TERTIARY PETROLOGY IN THE COLINGA DISCTRIC, CALIFORNIA

TERTIARY PETROLOGY IN THE COLINGA DISCTRIC,
CALIFORNIA
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Table of Contents.
Introduction
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Beueription of the Ooali
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Description
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Geologic history of the Coalinga district during
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TERTIARY PETROLOGY IH THE OOALISGA
DISTRICT,
CALIFORNIA.
INTRODUCTION.
An investigation,
begun to determine
the possible
utility
of the heavy minerals of the Tertiary rocks of California in
correlating formations and parts of formations, has led to a
study of the relations of those minerals
in the history of the series
this paper are presented
of formations chosen
a description
based
of samples
In
an ac-
from them, and a dis-
on data obtained from a study of some hundreds
taken from these formations,
heavy minerals
stages
as a type.
of the formations,
count of the history that may be deduced
cussion,
to the different
to the various
In the descriptive
stages
in a tynical cycle of erosion.
portion of the paper,
summary of the chief geographic
features
southern part of the Coalinga district
formations is discussed
following a brief
of the region,
- each
- the
of the Tertiary
under the following heads:
a. Structural and stratigraohic
b. General account
of the relations of the
relations;
of the fauna and flora;
Petrography of specimens chosen to illustrate the
more important lithologic phases of the formation.
Most of the statements
about faunas and floras are derived
either from earlier published
accounts
of the Coalinga district
F**A.Anderson, A stratigraphic study in the Mount Diablo Range,
California, Proc. Calif. Acad. Dei., 3d ser., Geology,
vol 2, No« 2, 1905, VV> 156-206.
F.!!.Anderson, A further stratigraphic study in the *'ount Diablo
Range of California, Proc. Calif. Acad. Sci., 4th ser.,
volT 3, 1908, pp. 1-40.
Arnold and Anderson, Geology and oil resources of the Coalinga
district, California, Bull. U.S. Geol. Survey, No. 398, 1910.
Nomland, J.0., The Etchegoin Pliocene of Middle California, Univ.
Lif. ?üb., Geology, Vol. 10, Ho. 14, 1917, pp. 191-254.
2
with varioms paleontologists.
or from conversations
ments concerning
the other aspects
The state-
of the formations are based
on data that have for the most part either become known or been
of the field and laboratory
verified in the course
In this part of the paper, and in
which this paper is based.
which follows it, the heavy mineral con-
the historical account
are mentioned
of the formations
tents
petrographic
characteristics
only incidentally, as
from which certain obvious deduc-
interest can be made.
tions of paleogeographic
of the paper is given over to a discussion
nected
'/=ith the heavy mineral assemblages
ion in the various
Tertiary formations
Description
Coalinga
of the
study upon
of the problems
con-
and their distribut-
of the district.
District:
The Coalinga district includes a somewhat
in the foothills along
The remainder
the western
ley in Fresno and Kings Counties,
indefinite area
edge of the San Joaquin val-
California.
I
hen viewed
from a high point, on Joaquin Ridge to the north, for example,
the area
is seen
to which attention is chiefly directed
to consist
dissected
in this paper
of three or four distinct parts:
hilly area
a much
are many ridges with a trend par-
in
allel to that of the mountains
- Reef
Ridge and Kreyenhagen
Hills; a plain a few miles wide running parallel to and immediately northeast
of the hilly area
man Plain and Pleasant
Valley; beyond
tinuous belt of hills about
miles wide
- the
just mentioned
- the
Kettle-
the plain a nearly con-
thirty miles long and five or six
Kettleman Hills; a series of steep alluvial
3
fans merging gradually into the San Joaquin valley.
belts are cut through by a considerable
stream channels,
creeks
number of usually dry
of which the most important, from south to
north, may be named:
Jacalitos,
The hilly
V»altham
f
Avenal, Big Tar, Garza, Canoas,
and Los Gates Creeks.
a few cottonwood
there are dwarf pines,
Along some of these
are growing.
trees
Zapato,
On the higher hills
oaks, junipers and chaparral.
er hills and plains are covered
with -grass,
ing most of the year, and sagebrush.
The low-
dry and brown dur-
A few springs,
either near the foot of the mountains
located
or inhere a stream channel
cuts through an anticlinal ridge, furnish mineral water
out the year.
The region is characterized
through-
by hot, rainless
summers and pleasantly cool winters during which there is an
extremely
variable rainfall, which may amount on the average
to five or six inches.
The rocks that underlie the region (See Plates
III)are distributed as follows:
dipping, hard Cretaceous
sandstone,
soft sandstone,
flat-lying, but otherwise
toward
and Kettleman Hills,
Tertiary age; in the plains, deposits
the last.
exposed
and both ordinary and
valley; in the Kreyenhagen
more gently folded beds of sand,
and sand,
and various meta-
shale or diatomite, all dipping 50 to 80 degrees
the San Joaquin
yotmger
and shale
steeply
group; in the higher foothills,
morphic rocks of the Franciscan
siliceous
in the Diablo Range,
sandstone
older Tertiary conglomerate,
I, IIand
and
shale of
of alluvial gravel
similar in appearance
to
In the Kettleman Hills an immense anticlinal fold
to view a few thousand
feet of late Tertiary rocks,
4
very similar to the upper portion of the series exposed in the
Kreyenhagen
Hills.
Ilie structure
is thus that of a broad mono-
cline of Tertiary rocks resting against
the pre-Tertiary forma-
tions that make up the Diablo Range; the monoclinal structure
being interrupted
by the great Kettleman Hills anticline, and
toward the north, near Coalinga,
The structure
contains
of the region north and west of Coalinga, which
the oil
and Anderson,
by some other folds and faults.
fields, has been described
but will be passed
over here.
in detail
by
Arnold
It is in general
R. Arnold and R. Anderson, op. cit.
similar to the part of the district already described.
DESCRIPTION OF FORMATIONS
Avenal Sandstone:
.
5
The Tertiary section along Reef Ridge has at the base sev-
in some
eral hundred feet of yellow, white and brown sandstone,
beds of which occur marine invertebrate
fossils of Eocene age.
This formation, called by F. M. Anderson the Avenal sandstone,
(as may
is faulted out at the western end of Reef Ridge, where
be seen in Jasper
tact against
Canyon) Miocene strata rest with a fault con-
dark Cretaceous
Spring Canyon, however,
It is present
shale.
and is continuous
in Sulphur
from there
about 30 miles to the end of Reef Ridge.
southeast
At the spring which
forms the head of Little Tar Creek, in the midst of an area
complex
structure
and poor outcrops,
Santa Hangar ita shale.
studied
The sandstone
by the
may be advantageously
in Big Tar Canyon, where it has its usual dip of about
75 degrees
toward the northeast.
glomeratic
zone rests
Cretaceous
sandstone.
Kreyenhagen
from ordinary Cretaceous
At its upper
in Tar Canyon as elsewhere,
that
rocks and
limit the forma-
into the diatomaceous
shale.
The fauna of the Avenal sandstone
consists
chiefly mollusks, of many species.
Smith has shown that the nearest
subtropical.
against
Farther west it rests upon strata
may possibly be earlier Eocene.
tion grades,
Its f ossiliferous basal con-
with a slight angular discordance
are different in appearance
tebrates,
it is over-lapped
of
110 vertebrate
of marine
Professor
inver
J. P.
living forms are tropical or
fossils or plants anpear
to have
J.P.Smith, Climatic Relations of the Tertiary and Quaternary
Faunas of the California Region. Proc. Calif. Acad. Sci.
Fourth Ser. Vol. IX, Ho. 4, 1919, pp. 123-173.
6
along Reef Ridge.
been discovered
Coalinga,
however,
ornia, as in the
with shale of Eocene age,
interbedded
al beds of poor coal occur.
;!t.
A few miles northwest
of
sever-
in Calif-
Similar beds elsewhere
Diablo region, have yielded an interesting
flora of laurels, magnolias,
forms that must have
and other
lived in a warm, rainy climate.
The lithology of the Eocene along Reef Ridge is rather
and more uniform than that of higher clastic forma-
simpler
with well-rounded
Near Tar Canyon a brown sandstone
tions.
igneous pebbles
of kinds
known in the Coast Ranges
only as con-
occur at the base.
stitutents of Cretaceous
of white, yellow and brown sandstone
places
The higher strata are
conglomerate/.
the brownish sandstone
of rather
with calcareous
seen to occur as large concretionary masses
In other places
it seems
common than darker-colored
varieties,
less resistant.
In places,
of Tar Canyon,
shaly members
in white sandstone.
In general,
is probably more
but less well seen because
as, for example,
about a mile south
are exposed.
One of the most comspicuous
sandstone
In
may be
cement
to occur as uniform beds.
however, all along Reef Ridge white sandstone
brownish calcareous
fine grain.
members
of the formation is the
with abundant
fossils.
A speci-
men of this phase from the Tar Canyon region was chosen for detailed petrographic
surface,
study.
the most conspicuous
In thin sections,
features
or on a polished
to be seen, are
arity of the grains and the large amount of cement
Fig. 1).
the angul-
(Plate IV,
The grains are for the most part rather uniform in
7
about among the smaller ones are occasional
size, but scattered
grains of much larger size, which are, likewise, not well rounded.
Because
each grain is surrounded
from its content
nearly opaque
by calcareous
of ferruginous
cement
which is
material, it is
difficult to distinguish quartz and untwinned feldspar in a
Scattered
thin section.
grains of fresh plagioclase
ever, be recognized,
with occasional
variety of feldspar,
and rare grains of accessory
A specimen
ment with dilute hydrochloric
cular instance
very turbid grains of some
by treat-
The loss in this parti-
acid.
The exact amount
to 62 percent.
amounted
minerals.
was disintegrated
of this sandstone
may, how-
would
no doubt vary within wide limits, depending on the proportion
of shell fragments
in the particular specimen
the heavier
being about
Studies of the lighter minerals showed
larger grains are noticeably worn.
quartz,
feldspar
feldspar
plagioclase
makes up fully
portion of the
but by no means all of it.
Of the altered grains that can be referred
ies of feldspar,
are
rare pinite, and
A considerable
is more or less altered,
of the whole.
The minerals present
Gontrary to expectations,
half of the detrital grains.
1%
that only some of the
unstria* ted feldspar, plagioclase,
muscovite.
The re-
into two portions by treat-
sidue of sand and silt was separated
ment with bromoform,
chosen.
to a definite spec-
the majority are orthoclase.
ost of the
is strikingly fresh, although it contains, enough
of the anorthite molecule
than that of quartz.
to have
an index noticeably higher
Among the minerals
heavier than bromo-
8
form, zircon, magnetite,
tourmaline, green amphibole and basaltic hornblende
In most samples
the last two very sparingly.
sandstone
no araphiboles
Kreyenhagen
also occur,
of the Avenal
occur.
