcoperculina sp.; b, Cymopolia decastroi; c, Jodotella koradae; d, Moncharmontia
apenninica; e, Dicyclina schlumbergeri; f, ? Dictyopsella sp. (or Antalyna sp. ?); g, Rotorbinella scarsellai;
h, rotaliid foraminifer (undetermined); i, lituolid foraminifer (undetermined); j, l, Accordiella conica; k,
Moncharmontia apenninica.
17
It is the type locality of Raadshovenia salentina and Pseudochubbina. Among the rudists,
the following species have been reported from the locality (revised after Cestari and Sirna,
1987): Biradiolites chaperi, Favus antei, Hippurites colliciatus, Joufia reticulata,
Mitrocaprina bulgarica, Pironaea slavonica, Plagioptychus sp., Pseudopolyconites
apuliensis, Radiolitella maestrichtiana, Radiolites angeiodes, Radiolites spongicola,
Sauvagesia sp. Similar deposits characterized by abundant articulated and large-sized
Joufia reticulata in life position (Fig. 2.6b) are exposed 200m N of the Vitigliano quarry.
Figure 2.4: a–e,Cava Longo (sample CL4); f–h, Cava Cocumola (sample COS1). a, Cymopolia barattoloi; b,
Lepidorbitoides sp.; c, Dictyoconus sp.; d, f, Accordiella conica; e, Cuneolina sp.; g, Stensioeina surrentina;
h, Cuneolina sp.
Here, abundant Pseudosabinia klinghardti are exposed in life position (see detailed
discussion below). This species is absent from the adjacent main quarry. Records of
18
Sabinia in the Vitigliano quarry (Cestari and Sirna, 1987; De Castro, 1990) refer to Favus
antei (Laviano and Skelton, 1992).
Cava Vitigliano South. At the bottom of the sequence that is exposed at the southern wall
of the Cava Vitigliano (40°02’03N, 18°24’36E), light-coloured mudstones contain
abundant planktonic foraminifera. This indicates a more distal depositional environment
than that of the typical Ciolo Lst., which is exposed near the top of the quarry.
Figure 2.5: Karstic cavities in Cava Cocumola. a, field photograph; b, interpretation.
19
It contains Pironaea sp. and the new taxon of Sabinia-like recumbent rudist. This locality
yielded no suitable material for SIS.
Cava Longo. The limestone quarried at the Cava Longo (40°03’02N, 18°25’41E) is fine
grained, rich in bioclastic material, with a high mouldic porosity. It changes upsection to a
coarser-grained texture similar to the Ciolo Lst. at its type locality. Among the
microfossils, Lepidorbitoides sp., Orbitoides apiculata, O. cf. media, Siderolites
calcitrapoides, ?Sulcorperculina sp., Dicyclina schlumbergi, Moncharmontia apenninica,
Dictyoconus sp., Cuneolina sp., Cymopolia barattoloi, C. decastroi, Jodotella koradae,
and Zittelina fluegeli have been identified (see Figs. 2.3–2.4, 2.7), indicating the
Maastrichtian. The macrofauna is dominated by rudists: ?Sabinia sp., Pironaea polystyla,
Joufia reticulata and the new taxon of canaliculate recumbent (Figs. 2.6, 2.8).
Cava Soframa. The thick succession of the Ciolo Lst. (up to 40m) at the Cava Soframa
(40°01’52N, 18°25’02) is truncated by an erosional unconformity followed by the Upper
Oligocene (Chattian) Castro Lst. with Lepidocyclina (Eulepidina) dilatata, L.
(Neophrolepidina) praemarginata and Neorotalia cf. viennoti. Among the rudists, we
identified in the Ciolo Lst. the new canaliculate taxon, Biradiolites cf. chaperi, Hippurites
cornucopiae, Pironaea polystyla, and Pseudopolyconites sp. Samples for geochemical
analysis were collected at the lower part of the quarry (Biradiolites cf. chaperi) and 4–5 m
below the Chattian unconformity.
Cava Due. At Cava Due (previously named Cava Chiatante, 40°01’25N, 18°25’23E), the
Ciolo Lst. is truncated by the Upper Oligocene (Chattian) Castro Lst., as indicated by
benthic foraminifera: Lepidocyclina (Nephrolepidina) praemarginata, Neorotalia cf.
viennoti, Amphistegina sp., Austotrillina cf. asmariensis and Miogypsina (Miogypsinides)
sp. Similar to the facies at the type locality, the Ciolo Lst. consists of thick-bedded
bioclastic limestone with abundant debris of rudists, echinoderms, larger foraminifera, and
corallinacean algae. Bioclasts are frequently rounded, and the grain size is on average
smaller than at the type locality. Due to reworking in a high-energy environment, rudists
are less well preserved, but Biradiolites cf. chaperi and the new canaliculate taxon have
been identified.
20
For SIS, the outer shell of compact-shelled radiolitids was collected, obtained from the
lowermost part of the SE wall of the quarry, i.e. from the lowest exposed level of the Ciolo
Lst.
Ciolo cove. The Ciolo cove (39°50’39N, 18°23’06E) is the type locality of the Ciolo Lst.
(Parente, 1994), which has several outcrops along the eastern coastline of the Salento
peninsula (Bosellini et al., 1999). Previous results from SIS indicated a latest Maastrichtian
age (Steuber et al., 2007), time-equivalent to similar deposits exposed on the Ionian Islands
(Greece). At the type locality, the Ciolo Lst. is about 50m thick and consists of coarsegrained bioclastic grainstone (Parente, 1994) with larger foraminifera, coral debris and
large-sized (up to one metre) rudist fragments. The top of the Ciolo Lst. is characterised by
a sharp unconformity overlain by Oligocene limestones (Parente, 1994).
The following foraminifera have been reported from Ciolo cove (Parente, 1994):
Orbitoides apiculata, Orbitoides gensacica, Lepidorbitoides socialis, Omphalocyclus
macroporus
and
Siderolites
calcitrapoides,
Contusotruncana
contusa
and
Racemiguembelina fructicosa. The first record of rudist species is from Dainelli (1901,
1905), and subsequent publications indicated further taxa (Tavani, 1958; Parente, 1994;
Laviano, 1996a; Steuber et al., 2007): Hippurites cornucopiae, Hippuritella lapeirousei,
Pironaea polystyla, Joufia reticulata, Mitrocaprina sp., Petkovicia sp., Pseudopolyconites
sp., aff. Pseudosabinia sp. (abundant), ?Sabinia sp.
While Hippurites cornucopiae is considered to be characteristic of the Maastrichtian
(Pons and Sirna, 1994), benthic and planktonic foraminifera indicate the Upper
Maastrichtian. The base of the Ciolo facies has not been observed in Salento so that its
thickness, stratigraphical range, and the nature of the boundary with the underlying S.
Cesarea Lst. are unknown.
2.3.4 Strontium-isotope stratigraphy
2.3.4.1 Elemental composition
In the samples that were chosen for Sr-isotope analysis, the concentrations of Fe and Mn
are, with a single exception, below the analytical detection limit of 193 and 16 ppm,
respectively (Tab. 2.1), suggesting minor diagenetic alteration (McArthur, 1994; Steuber,
2003b). The Sr concentrations range from 270 to 1683 ppm. High Sr concentrations - i.e.
above 1000 ppm - in skeletal calcite suggest the retention of the original seawater
21
Figure 2.6: a, d, e, g, Cava Vitigliano S; b, c, Cava Vitigliano N; f, h, Cava Longo. Diameter of coin is 22
mm. a, Pseudosabinia with cystose tabulae and internal moulds of canals seen near apex of shell. b, large
bivalve specimens, preserved in life position, of Joufia reticulata (lower right) and Pseudosabinia (upper
left). Note almost complete leaching of originally aragonitic inner shell of RV of Pseudosabinia so that only
radiolitidiform outer shell with distinct growth increments is preserved. Canals of LV are partly preserved as
internal moulds. c, abapical view of RV of Pseudosabinia, showing asymmetrical, radiolitidiform dentition
and main body cavity. d, Pseudosabinia with cystose tabulae and internal moulds of canals near apex. Note
regular tabulae that cross recrystallized canals in commissural part of shell. e, adapical view of shell of
Pseudosabinia with angular canals and cystose tabulae in main body cavity. f, curved shell of Pseudosabinia
with angular canals near periphery that are crossed by regular tabulae, producing a rectangular pattern in
longitudinal section of shell. g, h, unidentified taxon with regularly spaced tabulae in main body cavity and
thin canaliculate inner shell. Septum subdivides main body cavity longitudinally, and main body cavity is
much larger than in Sabinia.
22
Figure 2.7: a, b, Cava Longo (sample CL1); c–j, Cava Longo (sample CL3). a, bioclastic grainstone with
Orbitoides sp.; b, Orbitoides cf. media; c, Siderolites calcitrapoides; d, Siderolites calcitrapoides; e,
Lepidorbitoides sp.; f, Orbitoides cf. media (juvenile specimen); g, Cymopolia barattoloi; h, Scandonea sp.;
i, Orbitoides cf. apiculata; j, ? Sulcoperculina sp.
23
Figure 2.8: New canaliculate rudist taxon, a, d, e, h, Cava Soframa; b, f, Ciolo cove; c, g, Cava Longo.
Diameter of coin is 22m. a, large, gently curved shell. Note thick canaliculate inner shell and relatively
narrow main body cavity. b, canaliculate inner shell. c, Body cavity and/or tubes with remnants of widely
spaced tabulae. Canals of inner shell preserved as internal moulds. d, e, internal moulds of angular canals
(d) and tubes (e). Angular canals most probably crossed by tabulae. f–h, transverse sections. Diameter of
shell in F is 45 mm. Note presences of larger tubes and relatively small main body cavity.
strontium-isotope ratio (McArthur, 1994; Steuber, 2003b). Two samples from Vitigliano
that have concentrations lower than 1199 ppm were also chosen for Sr-isotope analysis to
assess the impact of diagenesis on the 87Sr/86Sr value. Mg concentrations range from 1103
24
to 2563 ppm, and are within the range of well-preserved skeletal calcite of rudist bivalves
(Steuber and Rauch, 2005).
2.3.4.2 Sr ratio and derived ages
Numerical ages are derived from the ‘look-up’ table of McArthur et al. (2001), after
adjusting the
87
Sr/86Sr values to a ratio of 0.709175 for modern seawater (EN-1 standard,
McArthur et al., 2001). Sr-isotope ratios are calibrated to the time scale of Cande and Kent
(1995) and Obradovich (1993) for 62–70 and 70–74 Ma, respectively. Our own
unpublished data show that the Sr-isotope evolution of Santonian–Campanian seawater is
better constrained in McArthur et al. (2001) so we are not using the revised version of the
‘look-up’ table (McArthur, 2004), which refers to the time scale of Gradstein et al. (2004).
The
87
Sr/86Sr values, from which numerical ages were derived, range from 0.707419 to
0.707828 (Tab. 2.1). The limestones from Torre Tiggiano represent the oldest Cretaceous
(Coniacian) samples studied, with an age of 85.9 Ma (+/- 0.6). The youngest limestones are
found at the Ciolo cove with a Sr-isotope ratio of 0.707828 and a numerical age of 66.4 Ma
(+/- 1.5; Steuber et al., 2007). The oldest deposits of the Ciolo Lst. studied (72.8 Ma +/0.4) crop out at the Cava Longo (c. 40 km north of Ciolo cove) with a Sr-isotope ratio of
0.707685 (Tab. 2.1). The base of the Ciolo Lst. is therefore revised to the middle part of
the Campanian.
With the exception of Vitigliano, the data set comprises single samples of various
distinct levels exposed in the quarries. The three samples from Vitigliano define the
frequently reported trend that diagenetically altered samples have a more radiogenic Srisotope composition. The lowest Sr-isotope value is found for the single sample that is well
preserved according to its high Sr concentrations. This trend is similar to that reported
from the latest Maastrichtian Ciolo Lst. at its type locality (Steuber et al., 2007). As is the
case with many other diagenetic environments, alteration of skeletal carbonates thus
involved a decrease in Sr concentrations and an increase in the 87Sr/86Sr value (McArthur,
1994). Mn and Fe concentrations below the analytical detection limit may indicate that
these elements cannot be expected to reach high concentrations even in altered samples
due to the low concentrations of Mn and Fe in the diagenetic fluids of the pure limestones.
At two other localities (Cava Soframa and Cava Cocumola), numerical ages were
derived from various levels of the exposed limestones. At Cava Soframa, samples were
analyzed from the base of the exposed, 40m thick sequence of the Ciolo Lst. (samples:
CS1a, CS2c), and from 8m (CS3b) and 4m (CS4a), respectively, below the unconformity
25
to the overlying Upper Oligocene Castro Lst. Although the numerical age calculated from
mean values of the samples from the base (CS1a, CS2c) are 0.5 Mio years older than that
derived from the mean value of samples from the top (CS3b, CS4a) of the exposed part of
the Ciolo Lst., this difference is statistically insignificant, and marks the limit of resolution
of the method (Tab. 2.1). At Cava Soframa, four samples are derived from significantly
different facies that are exposed along different faces of the quarry. Sample CO4 is from
the eastern face of the quarry, where inner platform packstones contain large-sized
articulated specimens of Favus, Joufia and Pironaea, and are remarkably similar to
limestones exposed at the Vitigliano Quarry. Similar deposits are exposed in the SE, at the
top of the quarry (CO16), equivalent to the top of the section described by Laviano (1996a,
fig. 6a), and also correlated with similar deposits in the Vitigliano area. There is a small
difference in numerical ages between samples from Cocumola and Vitigliano (Tab. 2.1),
which is however statistically insignificant. Along the southern face of the Cocumola
quarry, micrites with abundant miliolids, gastropods and a few small radiolitids were
sampled (CO-S1, CO-S2). According to the bio- and lithofacies, these formed in a much
more restricted inner platform environment. They are dissected by the karstic cavities
described above. The numerical age of bioclasts from these micritic limestones is slightly
higher than those of the Vitigliano-type rudist limestones, but the difference is again
statistically insignificant. In summary, the different limestones that are exposed in the
Cocumola quarry, which are offset by several faults and difficult to correlate in the field,
have very similar numerical ages. Differences are within the range of analytical precision
of Sr-isotope analysis.
2.4 Taxonomy of large-sized, canaliculate recumbent rudists
A characteristic and abundant component of the Late Cretaceous rudist associations of
Salento are large-sized shells of a canaliculate recumbent rudist. These are particularly
abundant in the platform margin deposits of the Ciolo Lst. and occur together with
Pseudosabinia Morris and Skelton and possibly Sabinia Parona. They have been
previously assigned to either one of these genera (De Castro, 1990; Laviano, 1996a), but
differ significantly from both. Due to the high-energy environment, only fragmented shells
are preserved, and these may be up to one metre long. No originally calcitic outer shell
layer has been observed. The shells are commonly preserved as internal moulds, and parts
of the shell that were not filled by fine-grained sediments prior to aragonite dissolution, are
commonly not preserved (Fig. 2.6). Additionally, single specimens are almost impossible
26
to collect from the thick-bedded and massive Ciolo Lst. This makes it rather difficult to
evaluate the full range of characters necessary for a detailed description and an
unequivocal separation from previously described taxa. The myocardinal elements in
particular, have not been observed in much detail in the specimens examined. The new
taxon is therefore not formally described here, but some morphological features which are
different from those of previously described taxa are highlighted. Considering the
insufficient knowledge of the group, which is largely due to the poor preservation of the
aragonite-dominated shells, it appears likely that the diversity of canaliculate recumbent
rudists in the late Campanian–Maastrichtian is at present seriously underestimated. In the
following, the taxonomy of Sabinia and Pseudosabinia is briefly summarized, and the
characters of what is considered to be a new taxon are briefly described.
Sabinia is characterized by canals in both valves. The myocardinal elements of the left
valve (LV) are very similar to those of Plagioptychus. There are apparently no tabulae in
the main body cavity of the RV. The genus probably has no cellular structure in the outer
shell layer in the right valve (RV), although Parona’s (1908) figures show remnants of a
relatively thick RV outer shell layer that was, however, not described in any detail (Morris
and Skelton, 1995). At the localities studied, we did not record any specimens which
would unequivocally correspond to Sabina.
