professor liviu ionesi`s contributions to the paleogeographical
Transcription
professor liviu ionesi`s contributions to the paleogeographical
ACTA PALAEONTOLOGICA ROMANIAE V. 6 (2008), P 97-103. PROFESSOR LIVIU IONESI’S CONTRIBUTIONS TO THE PALEOGEOGRAPHICAL EVOLUTION OF THE EASTERN CARPATIANS FORELAND KNOWLEDGE Petru ENCIU1 & Cristina DUMITRICĂ1 Abstract Academician Liviu Ionesi has published between 1964-1972 and 1991-1996 many papers regarding the paleogeographical evolution of the Eastern Carpathians foreland, as result of the cooperation with doctor in geography and university professor Nicolae Barbu and with doctor emeritus professor Bica Ionesi, specialist in paleontology. The contribution of the first stage was based on the lithological, internal mechanical structures and fossil fauna content (age and facieses markers) studies. The existence of some sedimentary gaps for Upper Kossovian – Early Buglovian, Early Basarabian and part of Hersonian intervals, sustained by the authors, are based on fauna analysis of Badenian – Maeotian deposits. Then, between 1996-2005, continuing the second stage of researches in this field, academician Liviu Ionesi together with a group of four authors has synthesized a good part of the paleogeographic elements in a paper dedicated to the Middle and Upper Sarmatian of Moldavian Platform. In this second stage, the researches were diversified and the results were obtained mainly from the modern interpretation of the biofacies significance, constructed by foraminifers, bivalve mollusks, gastropods, marine vertebrates or terrestrial vertebrates. For the western strip of the Moldavian Platform, new arguments were presented regarding the existence, even in Volhynian, of a mature courses network originated in the emerse terrains of the Eastern Carpathians with the solid burden deposited as deltas and littoral deposits in the coupling zone with the Moldo-Galitian Gulf. In the monographic paper dedicated to Medium and Upper Sarmatian period, published in 2005, for each of the 12 component formations, sedimentological and paleontological considerations were presented and 5 significant paleogeographical stages were separated for the whole Badenian- Romanian sedimentary cycle. Keywords: Carpathians, Moldavian Platform, Miocene, Pliocene, paleogeography. INTRODUCTION The paper was presented on September 2007 at the scientific workshop of the Romanian Paleontological Society as homage to academician Liviu Ionesi who passed away almost a year ago. The geological community is well aware of Liviu Ionesi contributions regarding the northern part of the Eastern Carpathians flysch formations stratigraphy and tectonics, an activity developed on a large period (1950 – 1968). But even in the years of intense efforts for Eastern Carpathians geology knowledge, together with other geological and geographical researchers, Liviu Ionesi had a constant interest in paleogeographical field, rewarded with important results. SHORT HISTORY OF RESEARCHES In case of structural units situated in front of the Eastern Carpathians, the first reference regarding the paleo-geographical conditions during Miocene – Present time dated in the second decade of the XX-th century (David M., 1916). A brief analyze of the papers elaborated after, for about nine decades, indicate the existence of four stages. In each stage the paleogeographical approaches were based on information from related fields and the results were dependent on the general evolution in bio- and geo- sciences. Here is a condensed characterization of each stage: 1. The first stage is one of punctual remarks, especially about the paleo-climate 1 Institute of Geography, Romanian Academy, Bucharest and was based on the studies of leafs prints founded in rocks of different ages; David M., 1916; Simionescu I. 1927; Barbu I. Z., 1934, etc. 2. Using combined morphogenetic and stratigraphic arguments, the second is the stage of age estimation for the Eastern Carpathians hydrographic network and for the associated accumulative relief built at the transition zone