Shale:
The distribution of the Kreyenhagen
shale along Reef Ridge
In fact, the
is very similar to that of the Avenal sandstone.
two were
Epidote,
and rutile are most abundant.
tentatively
as members
classed
by Arnold and Anderson.
The Kreyenhagen
of a single formation
is in general about
twice as thick as the Avenal, and is nearly everywhere
muddy, frequently oil-stained
Canyon the Kreyenhagen
diotemite.
appears
shale with several sandstone
v. est of Sulphur Spring
to be represented
by a clastic
beds, which contain a fairly large
marine fauna, not yet studied.
Fossils in the rest of the forma
foraminifera,
tion along Reef Ridge are limited to occasional
many diatoms,
a rather
and fish scales.
There are a few calcareous
len
ses and nodules in some localities which may, upon close study,
yield a larger fauna.
One such nodule will be described
The upper limit of the Kreyenhagen
is beautifully exposed
Above the surface
at several
is an erosion surface
is a bed a few inches
sidered
to be
and the conglomerate
thick composed
of peb-
with gypsum.
bed resting upon it are con-
evidence of a break in sedimentation,
bably of at least a brief emergent
which
places near Big Tar Canyon.
bles of siliceous shale and other rocks cemented
This surface
below.
interval.
ity is marked by a thick conglomerate
and pro-
The unconform-
and considerable
dis-
9
cordance
in dip in the region of the Coalinga anticline, ten
miles north of Coalinga.
shale, except a very few
The fossils in the Kreyenhagen
mollusks, have not yet been studied in any detail.
formation grades
stated
into clastic shale,
with marine
That the
fossils,
as
above, at the west end of Reef Ridge, seems not to have
been not£d by previous
observers.
The diatoms of the diatomite
facies have been studied only in a casual manner.
fera appear
been passed
to have
usual to find Vertebrate
nodules associated
It is not un-
by entirely.
bones in the calcareous
with diatomaceous
shales
The foramini-
lenses and
in California, but
none are known to have been found in Kreyenhagen.
at present,
therefore,
There is
little to be said about the fauna and
flora of the formation.
To illustrate the petrography
the diatomite and of the calcareous
Two sections
matrix.
spar.
in the fine-grained
with sev-
siliceous
Both show rare clastic grains of angular quartz or feld
The limestone
foot in diameter,
came from a spheroidal
of Big Tar Canyon.
section of this rock showed disappointingly
areas
of colorless
of find mud.
A thin
little.
calcite and rare sections
minifera the whole slice consists
with an abundance
concretion about a
which was found about 50 feet below the top
of the formation a mile southeast
rounded
One is gray,
the other relatively clear,
of foraminifera
of
variety will be described.
of the former show much variation.
muddy and nearly opaque;
eral sections
of the formation .samples
Aside from
of fora-
of very fine-grained
calcite
Angular detrital grains of
10
quartz or feldspar occur very sparingly.
fragment
with dilute hydrochloric
mud rock which could be reduced
Upon dissolving a
acid, it changed
the fingers.
to mud between
By washing away the finest mud and separating
to a soft
bromoform a small amount of the heavier constituents
cured.
sponge
They consist
spicules,
with
the residue
chiefly of pyritized diatoms,
and irregular grains and masses
were se-
pyritized
of pyrite.
There are also crystals of zircon, rutile and kyanite, but
minerals.
none of ferromagnesian
Two or three fairly large
grains of an unknown blue mineral of high relief and variable
optical character
were noticed.
been found only in samples
This mineral has previously
of the Simpson formation from Okla-
Its identity is not yet certainly known.
homa.
The Temblor Formation:
shale occurs a sandstone
Above the Kreyenhagen
several hundred feet thick.
this formation makes
as Reef Ridge.
Busane Peak
the conspicuous
It outcrops
between Jasper
and for about a mile at the southeast
feature known
of
and Zapato
end of the ridge,
of the Temblor fail, and the crest of the
ridge is made by other formations.
H
topographic
from the small hill just west of
At two places,
stent members
the re; i
the
to erosion
to the head of Little Tar Creek, a distance
nearly 25 miles.
Creeks,
By its resistance
formation
These resistant
members,
Reef Beds*, occur near the middle of the formation, as mapp-
ed by Arnold and Anderson,
tempts
to trace
but are themselves
a single bed show
fairly continuous,
that
lenticular.
the ridge crest,
is made first by one, then by another,
At-
though
of
11
These beds are alike in being somewhat
the resistant
strata.
conglomeratic
and highly fossiliferous,
ous cement.
A typiGal sample
The other strata
low.
, with
abundant
calcare-
from one of them is described
be-
of the formation do not differ notice-
ably from the usual type of sandstone
in other formations of
They are soft, yellowish or whitish and moderate-
the region.
ly fine-grained.
The upper limit of the Temblor has not previously been de-
During the present
fined.
investigation,
however,
typical
Santa Margarita fossils have been found at three localities in
a conglomeratic
member in the upper part of the sandstone
previously mapped
are:
on
as Temblor ("Vaqueros").
the northwest
These localities
slope of Busane Peak,
just above the
main Reef Bed; in Garza Canyon, 100 feet or so above
Reef Bed; and at the point where the Aeablor ceases
crest
of Reef Ridge, four miles southeast
The presence
gests
places
the main
to form the
of Big Tar Canyon.
of these fossils and of a conglomerate
horizon at three widely separated
group
at the same
along the ridge sug-
strongly that the unconformity is general for the region,
and that along with the overlying diatomite, doubtfully referred by Arnold and Anderson to the Santa Margarita, some of the
underlying clastic rocks must also be referred to that epoch.
The fossils of the Temblor are marine invertebrates
many species.
Conspicuous
now considered
to designate
Vaqueros.
among them is Turritella ocovana,
a horizon younger
The Reef Ridge "Vaqueros"
alent to the type Vaqueros
of
is thus not faunally equiv-
of the Salinas
fore called Temblor, as suggested
than the typical
Valley, and is there-
by F. M. Anderson.
In gen-
12
eral, the fossils are poorly preserved
Reef Ridge, but excellent examples
some others
of Turritella ocoyana and
In addition to the
were noted in Garza Canyon.
one or two bones of higher vertebrates
marine invertebrates
been found.
in the Temblor along
have
No plant fossils have been found in this area.
To illustrate the petrography
of the formation, a sample
top of the 2558-foot hill immediately
the Reef Bed, from the
This specimen
northwest of Big Tar Canyon was selected.
is
typical of all the Reef Beds, and, so far as the accessory
erals are concerned,
for all the samples
formation chiefly in the character
and polished surfaces
and fine grains and shall fragments
in abundant
about
little rounding.
min-
of the formation that
It differs from other portions of the
have been examined.
Thin sections
of
calcite cement.
Compared
and abundance
of cement.
of the rock show coarse
scattered
promiscuously
Even the larger grains show
with the Tejon sample previously des-
cribed, the Reef Bed contains more large grains, more grains of
turbid feldspar,
and more white mica.
which are extremely rare in all the samples
grains of amphiboles,
examined
from the Eocene
A fragment
There are also scattered
beds of the Coalinga district.
of the specimen
broke down rapidly in dilute hy-
drochloric acid, with a loss of a little more than 50 per cent.
The residue was separated
form.
coarse,
into two parts by treatment
The light fraction, which makes up
poorly sorted
white sand.
99>i
with bromo-
of the whole, is a
Even with the naked eye many
grains of muscovite
and turbid feldspar
grains are angular,
with little evidence
can be seen.
of wear.
All the
Under
the
13
polarizing microscope,
to rather more than
the sand may be seen
50$.
Of the feldspar
to consist
of feldspar
grains about half are
fairly fresh, and of the fresh grains somewhat
more than half
with indices higher than 1.54, the refract-
are of plagioclase
ive index of an immersion
fluid in which the grains were examined.
The quartz grains are chiefly of the type with "irregular" in-
clusions, as defined by Hackle, though "regular" ones also oc-
.
Jackie,
Bdin.
The sands and sandstones
of Eastern Moray, Trans.
Geol. Soc. VII, 1896, p. 148.
In the fraction of higher density than bromoform there are
cur.
minerals,
many ferromagnesian
and brown amphibole,
chief among them glaucophane,
basaltic hornblende,
jagged ends, and magnetite;
there
pyroxene
green
grains with
are also grains of zircon, tour
maline, garnet of various colors, and epidote.
the similar fraction from the Avenal sandstone
Compared
with
this assemblage
is highly distinctive.
Saata Margarita Formation
Overlying the Temblor all along Reef Ridge is a variable
formation, about 1000 feet thick, consisting of sandstone
and
shale at the base,
and
shale at the top.
diatomite in the middle, and sandstone
The basal conglomerate
has already been mentioned.
stone
and of many spherical
derived,
It consists
pebbles
of this formation
of fragments
of various igneous
in all probability, from the Cretaceous
of sand-
rocks,
conglomerate.
The diatomite is whiter and harder than most of that in the
Kreyenhagen,
and contains
more calcareous
lenses
and nodules.
14
The shale and sandstone
ied separately
above
the diatomite has not been stud-
from the Etchegoin strata.
The upper limit of
the formation was, in fact, left in doubt by the earlier mapping,
but has been defined for the northwestern
.
Nomland
part of the area
bf
J. 0. Nomland, op. cit., p. 201.
The fossils of the formation are varied:
gigantic forms,
Tamiosoma gregaria, Ostrea titan, etc., in the basal conglomersome unidentified gastropods
ate;
beds of the siliceous
shale; many unidentified Foraminifera and
diatoms, both in calcareous
and siliceous parts
tion; and some unidentified vertebrate
bones,
in calcareous
and pelecypods
likewise in the calcareous
than diatoms have been described
of the forma-
bones, probably whale
No fossil plants other
beds.
from the formation in this area.
In the Mt. Diablo region, however, a good flora of broad -leaved
trees has been collected from beds of the same age.
Inasmuch as the lithology of the upper and lower parts of
the formation are practically indistinguishable
from that of
the underlying and overlying strata, attention will be limited
here to the diatomite.
Compared
to the Kreyenhagen,
Margarita diatomite is whiter, harder,
the Santa
with less clastic mat-
erial and less indication of oil, and has much more calcareous
material in the form of beds,
lenses, and nodular concretions.
This material is light or dark gray on a fresh fracture, but
weathers
ally.
yellow.
Some specimens
have been
studied
petrographic-
Thin sections usually show little except an extremely
15
fine-grained
mass of calcite, in which there are a few diatoms
and foraminifera,
feldspar.
with occasional angular
grains of quartz or
One section showed many small, angular grains of
quartz and feldspar and some sections
solution of the calcareous
Upon
of small mollusks.
material in hydrochloric acid, the
residue
is a fine silt, much less muddy than that left from the
samples
of Kreyenhagen.
of quartz and feldspar,
The light minerals are angular
with many diatoms.
are pyrite, zircon, garnet, magnetite,
grains
The heavy minerals
green hornblende and ba-
saltic hornblende.