Pseudosabinia klinghardti resembles Sabinia but has a finely cellular outer shell layer of
the RV and radiolitidiform myocardinal elements. The tabulae of the RV have been
described as "cystose", and this appears to be a characteristic feature of the genus, which is
also obvious in specimens from the old quarry N of Vitigliano, from Cava Vitigliano south,
as well as from the Ciolo Lst. at the type locality (Figs. 2.6, 2.8). Its range in Salento
consequently is from the middle Campanian to the uppermost Maastrichtian. “Schiosia”
bilinguis was tentatively included in Pseudosabinia (Morris and Skelton, 1995). The
original description is insufficient, the outer shell layer in the RV was considered
‘destroyed’ (Böhm, 1927), but the coiling of the LV is less pronounced than in the type
species of Pseudosabinia, Ps. klinghardti.
Pseudosabinia rtanjica tunisiensis has the same type of tabulae, although the cystose
structure is somewhat coarser than in the shells from Vitigliano. The outer shell layer of
the RV is apparently thin and compact (Philip, 1986; Morris and Skelton, 1995), and thus
27
different from that of Pseudosabinia klinghardti. The canals of the inner shell have
tabulae. According to the available descriptions, this taxon deserves to be ranked at the
genus level, because the absence of a radiolitidiform outer shell layer combined with the
characters of Pseudosabinia is rather unique, unless the compact outer shell layer of Ps.
rtanjica tunisiensis is similar to that of certain radiolitids that can either switch between
both types of structures or have them both developed in different portions of the shell. A
detailed study of the outer shell layer is necessary before this character may be considered
diagnostic among the group in question. The species is of Campanian age.
Dalla Vecchia et al. (2004) described typical, but relatively small specimens of
Pseudosabinia with radiolitidiform myocardinal elements, and cystose tabulae in the RV
main body cavity. The outer shell layer of the RV is relatively thick, but its structure
remained undescribed. The overall morphology of the strongly coiled LV and the short,
conical RV otherwise resemble Sabinia Parona. The major difference of the specimens
described by Dalla Vecchia et al. (2004) is that they are much smaller than those observed
in the Vitigliano quarries. Also, the overall morphology is different, as Pseudosabinia from
Vitigliano has a large RV and a relatively small overhanging LV similar to that of
Plagioptychus. Isolated RVs from Vitigliano could be easily confused with Joufia or other
radiolitids, particularly in specimens in which the cystose inner shell is not preserved (Fig.
2.6b). Pseudosabinia described by Dalla Vecchia et al. (2004) has a large LV, and a small
RV that is externally similar to that of Plagioptychus.
The large canaliculate recumbent that is abundant in the Ciolo Lst., and also in the Late
Maastrichtian of the Ionian Islands differs from both Sabinia and Pseudosabinia in the
simple, widely spaced tabulae of the main body cavity of the RV (Fig. 2.8a, c, e). None of
the specimens studied shows remnants of an outer shell layer. The shells are found in highenergy platform-margin facies so that a thin outer shell layer may have been easily
removed during repeated reworking, similar to the preservation frequently observed in the
Caprinidae. The large, straight, or only slightly curved shells that are abundant in the Ciolo
Lst. have several tube-like cavities, subdivided by septae; the main body cavity is
relatively small (Fig. 2.8f–h). In cross section, these shells resemble the Antillocaprinidae
of the New World. Details of the myocardinal elements have not been identified.
Based on the myocardinal organisation and the structure of the outer shell layer,
Sabinia and Pseudosabinia may belong to different families, the Plagioptychidae and
Radiolitidae, respectively (Morris and Skelton, 1995). For the new taxon, an affinity to the
28
Radiolitidae appears to be unlikely because of the absence of a cellular outer shell layer,
but this remains unclear until the myocardinal arrangement is known.
Less frequently, we observed another unidentified taxon, which is also characterized by
regularly and widely spaced tabulae in the main body cavity, but differs in possessing a
thin canaliculate inner shell (Fig. 2.6g, h). A septum that longitudinally subdivides the
main body cavity suggests a plagioptychid affinity. The main body cavity is much larger
than in Sabinia. It has no preserved outer shell layer in the RV, and details of the left valve
are not known.
2.5 Discussion
The oldest Cretaceous limestones studied are those exposed near Torre Tiggiano. The age
derived from SIS (85.9 Ma +/- 0.6) corresponds to the Coniacian/Santonian boundary
(85.8 Ma), and it is thus significantly younger than previously believed. According to the
subdivision of Bosellini et al. (1999), the rocks must be assigned to the Melissano Lst.
(Fig. 2.2). The distinction between the Melissano and S. Cesarea Lst. is based on the
predominance of peritidal deposits in the first, and their subordinate occurrence in the latter
(Bosellini et al., 1999). Both were deposited in inner platform environments, but the
abundance of rudists in the S. Cesarea Lst. argues for less restricted water circulation
closer to the platform margin. The contact between these units has never been observed in
the field so that it is not clear if they represent a continuous sequence, or if they are
separated by an unconformity. The latter hypothesis is more consistent with the regional
stratigraphy of the Upper Cretaceous of the Apulian Platform. In the Murge area an early–
middle Campanian unconformity separates the inner platform facies of the Altamura Lst.
from the rudist-rich facies of the Ostuni Lst. and from the bioclastic calcarenites of the
Caranna Lst. (Luperto Sinni and Borgomano, 1989; Luperto Sinni and Reina, 1996;
Borgomano, 2000). Both facies and age relationships suggest that the Melissano and the S.
Cesarea Lst. of Salento are the equivalent of the Altamura and Ostuni Lst. of Murge,
respectively. The equivalence between the rudist limestones of the Poggiardo area (S.
Cesarea Lst.) and the Ostuni Lst. was suggested also by Guarnieri et al. (1990).
Our data indicate that the stratigraphical range of the Ciolo Lst. must be revised to
include part of the upper Campanian (Fig. 2.2). While the oldest numerical age of the Ciolo
Lst. has been obtained at the Cava Longo, the youngest numerical ages of the S. Cesarea
Lst. were recorded in the Cava Vitigliano N and in the Cava Cocumola. A stratigraphical
boundary between the two formations has not been observed in the quarries studied, and
29
has not previously been reported from the region. Giudici et al. (1994) reported ammonitebearing infillings of erosional pockets on top of the S. Cesarea Lst. at Vitigliano. The
ammonites indicate the uppermost Campanian Nostoceras hyatti zone. It still remains to be
documented if the typical inner shelf deposits of the S. Cesarea Lst. with rudists preserved
in life position grade conformably into the high-energy outer margin deposits of the Ciolo
Lst., or if the formations are separated by an unconformity. The large karstic cavities
exposed in the Cava Cocumola could be the result of a middle-Campanian (74–76 Ma)
emersion event and resulting karstification. Such karstic cavities have never been described
before in this region, neither from the Ciolo Lst. nor from the Paleogene units.
On the Adriatic carbonate platform exposed on the Island of Brač, a major subaerial
exposure surface separates the rudist-rich Pučišća Formation from the peritidal Sumartin
Formation (Gušić and Jelaska, 1990). The hiatus has been dated by SIS at 75–77 Ma
(Steuber et al., 2005), which falls in the time interval of the boundary between the S.
Cesarea and Ciolo Lst. This emersion would also correspond to a sequence boundary dated
at 75.6 Ma in the Boreal of Europe and North America (Hardenbol and Vail, 1998), the
'Upper Campanian event' of Jarvis et al. (2002), and a significant regression observed in
the Boreal chalk (polyplocum regression; Niebuhr, 1995) that has been dated by SIS at 74.8
Ma (Jarvis et al., 2002). These data support the existence of an unconformity between the
S. Cesarea and Ciolo Lst., probably related to the formation of karstic cavities observed in
the Cava Cocumola.
The rudist associations of the S. Cesarea Lst. exposed in the Cava Cocumola and the
quarries near Vitigliano, and of the overlying Ciolo Lst., i.e. from a time interval of more
than 12 Mio years, are remarkably similar. Characteristic genera such as Favus, Joufia,
Pseudosabinia and other canaliculate recumbents are abundant throughout this time
interval. Phyletic size increased has been documented for several lineages of rudists
(Steuber, 2003a), but is not seen in the genera mentioned above. In fact, the largest
representatives of these taxa occur in the Cava Cocumola (Favus, canaliculate recumbents)
and in the quarries near Vitigliano (Joufia, Pseudosabinia). No clear pattern is evident in
the stratigraphical distribution of the canaliculate recumbents described above, with the
exception that the taxon with the widely and regularly spaced tabulae (Fig. 2.6g, h) seems
to occur only in the basal part of the Ciolo Lst.
Post-Cretaceous tectonics in Salento are considered to have been mild (Bosellini and
Parente, 1994) and Cretaceous limestones are commonly tilted only at low angles.
However, the close proximity of outcrops exposing the uppermost Maastrichtian (Ciolo)
30
and the upper Coniacian–lower Santonian argues for significant vertical tectonic
movements. These must have occurred in the Early Paleogene, because the tectonic
displacement of the Eocene deposits is minor, and the post-Eocene deposits are not
evidently tilted or tectonically deformed (Bosellini et al., 1999). Significant vertical
tectonic displacement is also obvious from the age of the Cretaceous limestones underlying
the unconformity with the Upper Oligocene (Chattian) Castro Lst. It is late Coniacian–
early Santonian (86 Ma) at Torre Tiggiano, latest Maastrichtian (66 Ma) at Ciolo, and early
late-Maastrichtian (69 Ma) at Cava Soframa. Because of the limited outcrops and the
generally shallow dip of the Cretaceous limestones, the thickness of the units described is
very difficult to estimate.
2.6 Conclusions
Numerical ages derived from SIS for the Upper Cretaceous limestones of the Salento
peninsula contribute to a precise chronostratigraphy of the Ciolo Lst., which ranges from
the middle Campanian to the latest Maastrichtian. The oldest (72.8 Ma +/- 0.4) and
youngest (66.4 Ma +/- 1.5) levels of the Ciolo Lst. are exposed at the Cava Longo and
Ciolo cove, respectively. The oldest Cretaceous carbonates studied crop out at Torre
Tiggiano (85.9 Ma +/- 0.6). They belong to the Melissano Lst. Karstic cavities with in the
S. Cesarea Lst. observed at the Cava Cocumola may correspond to a middle Campanian
(74–76 Ma) emersion event, which correlates with evidence for a significant drop in sea
level recorded on the Adriatic island of Brač and in the Boreal of Northern Germany.
A new taxon of large, canaliculate recumbent rudist is abundant in the S. Cesarea and
Ciolo Lst. Rudist associations of the S. Cesarea and Ciolo Lst. are remarkably similar,
arguing for long stratigraphical ranges of most characteristic mid-Campanian
Maastrichtian taxa.
Acknowledgements
The authors are grateful to Barbara Raczek for her encouragement in the lab, to Dieter
Buhl for support with the analysis of the Sr-isotope ratios, and to Gianluca Frija for useful
comments and support during the fieldwork. Review of the manuscript by Peter Skelton is
gratefully acknowledged. Funded by the Deutsche Forschungsgemeinschaft (Ste 670/13).
Appendix. List of taxa mentioned in the text
Rudist bivalves:
31
Biradiolites angulosus Orbigny, 1850
Biradiolites chaperi (Toucas, 1909)
Favus antei Laviano and Skelton, 1992
Hippurites colliciatus Woodward, 1855
Hippurites cornucopiae Defrance, 1821
Hippuritella lapeirousei (Goldfuss, 1840)
Joufia reticulata Boehm, 1897
Mitrocaprina bulgarica Tzankov, 1965
Mitrocaprina Boehm, 1895
Pironaea Meneghini, 1868
Pironaea polystyla (Pirona, 1868)
Petkovicia Kühn and Pejović, 1959
Pseudopolyconites Milovanovic, 1935
Pironaea slavonica Hilber, 1902
Plagioptychus Matheron, 1842
Pseudopolyconites apuliensis Sladić-Trifunović and Campobasso, 1980
Pseudosabinia klinghardti (Boehm, 1927)
Pseudosabinia rtanjica tunisiensis Philip, 1986
Radiolites angeiodes (Lapeirouse, 1781)
Radiolites spongicola Astre, 1954
Radiolitella maestrichtiana Pejović, 1968
Sabinia Parona, 1908
Sauvagesia Choffat, 1886
“Schiosia” bilinguis Boehm, 1927
Foraminifera:
Accordiella conica Farinacci, 1962
Amphistegina sp.
Austotrillina cf. asmariensis Adams, 1968
Cuneolina sp.
Contusotruncana contusa (Cushman, 1926)
Dicyclina schlumbergeri Munier-Chalmas, 1887
Dictyoconus sp.
Dictyopsella sp.
32
Lepidocyclina (Eulepidina) dilatata (Michelotti, 1861)
Lepidocyclina (Nephrolepidina) praemarginata (Douvillé, 1908)
Lepidorbitoides socialis (Leymerie, 1851)
Miogypsina (Miogypsinoides) sp.
Moncharmontia apenninica (De Castro, 1966)
Murciella cuvillieri Fourcarde, 1966
Neorotalia cf. viennoti (Greig, 1935)
Omphalocyclus macroporus (Lamarck, 1816)
Orbitoides apiculata Schlumbeger, 1901
Orbitoides gensacica (Leymerie)
Orbitoides media (D’Archiac, 1837)
Pseudochubbina bruni De Castro, 1990
Pseudosiderolites vidali (Douvillé, 1907)
Raadshovenia salentina (Papetti and Tedeschi, 1965)
Racemiguembelina fructicosa (Egger, 1899)
Rotalia sp.
Rotorbinella scarsellai Torre, 1966
Scandonea sp.
Siderolites calcitrapoides Lamarck, 1801
Stensioeina surrentina Torre, 1966
?Sulcorperculina sp.
Algae:
Cymopolia barattoloi Parente, 1994
Cymopolia decastroi Parente, 1994
Decastronema kotori (Radoičić, 2006)
Jodotella koradae (Deni, Massari and Radoičić, 1983)
Thaumatoporella parvovesiculifera (Raineri, 1922)
Zittelina fluegeli Parente, 1994
Ammonite:
Nostoceras hyatti Stephenson, 1941
33
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offshore. Memorie Società Geologica Italiana 51, 719–727.
Martinis, B., 1967. Note geologiche sui dintorni di Casarano e Castro (Lecce). Rivista
Italiana di Paleontologia e Stratigrafia 73, 1297–1380.
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McArthur, J.M., 1994. Recent trends in strontium isotope stratigraphy. Terra Nova 6, 331–
358.
McArthur, J.M., Howarth, R.J., Bailey, T.R., 2001. Strontium Isotope Stratigraphy:
LOWESS Version 3: Best Fit to the Marine Sr-Isotope Curve for 0–509 Ma and
Accompanying Look-up Table for Deriving Numerical Age. The Journal of
Geology 109, 155–170.
Ogg, J.G., Smith, A.G. (Eds.). A Geologic Time Scale 2004. Cambridge
Morris, N.J., Skelton, P.W., 1995. Late Campanian–Maastrichtian rudists from the United
Arab Emirates-Oman border region. Bulletin of the Natural History Museum,
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Nardin, M., Rossi, D., 1966. Condizioni strutturali della zona compresa nel Foglio Otranto
(Provincia di Lecce). Memorie Museo Civico di Storia Naturale di Verona 14,
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Niebuhr, B., 1995. Fazies-Differenzierungen und ihre Steuerungsfaktoren in der höheren
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Geowissenschaftliche Abhandlungen A 174, 1–131.
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(Eds.). Evolution of the Western Interior foreland basin. Geological Association
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Parente, M., 1994. A revised stratigraphy of the Upper Cretaceous to Oligocene units from
southeastern Salento (Apulia, southern Italy). Bollettino della Società
Paleontologica Italiana 33, 155–170.