to the foreland. Here we have the papers signed by Martiniuc C. (1948); Tufescu V. (1957); Barbu N., Ionesi L., Ionesi Bica (1966), Donisă I., Barbu N., Ionesi L. (1973), etc. 3. The third is dedicated to the relief evolution of the structural units situated in front of the Eastern Carpathians. Main contributions are considered the paper of Sficlea V. (1980) for Covurlui Platform, others, signed by Ionesi L., Barbu N. and Ionesi Bica (1991, 1993), regarding the weathering model upon the Carpathians foreland in Badenian and Sarmatian time, or about the Moldavian Plain Genesis (Ionesi L., Barbu N. 1996), etc. 4. The stage regarding the sedimentation conditions and the depositional ambiances obtained by detailed analysis of the internal structures and the sedimentary rocks petrography (Miclăuş Crina, 2001; Grasu C., Miclăuş C., Brânzilă M. & Boboş I., 2002). In the same stage, paleoclima studies diversify using spore – pollen analysis on large sets of clays samples deposited in Basarabian time: Ţabără D. and Olaru L., 2004; Brânzilă M. and Ţabără D., 2005, etc. 97 P. ENCIU & C. DUMITRICĂ MAIN PALEOGEOGRAPHIC STAGES In the paleogeographical evolution knowledge field of the Moldavian, Barlad and Covurlui Platforms that evolved as a single block between Middle Miocene and Quaternary, Liviu Ionesi’s contributions are the result of a complex team work. In the first interval the work was done together with Nicolae Barbu and Bica Ionesi (1964, 1966, 1972, etc.). After 1989 in this team were included researchers as Vladimir Roşca and Alexandru Lungu from the Republic of Moldavia. The results of this long collaboration were fructified in 2005. In the final part of the most valuable geological study dedicated to the Middle and Upper Sarmatian of the Moldavian Platform, the main positive oscillations of the basement (generating land), and implicitly, the main morphogenesis stages were presented (Liviu Ionesi and contributors, 2005). These will be presented in the following paragraphs. 1. Weathering Model – Dorohoi Surface After Cretaceous (in the eastern part) and after Middle or Upper Eocene (in the western part), most of the foreland units become land for about 40 Ma (Ionesi, 1984), been a sediments source for the carpathic geosynclinal (on the west). In this considerably long time range, a weathering modeling of the cretaceous, eocene and paleozoic deposits took place. Now it was mould the Dorohoi peneplene surface. It has a plain character and it was crossed by a network of valleys with NE – SW orientation in the northern part of the platform, and E – W in the southern part; valleys marking the ditch of the Carpathian geosynclinal (Paraschiv, 1987). 2. The New Stiric orogenetic phase from Upper Badenian Now, the Dorohoi Surface was buried and deformed gradually by the western plunging; a process more obvious to the west of the Siret valley. Do to the eastern thrusting of the carpathian units, the western margin of the Dorohoi Surface was masked by tectonic covering, presently been situated at about 50 km west of the pericarpathic line. That means a 50 km shortening of the alpine formations stack in Carpathians, their thrusting over the Moldavian Platform and the differentiated subsidence of the latest with accumulation of three Badenian formations: detritic, anhydrite and marl-argillaceous (see Figure 1). Analyzing the basement position, Ionesi et al., 2005, sustained that the bending 98 of the platform to south and west is tectonic, possibly along some fractures. Isobaths to the base of Badenian are 0 – 100 m to NE and at 1500 m in front of the orogene (Ionesi, 1994). Under the orogene, the depth of the above mentioned limit grows abruptly to 2000 and 5000 m. 3. Formation of the Moldo-Valachian Land between Kossovian and Early Buglovian Between Kossovian and Early Buglovian, ~14 – 13.8 Ma BP, the Subcarpathian Nappe was put in place. The uplift can be linked with the Moldavian (Attic) Phase of the Carpathian alpine cycle. This process affected the whole foreland of the Eastern and Southern Carpathians, inclusively the South Dobrogea and the centre of the Valachian Platform, and has generated among others the Moldo-Valach land (Ionesi L., Barbu N. & Ionesi Bica, 1991). The Moldavian Orogenetic Phase has stimulated the generation of a hydrographic network and landforms into Carpathians. The maximum erosion value, ~ 0.5 mm/year, took place at about 13±0.2 Ma. At the river courses outlet, piedmont cones on the land (Clit, Ciungi a.o.) and deltas at the entrance of the MoldoGalitian Gulf, were formed. 