Etchegoin Group:
Above the Santa Margarita formation in the Kreyenhagen
Jacalitos
Hills there are about 7000 feet of sandstone
and shale.
The uoper half of the formation is excellently exposed
the Kettleman Hills.
Anderson,
Etehegoin.
and
also in
This group of rocks was, by Arnold and
divided into two formations,
- the
Jacalitos
Nomland holds, on the other hand,
and
that it is
really a single formation, which he calls the Etchegoin group.
For the purpose
more advantageous,
the
study, Nomland* s views are the
of the present
and will be adopted.
group with special reference
to the
be found in Nomland *s admirable paper,
A detailed study of
invertebrate
fauna may
"The Etchegoin Pliocene
of California."
J. 0. Nomland, op. cit.
A brief description that
should do justice to so thick and
variable a group of rocks as this one would obviously be an im-
16
The group contains
possibility.
and colors:
calcareous
resistant
beds, cross-bedded
or fresh water fossils; drab, cross-bedded
shale pebbles,
occasional
sandy,
bedding planes
the group nevertheless
oolitic limestone,
limestone of considerable
beds and many pebbles
of other kinds.
Shell limestone,
nodu-
It has some conglomerate
In addition to these more common varieties
some striking beds of white, voland some beds high in gypsum.
The group contains an abundance
papers,
has lime-
almost at random through strata
scattered
some lignitic streaks,
The invertebrates
ent kinds.
With a
and beds of structureless
extent.
of rock, the group contains
canic ash,
concretions.
of several different kinds:
lar limestone,
The shales are
usually without fossils
or calcareous
minor amount of limestone,
some with
shells, or with
strewn with shells.
limy, clayey, and gypsiferous,
stone beds
sands,
some with scattered
but often with ironstone
thin
with various marine, brackish water,
reddish and brown strata
angular
blue sand-
concretions,
with different kinds of conspicuous
stone
beds of all kinds
sandstone
of fossils of many differ-
have been the subject of several
The vertebrates,
notably those of Arnold and Nomland.
most of them from the area north of Coalinga, have been described in a series
of papers
plants do not appear
to a few definite horizons.
suggest
varied immensely at any one time.
assemblages
to
of silicified wood and bark, large-
like the lithological varieties,
onments
The fossil
They appear
to have been described.
consist mainly of fragments
ly restricted
by J. C. Merriam.
The organic remains,
that the local envir-
The faunal and floral
accordingly differ so much because
of ecological
17
factors that their chronological
cult to determine.
al temperatures,
The marine invertebrates
subtropic-
suggest
the brackish and fresh water invertebrates
lower temperature,
a
the fossil wood and gypsum partial aridity,
a land area with an abundance
and the vertebrates
attempt
implications have been diffi-
will be made later to harmonize
of grass.
these somewhat
An
conflict-
ing data.
An adequate
account
of the petrography
It must suffice here merely
would probably req\iire a volume.
to discuss
briefly three samples
freshwater
of prominent
lithologic types:
vivianitic; the brownish
formerly considered
the blue sandstone
of the Etchegoin
bed (Lower Mya zone of Arnold and Anderson) fotind
about 2000 feet below the top of the formation; and the blue
clay shale which forms a good deal of the upper 1500 feet of
the formation.
strata
The blue sandstone
in places;
occurs in cross-bedded
20 or more feet thick.
They are found chief-
ly in the upper middle portion of the group.
about equal amounts
of quartz,
gray coating on the surface,
and of dark grains
Attempts to scrape
bright blue.
of scattered
the examination.
the phosphate
of chert and
of a similar coating,
off enough of the
coating for optical study were unsuccessful,
presence
shows
either clear or with a thin
turbid feldspar which, from the presence
appear
A sample
because
of the
grains of fine silt which interfered with
It was this silt, probably,
that furnished
in the early analysis which gave rise to the vivi-
anite hypothesis.
A later analysis,
cited by Anderaon and Pack,
Anderson and Pack, Geology and Oil Resources of the ..est Border
of the San Joaquin Valley, North of Coalinra, California.
Bulletin 603, U.S.Geol. Survey, 1915, p. 82-83.
18
is said to show that the coating is composed mainly of silica,
alumina, and ferric iron, with no phosphate.
suggest,
however,
that
These
writers
the alumina and iron in this analysis
may have come from some of the grains and not from the coatPerhaps
ing.
the silica did the same.
that the coating is composed
was secondarily
deposited
decomposition
in the sandstone,
of the
that
of fine volcanic
water in which the sand
or of clayey material resulting from the
of portions of the sand."
is known either in favor of or against
ceivable hypotheses,
however,
of opal or chalcedony,
dust that settled on the surface
was being deposited,
They suggest,
Ho definite evidence
these or any other con-
and the problem must be left for the pre-
sent as an insoluble mystery.
The phase
ish, arenaceous,
of the Lower Mya zone chosen for study is a brownoolitic limestone,
and sand grains have
served
in which minute gastropods
as nuclei, (Plate IV, Fig. 4).
The
oolites are unusually large (pisoli tic) and some of them show
traces
of both concentric
and radial structure.
The minerals
serving as nuclei include quartz, feldspar, chert, and some ferromagnesian
minerals.
This oolitic bed offers some analogies
the oolites now forming in Great Bait Lake.
with
The oolitic phase
was found only in a single place, although the fossilif erous
brown sandstone
bed of which it forms a part was traced several
miles in the northern part of the Kettleman Hills.
It occurs
a hundred feet or so above the highest horizon at which Kulinia,
an abundant
mollusk in lower strata,
was found.
It gives the
19
suggestion
earliest
of the coming of lacustrine
conditions in t c
San Joaquin basin.
of the blue clay that forms much of the upper
A specimen
part of the Etchegoin was studied,
without very striking results.
The clay broke down to a flocculent mass upon being eoaked
By panning away the clay material, minor amounts
water.
rounded
erals were found..
Not enough
of them were obtained
of any foraminif era.
a part of the lighter material,
covered
Gypsum forms
as may be seen with a lens on
It is probably the presence
of the clay.
this mineral that causes
to make a
Examination of the clay material
good crop of heavy minerals.
a fresh fracture
of
grains of quartz and a few other min-
small but somewhat
failed to show the presence
in
the outcrops
of
to "slack", and become
with a loose, porous coating of mud to a depth of about
two feet.
The examination
information that serves
failed to give any
definitely to suggest
the conditions
Some other data bearing on the problem
of its deposition.
will be mentioned
of this shale
below, under Geologic History.
The Tulare Formation:
Overlying the Atchegoin group of strata
of unconformity
is a dominantly
ies with a maximum
thickness,
lacustrine and fluviatile ser-
as measured
in the Kettleman Hills, of 31GC feet.
the Etchegoin
which persists
by Arnold and Anderson
»* boundary between
sandstone
and Tulare is drawn at the baee of I
throughout
in most exposures
the associated
without evidence
the r.ettleman
hills, and which ie
filled with shells of minute gastropods.
strata larger shells, chiefly pelecypods,
In
also
20
lacustrine types,
are found in abundance.
as marine
Inasmuch
shells have been found in only one higher horizon at one localshells are found in probably only one lower
ity, and freshwater
horizon, this conspicuous
10,000 feet of Pliocene
bed serves
strata
very well to divide the
of the region into two portions:
a dominantly marine lower portion, 7000 feet
thick, and a domin-
The upper
upper portion about half as thick.
antly freshwater
portion is presumably
Robles formation,
at least
in part equivalent
which occupies
an analogous
to the Paso
position in the
Salinas Valley section.
Lithologically, the Tulare formation differs from the Itchegoin chiefly in the abundance
the sand and clay strata.
of gravel interbedded
with
and dis-
A study of the character
tribution of the gravel in the Kettleman and Kreyenhagen Hills
yielded some
suggestive
facts, which may be summarizec
here.
map,
In the first place, as is shown even by the topographic
the basal
Tulare beds outcrop here and there, especially
the Kreyenhagen
Hills, as prominent groups of hills.
group fronts Big Tar Canyon; another
farther northwest
or so northeast
in front
of Canoas
of Dagany Gap; and
coarser
ities.
graye
1£
shows
is situated a few miles
Canyon; a third a mile
A field examination
that they have much thicker beds
gravel than do corresponding
This fact suggests
dumped
One such
a fourth, the Guijarral
Hills, eight miles east of Coalinga.
these hilly areas
at the mouths
in
of
of
horizons at other local-
that the hills may be simply the
of Pliocene
a little further light on the matter,
streams.
examinations
To throw
of the con-
21
stituents
of the gravels in these
the hills in front of Canoas
blocks of Cretaceous
and
various
Canyon,
Tertian
hills were made.
the pebbles
are almost all
or igneous pebbles
sandstone,
that must have come from the Cretaceous
In
beds;
conglomerate
they
are just the kinds of material most abundant along Canoas Creek
now.
In the Guijarral Hills on the other hand, as in the north
end of the
Kettleman Hills in general, the pebbles are largely
red and greenish cherts
derived from the Franciscan.
In gen-
eral, the studies indicate that the pebbles in each area are
exactly of the kinds that are now being brought down by the
streams
that flow nearest
likely, therefore,
ancestors
that these
of the present
gravel deposits
fact mentioned by Arnold and Anderson,
Tulare gravel beds, a
is of much interest.
in them of Eocene and Miocene sandstone
additional evidence
angular concordance
among the various members
their deposition was not everywhere
unconformities
described
above, and perhaps
probably be still more apparent
could examine
Tertiary strata
blocks.
of the Reef Ridge
continuous.
The
some others,
would
than they are at present
the marginal portions of the formations,
tions now removed
It
that in spite of the
This fact furnishes
section,
were made hy the
streams.
One other fact In regard to these
is the occurrence
It appears
the hills in question.
if
w©
the por-
by erosion.
in neighboring areas:
Along Reef Ridge, then, and in the Kreyenhagen
and Kettle-
man Hills, the Tertiary group of rocks consists
of at least
13,000 feet of strata, dominantly sandstone
shale, with
and
22
two thick diatomite formations.
Before turning to the geologi-
cal history deducible
strata,
say something
from these
in regard to the changes
are traced short distances
Hills area,
it will be necessary
found in them when they
along the strike.
In the Alcalde
immediately north of waltham Creek, and only a few
miles from the western part of Reef Ridge, the section
is so
different that the exact relation of its various components
those described
made out.
to
for the Reef Ridge section has not yet been
strata,
The Eocene
for example,
with beds of coal; the Kreyenhagen
stone;
to
the very existence
to be definitely proved;
are largely shale,
has a good many beds of sand-
of femblor strata can hardly be said
the Santa Margarita
by a foot or two of conglomerate
is represented
only
found in a single spot; the
lower Itchegoin seems
to be terrestrial;
is only a few hundred
feet thick,
and the upper Etchegoin
In general,
as compared
with
the Reef Ridge section,
the formations
in Alcalde Hills appear
to be either non-marine,
or marginal;
they have fewer fossils
and, measured
by thickness
of strata cut out, greater uncon-
formities.