Parente, M., 1997. Dasycladales from the Upper Maastrichtian of Salento peninsula
(Puglia, southern Italy). Facies 36, 91–122.
Parona, C.F., 1908. Notizie sulla fauna a rudiste della Pietra di Subiaco nella valle
del'Aniene. Bollettino della Società Geologica Italiana 27, 299–310.
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benthic communities. Bollettino della Società Paleontologica Italiana, Spec. Vol.
2, 269–278.
36
Ricchetti, G., Ciaranfi, N., Luperto Sinni, E., Mongelli, F., Pieri, P., 1992. Geodinamica ed
evoluzione sedimentaria e tettonica dell'Avampaese apulo. Memorie Società
Geologica Italiana 41, 57–82.
Rossi, D., 1969. Note illustrative della Carta Geologica d’Italia F. 215, Otranto. Servizio
Geologico d’Italia, 69 pp.
Sladić-Trifunović, M., Campobasso, V., 1980. Pseudopolyconites and Colveraias from
Maastrichtian of Poggiardo (Lecce, Puglia), Italy. Geoloski Anali balkanskoga
Poluostrva 43–44, 273–286.
Steuber, T., 2001. Strontium-isotope stratigraphy of Turonian-Campanian Gosau-type
rudist formations in the Northern Calcareous and Central Alps (Austria and
Steuber, T., 2003a. Strontium-isotope stratigraphy of Cretaceous hippuritid rudist bivalves:
Steuber, T., 2003b. Strontium-isotope chemostratigraphy of rudist bivalves and Cretaceous
carbonate platforms. In: Gili, E., Negra, M.H., Skelton, P.W. (Eds.). North
African Cretaceous carbonate platform systems. NATO Science Series, Earth and
Environmental Sciences 28, 229–238.
217, 199–213.
Upper Cretaceous platform carbonates of the island of Brač (Adriatic Sea,
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2007. Latest Maastrichtian species-rich rudist associations of the Apulian margin
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37
Veizer, J., 1989. Strontium isotopes in seawater through time. Annual Review of Earth and
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Korte, C., Schaaf, M., Ala, D., Azmy, K., 1997. Strontium isotope stratigraphy:
potential resolution and event correlation. Palaeogeography, Palaeoclimatology,
Vlahović, I., Tišljar, J., Velić, I., Matićec, D., 2005. Evolution of the Adriatic Carbonate
Platform:
Paleogeography,
main
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and
depositional
38
dynamics.
Chapter 3 ◦ Evolution of a Maastrichtian–Paleocene shallow-water carbonate platform
3. Evolution of a Maastrichtian–Paleocene tropical shallow-water
carbonate platform (Qalhat, NE Oman)
M. Schlüter1, T. Steuber2, M. Parente3, J. Mutterlose1
1
Institut für Geologie, Mineralogie und Geophysik, Ruhr-Universität Bochum, Universitätsstr. 150, 44801
Bochum, Germany; malte.schlueter@rub.de; Tel: +49 (0)234 3225459, Fax: +49 (0)234 3214571
2
The Petroleum Institute, Abu Dhabi, PO Box 2533, Abu Dhabi, United Arab Emirates
3
Dipartimento di Scienza della Terra, Università “Federico II” Napoli, Largo San Marcellino 10, 80138
Napoli, Italy
(published in Facies 57, 513–527; doi: 10.1007/s10347-008-0150-8)
Abstract
The biostratigraphy (larger foraminifers, dasycladaleans), microfacies, sedimentology, and
geochemistry (δ13C, strontium-isotope stratigraphy) of a continuous, 148 m thick section of
shallow-water platform carbonates that contain the Cretaceous–Paleogene (K/P) boundary
was analyzed. The boundary is constrained within a 7 m thick interval, between the last
occurrence of Maastrichtian larger benthic foraminifers and the first occurrence of Danian
benthic foraminifers. Although this interval is intensively dolomitized, there is no
sedimentological evidence for a major hiatus at the K/P boundary. The correlation of bulk
rock δ
13
C values with stable isotope data from DSDP Site 384 (NW Atlantic Ocean)
supports this interpretation and indicates a Selandian age for the top of the section. The
Qalhat section is a unique example of a carbonate platform that has recorded persisting
open marine environmental conditions across the K/P boundary (Maastrichtian–Selandian),
as indicated by the abundance of rudists, larger benthic foraminifers (Maastrichtian),
calcareous algae and scleractinian corals.
Keywords:
Cretaceous–Paleogene,
shallow-water
carbonates,
biostratigraphy,
chemostratigraphy, rudists, Oman
3.1 Introduction
Rudist bivalves, scleractinian corals and larger benthic foraminifers were the major
carbonate producer association of Late Cretaceous Tethyan carbonate platforms. While the
corals largely survived the mass extinction at the Cretaceous–Paleogene (K/P) boundary
(Kiessling and Baron-Szabo, 2004; Aguirre et al., 2007), the rudists and larger benthic
39
foraminifers became extinct. The patterns of evolution and demise of the latest Cretaceous
rudists are not known in detail due to a poor biostratigraphy of the shallow-water carbonate
platforms that is mainly based on relatively long-ranging taxa of benthic foraminifers. The
scarcity of data on continuous sequences of Late Cretaceous to Paleocene shallow-water
carbonate-platform facies contributes significantly to this problem.
The few known rudist assemblages of latest Maastrichtian age (e.g. Apulia, Jamaica)
proved to be species-rich (Steuber et al., 2007; Schlüter et al., 2008) and include a
significant number of new taxa. On the Apulian platform, an erosional unconformity
truncates latest Maastrichtian platform margin deposits (Parente, 1994; Vecsei and
Moussavian, 1997; Steuber et al., 2007; Schlüter et al., 2008) and platform-type
sedimentation resumes only in the Late Danian to Early Thanetian (Maiella; Vecsei and
Moussavian, 1997) or in the Eocene (Apulia; Parente, 1994). In the northern part of the
Adriatic carbonate platform exposed in Slovenia and Croatia, latest Maastrichtian
limestones were deposited under restricted environmental conditions and their rudist
associations are of moderate to low diversity (Drobne et al., 1989; Drobne et al., 1996;
Steuber et al., 2005b). Other Late Maastrichtian carbonate platforms in Jamaica (Steuber et
al., 2002) or in Tibet (Wan et al., 2002) are truncated at their top and covered by
volcaniclastic or terrigenous deposits, respectively.
Carbonate platform sections which cover the K/P boundary interval are rare and thus of
particular interest. Le Callonnec et al. (1998), Roger et al. (1998), and Ellwood et al.
(2003) reported platform-carbonate deposits from Oman ranging from the Maastrichtian to
the Paleocene, and focused on the distribution of rudists, evolution of depositional
environments, and the geochemistry of these deposits.
The aim of the present study is to document and analyze the Late Cretaceous to Paleocene
carbonate platform deposits at Qalhat (Sur, Oman) and to confine the K/P boundary
interval with biostratigraphical and geochemical data at this locality. For that reason we
used stable isotopes (δ 13C, δ 18O), strontium-isotope stratigraphy (SIS) and microfacies
analysis to complement the biostratigraphy and to evaluate environmental changes at the
K/P boundary.
3.2 Regional geotectonic setting and previous studies
The Oman Mountains belong to the Alpine-Himalayan fold-belt system, deformed in the
Late Mesozoic–Cenozoic (Alsharhan and Nasir, 1996). Sedimentary deposits are mostly
represented by Permian to Late Cretaceous deep-sea to shelf limestones (Le Métour et al.,
40
1995). During the Late Cretaceous, the Oman was situated in a paleo-equatorial position
(Dercourt et al., 1993). Uplift during the onset of ophiolite obduction changed the
depositional setting during Turonian time (Grelaud et al., 2006). The Aruma Group
comprises the sedimentary cover of the ophiolite (Le Métour et al., 1995; Fig. 3.1).
Influenced by the ophiolitic basement, the Campanian–Maastrichtian transgressive
deposition started with terrigenous clastics including immature sandstone to siltstone of the
variegated succession of the Qahlah Formation that is followed by the shelf margin
carbonate deposits of the Simsima Formation (see explanatory notes to the map of Sur
1:250.000, Wyns et al., 1992; Fig. 3.1). Along the
border of the United Arab Emirates and Oman, the
lower part of the Simsima Formation consists of
chalky limestones with intercalations of chert bands
and nodules, while the upper part combines some
marls and carbonate siltstones (Abdelghany, 2003). In
Oman the rudist-bearing bioclastic limestones of the
Simsima Formation (Late Campanian–Maastrichtian)
yield larger benthic foraminifers such as Loftusia and
others. The contact of the Simsima Formation and the
overlying
Paleogene
deposits
was
previously
considered to be unconformable, containing a hiatus
of unknown duration (Le Métour et al., 1995). In the
eastern part of Oman, e.g. in the region north of Sur
(Fig. 3.2), the Simsima Formation is overlain by
Fig. 3.1: Chart of regional chronoand lithostratigraphy (after Alsharhan
and Nasir, 1996 and Wyns et al.,
1992).
Paleocene shallow-marine carbonates of the Jafnayn
Formation (Le Métour et al., 1995). The limestones
immediately below and above the K/P boundary
interval have been informally included in the Murka Formation (Roger et al., 1998), which
is equivalent to the Murka facies within the Jafnayn Formation (Fig. 3.1) described by
(Wyns et al., 1992). For further descriptions and stratigraphic relations of the Qahlah and
Simsima formations see Wyns et al. (1992) and Le Métour et al. (1995). For a detailed
description of the Upper Cretaceous formations in the UAE/Oman border region refer to
Nolan et al. (1990), Skelton et al. (1990, and references therein), Morris and Skelton
(1995), and Abdelghany (2003, 2006).
41
Figure 3.2: Simplified geological map of the region studied (after Le Métour et
al., 1995).
Le Callonnec et al. (1998), Roger et al. (1998) and Ellwood et al. (2003) studied K/P
sections in the region of Sur in detail, using a multidisciplinary approach. According to
these studies, the K/P boundary occurs within a carbonate-platform sequence deposited
during an interval of relative tectonic quiescence, and no major change of the depositional
environments and biofacies occurred from the latest Maastrichtian to the earliest
Paleocene. No detailed biostratigraphy of these shallow-water platform-type deposits was
yet provided, and the position of the K/P boundary was based on a negative carbon isotope
excursion of -3‰ coupled with a moderately increased iridium concentration. Roger et al.
(1998) traced the K/P boundary in the region of Buraymi, in the valley west of Abat and in
the eastern part of Jabal Ja’alan, but not next to Bir’bira, north of Sur (Fig. 3.2), where
their section is truncated by erosion down to a level within the Maastrichtian.
3.3.1 Field methods
The studied section near Qalhat (22°40’50 N, 59°22’25E) is located 20 km northwest of
Sur (Fig. 3.2) and two kilometers north of the Bir’bira section, described by Roger et al.
(1998) and Le Callonnec et al. (1998). Samples have been collected at two-meter intervals
42
for the complete 148-m-thick section, and at 50 cm intervals for the critical K/P boundary
interval (Fig. 3.3). Eighty-nine thin sections were analyzed for microfacies and microfossil
content, with special emphasis on benthic foraminifers and calcareous algae. Microfacies
textures were classified after Dunham (1962) and Embry and Klovan (1972).
Figure 3.3: Lithological log of the Qalhat section with sedimentological textures and distribution of
main bioclasts as well as carbonate and oxygen stable isotopic composition of carbonates (open circles
indicate dolostone samples).
43
The selection of suitable material for SIS in the field was based on visual screening of the
preservation of original shell structures. The compact, originally low-Mg calcite outer shell
layer of hippuritid and some radiolitid rudists has been proven in previous studies to be the
most promising material to have preserved the original Sr-isotope composition of ancient
seawater (Mc Arthur, 1994; Steuber, 1999; McArthur et al., 2001; Steuber et al., 2005a).
While hippuritids are rare in the section studied, the plagioptychid rudist Dictyoptychus
Douvillé is abundant and the thick, compact outer shell of this genus provided promising
material for SIS.
3.3.2 Laboratory methods
Preparation of the samples for analyses of elemental concentrations and Sr-isotope ratios
followed methods described in detail elsewhere (Steuber 2001, 2003a).
Only samples of skeletal calcite with Fe concentrations below 180 ppm, and Sr
concentrations above 1000 ppm are expected to have preserved the original Cretaceous
seawater
87
Sr/86Sr value (Mc Arthur, 1994; Steuber, 2003b), but three samples (Q6b-1,
Q6b-2 and Q7) with lower Sr concentrations were also selected for Sr-isotope analysis to
delineate the impact of diagenesis on the Sr-isotope values. Analytical precision (2
standard error, s.e.) was ± 10 * 10- 6 as monitored with USGS-EN 1 standard material run
together with the samples (mean value = 0.709154; n = 3). For comparison with previously
published data, the
87
Sr/86Sr values were adjusted to a ratio of 0.709175 for modern
seawater (EN-1 standard, McArthur et al. 2001).
For the analyses of stable isotope ratios (δ13C, δ18O) a GasBench II preparation system
and a Finnigan MAT Delta S mass spectrometer were used. Splits of c. 0.5 mg of the
sample powder were reacted with phosphoric acid. The external reproducibility was better
than 0.1‰ for δ 13C and δ 18O as monitored by NBS 19 and an internal laboratory standard.
All δ−values are given in ‰ relative to the V-PDB standard.
3.4 Results
3.4.1 Lithology and microfacies
The largely terrigenous Qahlah Formation is poorly exposed at the lower slope of the
locality studied and consists of red and green coloured sandstones and siltstones with
marly and clayey intercalations. Some isolated, m3-sized blocks of grey to black coloured
limestone are also exposed. They contain abundant rudists (Biradiolites sp., Bournonia sp.,
44
Hippuritella sp.) accompanied by solitary scleractinian corals and Loftusia sp., and are
considered to be limestone lenses within the Qahlah Formation. They show a significantly
different lithofacies and biofacies and are not derived from the cliff-forming Simsima
Formation above.
The base of the studied section forms a prominent escarpment, c. 70 m above the
exposed Qahlah Formation. A 148 m-thick continuously exposed section was logged in
detail (Fig. 3.3). Lithostratigraphically it corresponds to the Simsima and Jafnayn
Formation and consists of limestones, dolomitic limestones, and dolostones with no
significant input of siliciclastics. The section is subdivided into four facies units
characterised by different microfacies and fossil associations (Tab. 3.1; Fig. 3.3).
Table 3.1: Facies units of the Qalhat section as observed in the field and in thin sections.
Facies
unit
Distribution
Classification
Dominant biota
Comments
4
136 – 148 m
packstone
red algae, corals
- scarce dasycladaleans
3
65 – 136 m
frequently changing from
wackestone to floatstone
codiacean and
dasycladalean algae,
echinoderms,
gastropods
- abundant bioturbation
within the lower part
- distinct layers of abundant
foraminifers and gastropods
2
55 – 65 m
dolostone with packstone
intercalations
coarse echinoid debris,
gastropods
- FO of Kolchidina
paleocenica
1
0 – 55 m
packstone to rudstone,
partly dolomitized
rudists, larger benthic
foraminifers
- few scleractinian corals
Facies unit 1 (0–55 m, Fig. 3.4) is dominated by packstones to rudstones with common
rudists and larger benthic foraminifers. Echinoderms, corallinaceans (mainly Sporolithon
sp. Fig. 3.5o) and dasycladaleans (Cymopolia eochoristosporica Elliott (Fig. 3.4a), C.
tibetica Morellet and Trinocladus radoicicae Elliott (Fig. 3.4b) are common components in
this unit, while scleractinian corals are abundant in some levels only. Rudists include
Dictyoptychus morgani Douvillé, Dictyoptychus sp., Vaccinites cf. oppeli Douvillé,
Vaccinites sp., Mitrocaprina sp., Bournonia excavata Orbigny, as well as other
unidentifiable Radiolitidae. Larger benthic foraminifers are mainly represented by
Omphalocyclus macroporus Lamarck (Fig. 3.4d, j), Siderolites calcitrapoides Lamarck
(Fig. 3.4g) and Orbitoides apiculata Schlumberger (Fig. 3.4c, h). Loftusia (Fig. 3.4e,
45
including L. morgani Douvillé) and Pseudomphalocyclus blumenthali Meriç (Fig. 3.4i) are
also present, but never abundant.