4. A marine transgression in Upper Buglovian The moldo – valachian land was buried after the sedimentation was restored in Upper Buglovian time, when a new marine transgression has covered Moldavian and Barlad platforms, part of the Covurului Platform, north and west of the Moesian Platform, as well as South Dobrogea. As a consequence of the piroclastic emissions of the Carpathian Volcanic Chain, Hudesti dacitic tuff was deposited (see Figure 1). 5. Intra – Volhynian orogenetic phase. Now is the time of the final put in place of the Subcarpathian Nappe. The thrusting process of the foreland (Maţenco et al. 2003) was blocked first north of the Bistrita fault and then between Bistrita and Trotus faults. South of Trotus, Subcarpathian Nappe plunges progressively, generating the Odobesti depositional area; a high subsiding basin during Upper Sarmatian – Middle Romanian time. The Moldavian Orogenetic Phase (12.5 Ma) has generated trusting and shortening of the Carpathians Units, with a litostatic overburden and a subsidence on the western edge of the PROFESSOR LIVIU IONESI’S CONTRIBUTIONS TO THE PALEOGEOGRAPHICAL EVOLUTION OF THE EASTERN CARPATIANS FORELAND KNOWLEDGE Figure 1 – Foreland’s stratigraphic synthesis during Middle Miocene – Holocene time (ro3 – Upper Romanian; ro2 – Middle Romanian; ro1 – Lower Romanian; P1-2 - Pontian; m Maeotian;hs - Hersonian; bs - Basarabian; vl - Volinian; b - Buglovian; bn – Badenian; 15.0…1.8 million years BP) 99 P. ENCIU & C. DUMITRICĂ platform units, configuring the Carpathian Fore-deep. On the north – western edge in Upper Volhynian time dryness has appeared and prolonging them, low plains with marshes (now, three coal layers). The vegetation (grass and broadleaves woods mixed with mediterranean species) denotes a humid temperate climate (in transition to sub-tropical). Generally, Volhynian age has 150 m thickness east of Siret valley, 500 m between Siret and Moldova rivers and 800 m in front of the Carpathians Chain, indicating a differentiated plunge. 6. Volhynian – Lower Basarabian Between Volhynian and Lower Basarabian time at the contact zone of the Carpathian land and the Sarmatian Sea, hydrographic courses existed: paleo-Suceava, paleo-Suceviţa, paleoMoldova, paleo-Ozana, paleo-Cracău, paleoBistriţa, etc. The Upper Buglovian – first part of Basarabian paleogeographic evolutionary time was called Bahlui. This range is characterized by two reefs barriers in the eastern part. The first Buglovian barrier has extended from south of Iasi till Podolia and the Late Volhynian – Early Basarabian barrier was installed east of the first one. The two barriers and the sandy – limestone layers reveal the oscillating levels of Moldavian Platform (n.n. – induced by Planetary Ocean’s oscillations). 7. The general uplift of the Moldavian Platform from Upper Basarabian The sedimentation was maintained constantly until the first part of the Upper Basarabian when a tectonic uplift process (without any folding effects) and land generation took place. The limit between the land, build in the northern part, and the aquatic basin, from south, was the trace of the N Roman – Oţeleni – Iaşi – Făleşti fracture, named Bahlui fault (David, 1922), with a prolongation east of Prut valley. With this differentiated uplift, more important in the north, important changes are made. Water’s freshening was the first important consequence. Information are supplied by the Upper Basarabian deposits, with Mactra macarovicii, congerias and layers with freshwaters fauna between Clays with Criptomactra pesanserii and the Repedea