When one examines
the corresponding
strata
east of the Alcalde Hills, in the neighborhood
anticline, he finds still other conditions:
ten miles northof the Coalinga
the Eocene
is here
twofold, a lower shale series and an upper one of sandstone;
Kreyenhagen
and Temblor again resemble
the corresponding
forma-
tions along Reef Ridge, but with some striking differences;
Temblor is overlain by a formation composed
of serpentine
the
the
de-
23
tritus, the "Big Blue", the stratigraphic
rendered
relations
of which are
doubtful by an entire lack of marine fossils;
Margarita is entirely clastic,
sils; and the Etchegoin
with several
the Santa
zones of giant fos-
is again largely, but not entirely, ter-
restrial in origin.
Southward
from those
crosses
from Reef Ridge, conditions are equally different
found along that ridge.
In fact, every time one
an important zone of faulting, such as those along
Alcalde Canyon, Los Gatos Creek, or Avenal Creek, he/ls likely
to find himself In a new Tertiary section.
Coast Ranges is broken into fault-blocks,
to have been elevated
and depressed
or less independently
of the others.
This portion of the
each
of which appears
during Tertiary time more
The stratigraphic
and
sedi
mentational problems resulting from this complex diastrophic
his-
tory are of course
sent
discussion
extremely difficult.
as much as possible, attention is drawn almost
entirely, both in the preceding
deductive discussion
Reef Ridge.
To simplify the pre-
descriptive
portion and in the
that is to follow, to the conditions along
24
GEOLOGIC HISTORY OF
The pebbles
THE
COALINGA DISTRIC
DURING THE TERTIARY.
in all the Eocene conglomerate
of kinds that could have come from Cretaceous
of those
characteristic
of the Franciscan.
are of the extremely stable species
beds studied are
rocks, with none
The heavy minerals
that would be expected to
survive more than one cycle of weathering and transportation.
The relation of the Eocene
formity with moderate
gest that the Eocene
up of slightly
naj have
Cretaceous
ness of the Cretaceous
that covered
pre -Cretaceous
been bordered by lands made
strata.
The known great thick-
in miles, makes it
Eocene time the area
So far as the available evid-
it may be assumed
that the source
Eocene detritus was a land area probably somewhere
of the present
Coast Ranges,
slightly consolidated,
Professor
composed
Cretaceous
of moderately
also that
folded,
strata.
represent-
fauna are tropical species.
the known floras of the California Eocene,
both of the Heganos and Tejon divisions, are of species
must have required not only a high temperature
ly high annual rainfall, 40 inches or more.
therefore,
that
but also a fairIt seems
probable,
that the weathering of the detrital materials now
found in the Eocene formations must have
ditions of high temperature
orable
of the
in the region
J. P. Smith has shown that the living
atives of the Eocene invertebrate
He states
tributary
the Coalinga district may have had no
rocks exposed.
ence goes, therefore,
one of uncon-
is such as to sug-
formations, measured
easy to believe that throughout
to the sea
Cretaceous,
angular discordance,
sea
folded
to the
and humidity,
to chemical decomposition
taken place under
con-
such as would be fav-
of the rocks.
Under these
25
circumstances
the high percentage
specimens
of the Coalinga Eocene
undoubted
Tejon from Tejon Ranch,
of feldspar
found in various
(as well as in specimens
of
south of Bakersfield)
becomes
a difficult problem.
In general,
two possibilities
are suggested
The first is that in addition to the Cretaceous
are known to have furnished materials
may have been an additional source
by the facts.
rocks
to the Eocene
of feldspathic
which
sea there
materials.
This possibility is not favored by any other facts, such as
the existence
in the Eocene of rare minerals different from
those of the Cretaceous
additional source,
assumed
itely eliminated.
that might have come from the
rocks,
but it cannot
at present
be defin-
Another possibility is that the weather-
ing took place on mountains so high as to have a sub-arctic
type of climate.
After the deposition of 500 feet or more of Eocene
stone
in the area now occupied
pear to have undergone
als that were brought
sand-
by Reef Ridge, conditions ap-
a gradual
change.
The detrital materi-
into the sea were of the same kinds as
before, but they were small in amount.
At the west end of
Reef Ridge they make up a few hundred feet of clastic shale
with intercalated
sandy strata;
the Devils Den region.
amount
the same thing may be true in
In the intervening area, however,
the
of clastic material reaching the sea was insignificant
compared
to the enormous
quantities
that collected on the bottom.
of diatoms and foraminifera
While the
present
investigation
has revealed nothing new in regard to the puzzling question of
26
the conditions of deposition
vealed nothing at variance
of this material,
it has also re-
with Dr. Branner*s interesting sug-
gestion that the diatoms may have been carried into a partly
land-locked, probably shallow sea by currents
and killed by the unfavorable
from the north,
conditions there.
J. C. Branner, Bull. Geol. Soc. Am., Vol. XXIV, 1913, pp. 94-95
At the conclusion of the deposition of diatomaceous
the sea bottom was exposed
the shaly strata
inga anticline.
gressed
to erosion
were folded along the axis of the present
sandstone
has two beds,
series
feet thick, of pure diatomite, interbedded
The most obvious conclusion
sandstone.
to cause
the
and that of clastic shale and
to begin was not so great
the great differences
with the
from this strik-
ing fact is that the change in conditions necessary
deposition of diatomite to cease
with
In the region of the Coalinga
anticline, hox^ever, the succeeding
sandstone
Coal-
After a longer or shorter time the sea trans-
more or less gravel intermixed.
coarse
in the Reef Ridge area, and
again and laid down at first gravel, later sand
each several
material,
as might be inferred from
The sug-
in the two types of sediment.
gestion is strong that diatomite is a shallow-sea
deposit
in
this region.
During the deposition
invertebrates
swarmed
of the Temblor sandstones,
over parts of the sea bottom.
of bones of land animals were occasionally brought
North of Coalinga,
the bones
of the Merychippus
marine
Fragments
in by streams.
zone accumulated
27
during a late part of the epoch.
A little later began
the de-
J. 0. Merriam, Tertiary Vertebrate Faunas of the North Coalinga
Region of California, Trans. Am. Phil. Soc. XXII, Part
111, 1915.
detritus derived presumably
position of serpentine
from the Fran
several miles &est and north of the Coal
ciscan area now exposed
inga oilfield*
In regard to the climate of the region during Temblor time,
Professor
Smith f s studies
were still of subtropical
evidence
in this region."
of evidence
time.
greater
than
The Mery-
that during the later
time "the land mammals
furnished more grass
shreds
that it was somewhat
to :.terriam to show
fauna seemed
invertebrates
In regard to rainfall, such
by the region at the present
portion of Temblor
undant
that the marine
types.
as there is suggests
that possessed
chippus
show
found here were ab-
If so, it is likely that the region
than it does at present.
point to the same conclusion,
finite proof for it can at present
A few other
but no de-
be given.
During the latter portion of Temblor time, the serpentine
detritus of the Big Blue was swept into the sea, or accumulated
Coalinga.
on a low coastal plain in the region just north of
At the close of the epoch, the recently deposited sediments appear to have emerged
for at least a short time, but are not
known to have undergone
any considerable
The next definite episode
is the
amount
of erosion.
in the history of the region
sweeping of sand and coarse
gravel into the sea, while
28
oysters,
pectens,
These organisms
barnacles,
persisted
etc., were living on the bottom.
during the deposition
of much of the
formation in the region north of Coalinga, but died out farther
south after
the deposition
of the basal gravels.
A little
later there began in the southern region the deposition of
another
series
of diatomaceous
this material is present
there
is a much greater
beds.
Only about 50 feet of
at the west
end of Reef Ridge, but
thickness farther west ana many times
as much toward the south.
During the time of the diatom ac-
cumulation, at least a few mollusks were living in this
the
sea, as well as a few vertebrates,
probably whales;
were also foraminifera in such abundance
numerous
lenses
as
there
to give rise to
At a later time deposition
of limestone.
clastic materials
part of
was resumed over the whole region.
still there was a break in deposition,
of
Later
and probably a with-
drawal of the sea from at least a portion of the area.
Nomland, Etchegoin Pliocene,
page
201.
of the Santa Margarita formation
The clastic materials
were furnished, without reasonable
doubt, by an area of Fran-
ciscan and other rocks which lay to the west of the sea in
which they accumulated.
The climate
was probably not very
different from that which prevailed over the region during
Temblor time.
The giant
faunas
such conditions as favorable
suggest
temperature,
a concurrence
of all
salinity and abund-
29
ant food supply,
found at present,
The interbedding
Indies.
ic sediments
and the
in the East
of pure diatomaceous
as did the Temblor,
shows again,
conditions necessary
for example,
to cause
cessation
shale and clastthat the change
of deposition
of
of the one
beginning of deposition of the other was not so radical
As before, however,
as it would seem.
can merely appeal
for an explanation
indefinite way to changes
in a rather
one
of cur-
rents.
as Santa Margarita
After the deposition of the beds classed
was at least
there
a local break and an
of the sea-
After a longer or shorter period marine conditions
bottom.
were again established
over the region and persisted
series of lenticular sandstone,
great
emergence
conglomerate,
until the
and sandy
shale beds referred by Nomland to the Itchegoin group, had been
deposited.
During th« long period required for the deposition
goin strata
changes
lands.
to a thickness
occurred
the presence
of a mile and a half, a great many
in the San Joaquin
The determination
of these
of the period.
be shown, the period witnessed
change
and on the adjacent
changes
is complicated
mitfc a final
In a general
a contest
way, however,
and as will now
between
subsidence
victory for the latter; and
from a climate of subtropical
by
of local varia-
have recognized,
as all previous investigators
deposition,
sea,
in the strata of many evidences
tions at all stages
of Etche-
a gradual
warmth and moderate
hum-
idity to one that was relatively cool and arid.
In regard to the source
of t..chegoin
there is less doubt than in any preceding
detrital materials,
period.
and
In many
30
strata occur pebbles
varieties
of fractured
and veined
chert and
the other
of rock that are found abundantly in the beds of mod-
ern streams
which drain areas
of Franciscan
Along with
rocks.
the chert there are chips of diatomite and other materials
show the presence
of earlier Tertiary rocks on the land areas.
Hard blocks and pebbles
of dark brown sandstone
of the Cretace-
These and the other available facts indic-
ous are also found.
ate that the
that
materials came from exactly such a land area as
that which now exists immediately
west
of the Coalinga
district
in the Diablo Range.
the mollusks
In regard to the temperature,
found in all
but the highest Etchegoin strata are warm-temperate
tropical species.