Figure 3.4: Characteristic flora, fauna, and facies of the Late Cretaceous (Maastrichtian), a Cymopolia
eochoristosporica Elliott. b Trinocladus radoicicae Elliott. c, h Orbitoides apiculata Schlumberger. d, j
Omphalocyclus macroporus (Lamarck). e Loftusia spp. f Cymopolia tibetica Morellet. g Siderolites
calcitrapoides Lamarck. i Pseudomphalocyclus blumenthali Meriç. Scale bar is 500 µm for b, 1 mm for all
other figures.
46
The larger benthic foraminifers have their last occurrence (LO) at 55 m (Fig. 3.3). Four
horizons with abundant rudists can be distinguished (Fig. 3.3). A few rudist shells are
preserved in life position but most are broken, their fragments forming coarse-grained
rudist rudstones. No rudists or rudist fragments can be observed above 53 m of the section
(Fig. 3.3), although the depositional environment shows persisting normal marine
conditions and depth within the photic zone as indicated by the still abundant larger
benthic foraminifers.
Three red-coloured mudstone horizons occur at 15 m, 22 m, and 34 m. The deposits
consist of very fine-grained, occasionally brecciated lime- to marlstones with some
dissolution cavities. Each of the red-coloured mudstones is only a few centimetres thick
and the contact to the layers above is mostly sharp. No further indications of significant
discontinuities can be observed along the studied section.
Facies unit 2 (55–65 m) shows different degrees of dolomitization, as some limestones, i.e.
packstones are only partly altered while others are completely recrystallized to blocky
dolomite. Macrofossils, i.e. gastropods, echinoderms, and bivalve fragments are found in
the less dolomitized levels of this unit (Fig. 3.3). Microfossils are rarely preserved but
some arenaceous foraminifers can be observed in the upper part of the interval.
From 60–65 m, thin sections show blocky dolomite crystals that formed during late
burial diagenesis of an echinoderm packstone. In contrast to other bioclasts, many of the
large skeletal fragments of echinoderms are well preserved but contain abundant
microdolomite.
Facies unit 3 (65–136 m, Fig. 3.5) consists of variable textures ranging from wackestone to
floatstone with very abundant dasycladaleans and common codiaceans and gastropods. The
dasycladaleans are attributed to Broeckella sp. (Fig 3.5l, Clypeina spp. (Fig. 3.5m),
Cymopolia spp., Cymopolia elongata Defrance, Dissocladella gracilis Radoičić, Indopolia
satyavanti Pia (Fig. 3.5h), Jodotella sloveniaensis Deloffre et Radoičić, Neomeris spp.
(Fig. 3.5j), Thyrsoporella sp. (Fig. 3.5g), Thyrsoporella longa Radoičić and Trinocladus
sp. (including T. perplexus Elliott Fig. 3.5f) while codiaceans are represented by Ovulites
sp. and Halimeda nana Pia (Fig. 3.5a). The FO of this floral assemblage marks the base of
facies unit 3, while the top is drawn where dasycladalean algae decrease considerably in
abundance (Fig. 3.3). Codiaceans dominate between 67 to 86 m while the dasycladaleans
47
Figure 3.5: Charateristic flora, fauna, and facies of Early Paleogene (Danian – Thanetian), a Halimeda nana
Pia. b, k Kolchidina paleocenica (Cushman). c–d Valvulina sp. (cf. Valvulina ? sp. 1 in Sirel 1998). e
Kayseriella decastroi Sirel. f Trinocladus perplexus Elliott. g Thyrsoporella spp. h Indopolia satyavanti Pia.
i Orioporella villattae Segonzac. j Neomeris spp. l: Broeckella sp. m Clypeina spp. n Idalina sp. o
Sporolithon sp. p Polystrata alba (Pfender). Scale bar is 250 µm for e, f, g and n; 500 µm for all other
figures.
are particularly abundant in the interval from 86 to 138 m. At 70 m bioturbated beds can be
observed.
48
On a macroscopic scale, the interval from 80 to 105 m is dominated by echinoderms while
gastropods are also abundant. A distinct grainstone bed at 92 m yields a few scleractinian
corals, as well as unidentified planktonic and benthonic foraminifers; another bioclastic
grainstone is observed at 132 m. Rapid variations in the depositional setting can also be
observed at 105 m and 119 m where changes from wackestone to grainstone, floatstone,
and back to wackestone are recorded.
Facies unit 4 (136–148 m) is dominated by packstone yielding abundant red algae
(corallinaceans and peyssonneliaceans). Throughout the whole interval they are associated
with scleractinian corals and some codiaceans (e.g. Halimeda nana, Fig. 3.5a). The size of
the red algae accumulations in some layers is larger than two millimetres. Within these
topmost 12 meters almost no dasycladaleans can be observed, while porcelaneous
foraminifers and complex rotalids become increasingly common among the benthic
foraminifers.
3.4.2 Biostratigraphy
The biostratigraphy of the Qalhat section is based on larger foraminifers in the
Maastrichtian and on smaller benthic foraminifers and dasycladalean algae in the
Paleocene (Fig.3.6).
Benthic foraminifers. The concurrent range of O. apiculata, S. calcitrapoides and O.
macroporus (Fig. 3.6) can be correlated with the upper part of the Gansserina gansseri to
Abathomphalus mayaroensis planktonic foraminifer zones (Bilotte in Hardenbol et al.,
1998a). Therefore the base of the section is not older than the late part of the Early
Maastrichtian. A probable Late Maastrichtian age, starting from about 20 m above the base
of the section, is suggested by the occurrence of P. blumenthali and of specimens of O.
apiculata with very large embryos (Li+li up to 1160 microns, see Caus et al., 1999). This
is further supported by the occurrence of specimens of O. macroporus with biometric
parameters indicative of the A. mayaroensis zone (Li+li up to 900 microns, see Özcan,
2007). The last observed Maastrichtian datum is at 55 m as defined by the last occurrences
(LO) of O. macroporus and S. calcitrapoides.
Larger foraminifers were almost completely wiped out by mass extinction at the K/P
boundary (Brasier, 1988; Tappan and Loeblich, 1988). Laffitteina was the only survivor
49
Figure 3.6: Ranges of foraminifers and calcareous algae.
among Maastrichtian complex benthic foraminifers with a canal system. Laffitteina
bibensis Marie, along with Bangiana hanseni Drobne, is the marker for the SBZ 1
(Shallow Benthic Zone) that indicates a Danian age in shallow-water facies and is
correlative of the P0 to P2 planktonic foraminifer zones (Serra-Kiel et al., 1998). Neither
of these species is present in the Qalhat section. The first evidence of a Danian age is given
by the first occurrence (FO) of the benthic foraminifer Kolchidina paleocenica (Fig. 3.5b,
k) at 61.6 m. This species co-occurs with L. bibensis in several reference sections of
50
Danian shallow-water carbonates in Turkey (Sirel, 1999), and can be therefore confidently
taken as indicative of SBZ 1. A few meters above, at about 65 m, Valvulina sp. (cf.
Valvulina? sp. 1 in Sirel, 1998; Fig. 3.5c-d), another arenaceous foraminifer, joins K.
paleocenica. This species has also been found together with L. bibensis in Turkey (Sirel,
1998, 1999), further confirming an SBZ 1 age for this part of the Qahlat section. Therefore
benthic foraminifers allow constraining the position of the K/P boundary between 55 and
61.6 m above the base of the Qalhat section. Pervasive dolomitization hinders the
identification of microfossils in the critical interval, so that the position of the boundary
cannot be documented more precisely.
The next significant biostratigraphic event of benthic foraminifers is the FO of
Kayseriella decastroi Sirel (Fig. 3.5e), at about 120 m. At the type locality of K. decastroi
Sirel and in other sections of central Turkey, the range of this species coincides with the
upper part of the range of L. bibensis (Sirel, 1999). Therefore its FO could be correlated
with the Upper Danian.
No significant biostratigraphic marker occurs in the upper part of the Qalhat section
and therefore only indirect evidence can be used to constrain the age of this part of the
section. After the extinction at the K/P boundary, larger foraminifers become again
abundant and diverse in shallow-water facies starting from the Late Selandian–Early
Thanetian (Hallock et al., 1991). Many new genera first occur at this time, including
Alveolina, Nummulites, Discocyclina and some conical imperforate foraminifers. Their
FOs mark the base of SBZ 3 that can be correlated with the lower part of the P4 zone of
planktonic foraminifers (Serra-Kiel et al., 1998). The absence of larger foraminifers in the
upper part of the Qalhat section is taken as indirect evidence of its pre-SBZ 3 age. This
hypothesis is broadly consistent with the occurrence of Idalina sp. (Fig. 3.5n) at about 135
m, as the Paleocene species of the genus Idalina first occur at the top of SBZ 2 in the
Pyrenees and in the Adriatic realm (Drobne et al., 2002).
Dasycladalean algae. After the mass extinction at the K/P boundary, dasycladalean algae
underwent a major radiation in the Danian (Aguirre et al., 2000, 2007) and they are
common components of Early and Middle Paleogene low latitude shallow-water carbonate
facies. Two main phases have been recognized in the recovery and radiation of this algal
group in the Paleocene and a correlation has been proposed with the SBZ of larger
foraminifers (Barattolo, 1998, 2002). The first dasycladalean assemblage, correlative of the
lower part of SBZ 1 (Lower Danian) has been found so far only in very restricted inner
51
platform environments. This is a species-poor assemblage, characterized by the presence of
Decastroporella tergestina Barattolo, Drobnella slovenica Barattolo and Acroporella
chiapasensis Deloffre, Fourcade and Michaud (one of the few Maastrichtian survivors).
The second assemblage is correlated with the upper part of SBZ 1 to SBZ 3 (Upper
Danian−Thanetian pp.). It is marked by the appearance of many new taxa (refer to
Barattolo, 2002, for a complete list) and is typically dominated by the genus Cymopolia
(hence the name Cymopolia assemblage). This phase marks the Phanerozoic maximum in
dasycladalean generic diversity (Aguirre and Riding, 2005).
The range chart of dasycladaleans in the Qalhat section shows two clearly separate
assemblages above the K/P interval. The lower one is species poor and is characterized by
Trinocladus perplexus and Neomeris spp., with a few specimens of Thyrsoporella spp.,
Dissocladella gracilis, and Cymopolia spp. (Fig. 3.6). This assemblage first occurs a few
meters above the K/P interval at 66.5 m. From about 90 m upwards dasycladaleans become
increasingly more diverse and abundant. The new assemblage is dominated by Cymopolia
spp. and Indopolia satyavanti Pia. Other common taxa are Jodotella sloveniaensis,
Clypeina spp., Neomeris spp., and Thyrsoporella spp. (Fig. 3.6). This second assemblage
could represent an equivalent of the Cymopolia assemblage of the Adriatic platform.
Following the correlation proposed by Barattolo (2002) its FO at 90 m could be correlated
to the upper part of SBZ 1 (Upper Danian).
3.4.3 Strontium-isotope stratigraphy
The elemental composition of low-Mg calcite can be used to assess the diagenetic
alteration of the sampled material (Brand and Veizer, 1981). Considering only the samples
with more than 1000 ppm Sr results in a set of samples that have Mg, Fe, and Mn
concentrations characteristic for pristine skeletal calcite (Mc Arthur 1994). The mean value
of five samples from the Simsima Formation (Q8, Q11, Q16; Tab.3.2) is 0.707853 +/0.000008 (2 s.e.), which is slightly higher than the highest Cretaceous
87
Sr/86Sr seawater
value of 0.707830 that is reported to occur close to the K/P boundary (65.6–66.0 Ma;
McArthur and Howarth, 2004). The
87
Sr/86Sr value of two (Q6b-2, Q7b) of the three
samples that are considered diagenetically altered due to low Sr concentrations are higher
than those of the best preserved samples, following the expected trend of diagenetic
modification (McArthur, 1994). However, SEM images of the rudist shells (Fig. 3.7) show
significant alteration of the original fibrous-prismatic shell structure. It is therefore
52
concluded that the original Sr-isotopic composition is probably not preserved despite the
elemental concentrations that suggest retention of the original seawater values.
Qahlah
Formation
Simsima Formation
Table 3.2: Results of elemental analysis, and Sr-isotope values of skeletal calcite from the Cretaceous
interval of the Qalhat section. Underlined samples are suggested to be influenced by diagenesis. Sample Q70
was taken from isolated limestone blocks ~50 m below the continuously exposed section of the Simsima
Formation (Fig. 3.3).
+/- 2s.e.
(x 10-6)
Material
0.707849
7
Dictyoptychus
253
0.707866
7
recrystallized
shell
14
153
0.707877
7
Hippuritidae
940
1
62
0.707858
7
Dictyoptychus
1520
1492
1
173
0.707850
7
Dictyoptychus
20.2
1214
2576
1
123
0.707840
7
Dictyoptychus
Q16b1
36.9
1221
1083
1
110
0.707855
7
rudist indet.
Q16b2
36.9
1261
1392
1
88
0.707864
7
rudist indet.
Q70
- 50.0
1409
1612
1
100
0.707844
7
Hippuritella
Q70
- 50.0
1409
1612
1
100
0.707835
7
Hippuritella
Sample
Section
[m]
Sr
[ppm]
Mg
[ppm]
Mn
[ppm]
Fe
[ppm]
Q6b1
5.4
666
2471
3
83
Q6b-2
5.4
255
91296
14
Q7b
7.5
688
2938
Q8b1
10.4
1376
Q8b2
10.4
Q11b
87
Sr / 86Sr
3.4.4 Stable isotopes
The δ
13
C and δ
18
O values range from -1.8‰ to 3.3‰ and from -8.6‰ to -1.1‰,
respectively (Fig. 3.3). The low values of δ 18O are considered to be the result of diagenetic
alteration, due to burial diagenesis and/or interaction with meteoric water during early
cementation (Hudson, 1977). The oxygen isotopic composition of bulk rock samples
generally tends to be more affected by diagenesis than the δ 13C values because of the mass
balance of water-rock interaction (Brand and Veizer, 1981). The oxygen isotopic
composition of the bulk rock samples is therefore here excluded from further discussion
because of the unknown impact of diagenetic alteration.
In the basal part of the section, up to 50 m, the δ 13C values scatter around a mean value
of +1.6‰ (Fig. 3.3). Between 50 and 60 m and a few meters above the dolostone unit (85–
105 m), the δ 13C values show only minor variations around +1‰. Higher values from
53
+1‰ to +3‰ and back to +1‰ (between 60–66 m) correspond to the dolostone unit that
contains the K/P boundary interval (Fig. 3.3). Following a first negative excursion at 64.7
m (-0.27‰), the δ13C values increase from c. +1‰ to +2‰ at 80 m (Fig. 3.3). The upper
part between 110 and 140 m is characterized by an increase from the most negative values
of the section (-1.8‰) to relatively stable values around +1.3‰ δ 13C of the topmost five
meters of the section.
Figure 3.7: SEM image of diagenetically
altered, originally fibrous-prismatic outer shell
layer of hippuritid rudist (sample Q7). The
recrystallization of the former fibrous crystals
with distinct prism boundaries resulted in
considerably larger crystals with an irregular
shape.
3.5 Discussion
3.5.1 Completeness of the sedimentary record across the K/P boundary
Roger et al. (1998) identified the K/P boundary interval of the basinal deposits of the
Oman Mts. (Abat, E of Jabal Ja’alan and Jabal Muthaymimah, Buraymi) with the FO of
typical planktonic foraminifers, while their biostratigraphical zonation of the coeval
platform deposits is less well defined.
Although the critical interval of the studied section at Qalhat is partly dolomitized, and
details of the micro- and macrofacies are thus obliterated, it most likely represents a
continuous succession of tropical shallow-water carbonates across the K/P boundary.