Limestone (Ionesi, 1993). In the same period Crimeea – North Dobrogea barrier was uplifted, isolating the Moldo – Galitian Gulf from the Euxinic Basin. The marine – brackish waters retreated in the north as a consequence of the uplift, leave a plain land on which the hydrographic network was developed. Over the Criptomactra Formation and Darabani – Mitoc clayey Beds will flow the Upper Basarabian paleo – Bahlui, 100 paleo – Jijia and is installed the Prut valley (Ionesi et al., 2005). It cannot be excluded that Jijia, Bahlui and Prut (north of Bahlui fault), Rautz, Cubolta and Cainar valleys to be the heirs of this network. The land remains the same till now. On the land vegetation developed and a community of herbivores and carnivores, known as Hipparion moldavicum fauna, lived. On foreland’s western edge, the paleo – hydrographic networks of the actual Siret, Suceava Sucevita, Solonet, Moldova, Suha, Ozana and Cracau courses drains the Carpathian land. Ionesi and Barbu (1996) consider that by the union of this courses the medium course of Siret was build. On its right side, between Toplita and Bistrita valleys, an Upper Basarabian land (without the accumulation of Barnova – Muntele Formation) existed. The structural researchers say that in the Upper Basarabian the subsidence was blocked/stopped in a strip north of Trotus, and sedimentation process on the frontal platforms of Eastern Carpathians was mainly under a N – S control (Maţenco & Bertotii, 2000). 8. Reneweing the link with the Sarmatian Sea In the south – central part of Moldavian Platform, after the accumulation of small mactras and congerias deposits, the link with the Sarmatian Sea was restored. In the aquatic area, named by the authors the Moldo – Galitian Gulf, marine – brackish waters enter (with Mactra fabreana, M. vitaliana, M. podolica) and a severe reduction of the terigene material input took place. This stage, named Repedea, ended in Late Basarabian. As a consequence, Repedea, Şişcani, Şcheia, Bălăneşti, Măgura, Bujor, Lăpuşna and Bohotin formations resulted (see Figure 1). By the lithology (oosparite, biosparite, sands), by the structure (wave ripples, rib and furrow, oblique – crossing bedding) and by faunal composition, there are littoral formations. An additional argument is the presence of the terrestrial (Helix) and fresh-waters (Anodonta, Unio, etc.) mollusks transported from the nearby land. 9. Reduction of sedimentation area Due to the Carpathians geodynamic processes, at the Basarabian - Hersonian boundary, approximately between 11.0 – 10.8 Ma BP, the whole foreland, inclusively the strip of the Black Sea shelf, was emerged. Then, in Hersonian time, the south central part, approximately between the Paun and Barlad localities meridians, was dominated by a delta environment (Valeni sands). PROFESSOR LIVIU IONESI’S CONTRIBUTIONS TO THE PALEOGEOGRAPHICAL EVOLUTION OF THE EASTERN CARPATIANS FORELAND KNOWLEDGE The salinity diminishes, generating the extinction of Mactra fabreana fauna and the installation of small mactras fauna. Beside the small mactras fauna, deposits with fluviallacustrine and terrestrial fauna (Balta – Paun Formation) are preserved. Because of the intense volcanic activity from the Calimani Mountains, are accumulated also Nutasca – Ruseni cinerites (an important stratigraphic marker). Sedimentation continues between Maeotian – Middle Pontian time, been preponderantly epiclastic (sands, sandstones, silts and, subordinated, clays). The weakly brackish waters regime permits development of some species as Congeria panticapaea, Dosinia meotica, Syndesmia tellinoides, Unio moldavicus, etc., and on land mammals of warm climate that lived in luxurious vegetation conditions (Ionesi, 1994). From the rocks deposited in Maeotian are known three outcrops with flora (Păun-Iaşi, Hârşova-Vaslui and, possibly, Nisporeni) from which were identified taxons of warm and humid, almost subtropical climate (Laurus, Cinnamophyllum, etc.); character proved also by the vertebrate remains. The fauna deposit of Cimislia contains proboscideans (Zygolophodon, Tetralophodon, Deinotherium giganthissimus Ştefănescu, D. longirostris), birds (Struthio), carnivores and many herbivores. Regarding the Pontian time, Ştefârţă Ana (in: Ionesi et al., 2005) presents some data of paleo-flora from the outcrops Moscova and Taraclia. The presence there of some species of Parrotia, Betula, Salix, Acer, Typha, etc., denote a warm towards subtropical climate. 