The freshwater
found in the upper strata,
and brackish
on the other hand, appear
a gradual change, probably complieatedby
tions not now discernable.
areas is
of the lano
quantities
These facts
many minor varia
The evidence in regard to humidity
not definite.
The presence
consistent
of great
with aridity rather
humidity, which would promote decomposition
.
to be re-
of silicified wood in some of the upper Etchegoin
strata, however, seems
Cf
fossils
water
lated to types now living in Northern California.
suggest
or sub-
than high
and not preservation
H. G. Lyons, On the stratigraphy and Physiography of the
Libyan desert of Igypt, Quart. Jour. Geol. 3oc. vol.
pp. 545-547.
of the wood.
The remains
of vertebrates
suggest,
on the other
hand, that there was probably more grass in the region at that
31
The presence
time than at present.
per part of the series appears
in a semi-arid region;
of much gypsum, in the up-
to suggest
marginal salt lakes
do the peculiar nodular,
so, perhaps,
Of. Nomland, op. cit., page 209.
and in one case
sun-cracked
limestone beds.
The great faunal changes
noticeable
of the upper Stchegoin demonstrate
changes
from horizon to horizon
that important physiographic
the kinds of change.
were taking place, but merely suggest
The views of Arnold and Anderson on this point are suggestive.
of enormous
¦The presence
by no other fossils,
accompanied
Stchegoin
sands
throughout
the
in some of the middle or upper
indicates
that at various periods
(epoch) extensive
prevailed along the edge of the San Joaquin
the evidence
(Dendraster),
quantities of Bchinarachnius
shallow sand flats
sea."
from the upper part of the series,
Summarizing
they show that
it indicates "that a close connection existed between areas of
salt water and nearly If not entirely fresh water during much
of the (upper) Stchegoin period, and that, especially
in the
later portion of the period, conditions were on the verge of
becoming such as existed during early Tulare time.
The great
thickness of inky-blue fine clay in the upper portion of the
Itchegoin of the Kettleman Hills below the sands of the upper
as fine delta deposits,
Mya zone is believed
to have originated
possibly subaerially
and above the reach of the tide."
The absence
and the presence
from the "inky-blue fine clay" of mud cracks,
in the corresponding
strata exposed
in the
32
Kreyenhagen
Hills of several
fairly thick and unusually uniform
beds of fine, gray sandstone,
gested
origin of the series.
tend to cast
doubt upon the sug-
The clay is very similar, on the
other hand, to the upper Etchegoin clay associated
beds in Priest Valley.
not, however,
Whether it accumulated
or even whether
subaerially
it is, properly speaking,
taic origin or not, the general conditions
quotations
with lignite
suggested
of dea-
in the
from Arnold and Anderson are probably correct.
ilar views, in fact, have been suggested
or
Sim-
by other workers in
the region, and may be taken as established.
In regard to the depth of the sea in this region, the evidence is clear.
The Kettleman Hills strata were certainly depos-
ited several miles from shore,
the Kreyenhagen
since
the corresponding
Hills, though deposited
were apparently not actually littoral.
strata
sand,
nevertheless
strata
some miles nearer
of
shore,
The Kettleman Hills
contain so many beds of gravel and coarse
and so much material
of freshwater
or even subaerial
origin,
as to make it clear that the sea must have been shallow even at
a considerable
summarized
distance
from the diore.
The faunal evidence,
by Homland, is equally conclusive:
fauna of the Etchegoin is composed
shallow water.
At some horizons,
"The invertebrate
entirely of forms living in
locally, forms characteristic
of brackish or even fresh water are present.
istic of considerable
Species
depth have not been found."
Nomland, op. cit., page 216.
as
character-
33
Three or four times during the epoch,
volcanic ash fell
over the region in such quantities as to make beds as much as
10 to 20 feet thick.
Two of these
beds,
middle of the formation along Jacalitos
occurring about
the
Greek, have already been
Another is mentioned by Nomland in the following words:
noticed.
Nomland, op. cit., page 209.
"Closing the period of deposition
immediately before
the transition of these
vailing terrestrial deposits
beds into the pre-
of the Tulare, volcanoes
were again
This is shown by the large proportion
active in this region.
of tuffaceous
or
of the marine Etchegoin,
material mixed with the clays of the Mya japonica
zone of the North Coalinga region
...........
It appears
rather
that they (i.e., ash beds) have not been found in the
remarkable
Kettleman Hills and in the Kreyenhagen
the south."
As a matter
canic ash in places
zone over a distance
Hills, a few miles to
of fact, a bed of fresh white vol-
10 feet thick occurs near the Mya japonica
of at least 20 miles in the Kettleman Hills.
Pits have been opened in at at several
places,
and some of the
material has been quarried for use as Fullers earth.
occurs generally
in a steep
The bed
bluff made by a thick sandstone,
the
Bed at the base of the Tulare, and is in many places
Freshwater
covered by talus.
The post-Etchegoin
purposes
pears
be
summarized very briefly.
to be, in general,
deposits
history of the region may,
for present
The Tulare formation ap-
an interbedding of lacustrine and swamp
with fluviatile materials brought down by streams
from
34
the mountains
surrounding
the
portions of the formation now
southern San Joaquin valley.
exposed
are near
Freshwater
the McKittrick district; also beds
from records
doubt-
of clay and lignite,
A good
wimilar
deal of the material deposit-
was no doubt drifted about
the dust and fine sand,
The Tulare formation is,
by the wind before its final burial.
in short, very similar to the materials
ing in the southern
in
of deep wells to be much more common
farther out in the valley.
ed, especially
limestone,
origin, is found at a good many places
less of lacustrine
beds appear
the mountains
fluviatile material,
and naturally contain a good deal of coarse
ancient alluvial fans, in fact.
The
that are now accumulat-
San Joaquin valley.
in
After about 3000 feet of such material had accumulated
the region
of the Kettleman Hills, there was a great period of
perhaps
folding, the greatest
times.
since Jurassic
The push
came, probably, from the San Andreas rift, which is not many
of the Coalinga district.
miles southwest
fault planes
the series
of
Movements
along old
and axes of folding threw the Tertiary strata
folds
and broke them into the fault-blocks
As a result presumably
on the map (Plate I).
ment of the great
folds and monoclines,
formation accumulated
the Kreyenhagen
overlying porous
into
shown
of the develop-
the oily material of
in the portions
of the
from which much of it has recently been pumped.
An uplifted erosion
surface
dissected
by narrow,
steep-
Hills, and
sited valleys in the northern part of the Kettleman
many upraised
terraces
in some other parts of the district tell
35
something
of the events
of the long
Tulare folding occurred.
erted a distinct geographic
period
Of other events
and the unraveling
that must have ex-
influence in the region, such as the
glacial period, no trace has been detected.
traces,
since the post-
The finding of such
of the history underlying
them, waits,
like many similar problems,
in most other parts of California,
upon detailed physiographic
investigation.
A
36
THE PROBLEMS OF THE HEAVY MINERALS.
The rest of this paper deals with a number of problems
suggested
by a more of less detailed study of the heavy min-
erals obtained from a few hundred samples
tiary rocks,
of the Coalinga
Ter-
taken from many horizons and many localities.
order to make the relation of the various problems
In
to one another
and to the principles of general geology as clear as possible,
the problems
will be discussed
in the order suggested by a typical
The "broad principles governing the trend of
cycle of erosion.
events during any given cycle of erosion involve, among others,
three fundamental
land-mass,
fact0r5.
.......
the transportation
chanical agency,
conditions."
the weathering
of the weathered
and the accumulation
suitable basin of deposition,
aqueous
,
.viz.
material by me-
of that material in a
under varying subaerial
A complete
discussion
Milner, Introduction to Sedimentary
p. 85.
of a
or sub-
of the relation of
Petrography,
London, 1923,
the heavy minerals to these broad principles has yet to be written*
of the subject
Various aspects
by Milner, Boswell, Cayeux,
Milner,
Boswell,
pages
1915,
Introduction to
are discussed,
Goldman and others.
Sedimentary
Petrography,
however,
In this paper
pages
85ff.
ueol. Mag., 1916 pp 105, 163. Cayeux, Introduction,
Sci.,
45-48. Goldman, Catahoula sandstone, Amer. Jour.
p. 261.
general principles
are
rocks of the Coalinga
discussed
district.
only in relation to the Tertiary
37
Like the other constituents
heavy minerals may be examined
on such features
weathering),
rocks, the
for the light they may throw
of the distributive province (region of
as its chief types of rock, its location,
the climate under
agency
of sedimentary
or agencies
which the weathering
of transportation,
took place;
on the
and the length of time
they worked; and on the kind of basin of deposition,
conditions that prevailed in it.
chiefly in mind during the course
and
and the
The problem that has been
of the investigation upon
?^hich this pa- er is based has to do with the possibility of
correlating definite horizons over limited areas
of the distribution of the heavy minerals
Their distribution would be expected
tions, especially changes
province,
of
by a study
in the formations.
to depend
both on condi-
conditions, in the distributive
and in the basin of deposition.
In regard to the kind of rocks that outcropped
in the dis-
tributive province that furnished detrital materials
Coalinga Tertiary formations,
the heavy minerals give some debeds as well as the
finite information, and the conglomerate
quartz and feldspar grains give some more.
information furnished by the conglomerates
available,
and has already been used.
Tertiary formations
to the
In general,
the
is the more readily
It suggests
that
all the
derived materials from the Cretaceous
Arnold and Anderson, op. cit, p. 145, 185, etc.
formations;
that the Santa Margarita and later formations contain
38
in addition more or less material derived from Franciscan
rocks;
and that the Btchegoin-Tulare
detritus was partly furnished by
earlier Tertiary formations.
Detailed studies,
comparison
of thin sections
various conglomerates
of all classes
?d.th sections
involving the
of pebbles
of the various
known in the different mountain areas
in the
types of rocks
in California, would doubt-
less furnish a good deal of additional information.
If compari-
sons were to be made, further,
minerals
in the pebbles
of the rare
and in the various primary occurrences,
formation might possibly gain considerably
a possibility, however,
of the pebbles
merely emphasizes
leave something
heavy detrital minerals
been rather scant.
and that the
to see to what
The information gained from a
grains in these
Most of the quartz
formations has
grains have fluid in-
have not been
clusions, and th® exceptions
such
the fact that studies
should be investigated
study of the quartz and feldspar
the in-
in def initeness;
to be desired,
extent they may supply the lack.
finite source.
accessory
traced to any de-
Detailed study of the inclusions,
especially
of
those of the "regular" type of Mackie might very possibly furnish valuable information.
These "regular" inclusions, how-
ever, are nothing more nor less than heavy minerals themselves.