Except for the surfaces of subaerial exposure below the last occurrence of Maastrichtian
benthic foraminifers (Fig. 3.3), there are no further sedimentological indications of a major
hiatus in the upper part of the section. The chemostratigraphical data (δ
13
C,
87
Sr/86Sr)
support this interpretation. Although the Sr-isotope values are considered to have been
diagenetically altered, the
87
Sr/86Sr values of the best preserved samples do not argue
against a latest Maastrichtian age of the rudist shells studied. Even a preservation of
pristine seawater values would, in this case, not constrain the K/P boundary more precisely
54
than our biostratigraphical data, as the resolution of SIS is not better than +/- 0.5 myrs, and
even worse close to the K/P boundary (Steuber et al., 2002).
The correlation of the δ 13C curve of the Qalhat section with the data from Berggren et al.
(2000; DSDP 384, J-Anomaly Ridge, Grand Banks Continental Rise, NW Atlantic Ocean)
supports our biostratigraphical zonation of the Danian to Selandian of the post-boundary
deposits, and the absence of an Early Paleocene hiatus (Fig. 3.8). Berggren et al. (2000)
correlate the peak of the first negative excursion of the Early Paleocene with the base of
the magnetic polarity chron C26R, which corresponds to the base of the Selandian stage
(Fig. 3.8). There is much more scatter in the δ 13C values of the bulk rock samples from
Qalhat, but the peak of this negative excursion can be observed in the upper part of the
section at c. 120 m. Our biostratigraphic data confirm that this level corresponds to the
base of the Selandian stage.
Figure 3.8: Correlation of the Qalhat section with DSDP Site 384 (Berggren et al. 2000) based
on δ13C values.
Sedimentary dolomites are expected to have δ
13
C values that are 2‰ higher than co-
genetic calcite (Friedman and O’Neill, 1977). This explains the distinct positive shift of the
δ 13C values in the K/P boundary interval. However, as the blocky dolomite observed in
this interval is considered to be of late diagenetic origin, interpretation of the carbon
55
isotope record across the boundary interval in terms of depositional or environmental
change is difficult.
The negative excursion of almost 3‰ δ 13C at 64.7 m (Fig. 3.3) may reflect a decrease of
the marine primary productivity due to biological crisis at the K/P boundary (Barrera and
Keller, 1994). However, due to the dolomitization and its effect on the δ 13C values, the
preservation of this event in the carbon isotope record at Qalhat is difficult to evaluate, and
the single negative value recorded immediately above the dolostone unit may be an artifact
of diagenesis. While the general trends of the δ 13C curve from Qalhat correspond to those
of other K/P boundary sections (Berggren et al., 2000; Hart et al., 2004), excursions based
on single samples should be interpreted with caution, considering the large scatter of δ 13C
values (Figs. 3.3, 3.8) that is typically found in bulk rock data of shallow-water limestones.
Le Callonnec et al. (1998) measured several Maastrichtian–Paleocene carbon isotope
sections of the northern and eastern Oman (Jabal Muthaymimah near Buraymi, and region
of Abat) that show a narrow range of δ
13
C values. These curves exhibit no distinct
structure except of a prominent negative peak of -3‰ δ 13C in the Abat section, associated
with a moderate increase in Ir concentrations that was interpreted from Le Callonnec et al.
(1998) to indicate the K/P boundary. There, the sequence of disappearance of rudists and
larger benthic foraminifers in the terminal Maastrichtian, and the dominance of
dasycladaleans in the limestone above is very similar when compared to the Qalhat section
described here. However, our detailed biostratigraphy places the K/P boundary close to the
LO of larger foraminifers, while the K/P boundary at Abat based on geochemistry was
drawn substantially higher, in the middle of the dasycladalean-rich unit (Roger et al., 1998;
Le Callonnec et al., 1998), i.e. within the facies unit three of the Qalhat section between
100 and 130 m (Fig. 3.3).
3.5.2 Environmental change across the K/P boundary
The Upper Maastrichtian carbonate platform at Qalhat obviously formed under open
marine conditions which persisted up to the Selandian. At Qalhat, the prominent tropical
carbonate platform biota of the Late Cretaceous disappear at well-defined levels (Figs. 3.3,
3.6); the rudists first, followed by the larger benthic foraminifers. No stepwise extinction
pattern can be observed within the different groups of biota. While the larger benthic
foraminifers are abundant up to the dolomitized interval and just five meters below the FO
of Paleocene foraminifers (Fig. 3.6), rudists occur only in three discrete levels below the
56
boundary (Fig. 3.3). This observation is similar that on the occurrences of latest
Maastrichtian species-rich rudist associations in Jamaica (Steuber et al., 2002) and Italy
(Steuber et al., 2007). The patterns of distribution of the rudists and larger benthic
foraminifers do therefore not argue against a catastrophic extinction of both groups at the
K/P boundary at Qalhat. The sequence of FOs of the Early Paleocene (Zone P0–P1) biota
is difficult to evaluate because of the scarce data available for comparison with other
carbonate platforms. Not much is known about early Danian shallow-water flora and fauna
(e.g. Vecsei and Moussavian, 1997; Kiessling and Baron-Szabo, 2004; Ogorolec et al.,
2007), due to extended periods of non-deposition that occurred on most tropical carbonate
platforms. Therefore, the observed pattern of turnover among the major carbonate
producers at the Qalhat section is particularly important.
The rapid change in the temporal distribution of characteristic biota such as rudists,
larger benthic foraminifers, and calcareous algae may also suggest a significant
environmental change. However, the environmental setting in the latest Maastrichtian
interval is considered to be open marine and of moderate to high energy, and the diversity
of the dasycladaleans at the Qalhat section shows that also during the Danian the
conditions remained open marine. The energy levels of the different depositional settings
show a change from relatively high, as indicated by rudist rudstones and occasional
grainstones of facies unit 1, to a period of moderate energy levels recorded in the thick
packstone-dominated deposits of facies unit 3 (Fig. 3.3). Lower energy-level wackestones
with abundant dasycladaleans dominate the upper part of facies unit 3 while grainstones
and packstones re-occur in the topmost, i.e. Selandian part of the section, associated with a
change in dominance from green algae (dasycladaleans) to red algae (corallinaceans and
peyssonnelliaceans). With the demise of the rudist association at the end of facies zone 1,
the episode of sediment baffling carbonate producers at Qalhat is ending. A shallowing
upward sequence with a lagoonal character follows and is indicated by the high abundance
and high diversity of dasycladaleans after the K/P boundary. Finally the synchronous
occurrence of red algae and corals mark the facies zone 4 as an interval of agitated water
on the former carbonate platform at Qalhat.
Detailed interpretations of environmental change at the K/P boundary are precluded by
the dolomitization of the critical interval. However, it is remarkable that the late diagenetic
dolomitization preferentially affected units of the section that are rich in echinoderm debris
with an originally high-Mg-calcite mineralogy (refer to Lohmann and Meyers, 1977 and
Dickson, 2001, for a detailed view on geochemical background). The abundance of
57
echinoderm debris, however, suggests that marine primary production persisted on the
platform and provided the necessary resources for echinoderms.
3.5.3 Sea-level change
Evidence for Late Maastrichtian relative sea-level change is provided by the distinct
surfaces of subaerial exposure between 15 and 34 m. The lowest one of these horizons may
correspond to an Upper Maastrichtian sequence boundary (Hardenbol et al., 1998b; Li et
al., 2000; Miller et al., 2005). There is no further evidence for significant change in water
depth of the generally shallow subtidal depositional environment recorded throughout the
section. The presence of some planktonic foraminifers above the K/P boundary may
indicate more open marine conditions but there is no evidence of a sea-level change. Roger
et al. (1998) concluded that the remarkably uniform sedimentation during the Late
Cretaceous and Paleocene in the region of Sur is due to the lack of regional tectonic
activity during this time period (e.g. Abat basin) while elsewhere in Oman and the United
Arab Emirates, the Simsima Formation is unconformably overlain by Paleogene
formations (Nolan et al., 1990).
3.6 Conclusion
The limestones of the Qalhat section, comprising the Cretaceous/Paleogene boundary
without an apparent hiatus, were deposited under open marine conditions that persisted
from the Maastrichtian into the Selandian. This provides a unique opportunity to study the
effect of the K/P boundary event on a tropical Tethyan carbonate platform and its biota, as
other examples reported previously is characterized by either a major hiatus or restricted
environmental conditions during the critical boundary interval. We provide the first precise
biostratigraphical zonation of the platform carbonates of the region. At Qalhat, the K/P
boundary is contained within an interval of less than seven meters, as indicated by the LO
of Siderolites calcitrapoides and the FO of Kolchidina paleocenica. A more precise
delineation of the boundary was not possible due to dolomitization of the critical boundary
interval. Biostratigraphy and chemostratigraphical correlation using δ 13C values support
the assumption of a continuous succession without a major hiatus.
Typical biota of the Maastrichtian, i.e. rudists and larger benthic foraminifers, are
abundant in the Maastrichtian deposits, and their vertical distribution argues for a
catastrophic rather than a stepwise extinction pattern at the K/P boundary. Although no
dramatic facies change seems to have occurred during the K/P boundary interval, there is
58
an abrupt change to calcareous green algae (codiaceans and dasycladalean) as the dominant
biota in the Early Paleocene. It is unclear, whether the dominance of echinoderm bioclasts
in the boundary deposits reflects an ecological signal or is related to the preferential
preservation of the originally high-Mg calcite bioclasts during dolomitization of this
critical unit.
Acknowledgements
We thank D. Buhl, B. Raczek and B. Gehnen for their support during laboratory work; O.
Weidlich for his “resident knowledge” and support during the field work. We are also
thankful to M. Wilmsen for his valuable comments and suggestions, which helped to
improve this contribution. Funded by Deutsche Forschungsgemeinschaft (Ste 670/13).
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Tethys and description of two new taxa. Cretaceous Research 28, 621–641.
southeastern Salento (Apulia, southern Italy). Bollettino della Societa
Roger, J., Bourdillon, C., Razin, P., Le Callonnec, L., Renard, M., Aubry, M.P., Philip, J.,
Platel, J.P., Wyns, R. and Bonnemaison, M., 1998. Modifications des
paléonvironments et des associations biologiques autour de la limite CrétacéTertiaire dans les montagnes d'Oman. Bulletin de la Société Géologique de
France 169, 255–270.
Schlüter, M., Steuber, T., Parente, M., Mutterlose, J., 2008. Chronostratigraphy of
Campanian – Maastrichtian platform carbonates and rudist associations of
Salento (Apulia, Italy). Cretaceous Research 29, 100–114.
Serra-Kiel, J., Hottinger, L., Caus, E., Drobne, K., Ferrandez, C., Jauhri, A.K., Pavlovec,
R., Pignatti, J., Samso, J.M., Schaub, H., Sirel, E., Strougo, A., Tambareau, Y.,
Tosquella, J., Zakrevskaya, E., 1998. Larger foraminiferal biostratigraphy of the
Tethyan Paleocene and Eocene. Bulletin de la Société Géologique de France 169,
281–299.
Sirel, E., 1998. Foraminiferal description and biostratigraphy of the Paleocene-lower
Eocene shallow-water limestones and discussion on the Cretaceous-Tertiary
boundary in Turkey. General Directorate of the Mineral and Research and
Exploration, Ankara, 117 pp.
Sirel, E,. 1999. Four new genera (Haymanella, Kayseriella, Elazigella and Orduella) and
one
new
species
of
Hottingerina
from
the
Paleocene
of
Turkey.
Micropaleontology 45, 113–137.
Skelton, P., Nolan, S.C., Scott, R.W., 1990. The Maastrichtian transgression onto the
northwestern flank of the Proto-Oman Mountains: sequences of rudist -bearing
beach to open shelf facies, Geological Society, London, Special Publication 49,
521–547.
Steuber, T., 1999. Isotopic and chemical intra-shell variations in low-Mg calcite of rudist
bivalves (Mollusca-Hippuritacea): disequilibrium fractionations and Late
Cretaceous seasonality. International Journal of Earth Sciences 88, 551–570.
63
rudist formatios in the Norhern Calcareous and Central Alps (Austria and
Steuber, T., 2003a. Strontium isotope chemostratigraphy of rudist bivalves and Cretaceous
carbonate platforms. In: Gili, E., Negra, M.H. and Skelton, P.W., North African
Cretaceous carbonate platform systems. NATO Science Series, Earth and
Environmantal Sciences 28, 229–238.
Steuber, T., 2003b. Strontium isotope stratigraphy of Cretaceous hippuritid rudist bivalves:
Steuber, T., Mitchell, S.F., Buhl, D., Gunter, G., Kasper, H.U., 2002. Catastrophic
extinction of Caribbean rudist bivalves at the Cretaceous-Tertiary boundary.
Geology 30, 999–1002.
Steuber, T., Korbar, T., Jelaska, V., Gušić, I., 2005a. Strontium-isotope stratigraphy of
Steuber, T., Rauch, M., Masse, J.-P., Graaf, J., Malkoč, M., 2005b. Low-latitude
seasonality of Cretaceous temperatures in warm and cold episodes. Nature 437,
1341–1344.
Steuber, T., Parente, M., Hagmeier, M., Immenhauser, A., van der Kooij, B., Frija, G.,
2007. Latest Maastrichtian species-ruch rudist associations of the Apulian margin
of Salento (S Italy) and the Ionian Islands (Greece). In: Scott, R.W., Cretaceous
Rudists and Carbonate Platforms: Environmental Feedback. SEPM, Special
Tappan, H., Loeblich, A.R., 1988. Foraminiferal evolution, diversification and extinction.
Journal of Paleontology 62, 695–714.
Vecsei, A., Moussavian, E., 1997. Paleocene reefs on the Maiella platform margin, Italy:
An example of the effects of the Cretaceous/Tertiary boundary events on reefs
and carbonate platforms. Facies 36, 123–140.
Wan, X.Q., Jansa, L.F., Sarti, M., 2002. Cretaceous and Paleogene boundary strata in
southern Tibet and their implications for the India-Eurasia collision. Lethaia 35,
131–146.
64
Wyns, R., Le Metour, J., Roger, J., Chevrel, S., 1992. Geological map of Sur with
explanatory notes, sheet NF 40-08. Muscat, Directorate General of Minerals,
Oman Ministry of Petroleum and Minerals.
65
Chapter 4 ◦Rudist-bearing carbonate platforms of the latest Cretaceous
4. Rudist-bearing
carbonate
platforms
of
the
latest
Cretaceous
(Campanian–Maastrichtian) – strontium-isotope stratigraphy and rudist
provincialism
1
1
M. Schlüter, 2T. Steuber, 3M. Parente, 1J. Mutterlose
Institut für Geologie, Mineralogie und Geophysik, Ruhr-Universität Bochum, Universitätsstr. 150, 44801
Bochum, Germany
2
The Petroleum Institute, Abu Dhabi, PO Box 2533, Abu Dhabi, United Arab Emirates
3
Dipartimento di Scienza della Terra, Università “Federico II” Napoli, Largo San Marcellino 10, 80138
Napoli – Italy
(in preperation)
Abstract
Late Cretaceous (Campanian–Maastrichtian) rudist-bearing carbonate platforms of the
Mediterranean part of the Tethys were studied with respect to the timing and pattern of
their decline. Strontium isotope data confirmed the observation that species-rich rudist
associations are of latest Maastrichtian age, implying that rudists were still flourishing
close to the Cretaceous–Paleogene boundary. In contrast to previous age assignments the
strontium data rather supplied a late Campanian than a Maastrichtian age for various rudist
bearing limestones in SE Turkey. A pronounced endemism of the Campanian–
Maastrichtian rudist associations leads here to the definition of three faunal provinces; a
Caribbean, a Mediterranean and an eastern Tethyan (Arabia, Asia, E-Africa) province are
differentiated. It seems likely that this distinctive provincialism contributed to the demise
of the Campanian–Maastrichtian rudists. The increase of regional tectonic activities along
the Tethys in the Maastrichtian culminated in the decrease of shallow-water carbonate
deposits. The extinction of the rudists was probably influenced by these reductions of
shallow-water carbonate platform areas, going along with an increasing degree of
provincialism.