10. Development of the emerged territory After Middle Pontian, important paleogeographic changes took place, as in case of land development. Authors sustain that the enlargement of land happened as a consequence of the general uplift process. Is not impossible that the waters retreat to be a result of the general climatic depreciation and descend of the Dacic Basin’s water level, too (Clauson et al., 2005). As the authors, Ionesi et al., 2005, sustain the new land has higher levels than the existent one north of Bahlui fault. Consequently, Bahlui, Jijia and Rautz valleys arcuates toward Prut River. From the whole generation of valleys installed on the southern bench of the Moldavian Central Plateau, only Rautz has penetrated. As concerns the Pontian deposits, they are missing from the Moldavian Platform, been present south, on the Scythian (Barlad) Platform. There, Lower and Middle Pontian are represented by continental deposits (latheritic clays and red siltstones like residual products in the continental temperate, more humid climatic conditions). 11. The Malusteni stage was developed in Dacian – Middle Romanian time. Now, south of the Crăieşti – Fălciu – N Comrat – Căuşeni line it was a lake. In this lake were accumulated Malusteni – Beresti Formation, followed by Balabanesti Formation. The first formation has alluvial sands with many mammals (Terzea, 1981). Based on the mammals association, the Beresti fauna is attributed to Upper Dacian, and the Malusteni one with rodents, lagomorpha, medium and big herbivores, associated with carnivores and monkeys, is attributed to Lower Romanian. Judging after the thanatocenozes composition, the climate was warm and humid (almost subtropical), with herbal abundant vegetation, but also with forests. The next formation, Balabanesti, starts with gavels (5 – 10 m thickness) with lithoclasts of Carpathian’s origin in base, followed by sands (30 – 50 m). Here the contribution of Siret, Bistrita and Trotus rivers was highly. 12. The Valachian Orogenic Phase that followed during the Upper Romanian-Lower Pleistocene, generates an uplift of the Moldavian, Barlad and Covurlui Platforms, more important to NW, and reduced to SE. That explains the actual arrangements of all formations inclusively the Balabanesti Formation (oriented WSW – ENE and having SE bending of 6 – 8 m/km). The area of the existed Malusteni Lake becomes land. The upper course of Barlad River outlet into Prut and the lower course was deviated toward Siret due to the Focsani high subsiding area. 13. Thanks to an ingression of the Black Sea into the actual territory of Romanian Plain in Middle Pleistocene time, Babele – Barbosi Formation was accumulated, with fluvio – lacustrine (Corbicula, Pisidium, etc.) and brackish marine mollusks (Didacna, Adacna, etc.). 14. Over the all presented base formations, one mainly aeolian Loess Formation was accumulated (with loess, loess-like, fossil soils, etc.). This formation is variable in thickness from some meters in the north (the Moldavian Plain) till fifty-sixty meters in the south (Galati or Covurlui Plain). 101 P. ENCIU & C. DUMITRICĂ References Barbu I. Z. 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(1981), Remarques sur la biostratigraphie du Pliocene du sud de la Plaine Romaine (zone de Turnu Magurele), Trav. Inst. Spéol. „Émile Racovitza”, XX, p 113-126, Bucuresti. PROFESSOR LIVIU IONESI’S CONTRIBUTIONS TO THE PALEOGEOGRAPHICAL EVOLUTION OF THE EASTERN CARPATIANS FORELAND KNOWLEDGE Ţabără D., Olaru L. (2004), Contributions à l’étude palynologique des argiles du Basarabienne supérieur de Şcheia. Acta Palaeontologica Romaniae, vol. IV, Cluj-Napoca, 485 - 492. 103