"when they (the common minerals, like
Jayeux states the matter:
quartz)
definitely suggest
their ori-in, it is generally by
mineral inclusions of the same nature as the heavy minerals
If, then, a really thorough study of the pebbles
in question."
L. Cayeux, op. cit., page 47.
39
and the common detrital minerals
with reference
requires
a study of the heavy minerals
argument
should be necessary
to their origin
they contain, no further
to prove that
the heavy minerals
that exist as free detrital grains in the sediments
study
under
should also be considered.
case,
In the present
though in no sense
the study of the heavy minerals,
complete
in various definite respects
at the present
time, has supplemented
the information already secured
In the first place, it has
from studies of the pebbles.
In discussing
than had been supposed.
siderably sooner
origin of the "Big Blue" Arnold and Anderson State:
Arnold and Anderson,
it is the earliest
zone giving indubitable evidence
in it of fragments of the rocks associated
Franciscan
formation."
The occurrence
not to mention other minerals,
to give equally
Temblor appears
ample,
casual
tion*
*4„v»
that
of the heavy minerals
work
in^ this
of Arnold and Anderson possible.
though of no great practical
examination
glaucophane,
erosion during the whole
in geological
in a vivid manner the advantages
with the
indubitable evidence, however,
Only the complete neglect
that has hitherto prevailed
the statement
of abundant
of the
in nearly every sample of the
rocks were undergoing
of Temblor time.
"
the
op. cit., page 175.
occurrence
made
shown
rocks contributed detritus to the basin con-
that Franciscan
the Franciscan
al-
importance
to be gained
--
country
This ex-
in itself, illustrates
by at least a
e^-p +k« neavy
*« a
« sedimentary j forraaffli"^o 1 0 in
of
the Vs*t»»w minerals
40
These minerals have still other advantages,
however,
which
would be more evident in the study of a group of rocks in which
beds were less plentiful.
conglomerate
Even here the thick
Kreyenhagen
and Santa Margarita diatomites
of pebbles,
but are sparingly supplied
These have not been exhaustively
examination of a few samples
not exposed
are entirely devoid
with heavy minerals.
studied, but so far as an
shows,
the Franciscan
in the neighboring part of the Coast Ranges dur-
ing the deposition
the deposition
but were exposed
of the Kreyenhagen,
of the Santa Margarita shale.
does not detract
of the example
from its interest or conclusiveness
as an
of the value of the heavy minerals.
The circumstances
attending
particularly the emphasis
practical aspects
magnesian
during
And in this case,
too, the lack of Immeidate practical importance
evidence
were
rocks
the present
investigation,
that had to be given to certain
of it, and the relative abundance
heavy mine als that the samples
fortunately led to a partial neglect
It is theoretically
of ferro-
contained have un-
of the rarer heavy minerals.
likely that if these non-safic
minerals,
occurrence,
which have in general a relatively restricted primary
were studied exhaustively, they might furnish still more definite
evidence
in regard
to the geology of tne lands adjacent
to the
Tertiary sea.
to the location of the distributive province,
the
it is usually impossible to draw definite conclusions until
portions of the various possible provinces that remain accessible
ith reference
In regard to the
have been investigated
petrographically.
distributive provinces
that may have existed during the California
41
Tertiary, such studies are still far from complete.
the heavy minerals
about
of the various
by some interesting
plemented
mentary.
1% is therefore
recent
Information
types of rocks,
work, is especially
not to be expected
tho sup-
frag-
that very definite
conclusions
can be drawn from the available data in regard to the
sedimentary
rocks.
to the east
or to the west of the sea in which it was
must be left undecided
formations,
there
detritus came from lands
Whether the Eocene
In regard
for the present.
seems little reason
came at least in part from land areas
to doubt
deposited
to the later
that their detritus
only a few miles west of the
present Goalinga district, in the region of the present
Whether other more distant areas
Ranges.
Coast
also contributed
mat-
erials to the basis and where such areas may have been, cannot
be determined
at present.
In regard to the location and geology of the distributive
province
that furnished materials
have furnished
then, the
heavy minerals
evidence.
When more exhaustive
to their
to the Tertiary formations,
distinctly valuable
data are available
tn regard
distribution both as primary and detrital minerals,
the definiteness
of the evidence
is likely to be much increased.
their evidence
It remains
to consider
conditions
that prevailed
in regard to the climatic
in the distributive province at vari-
ous times.
The relation of
rock to the climate
the
mineral composition of a sedimentary
that prevailed at the time of its deposi-
tion has been discussed
in many papers.
The relation that is
42
See, for example,
Mackie, "Felspars in Sedimentary Rocks as Indicators of Climate",
Trans. Ed in. Geol. Soc. VII, 1896, p. 443.
Barton, D.C., *The Geologic Significance of Arkose Deposits,"
Jour. Geol. Vol. 24, 1916, pp. 417-450.
supposed
to exist between
the mineralogy
of a sediment
climate under which its detrital materials
therefore,
cerned,
So far as the heavy minerals are con-
well known.
sedimentary
types
is,
were seathered
it is obvious that only the less stable,
magnesian
and the
chiefly ferro-
If a
are worthy of special consideration.
rock contains a large proportion of such minerals,
as do the post-Eocene
formations here under discussion,
one
hypothesis
to account for the fact would be that the detrital
materials
were weathered under an arid or a cold climate; and
the materials
for such a formation as the Avenal sandstone,
which amphiboles
and pyroxenes
in
are almost completely absent,
might have been weathered under warm, humid climatic conditions.
That other possible
be entertained
hypotheses
to account
for these
facts may
will be evident from a reading of the first part
of this paper, where the facts are explained
in a different
manner, more in harmony with the other kinds of evidence
ished by the rocks.
expressed
will now be discussed
In the first place,
from rocks of Eocene
abundant,
that led to the views
The reasons
furnthere
in more detail**
the absence
of ferromagnesian
age is counterbalanced
largely fresh feldspar.
minerals
by the presence
of
The feldspar of the later
than that
formations is little, if any, fresher or more abundant
This fact suggests that some factor
in the Avenal sandstone.
43
other than climate is probably the cause
in content of f erromagnesian
the formations
sideration of the problem, it seemed
if possible,
of the difference
by a study of corresponding
the matter,
to test
formations in some region
where both the Eocean and later sediments
were supposed
been derived from the same parent rocks.
account
Upon con-
minerals.
desirable
of
to have
A reading of Pack's
of the Tertiary formations in the south end of the San
that this area might be suitable for
Joaquin valley suggested
It is likely, according to Pack,
the test.
that
the Tehachapi
Pack, R.W., The Midway-Sunset Oil Field, Calif., U.S. Geol. Survey Prof. Paper 116, especially pages 23 and 29.
Mountains, and perhaps
ing either Eocene
be expected
the San Eraigdios,
or Lower Miocene time.
that the ferromagnesian
formed in the two epochs
matic differences.
were not submerged
In that case,
mineral content
the Eocene
it might
of the rocks
should vary, if at all, because
If, for example,
dur-
of cli-
of that region
should be free from heavy minerals, while the Lower Miocene rocks
should have
entered
them abundantly,
into the matter
the chance
would appear
greater
A sample
of Socene
town of Maricopa.
tirely.
but if
from the Tejon Ranch was, therefore,
mapped by Pack as upper Vaqueros
grains,
than before;
would probably be less.
pared as to heavy mineral content
spathic,
climates
or differed in some other
the two did not differ in this respect,
way, the chance
that ancient
with a specimen
com-
from the beds
in the foothills south of the
This study showed
but the Tejon is abundantly
that both are highly feld-
supplied with amphibole
while the Lower Miocene sample lacks them almost en-
In other words, the conditions in this area,
if these
44
samples
are typical of the formations from which they come, are
the exact reverse
of those
in the Coalinga district, which was
part of the same basin of deposition,
hundred miles away.
portant
The chance
than a
that climate had anything im-
to do with the matter under discussion
considerably
is therefore
weakened.
So far as it goes,
ferences
and not much more
of the various
then, the evidence suggests
the dif
that
formations in heavy mineral and feld-
spar content
should probably be attributed chiefly to changes
of source.
That the matter is even less simple than it seems,
however, may be seen from the consideration
time streams
that at the present
are bringing down and spreading over portions of
the San Joaquin valley immense quantities
under the alpine conditions
us disintegrated
If the land areas
up in the Sierra Nevada.
that prevail high
of what is now
and Miocene
California varied as much in climate during Eocene
time as the various parts of the state
ceivable
degree
do now, almost .any con-
of variation in the composition
and Miocene sediments
detrit-
of feldspathic
of the Eocene
would be readily accounted
for.
whole problem of the relation of mineral composition
The
to ancient
climates
is in fact so beset
with difficulties as,
in many in-
stances,
to defy solution.
So far as the present
investiga-
tion shows, furthermore,
offer any advantages
In regard
the heavy
minerals do not appear
to
as climatic criteria over the feldspars.
to the transporting
agents
trital materials,
definite conclusions
ficult to draw.
The degree
that have carried de-
are likewise usually dif-
of rounding of grains
of quartz,
45
zircon, tourmaline,
of
wear
etc., is certainly a measure
to which they have been subjected
their history as detrital grains.
bles.
To consider
at
of the amount
during
sometime
So is the roundness
of peb-
but a single one of the complicating factors,
C.T.l.entworth, The shapes of pebbles, U.S. Geol. Survey Bull.
730, 1922, p.p. 91-114.
•V.H.Sherzer, Criteria for the recognition of the various types
of sand grains, Bull. Geol. Soc. America, Vol. 21, 1910,
pp. 625-662.
C.L.Dake, The problem of the St. Peter sandstone, Bull. School
of Mines and Metallurgy, Univ. Missouri, Vol. 6, 1921,
pp. 177-185.
formations,
however, it is certain that sedimentary
the Coast Range
Cretaceous
in thickness,
have
so frequently
throughout
strata
which aggregate
furnished materials
such as
several miles
for younger sediments
geologic history that such data as
the degree of rounding of grains must be used very cautiously.
It is not obvious, furthermore,
supplement
that the heavy minerals
will
the evidence of the pebbles and quartz grains in any
important respect,
unless possibly in studies of metamorphic
sediments.
The value of certain criteria for the determination
of foliated crystalline rocks, Jour. Geol. vol. 20, IV-US,
pp. 244-258.
J.D.Trueman,
By a slightly different approach
have been made
ing agents
to infer something
that affected
mica and of the amphiboles
good cleavage
by these
to the problem attempts
in regard
to the
transport-
detritus by noting the proportions
and
pyroxenes.
minerals is supposed
The possession
to cause
of
of
them to be
46
Goochild, Desert Conditions in Britain, Trans. Edin. Geol.
Soc. VII, 1896, p. 206.
Goldman, op. cit., page 278.
eliminated from sands
that are subject
to eolian action.
addition to the fact that some British dune sands
have been
found to contain mica, there are theoretical reasons
ing if the proposed
In
for doubt-
criteria have very general validity.