Keywords: Shallow-water carbonate platforms, rudist bivalves, strontium-isotope
stratigraphy, Campanian–Maastrichtian
66
4.1 Introduction
Low-latitude shallow-water carbonate platforms of the latest Cretaceous (Campanian–
Maastrichtian) are dominated by benthic communities of rudist bivalves, scleractinian
corals, larger benthic foraminifers and calcareous algae. The global pattern of the demise
of these characteristic Late Cretaceous ecosystems at the Cretaceous–Paleogene (K/P)
boundary was rather imprecisely constrained due to a lack of biostratigraphical precision.
Consequently, previous evaluations of the timing and pattern of their history had been
based on a limited data set (Philip, 1998; Steuber et al., 2007). Strontium-isotope
stratigraphy (SIS) has developed into a widely used method to improve global
stratigraphical correlation because it allows to derive numerical ages (McArthur, 1994;
Veizer et al., 1997; McArthur and Howarth, 2004). SIS has been used in several studies of
Late Cretaceous carbonate platform correlation, where biostratigraphy is notoriously
difficult so that substantial progress has been made in recent years to confine the
stratigraphical framework of rudist-dominated carbonate platforms (Swinburne et al.,
1992; Steuber et al., 2002; Steuber et al., 2007 and references therein; Schlüter et al.,
2008a). The observation of species-rich rudist assemblages in Italy (Steuber et al., 2007;
Schlüter et al., 2008a) or continuous shallow-water platform persisting from the
Campanian to the Paleogene (Schlüter et al., 2008b) are just two examples of new data
based on SIS.
With the present contribution we aim to summarize the existing data about the
extinction of the rudist bivalves, the dominant metazoan carbonate producers on many Late
Cretaceous carbonate platforms.
The evolution of the main carbonate producers and the development of the shallowwater carbonate platforms are intrinsically related to each other. Consequently, a precise
stratigraphy is the basis for a discussion of the controlling factors for the global demise of
the rudists and Cretaceous carbonate platforms
4.2 Latest Cretaceous carbonate platforms
The Campanian to Maastrichtian shallow-water carbonate platforms dominated by rudistlimestones are confined to low palaeo-latitudes between 30°N – 15°S (Fig. 4.1).
One of the main areas of latest Cretaceous shallow-water limestones is the Caribbean
and central American region, including Guatemala, Peru and Mexico (Schafhauser et al.,
2007). Along the Mediterranean Tethys, many rudist-bearing platforms can be observed on
the European plate, from southern Spain, the Alps, Italy, Croatia or Greece. In Turkey (i.e.
67
this contribution) the carbonate platforms from the European and former Afro-Arabian
plates are juxtaposed. Other rudist associations of the Afro-Arabian Plate have been
described from the United Arab Emirates (Skelton, 1988), Oman (Skelton and Wright,
1987; Roger et al., 1998; Schlüter et al., 2008b), Saudi Arabia (Philip et al., 2002), and
Fig. 4.1: Paleogeographic map of the Late Cretaceous including the global distribution of rudist-bearing
shallow-water carbonate platforms and currently available data (i.e. biostratigraphical or Sr isotope
stratigraphical).
Somalia (Pons et al., 1992). Further to the North and East, associations are known from
Iran and Afghanistan, and from southern Tibet (Wan et al., 2002). Additional regions and
localities treated by many other contributions and workers on Late Cretaceous carbonate
platforms are not listed here, see also Simo (1993), Ross and Skelton (1993) and Skelton
(2007) for further references and topics.
Recently, numerical ages based on SIS have been assigned to many localities (Figs.
4.1, 4.2). One of the first contributions using SIS of rudist-bearing shallow-water
carbonates has been made by Swinburne et al. (1992) of localities in Bulgaria.
Preferred material for geochemical analysis is the compact, originally low-Mg calcite outer
shell-layer of radiolitid and hippuritid rudists, which is known to preserve the original Sr
68
Fig. 4.2: Compilation of global strontium isotope stratigraphical data for the Campanian to Maastrichtian
rudist-bearing shallow-water limestones. The dashed lines and underlined taxa of the larger benthic
foraminifers indicating the corrected first appearance date due to numerical ages of the corresponding
localities (Cava Cocumola, Cava Longo, Vitigliano and Yayladağı).
69
seawater composition (McArthur, 1994; Steuber, 1999; McArthur et al., 2001; Steuber et
al., 2005).
The impact of diagenetic alteration can be assessed by different kind of methods and/or
the combination of these: a) by visual screening of the sample material directly in the field,
b) by analysing the microstructure of the sampled shell layer with SEM, and c) by
analysing the elemental composition of the sampled material (Brand and Veizer, 1981;
Steuber, 2001).
The geochemical analyses of the elements by ICP-AES followed the methods of
sample preparation and measurement described in Schlüter et al. (2008a). The separation
of the sample material used for Sr analysis also followed standard ion-exchange method,
and measurements were run in dynamic mode with a thermal-ion mass spectrometer
(Finnigan MAT 252). The analytical precision of the new data presented here was +/7*10-6 (2 standard error, s. e.) as monitored by samples of the USGS-EN 1 standard (mean
value 0.709157; n = 5) that was run together with the sample material. For further
information about analytical methods refer to Steuber et al. (2003).
The global
87
Sr/86Sr ratio of normal marine seawater shows a globally homogenous
distribution due to the relation of residence time of Sr (4*106 years) and mixing of the
ocean water (1*103 years), but it varies significantly with time (Veizer, 1989; McArthur,
1994; Veizer et al., 1997). Therefore Sr shows characteristic values for distinct time slices
and the Sr ratio reflects the seawater composition of the paleo-ocean (Schlüter et al.,
2008b). Sr concentrations between 1000 ppm and 2000 ppm are considered to be
characteristic for pristine skeletal low-Mg calcite (McArthur, 1994; Steuber, 2003) while
high Fe and Mn concentrations, and very low Sr concentrations indicate diagenetic
alteration (Al-Aasm and Veizer, 1986). Numerical ages have been derived from the ‘LookUp Table Version 4: 08/ 03’ of McArthur and Howarth (2004) after adjusting the measured
Sr-isotope ratios to a
87
Sr/86Sr value of 0.709175 for the USGS-EN1 standard. The
87
Sr/86Sr values are calibrated to the time scale of Gradstein et al. (2004).
4.4 Regional pattern and stratigraphy of shallow-water carbonate platforms
Many rudist-bearing carbonate platforms persisted into the latest Maastrichtian, e.g. in NE
Mexico (Schafhauser et al., 2007), Jamaica (Steuber et al., 2002; Mitchell and Gunter,
2006), around Adria (Italy and Croatia; Steuber et al., 2007; Schlüter et al., 2008a), or in
the SE part of the Arabian carbonate platform (Schlüter et al., 2008b). The comparison of
the evolution of these rudist-bearing carbonate platforms of the paleo-tropics, and the
70
precise stratigraphy of the last occurrence of rudist associations in each region are most
important data that help to understand the final development and demise of Cretaceous
In Cretaceous carbonate platform deposits, the precision of biostratigraphical data
depends mainly on the range of benthic foraminifers and calcareous algae. It is shown
below, that the first appearance datum of a few benthic foraminifera need to be revised,
following the numerical ages obtained for some localities where they co-occur with rudist
bivalves. The limits of precision of numerical ages derived from SIS are determined by the
analytical uncertainty of Sr isotope analysis, and the range of confidence limits of the
‘look-up table’ (McArthur and Howarth, 2004). In case that numerical ages are not
compromised by diagenetic alteration of the original Sr-isotopic composition, +/- 0.5 my is
the highest precision that can typically be achieved by SIS of Campanian–Maastrichtian
skeletal carbonates. Precision decreases close to the K/P boundary because of a turning
point of the Sr-isotope ratio with maximum values just below the boundary. Details of the
diagenetic screening, elemental compositions, and Sr-isotope analyses for samples from
each of the regions discussed are given in the cited references of the following section.
Bulgaria. Upper Cretaceous deposits of east-central Bulgaria consist of alternating
limestones, siliciclastic dominated sandstones and volcanoclastics (Swinburne et al., 1992).
The uncertainty of numerical ages given by Swinburne et al. (1992) for the Yambol and
Yaroslavtzi localities is not better than +/- 4.0 my (Fig. 4.2). According to these data, the
Pironaea-assemblage of the Bulgarian localities has an age of early Campanian to
Campanian / Maastrichtian boundary while the last deposits at the locality of Yambol are
dominated by the following rudists: Pironaea praeslavonica, Pironaea slavonica,
Vaccinites atheniensis. At Yambol the upper limit of the succession is not cropping out,
whereas at Yaroslavtzi the rudist-bearing deposits are unconformably overlain by
Paleogene limestones (Swinburne et al., 1992).
Croatia. The localities of the island of Brač (Croatia) belong to the Adriatic carbonate
platform (Vlahović et al., 2002), located in the central part of the Mediterranean Tethys.
The Cretaceous limestones are typically truncated by a sharp unconformity at their top, due
to a Paleogene major emersion event. The section of Likva is considered to be latest
Maastrichtian (Fig. 4.2) with a numerical age of 65.5 Ma for the last rudist occurrence
(Steuber et al., 2005). The samples used for SIS originated from requieniid rudists and
71
were collected from the last rudist-bearing horizon. Within this last bioclastic packstone
Apricardia sp., Biradiolites cf. fissicostatus, Bournonia excavata, Bournonia triangulata,
Bournonia sp. and Lapeirousia sp. have been observed (Steuber et al., 2005). The
limestone sedimentation at Likva resumes in the Eocene (Fig. 4.4).
Greece. The rudist-bearing limestones of Lefkas (Ionian Islands) are blocks within
megabreccias units intercalated in calciturbiditic and hemipelagic sedimentary rocks
(Steuber et al., 2007). The sediments are deposited at the former toe-of-slope of the
Apulian carbonate platform (Steuber et al., 2007). The only sample which is supposed to
have preserved the original Late Cretaceous sea-water signal of Sr concentration and
consequently used to derive numerical ages originated from a specimen of Pironaea
(Steuber et al., 2007). The uncertainty of the derived Late Maastrichtian age (66.4 Ma;
Fig. 4.2) is better than +/- 0.5 my. The latest Maastrichtian rudist association of Lefkas
consist of the following taxa (Steuber et al., 2007): Biradiolites chaperi, Hippurites
cornucopiae, Hippuritella lapeirousei, Joufia reticulata, Lapeirousia sp., Mitrocaprina
bulgarica, Pseudopolyconites apuliensis, Radiolitella maestrichiana, ?Pseudosabinia sp.
On the Ionian Islands, the K/P boundary interval cannot exactly located due to redeposition in the toe-of-slope sedimentary environment (Steuber et al., 2007).
Italy. The Cretaceous platform carbonates of the Carnian Prealps belong to the NW margin
of the Adriatic Carbonate Platform (Swinburne and Noacco, 1993). The Sr-isotope samples
of Swinburne and Noacco (1993) originated from Vaccinites, Katzeria and undefined
hippuritid rudists at the Monte Jouf (W of Maniago in the area NW of Udine) with a
chronostratigraphical uncertainty not better than +/- 2.0 my. Accordingly, the rudist
assemblage of the last unit has a Campanian / Maastrichtian boundary age and consists of
Apricardia sp., Colveraia variabilis, Hippurites lapeirousei, Joufia reticulata, Katzeria sp.,
Pironaea polystyla, Plagioptychus sp., Pseudopolyconites sp., Sabinia aniensis, and
Sauvagesia sp. These Upper Cretaceous limestones of the Calcari del Monte Cavallo are
unconformably overlain by the Paleogene Calcari di Andreis megabreccia (Swinburne and
Noacco, 1993).
At Ciolo (Salento) the intra-oceanic conditions of the Apulian carbonate platform
resulted in the deposition almost pure shallow-water limestones. Here, the Late
Maastrichtian rudist fauna of the Ciolo Limestone consists of Hippurites cornucopiae,
Hippuritella lapeirousei, Joufia reticulata, Mitrocaprina sp., Pironaea polystyla,
72
Petkovicia sp., Pseudopolyconites sp., aff. Pseudosabinia sp., ?Sabinia sp (Steuber et al.
2007). Samples for SIS (Steuber et al., 2007; Schlüter et al., 2008a) have been taken from
hippuritid and radiolitid rudists, respectively. The precision of the numerical age derived
for the Ciolo Limestone is better than +/- -0.9 my, due to a low gradient of the
87
Sr/86Sr
curve (McArthur, 2004). Schlüter et al. (2008a) studied additional localities of the Salento
peninsula; the ages of these samples vary from the mid-Campanian to the Late
Maastrichtian (Fig. 4.2). The youngest numerical age of the limestone successions of
Apulia is observed at Ciolo (mean value 66.4 Ma; Steuber et al., 2007). There, the rudistbearing limestones are slightly tilted and truncated by a major erosional unconformity, they
are followed by Oligocene carbonates (Chattian; Bosellini and Parente, 1994).
According to the numerical ages of several Apulian localities (Schlüter et al., 2008a),
the first appearance of the benthic foraminifers Accordiella conica, Raadshovenia
salentina and Omphalocyclus macroporus must be revised (Fig. 4.2), as these species
occur at Cava Cocumola (76.9 Ma +/-0.7), Vitigliano (76.1 Ma +/-0.6) and Cava Longo
(72.5 Ma +/- 0.5), respectively.
Jamaica. In the Caribbean region, Late Maastrichtian platform carbonates with prolific
rudist and coral association are followed by volcanoclastic rocks, owing to the active
tectonic setting of a volcanic arc. Samples from the Central, Maldon and Marchmont
inliers yielded latest Maastrichtian ages (Fig. 4.2), with the uncertainty of numerical ages
(c. +/- 0.9 my) containing the K/P boundary (Steuber et al., 2002).Samples were obtained
from the shells of Chiapasella, Hippurites or Plagioptychus of the Central, Maldon and
Marchmont inliers, while the complete rudist association consists of the following genera:
Antillocaprina, Biradiolites, Bournonia, Macgillavryia, Mitrocaprina, Parasarcolites,
Praebarrettia, Sauvagesia, Thyrastylon, Titanosarcolites.
Mexico. The depositional setting of the eastern part of the Mexican region starts with
shallow-marine carbonate sedimentation but changes significantly during the Late
Cretaceous (Campanian – Maastrichtian) to a siliciclastics-dominated setting, due to the
uplift of the Sierra Madre Oriental (Schafhauser et al., 2007). The samples from
Schafhauser et al. (2007) are from plagioptychid rudists, collected at Arroyo de la Atarjea
in San Luis Potosi (east-central Mexico) and date the last appearance of rudists at 68.4 Ma
(+/- 1.0 my; Schafhauser et al., 2007). At this last rudist-bearing horizon of the Late
Cretaceous carbonate platform Bournonia cardenasensis, Coralliochama gboehmi,
73
Hippurites perkinsi, Mitrocaprina cf. tschoppi, and Tampsia poculiformis constitute the
rudist association. Before the end of the Cretaceous, carbonate deposition ended and is
followed by continental red beds.
Oman. The situation on the Arabian plate is substantially different to most of the localities
mentioned above, due to the continuous carbonate succession crossing the K/P boundary at
the section of Qalhat (Sur region, E Oman), from the latest Maastrichtian into the Danian Selandian. The geochemical results are from samples of Dictyoptychus and Hippuritella.
The high
87
Sr/86Sr ratio argues for the Late Cretaceous maximum ratio near the K/P
boundary (McArthur et al., 2004; Fig. 4.2). At Qalhat, the demise of the main Cretaceous
carbonate producers (rudists, larger benthic foraminifers) and the evolution of carbonate
production are not linked to each other (Schlüter et al., 2008b). The environmental settings
and conditions for tropical shallow-marine biota persisted across the boundary, while the
associations of major carbonate producers changed (Schlüter et al., 2008b), i.e., the rudist
bivalves are replaced by calcareous algae and scleractinian corals.