In
the first place, dominant eolian action is likely to be associated with an arid or semi-arid
climate
large proportion of the ferromagnesian
line rocks to persist
disintegrated
- the
kind that causes
minerals in the crystal-
in the disintegrated
material.
material were left to long-continued
the wind, there is no doubt that the cleavable
minerals
would eventually
ferromagnesian
action of
ferromagnesian
If, on the other hand, the
action of the wind were occasionally
to be
seems perfectly possible
If this
be worn so fine as to be easily car-
ried away from the sandy regions.
violent rains, as seems
interrupted
by short but
true of all actual deserts,
that a considerable
it
proportion of the
minerals in the weathering products might escape
destruction by wind action and be carried by streams
basin of deposition.
to the
Unless aridity were so extreme,
there-
fore, as to eliminate water entirely from the role of
ing agent, it is doubtful if the resulting sediments
ly lack ferromagnesian
as suggested
a
transport-
would entire
minerals from this cause alone.
In fact,
above, it has been argued with at least an equal
show of probability that a considerable
proportion of ferromag-
47
nesian minerals
the
in a sediment often implies partial aridity in
distributive province and therefore, presumably, a consider-
able degree
of eolian action.
In conclusion,
it must be admitted
do not serve at present
to give us any
tion in regard to the agents
a sedimentary
rock.
that the heavy minerals
very definite informa-
that transported
the detritus of
So far as the rocks under
this paper are concerned,
the heavy minerals
ever to our knowledge of the transporting
discussion
in
add nothing what-
agents.
Everything
that is known about these rocks, including the nature and slight
rounding of many of the pebbles
and boulders,
gree of angularity of the quartz grains,
erial was carried by short streams
Diablo Range or other nearby areas.
minerals,
though consistent
and the high de-
suggests
that the mat-
from the region of the present
The character
of the heavy
with this view, confirms it only
indirectly.
Conditions in the Basin of
Deposition:
In an interesting study of the St. Peter sandstone,
writes against the view that the heavy mineral content
Dake
gives
any useful information about the conditions of deposition
formation.
igraphic
Instead, he states
relationships
the character
that "the structural and strat-
in the field, including such features
of bedding, cross-bedding,
gradation and similar associated
valid criteria for determining
posit was last laid down."
structural relationships
of a
unconformities,
phenomena
constitute
the conditions under
lateral
the only
which a de-
If among the stratigraphic
the author means,
as
and
as is likely, to
48
include the fossils,
ment of the case.
there
is little to criticize in his state-
In spite of this fact, however, Cayeux has
shown in convincing fashion that the distribution, if not the
actual presence,
may
£ield
of heavy minerals
much important
existed in the basin of
his discussion
in the beds of a formation
information about the conditions that
deposition.
A translation of part of
will make the matter clear.
Introduction, page 47.
"In addition (to certain other uses),
heavy minerals
several of these
are means incomparably more sensitive and cer-
tain than organisms
for determining the currents,
and their
introduction into a given region is ofter the werk of currents.
has been invoked to
But many animals whose presence
intervention of currents are endowed
locomotion.
Besides,
with their own means of
eggs and embryos fixed accidentally
otherwise upon swimming animals,
of the latter and be carried
point of origin, the currents
or
can profit by the movements
to great
distances
from their
remaining absolutely without
influence on their dissemination.....
hand) one may say without exaggeration
heavy minerals
prove the
is an inexhaustible
(On the other
that the study of the
mine of information in regard
"
to the history of the currents of the ancient seas...
Referring to the conditions
in the Upper Cretaceous
of the
Paris Basin, which he has studied for many years, he continues:
49
"It is known that a surface
the
came into this basin through
current
strait of Pel ton and that another
The first carried certain materials
slightest
trace
in the deposits
came down from the north.
of which one finds not the
To make our
of the second.
ideas definite, we may recall that all chalk which contains kyanite has been deposited
the southwest.
un^ler the influence of the current
So true is this that the area
current may be defined by the points where
in the chalk.
It suffices therefore
from
affected by this
this mineral is found
to hunt for kyanite in the
chalk of a given horizon in order to get the data for a current
There is no doubt that we have here the
map for that horizon.
principle of a method of defining the currents
of influence in the ancient
to render
the greatest
The researches
believe,
a method called, I
seas:
British geologists
by Cayeux applies
the principle suggested
rocks of all ages in Great Britain.
fact, several geologists
mineral content
the
"
to pal eo oceanography.
services
of various
and their zone
have
shown that
broadly to sedimentary
During recent
years,
in
have made more or less use of the heavy
of a formation in making correlations.
while
results have not always been above suspicion, and have oc
casionally fceen negative,
ly encouraging,
and parts
they have, on the whole, been distinct-
and have rendered
may have considerable
it very likely that the method
value as a means
of formations,
-
at least,
of recognizing
over limited areas.
formations
If it
will work at all, the method has certain marked advantages from
In the first place,
the point of view of the oil geologist.
every sample from an oil well can positively be counted upon
to furnish a supply of perfectly preserved
heavy minerals;
50
only a small percentage
of the
samples,
on the other hand, have
recognizable
fossils, even of micro-organisms.
place,
suites
while
of heavy minerals
in the second
are likely to be repeated,
and are certain not to be of so great lateral distribution as
many faunas,
are likely to be characteristic
they
finite horizons over short distances;
hand, are very likely to range
In the next place,
strata.
most fossils,
through a greater
the repetition
samples
one now matches
on the other
thickness
of
of heavy mineral
suites at intervals is not so great an obstacle
of well
of very de-
in the study
as it might be in some other cases.
Just as
and shale by their succession
beds of sandstone
in different wells, so he would be able to match the varied heavy
mineral assemblages
found in his samples.
of accuracy
ing degree
often attainable
And since a surpris-
in regard to underground
structure
is now.
by the study of the inaccurate data furnished
by drillers* logs, it would seem very likely that a proportionately greater
degree
of accuracy might be obtained from a con-
sideration of more accurate
including the
All things considered,
heavy mineral assemblages.
to be no inherent reason
lithological data,
why a study of the heavy
there
minerals
seemed
in
the California Tertiary formations might not yield results of
considerable
practical importance.
The discussion
of the distribution of heavy minerals
in a formation willbe preceded
presented
in part, in regard
by a summary of the data, already
to the general
minerals in the Tertiary series.
with-
distribution of the
It has been found, for ex-
51
ample,
that any sample of the Eocene taken anywhere
inga district can be readily distinguished
sample
of any later formation.
samples
from almost any
The only later bed that furn-
ished ft heavy mineral assemblage
all the Eocene
in the Coal-
resembling
those
furnished by
studied came from the basal conglomerate
of the Temblor formation near the axis of the Coalinga anticline.
It may be supposed
that on the low Lands adjacent
which the non-i-elastic Kreyenhagen
to the sea
shale accumulated,
in
the soil
at
became
so thoroughly decomposed
following period it furnished
est
be expected;
beginning of the
beds only the stabl-
to the basal
is correct,
If this supposition
types of heavy minerals.
it suggests
that/ the
that not many recurrences
of the phenomenon
and certainly no others have been found.
In regard
to the
distribution of the
heavy minerals
later formations, a few facts may be given.
the few taken north of that
creek contain it.
goin, on the other hand, contains an abundance
all localities, Some minerals,
ant in all the post-Eocene
such as augite,
is probably altered beyond recognition.
sufficiently detailed
minerals
at first
The necessity
The upper Stcheof hypersthene
in
are locally abundnot re-
In some samples,
So far as
bution of the very rare minerals are concerned,
to be made.
while most of
formations, but apparently
stricted to any particular horizons.
in the
The Temblor samples
taken south of Waltham Creek all lack hypersthene,
not been
are to
augite
the distri-
studies have
to permit any generalizations
of eliminating the ferromagnesian
was not
so as to study the rarer minerals adequately
The later studies suggest, as one would
realized.
52
expect,
that the rarer minerals are more variable
in their distribution from bed to bed.
furthermore,
than
the others
It is entirely possible,
that some of these minerals may prove to be limited
to certain formations.
To obtain the desired
ion of the heavy minerals
the outset
evidence in regard to the distributwithin a formation it was apparent at
that the solution of a fairly difficult preliminary
the problem of taking samples
problem was required: namely,
that would be more or less comparable
to those
one might get
from a drilling well, and the exact stratigraphic
From some points
which would be known in advance.
actual well samples
available.
considered
relations of
would have been advantageous,
of view
but none
were
could be
From other points of view outcrop samples
and they, at least, could be secured.
preferable
The
ideal way of taking them would probably be to dig a trench ac-
ross the outcrops perpendicular
to make of each
of samples
bed that could be recognized
places,
the samples
with reference
with others
the
sons this method has not been followed in the
it was considered
and by
taken similarly at other
one might hope to learn accurately
Instead
to a definite
with certainty elsewhere,
the heavy minerals in a part of a formation.
gation.
and
three-foot or five-foot section a single sample.
By taking the series
comparing
to the strike of the beds,
distribution of
For various reapresent
investi-
of intensive collecting of the kind suggested,
preferable to take samples in several verti-
cal and lateral series
from different portions of the Miocene
and: Fliocene strata.
This method offered the advantage
of
53
giving a better general notion of the distribution of
the heavy
minerals in the whole group of rocks, and was much
more readily
carried out.
It is sufficiently evident that only very intensive and
long-continued studies of a group of formations would enable
one to decide definitely with what degree of accuracy
might be correlated
by means
cal characteristics.
of heavy minerals
they
or other physi-
It is evident also that the degree
would
differ in different parts of the same formation, and that complete success
with one formation would not guarantee
cess with other formations.
equal suc-
The best that could be hoped from
a limited amount of study was to show whether or not the heavy
mineral assemblages
vary from bed to bed in the Miocene and
Pliocene formations,
and whether
is likely to be constant
If these
seemed
questions
the assemblage
for distances
could be answered
every reason
to hope
in any one bed
of a mile or a few miles.
in the affirmative there
that with continuous
series of samp-
les such as might be collected during the drilling of a deep
well, one could certainly recognize
To take a vertical series
Good sets
were obtained
some of the beds, at least.
of samples
is a very easy matter.
from the Temblor and Jacalitos
forma-
tions, and also from the Fernando formation north of Ventura,
along the Ventura River.
showed conclusively
The study of these
samples
that the various beds in such formations
as these differ surprisingly in their assemblages
erals.
(see Tables)
of heavy min-
Bven a bed only a few feet thick may have an assemblage
of heavy minerals
entirely different from a similar bed lying
54
upon it or under it.