The following rudist taxa have been recognized in the last rudist-bearing limestone horizon
of the Qalhat section: Bournonia excavata, Dictyoptychus morgani, Dictyoptychus sp.,
Mitrocaprina sp., Vaccinites cf. oppeli, Vaccinites sp. (Schlüter et al., 2008b).
Turkey. The rudist-bearing outcrops at Güzelyurt, Hekimhan, Sarıkız and Yazıhan
(Malatya) are located on the European Plate, while the localities of Alidamı, Eskikahta and
Yayladağı belong to the former Afro-Arabian Plate (Fig. 4.3).
The biostratigraphy of the studied localities is mainly based on the distribution of
benthonic foraminifers (e.g. Meriç, 1967), and most of the studied localities and their
rudist associations were previously considered to be of Maastrichtian age (Özer, 1993). SIS
resulted in a revision of this age to the Campanian for many localities (Tab. 4.1; Steuber et
al., in press).
The samples for SIS from Alidamı and Yayladağı have been taken from specimens of
Dictyoptychus. The high Sr values (1500 ppm – 1950 ppm) and Fe concentrations below
270 ppm suggest only minor, if any, diagenetic alteration. Consequently, all samples used
to derive numerical ages show an uncertainty which is better than +/- 0.7 my for the ages
of 70.9 Ma and 72.6 Ma, respectively (Tab. 4.1).
Samples from the Hekimhan region (Yazıhan, Sarıkız, Eskikahta and Güzelyurt) show
a distinct pattern of the elemental concentration, 87Sr/86Sr ratios and the derived numerical
74
ages (Tab. 4.1, Fig. 4.2). While the Fe concentrations are not higher than 400 ppm in any
of the samples, only samples with Sr concentration above 990 ppm are suggested to reflect
the original Sr-isotope seawater signal and were therefore selected to derive numerical
Fig. 4.3: Geological map of the SE Turkey; The stars indicating the studied localities on the European and
African-Arabian Plate.
ages. The uncertainty of the numerical ages for these localities is better than +/- 0.7 my,
while the numerical ages range from 76.1 Ma to 66.4 Ma.
The species-rich rudist associations of Hekimhan are the oldest samples studied among
the southern and southeastern Turkish localities (Fig.4.2) and yield a mean age of 76.1 Ma
(+/- 0.3), i.e. early Late Campanian. The prolific rudist associations of the KahtaAdıyaman area are also of Late Campanian age, while the overlying Dictyoptychus-bearing
levels of this region (Germav Formation at Alidamı, Eskikahta) can be assigned to the
Early Maastrichtian (Fig. 4.2). At Eskikahta the rudist association consists of Biradiolites
sp., Bournonia sp., Dictyoptychus sp., Dictyoptychus striatus, Hippurites sp., Lapeirousia
sp., and Pseudopolyconites sp. The youngest limestones with a mean age of 66.4 Ma (+/0.7; Late Maastrichtian; Tab. 4.1; Fig. 4.2) are observed at Sarıkız (Fig. 4.3), consisting of
a low-diverse rudist association dominated by Miseia.
75
The Upper Campanian Terbüzek Formation at Alidamı contains abundant rudists such
as Dictyoptychus euphratica, Dictyoptychus leesi, Hippurites syriaca, Paracaprinula sp.
Table 4.1: Element analyses, Sr-isotope values and numerical ages derived from
87
Sr/86Sr values of
biogenetic low-Mg calcite from south-eastern Turkey. Grey colours indicating matrix material
Locality
Sample
Sr
[ppm]
Mg
[ppm]
Mn
[ppm]
Fe
[ppm]
Hekimhan
HK I - I
HK I - IV
HK II - I
HK II - II
J35/1
J35/2
J63/1
J63/2
mean
1723
964
364
1279
1034
1250
1757
1747
4081
5454
1165
957
4924
3862
2967
2862
65
247
244
96
30
29
122
116
339
3403
1255
1070
234
190
4
7
Yazıhan
HN I - I
HN I - II
mean
HN II - I
HN II - IV
mean
both mean
HN I - I, 2
Sarıkız
S II
S II - 1
mean
S II - 3
Eskikahta
EK II
EK II
EK III
mean
EK IV
Güzelyurt
GY 2
GY 4
GY 5
1741
1962
3140
4559
16
24
108
131
2072
1700
3303
929
4
14
104
183
87
Sr / 86Sr
+/- 2 s.e.
( x 10-6 )
Age
[Ma]
0.707593
0.707600
0.707623
0.707647
0.707640
0.707620
0.707631
0.707628
0.707630
7
7
7
7
7
7
7
7
76.1 (+/- 0.3)
xxx
xxx
73.8 (+/- 0.5)
0.707755
0.707633
0.707694
0.707692
0.707650
0.707671
0.707659
0.707659
8
7
0.707826
0.707827
0.707827
0.707909
7
7
7
7
7
7
7
7
7
7
1281
6787
396
3025
1323
1276
4134
1563
94
31
403
184
533
9731
171
1773
1929
991
1589
4540
1899
3289
41
40
66
385
268
438
810
6729
115
3397
0.707763
0.707748
0.707781
0.707764
0.707719
620
2160
442
1266
1632
3358
280
32
130
434
250
3931
0.707679
0.707642
0.707643
74.5 (+/- 0.6)
72.1 (+/- 0.5)
7
7
7
73.0 (+/- 0.6)
73.4 (+/- 0.5)
7
66.4 (+/- 0.7)
7
69.5 (+/- 0.5)
74.0 (+/- 0.5)
Pseudosabinia klinghardti, Pseudopolyconites cf. ovalis, Vaccinites vesiculosus and
Vautrina syriaca, while Dictyoptychus and Radiolites sp., only, are reported from the
overlying, basal Germav Formation that is of latest Campanian age (Steuber et al., in
press).
76
The limestones from Yayladağı, south of Antakya and type locality of several rudist
taxa endemic to the Afro-Arabian Plate, also have been shown to be of Late Campanian
age (Steuber et al., in press).
There are also a few examples of latest Maastrichtian rudists occurrences that are
well constrained by biostratigraphical data, e.g. from the global stratotype section and
point of the K/P boundary at El Kef, Tunisia (Goolaerts et al., 2004) or from the
Maastrichtian stage at Limburg, Belgium (Philip, 1998).
At El Kef the last rudists are of unknown taxa and can be found six meters below the
K/P boundary within the Plummerita hantkeninoides zone (CF1; Goolaerts et al., 2004). At
this shallow continental shelf position, the Upper Cretaceous deposits consist mainly of
marls, interrupted by some limestone beds during the Maastrichtian while the Cretaceous
sedimentation ended with the prominent ;boundary clay’ layer of the K/P boundary (Keller
et al., 1995).
The last rudists of the Limburg region are observed five meters below the K/P
boundary within the middle part of the Abathomphalus mayaroensis zone (66.6 Ma, or
CF3, according to the GSSP of El Kef; Philip, 1998). They consist of the following taxa:
Biradiolites royanus, Hippuritella lapeirousei, ?Praeradiolites cremersi, ?Praeradiolites
faujasi, Praeradiolites hoeninghausi (Philip, 1998).
Orbitoides apiculata and Siderolites calcitrapoides are among the benthic foraminifers
that are frequently used to identify the Maastrichtian. Both species are present in the rudistbearing limestones at Yayladağı. They have also been recorded at Cava Longo (Italy,
Salento), associated with rudists with a numerical age of 72.8 Ma (Schlüter et al., 2008a).
Consequently, their first appearance datum has to be revised by c. 2 my to the Late
Campanian (see also Özcan, 2007).
4.5 Provincialism of rudists
The latest Cretaceous rudist associations are highly endemic, with a Caribbean, a
Mediterranean, and an eastern Tethyan (Arabia, Asia, E-Africa) faunal province. There is
also a certain degree of endemism between the western Mediterranean and central
Mediterranean (Philip, 1998b). Previous studies of Late Cretaceous rudist endemism were
based on old stratigraphic concepts and therefore need to be re-evaluated. The following
discussion of faunal provincialism is based on recently published and new (this paper)
numerical ages derived from SIS (Fig. 4.2).
77
The most important revision when compared to earlier interpretations of rudist
biostratigraphy (i.e., Laviano and Sirna, 1980; Philip, 1982, 1985, 1998a; Pons and Sirna,
1992), is that many species previously considered to be characteristic of the Maastrichtian
in the central-eastern Mediterranean (Turkey, Balkan), are of Campanian age or even older
(Steuber, 2001; 2003; Steuber et al., 2005). Consequently, the Maastrichtian rudist
diversity in this region is significantly lower than previously assumed. More specifically,
no species of the hippuritid genus Vaccinites seems to range into the Maastrichtian of the
Mediterranean Tethys. Stratigraphical revisions have been less drastic for the Caribbean
and eastern Tethyan provinces. The Maastrichtian age of the species-rich Guinea Corn
Formation (Jamaica; Steuber et al., 2002), and of the Cárdenas Formation (San Luis Potosi,
Mexico; Schafhauser et al., 2007) has been confirmed.
The new data presented here from southeastern Turkey, i.e. the northern margin of the
Afro-Arabian Plate, indicate that species-rich associations that were previously considered
to be of Maastrichtian age (Özer, 1993), are of Campanian age. A similar revision was
obtained for the Qahlah Formation in the Oman Mountains (UAE-Oman border region;
Steuber et al., 2008).
On the family-group level, the composition of Tethyan and Caribbean faunas is very
similar (Tab. 4.2). Most genera belong to the Radiolitidae, while Hippuritidae and
canaliculate recumbents are few. Noteworthy is the absence of Vaccinites in the
Mediterranean Tethys and Caribbean, where it was abundant from the Turonian to the
Campanian. Vaccinites aff. oppeli from the mid-Maastrichtian of the Oman Mountains is
the single exception in the eastern Tethyan Province (Morris and Skelton, 1995; age
confirmed by SIS, Steuber et al., 2008). Considering abundance, the Radiolitidae are
dominant in all three provinces. The Hippuritidae are relatively rare, although individual
lithosomes may be formed by large numbers of relatively small-sized Hippurites or
Hippuritella. The canaliculate recumbents are relatively abundant, particularly in highenergy platform-margin environments (e.g. Ciolo Limestone, Italy, Schlüter et al., 2008).
The aragonite-dominated canaliculate recumbents had been very rare from the Turonian to
the Campanian. Their increased abundance in the Maastrichtian may be related to the
increasing Mg/Ca ratio of seawater that favours the precipitation of aragonite over calcite
(Stanley and Hardie, 1998; Steuber 2002; Steuber and Veizer, 2002; Steuber and Rauch,
2005; Steuber et al., 2007). Requieniidae are occasionally abundant in Maastrichtian
restricted inner-platform environments. The similarities in rudist associations on the
78
Table 4.2: Maastrichtian faunal provincialism of rudists at the genus level. Underlined crosses indicating
genera present in all three provinces. Bold crosses indicating that the genera are endemic to the particular
province.
Region
Taxa
Hippuritidae
Hippurites
Hippuritella
Pironaea
Praebarrettia
Vaccinites
Radiolitidae
Biradiolites
Bournonia
Chiapasella
Colveraia
Distefanella
Durania
Joufia
Kuehnia
Lapeirousia
Lapeirousella
Macgillavryia
Miseia
Petkovicia
Praeradiolites
Pseudopolyconites
Radiolites
Radiolitella
Sauvagesia
Tampsia
Thyrastylon
Canaliculate recumbents
Antillocaprina
Coralliochama
Dictyoptychus
Eodictyoptychus
Mitrocaprina
Parasarcolites
Plagioptychus
Titanosarcolites
new taxon
Requieniidae
Apricardia
Gyropleura
Sum
Endemic
Caribbean
X
Mediterranean
Tethys
Eastern
Tethys
X
x
x
X
x
x
X
x
X
X
X
X
X
X
X
x
x
x
X
X
x
x
x
x
X
X
x
x
x
x
x
X
x
X
X
x
X
X
X
X
x
X
x
X
x
x
15
7
79
x
x
x
x
x
16
4
20
3
family-group level may represent adaptation to environmental change on a global scale,
e.g. to a changing seawater composition.
However, on the genus and species level, there was a distinct endemism between the
Caribbean, the Mediterranean and Eastern Tethys (Tab. 4.2). The Caribbean province in
particular was isolated during the Maastrichtian, with not a single species having records
elsewhere, i.e. on the other side of the Atlantic or Pacific Ocean, respectively. Endemism
of Caribbean rudists faunas increased significantly after the Early Aptian, reflecting the
opening of the central Atlantic (Skelton, 1982). After the Albian, there was almost no
faunal exchange across the Pacific or Atlantic Ocean. The degree of endemism, however,
was less extreme in the Campanian, when Macgillavryia and Torreites made it across the
Pacific and occurred in Oman (Skelton and Wright, 1987).
Three genera are common among the three provinces, and a few species, only, have
abundant records both in the Mediterranean and Eastern Tethyan provinces: Hippurites
cornucopiae seems to be a reliable marker of the Maastrichtian (Pons and Sirna, 1994).
Hippuritella lapeirousei is relatively abundant but may extend into the Campanian.
Numerous small species of Bournonia, including Glabrabournonia occur at many
Maastrichtian localities, but the species-level taxonomy of this group is in need of revision.
The Dictyoptychidae are restricted to the eastern Tethyan Province. Although the first
records are in the Campanian, they are particularly characteristic for the Maastrichtian
deposits of this province and occur in Turkey, Iran, Afghanistan, the Arabian Peninsula
and Somalia. A much larger number of endemic genera occurred in the Campanian, with
Praetorreites, Dubertretia, Glabrabournonia, Hatayia, Osculigera, Paracaprinula,
Semailia, and Vautrinia being restricted to the eastern Tethyan region.
In summary, endemism of rudists in the Caribbean existed since the early Cretaceous
with very little exchange of faunas during the Late Cretaceous. Westward migration across
the Pacific was the preferred route of dispersal (Skelton and Wright, 1987). The eastern
Tethyan region became isolated later and peak endemism occurred in the Campanian. The
lower number of endemic genera in the Maastrichtian is the result of extinction of endemic
Campanian taxa. Isolation of the eastern Tethyan region from the Mediterranean Tethys is
more difficult to explain because of the proximity of Eurasian and African tectonic units
during the Campanian-Maastrichtian. It could be explained with a strong clockwise
circulation in the eastern Mediterranean Tethys. After the Coniacian, rudists are almost
completely absent from the northeastern African shelf between Libanon and Libya, and
this has been explained by the upwelling of nutrient rich waters and stagnant condition that
80
created hostile conditions for the characteristic Tethyan benthic associations of carbonate
producers in this region (Steuber and Löser, 2000), and is reflected in regionally
widespread phosphorites and black shales. A clockwise circulation in the eastern
Mediterranean Tethys would have effectively blocked the westward migration of species
along the inimical waters of the northeastern African shelf.
4.6 Discussion
On a Phanerozoic time scale, the major decline of tropical carbonate shelf areas initially
starts at the beginning of the Late Cretaceous and continuous until the end of the Cenozoic
(Walker et al., 2002). The combination of sea-level change, poleward drift of continental
plates and associated shelf areas, and the biological evolution of calcareous plankton may
have contributed to the decline of tropical shelf-areas on a long-term scale (Walker et al.,
2002).
Results on the timing of the demise of Latest Cretaceous carbonate platforms show that
platform drowning is not involved in a single case. Platform drowning occurred was
associated to earlier during rudist extinction events, i.e. at the Cenomanian–Turonian
boundary (Philip and Airaud-Crumière, 1991) and is generally considered to be the result
of declining carbonate production being unable to keep up with relative sea-level rise
(Schlager, 1999). Consequently, there is no evidence for deteriorating carbonate
production by benthic communities that were stressed by environmental change. Instead,
tectonic factors (subaerial exposure, change from carbonate platform to siliciclastic or
volcanoclastic deposition) have been responsible for the end of carbonate platform
deposition in the examples described above. The single case of continuous platform
evolution across the K/P boundary (Qalhat, Oman) is characterized by a change in benthic
communities, but not associated with a crisis in carbonate production. Therefore, the global
reduction in carbonate platform area, which accelerated in the Campanian, must be
considered as a causal factor for the extinction of the rudists.
A widespread geographical distribution of clades was considered to be an advantage
for survivorship during mass extinctions (Jablonski and Raup, 1995). Conversely, endemic
clades have shown to be more susceptible to increasing changes in environmental
conditions. This could explain the extinction of rudists considering that their demise is
related to the reduction of their shallow-water habitat (Fig. 4.4). The last peak in rudist
diversity was shown to have occurred in the Late Campanian, species richness being only
slightly lower in the Campanian (Scott, 1995; Steuber and Löser, 2000). The revised
81
stratigraphy of latest Cretaceous rudist association based on SIS resulted in a significant
reduction of Maastrichtian species richness. Moreover, the Maastrichtian rudists show a
Fig. 4.4: Selected lithological sections of latest Maastrichtian carbonate platforms and their palegeographical
distribution.
82
high degree of endemism (see above, Chapter 4.5 Provincialism of rudists) that is
considered to increase the likelihood of extinction.
Not only rudists but the benthic community in general were obviously affected by the
change of the environmental conditions (Fig. 4.5). The accompanying biota consist mainly
of larger benthonic foraminifers, encrusting foraminifers (acervulinids), and red algae
(Solenoporaceae), evolving into the most important binder guild of Campanian to
Maastrichtian carbonate producers (Fig. 4.5; Moussavian, 1992). This significant
taxonomic change of major carbonate producers of tropical shallow-water limestones is
also evident in the Qalhat section (Oman, Schlüter et al., 2008b) where dasycladaleans,
codiaceans, and red algae are the dominant benthic biota at the beginning of the Danian
stage (Fig. 4.4).
This change in dominant carbonate producers also reflects a shift towards aragonite and
high-Mg calcite as the original carbonate mineralogy, replacing the calcite-dominated
rudists. This change occurs during a time of increasing Mg/Ca ratio of seawater (Steuber
and Rauch, 2005; Stanley, 2006; Timofeeff et al., 2006), favouring aragonite over calcite
as the original marine carbonate mineral. However, aragonite dominated rudists increase in
abundance during the Campanian-Maastrichtian, and aragonite-dominated canaliculate
taxa are volumetrically important in Latest Maastrichtian platform margin deposits of
Apulia (Steuber et al., 2007), indicating a response in skeletal mineralogy to a changing
seawater composition. Also, changes in the major ion content of seawater occur on long
time scales, and are unlikely to contribute to extinction in marine animals that exert a
significant control on their skeletal structure and mineralogy. In this context, it is important
to note that the original radiation of rudists occurred during a time period of a very low
Mg/Ca ratio, favouring calcite precipitation, but that early Cretaceous rudists were largely
aragonite dominated. We therefore dismiss the hypothesis of seawater chemistry
contributing to the extinction of the rudists.
A connection between extinction rate and decreasing ocean surface temperature has
been drawn by Kauffman and Johnson (1988). Likewise the cooling of the surface
temperature (from 20°C to 14°C) during the Maastrichtian (Fig. 4.5) may correlate with the
demise of the dominant shallow-water benthic community (i.e. rudists and larger benthic
foraminifers). However, low-latitude paleotemperatures did not drop significantly, and the
migration of rudists into presumably cool Boreal waters in the Latest Maastrichtian
(Limburg, The Netherlands) argues against climatic cooling as an important trigger of the
extinction.
83
Fig. 4.5: Compilation of environmental, sedimentological, oceanographical and biological changes of the
Late Cretaceous (Campanian–Maastrichtian) world and beyond, including the evolution of main carbonate
producers on shallow-water carbonate platforms.
84
4.7 Conclusions
Numerical ages derived from SIS constrain the range of numerous rudist associations into
the latest Maastrichtian, close to the K/P boundary. Many associations previously believed
to be of Maastrichtian age were shown to be older, i.e. of Campanian age. Still,
Maastrichtian rudist association are species-rich, with all Campanian families and
ecological morphotypes persisting into the Late Maastrichtian. There is a pronounced
endemism of Maastrichtian rudists that is believed to have contributed to extinction. Late
Cretaceous plate tectonic reorganization and the related reduction in carbonate platform
area is suggested as the major cause of extinction. None of the studied platforms drowned
in the Maastrichtian, but platform growth was terminated by subaerial exposure, or a
change from carbonate to siliciclastic or volcanoclastic sedimentation. Consequently, there
is no evidence for environmental deterioration that may have stressed carbonate producing
biota and resulted in the drowning of carbonate platforms.
Although there was a general Late Cretaceous trend of climatic cooling, the invasion of
rudists into the cool Boreal waters in the Latest Cretaceous argues against climate change
as a major control of rudist extinction. The hypothesis of a changing seawater composition
contributing to the demise of the rudists is rejected, as the major period of adaptive
radiation of aragonitic rudists in the Early Cretaceous occurred during a time period of
‘calcite seas’. Also, changes in seawater composition occur on long time scales so that
bivalves that exert a significant metabolic control on skeletal structure and mineralogy can
adapt to such long-term changes in the environment.
Still, the scarcity of observational data on changes in benthic communities in continuous
sections across the K/P boundary leaves questions about the effects of short-term
environmental perturbations at the end of the Cretaceous.
Acknowledgements
We would like thank D. Buhl, B. Raczek and B. Gehnen for their support during laboratory
work; Funded by Deutsche Forschungsgemeinschaft (Ste 670/13).
Appendix. List of taxa mentioned in the text
Rudists
Apricardia sp. Guéranger, 1853
Biradiolites aguilerae Böse, 1906
Biradiolites chaperi (Toucas, 1909)
85
Biradiolites cf. fissicostatus Orbigny, 1850
Biradiolites royanus Orbigny, 1850
Bournonia cardenasensis Böse, 1906
Bournonia excavata Orbigny, 1842
Bournonia triangulata Plenicar and Zucchi-Stolfa, 1988
Bournonia sp. Fischer 1887
Colveraia variabilis Klinghardt, 1921
Coralliochama gboehmi Böse, 1906
Dictyoptychus euphratica Karacabey-Öztemür, 1981
Dictyoptychus leesi (Kühn, 1929)
Dictyoptychus morgani Douvillé, 1904
Dictyoptychus striatus Douvillé, 1910
Dictyoptychus sp. Douvillé, 1905
Durania ojanchalensis Myers, 1968
Dubertretia sp. Cox, 1965
Glabrabournonia arabica Morris and Skelton, 1995
Hatayia sp. Karacabey-Öztemür and Selçuk 1981
Hippurites cornucopiae Defrance, 1821
Hippuritella lapeirousei (Goldfuss, 1840)
Hippurites muelleriedi Vermunt, 1937
Hippurites perkinsi Myers, 1968
Hippurites syriaca Vautrin, 1933
Hippurites sp. Lamarck, 1810
Joufia reticulata Boehm, 1897
Katzeria sp. Slišković, 1966
Lapeirousia sp. Bayle 1878
Macgillavryia nicholasi (Whitfield, 1897)
Mitrocaprina bulgarica Tzankov, 1965
Mitrocaprina cf. tschoppi Palmer, 1933
Mitrocaprina Boehm, 1897
Osculigera sp. Kühn, 1933
Paracaprinula Piveteau, 1939
Petkovicia Kühn and Pejović, 1959
Pironaea polystyla Pirona, 1868
86
Pironaea praeslavonica Milovanović et al., 1970
Pironaea slavonica Hilber, 1902
Plagioptychus sp. Matheron, 1842
Praebarettia sparcilirata (Whitfield, 1897)
Praeradiolites cremersi Geijn, 1940
Praeradiolites faujasi (Bayle, 1858)
Praeradiolites hoeninghausi (Des Moulins, 1826)
Praetorreites sp. Philip and Platel, 1994
Pseudopolyconites apuliensis Sladić-Trifunović and Campobasso, 1980
Pseudopolyconites cf. ovalis Milovanović, 1935
Pseudopolyconites sp., Milovanović, 1935
Pseudosabinia klinghardti (Boehm, 1927)
Pseudosabinia sp. (Böhm, 1927)
Radiolitella maestrichiana Pejović, 1968
Sabinia aniensis Parona, 1908
Sabinia Parona, 1908
Sauvagesia Choffat, 1886
Semailia sp. Morris and Skelton, 1995
Tampsia poculiformis Myers, 1968
Vaccinites atheniensis (Ktenas, 1907)
Vaccinites cf. oppeli (Douvillé, 1892)
Vaccinites vesiculosus (Woodward, 1855)
Vautrina syriaca (Vautrin, 1933)
Vaccinites Fischer, 1887
Foraminifers
Accordiella conica Farinacci, 1962
Omphalocyclus macroporus (Lamarck, 1816)
Orbitoides apiculata Schlumbeger, 1901
Raadshovenia salentina (Papetti and Tedeschi, 1965)
Siderolites calcitrapoides Lamarck, 1801
87
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94
Chapter 5 ◦Conclusion and perspectives
5. Conclusions and perspectives
5.1 Conclusions
The studied Late Cretaceous carbonate platforms of the Mediterranean region and the
Arabian Peninsula supplied new data and evidence for the understanding of the evolution
of shallow-water platforms and their interaction with rudists. The strontium-isotope
stratigraphy yielded a large number of numerical data and provided thus a new
stratigraphical framework for the age of latest Cretaceous tropical rudist-bearing
carbonates. The following conclusions are made with reference to the issues of the thesis
mentioned in Chapter 1.3 (Purpose of the present thesis).
The numerical ages of the Upper Cretaceous carbonates observed in Italy (Salento)
based on SIS provided a precise chronostratigraphy of the regional limestone formations.
The youngest Late Cretaceous deposition, the Ciolo Lst. ranges from the middle
Campanian to the latest Maastrichtian, where it is truncated due to the emergence of the
platform. A high to medium diversity of the rudist associations was observed for the
carbonate platform of Salento while stratigraphical long-ranging taxa seem to characterise
the mid-Campanian - Maastrichtian rudist-associations.
The SIS of the SE Turkey localities located on the Afro-Arabian plate show a latest
Campanian to earliest Maastrichtian age, whereas the localities of the European plate range
from Late Campanian to the latest Maastrichtian, very close to the K/P boundary. Many
localities which were previously thought to be of Maastrichtian age, however, have now
been revised to the Late Campanian, due to the numerical ages derived by SIS.
Accordingly, the stratigraphical ranges of many rudist taxa have been corrected and show
at some localities a distinctive provincialism of the Anatolian associations.
The carbonates of Qalhat (Oman) provide a single case of shallow-water platform
limestones ranging from the Maastrichtian into the Danian / Selandian. The carbonate
sedimentation shows no indications of restricted conditions or major hiatus and it can be
therefore concluded that normal marine settings with stable environmental conditions
prevailed through the Maastrichtian and Danian / Selandian times. The major shallowwater carbonate producers of rudists and larger benthic foraminifers, however, are replaced
by characteristically taxa of calcareous algae (e.g. dasycladalean, codiaceans, red algae).
For the first time a precise regional biostratigraphical zonation of the shallow-water
platform carbonates can be obtained.
The initial decline of the Late Cretaceous shallow-water carbonate platforms of the
Tethys started in the Campanian. Throughout the Maastrichtian several carbonate
95
Chapter 5 ◦Conclusion and perspectives
platforms got strongly influenced by regional tectonic events. These events leaded to
subaerial exposure of the platforms or to a modification of the depositional patterns,
including the change from predominantly carbonate to more siliciclastic or volcanoclastic
materials. Up to this point of decline the platforms of the Mediterranean and Arabian
region show patterns of limestone accumulations which can be regarded as deposited under
normal shallow-marine conditions. The good environmental conditions of the platforms are
reflected by the variety of the major shallow-water carbonate producers thrived throughout
the Maastrichtian, including larger benthic foraminifers and rudist bivalves. There is no
evidence of environmental stress conditions for the benthic organisms of the Maastrichtian
shallow-water platforms until the decline or even end of the platform sedimentation.
The species-rich rudist associations of the Maastrichtian provided a distinct
provincialism which can be differentiated into three paleogeographical faunal provinces. A
Caribbean, Mediterranean and eastern Tethyan (Arabia, Asia, E-Africa) province can be
recognized. Consequently, the reasons for the demise of the rudists can be seen as a
combination of the decline of the tropical shallow-water carbonate platforms and of the
provincialism. The major influence can be contributed to the reorganization of the platetectonic and the regional tectonic activities increased throughout the Maastrichtian of the
Tethys, while it is assumed that the pronounced endemism also made a contribution to the
extinction of the rudists.
5.2 Perspectives
The results, data and conclusions of the thesis presented here uncover various unsolved
problems and thus shed light on future research projects and tasks. First of all the
stratigraphical ranges of various Tethyan sequences of Campanian–Maastrichtian age must
be compared to the new numerical strontium-isotopic data introduced here. Likewise
several localities dated by the first occurrence of the larger benthic foraminifera
Accordiella conica, Omphalocyclus macroporus, Orbitoides apiculata, Raadshovenia
salentina and Siderolites calcitrapoides should also be compared to the new numerical data
and if necessary be revised. These new stratigraphical ranges are an important contribution
to the history of the Tethys evolution throughout the Campanian–Maastrichtian period, as
several geological events can than be re-examined.
96
Acknowledgments
First of all I would like to thank Prof. Dr. Thomas Steuber for initiating and supervising
this thesis. The continuous support and stimulating discussions during the last three years
were highly appreciated. I am very grateful to Prof. Dr. Jörg Mutterlose for his
encouragement and substantial support. Special thanks to Dr. Mariano Parente for his
considerable contributions and discussions about biostratigraphy. I am much obliged to
Prof. Dr. Sacit Özer and Dr. Bilal Sari for their hospitality and discussions during the field
work in Turkey. I also would like to thank the complete laboratory team, Dr. Dieter Buhl,
Dr. Ulrike Schulte, Beate Gehnen and Barba Radceck for introducing me to the lab and
mass spectrometer. I am grateful to my ‘office colleagues’ Matthias Malkoc and Sebastian
Pauly for their lively discussions. Many thanks to Dr. Petros Hardas and Andreas Rexfort
for indroducing me to the wonderful world of ‘How to teach paleontology’. For various
kinds of help I would like to thank Prof. Dr. Ulrich Heimhofer, Dr. Niels Rameil, Christian
Linnert and all the other friends and colleagues of the complete Mensa crew for the
relaxing lunchtimes. Special thanks to Dr. Oliver Weidlich for his confidence in young
PhD students.
Many thanks also to my family, parents and friends who supported me in many different
ways.
I would like to express my special gratitude to Anna and Jakob, who are always there for
me and who motivated me day by day throughout the last years.
97
Curriculum Vitae
Curriculum Vitae
Personal data:
Name
Malte Schlüter
Date of birth
17.09.1977
Place of birth
Unna
Martial status
married, one child
Education
since 10/2005
PhD student and research assistant at the Institute of
Geology, Mineralogy and Geophysics at the Ruhr-University
Bochum
10/1997 – 07/2005
Study of Geology at the Ruhr-University Bochum
Diploma thesis: „Sedimentation of the Messinian deposits
(Tertiary, Late Miocene) of the Carboneras-Nijar-Basin (SE
Spain): microfacies & geochemical aspects”
Graduation as “Diplom-Geologe”
09/1988 – 07/1997
Ernst-Barlach Gymnasium, Unna
1984 – 1988
Paul-Gerhardt Elementary School, Hengsen
Work Experience
06/2005 – 09/2005
Student assistant at the rubitec company – company for
innovation and technological-marketing of the RuhrUniversity Bochum
07/2003 – 12/2003
Internship at the company Wayss & Freytag Engineering AG
Stadtbahn Ostentor (Dortmund)
1999 – 02/2003
Student assistant at Institute of Geology, Mineralogy and
Geophysics at the Ruhr-University Bochum,
98

rudist-bearing carbonate platforms of the Mediterranean Tethys and

Transcription

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