Shale beds have the same assemblages
as
beds, and differ from one another as distinctly.
sandstone
In the earlier studies
it was noticed that the chief dif-
in mineral composition
ferences
in the abundance
of hornblende,
nesian minerals.
of the samples
glaucophane
The very stable minerals,
tourmaline, brookite, etc., seemed
were differences
and other ferromag-
sue% as zircon,
to be generally present
to
the extent of 10 to 30 percent, but not to vary noticeably in
different samples.
Theoretical considerations
suggested
that
these minerals, many of fhieh are of relatively restricted
ought to vary more, rather than less,
occurrence,
ated ferromagnesian
satisfactory
minerals.
than the associ-
A little experimenting
method for separating
the two classes
gave a
of minerals,
and thus allowing attention to be directed to the content
rocks in the rarer, more stable minerals.
investigation
The result of this
than had previously been realized;
that the proportions
determined
adequately
of the
was to show, first, that the number of rare miner-
als was decidedly greater
second,
primary
of the rarer minerals had not been
in the earlier work; and third, that the
rarer minerals differ from bed to bed rather more than the less
These results are considered to show that in all
rare minerals.
attempts
to make correlations
ferromagnesian
others,
by studying the heavy minerals,
minerals should be studied separately
if they are present
in any considerable
from the
quantities.
For methods of making these and other separations used in this
investigation, reference may be made to a paper entitled "Some
Heavy Eineral Investigations", to be published in
forth-coming number of Economic Geology.
methods^for
the
55
In addition to the reasons
some others may be added.
that the minerals
already given for this advice,
In the first place,
of relatively restricted
are the more likely to be restricted
content
of ferromagnesian
minerals
facts brought out by the present
which no entirely adequate
facts in regard
possible
strata
of a definite
in a formation in
is one of the most surprising
investigation,
and
reason can be given.
to the phenomenon
one for
Until more
are available it mill not be
feel sure that such variations can be trusted to be
to
In the second
laterally.
persistent
primary occurrence
to strata
The great variation of successive
age.
theory suggests
to find the ferromagnesian
place,
it is not unusual
minerals much decomposed
in one part
of a bed, even though they are perfectly fresh in other parts
This condition, due apparently
of the same bed.
it difficult to determine
alteration, makes
of the heavy mineral assemblages
of likeness
to secondary
the actual
degree
in the vari-
ous samples.
To learn whether or not the heavy mineral assemblages
a bed
are likely to be laterally persistent,
in
it was necessary
the
to find a bed that could be traced for a few miles without
slightest
MJfT of
doubt.
Even in a country of excellent
out-
crops, like the Coalinga district, such a bed was very difficult to find.
As a
result of prolonged
that met the requirements
many casts
bed,
several
beds
more or less well were discovered.
The best one will be described.
ish sandstone
search
It is a yellowish or brown-
two or three feet thick, which contains
of middle Etchegoin
mollusks.
It outcrops along
56
along one side of a range of hills that runs east and west paral-
lel to Jacalitos
Creek about 15 miles southwest
Immediately overlying this sandstone
white ash about 20 feet thick.
of Coalinga.
is a conspicuous
bed of
Inasmuch as the strata all dip
Mentioned by Nomland, op. cit., p. 208.
toward the hill, both beds maintain a nearly straight
75 degrees
course across ravines and spurs for the total distance
can be traced,
visible from the Parkfield grade across
ables one to collect strictly comparable
another
there
the Diablo Range
samples
a few
stratum en-
Its relation to the sandstone
along the whole distance
they
The ash bed is distinctly
or about two miles.
miles to the south.
that
from the latter
There is, to be sure,
of its outcrop.
ash bed several hundred feet higher in the section,
but
the two in this particular
is no possibility of confusing
area.
The results of a study of some samples
from this sand-
A glance at them is suffici-
stone bed are shown in Table A.
ent to show
taken
that the lateral persistency
of the assemblage
minerals
in this particular bed is decidedly encouraging.
distance
from the first sample
The
to the last, two miles, is suf-
ficient to carry one entirely across most oil fields.
this bed is much more peculiar
of
Unless
in the distribution of its heavy
minerals than there is any reason
to
suppose,
there
is no doubt
furnthat the heavy mineral method will, if adequately applied,
out subsurface
valuable aid in the difficult task of working
ish
57
in limited areas.
structure
Some other aspects
of the matter, for which the available
data do not furnish really satisfactory
answers,
will now be
In the first place, it would be interesting
mentioned.
know to what extent
the conclusions
the late Tertiary marine strata
water beds.
reached
to
in this study of
would apply to the Tulare fresh-
It is, of course, evident that the circumstances
attending the deposition
of a stratum decide whether or not
the heavy mineral distribution is such as to be useful in correlating the different portions
of the stratum.
There is un-
fortunately, however, an almost complete lack of data on the
character
ments.
of the distribution in different kinds of modern sediExamination of several
samples
of beach sand collected
at different places along the California coast
shows that they
differ immensely in their heavy mineral content.
probable, however, that If samples
of sand could be secured
enough from the shore so that they are being deposited
the influence of a dominating current,
in their
enables
heavy mineral composition.
under
In fact, so far as theory
in vfcich one
could hope to use heavy minerals for correlation are those
the
of which are swept by currents more or less uni-
formly over the bottom of the basin of deposition.
ocene conglomerates
The Pli-
of the Coalinga District, even those of
marine origin, vary greatly in composition from
place.
far
they would vary much less
one to see, the only kinds of sediments
constituents
very
It seems
place to
The sands vary less, and the silts and muds, presum-
ably, least of all.
Insofar as the Tulare beds are really
58
lake beds, then, it is probable
that their heavy mineral assembl-
ages are distributed much as those of the older, but very simil-
ar, marine strata.
have beds
In fact, the Tulare beds may be found to
of freshwater
the equivalent
limestone,
such as those outcropping
strata of the Buena Vista and Elk Hills, or other
equally good markers that will render
minerals unnecessary
in some places.
ready noticed, are composed
fans, and other subaerial
the study of the heavy
The Tulare beds, as al-
in part, however, of ancient alluvial
deposits.
If a well driller is so un-
furtunate as to strike a few hundred feet of these beds,
entirely improbable
feature whatever
his samples
Summary
in
that either the heav^ minerals or any other
will enable
to those
it is
him to determine
taken from neighboring
the relation of
wells.
of Conclusions:
The results of this inquiry into the usefulness
of the
heavy minerals in adding to our knowledge of Tertiary geological
history in the Coalinga district will now be summarized:
1.
On the land
were exposed
areas of Eocene and Oligocene time
chiefly sedimentary
of the central Coast Ranges.
then exposed.
the cessation
The diastrophic
of Kreyenhagen
of Temblor deposition appear
Franciscan
rocks, which
sand-
strata of conglomerate,
stone, and shale, such as those composing
series
there
the Knoxville-Chico
Franciscan
movements
rocks were not
that occurred between
shale deposition and the beginning
to have brought
to view masses
contributed detritus to all later for-
mations.
2.
of
While some of the finer sediment
the Sierra Nevada or other distant areas,
may have come from
the evidence
is
59
good that the later Tertiary detrital materials
ly from that portion of the Coast Ranges
present Coalinga district.
came
almost
entire
immediately west of the
It is likely that most of the mat-
erials for the earlier formations came from the same region.
3.
gest
The fresh feldspars
and ferromagnesian
that on some parts of the land areas
focks took place under conditions somewhat
minerals sug-
weathering of the older
different, either
colder or drier, than a study of the faunas and flors has sug-
gested.
This fact may point to the existence
local climatic variations,
on the land of
possibly due to the presence
of
high mountains.
4.
that transported
the
to the basin of deposition,
the
Upon the problem of the agents
detritus from the land areas
heavy minerals
throw no certain light.
In regard to conditions in the basin of deposition,
studies ha^ not proceeded sufficiently far to enable any gen5.
eralizations
suggest,
to be made about
however,
the
direction of currents.
that the action of the currents,
They
combined with
in the regions that furnished detrital materials were
recognized at least
such that some beds of the Tertiary may be
of heavy minerover small areas, by their distinct assemblages
changes
als.
If
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61
MINBHALOGICAL
ANALYSES,
Abbreviations:
hb
px
op
¦Jd-or+—
—-
hornblende
pyroxene
opaque
present in small amount.
absent.
Figures at head of columns refer to sample number.
Figures in columns are approximate percentages.
A.
Samples taken from a" sandstone bed about three feet thick which
underlies a white ash bed
in the Vacalit.o s"(£) formation,
on and near the Jacalitos Ranch. Samples are arranged in order
from east to r-est. Two miles from the first to the last. dumber,
designate grains counted in slide.
*•
3;28-E
Hornblende
Glaucophane
Basaltic * hb.
Augite
Colorless px.
Hypersthene
Epidote
Black op.
Turbid
Topaz
Titojitte.
Zircon
Tour aa line
Garnet
68
1
9
328-A, 327-a,
72
1
4
.m.
3
J. D
—
2
17
74
3
4
81
5
1
3 £4
80
2
77
1
75
2
2
2
i
<
#
4
hi
r
AZr-'*\ }
OmmO
#
68
5
1
?
326.
71
2
3
1
i181
#
?
?
12
14
9
17
4
5
9
5
3
#
1
1
i
f
#
#
12
mm
2
2
|
#
#
#
5
3
1
ft
#
I
#
I i
?
without sufficient care, from a sandstone bed
several feet thick underlying a white shale bed m the Jacalitos
formation, between Jacalitos and Waltham Creeks.
Total distance a little over 1/2 mile.
290, 231
289,
288,
287,
285,
283, 284,
35
14
26
11
34
17
25
17
Hornblende
31
Glaucophane
##
JW
ft
8
11
t
10
Basaltic hb.
11
J
J±
34
8
2
5
2
3?
Augite
3
Colorless px.
71
Z5
1
4
i
l
ft
4
Ipidote
12
,8
19
89
50
31
33
50
49
Om«e
18
B.
Samples
taken,
-
Titanite
Zircon
Garnet
—
-
63*5
1
111
*
1
¦
I
-
f
7
|
*
*
*
Til
J
62
•ttIN.BHALQGIC.AL ANALYSES.
C.
Vertical section of Temblor in Tar Canyon.
Hornblende
Glaucopliane
Red amphibole
Augite
Colorless px.
Hypersthene
Ipidote
Black Opaque
Turbid
Titanite
Zircon
Rutile
Tourmaline
Garnet
D.
Eapato
Zircon
Turbid
Black opaque
Basaltic hb.
Rutile
Garnet
Tourmaline
Titanite
Augite
Hornblende
Glacophane
Bpidote
246 249
53
60
1
11
4
-252
44
37
4
8
8
3
2
255 258 261 264 270
22
38
56
42
75
14
1
14
ki-f w
14
4
2
56
7
56
9
8
4
14
5
1(?) 4
8
11
14
1-
4
2
1
14
5
104
5
4
4
9
1
10
4
~3--f*|l3-f
Creek Eocene
312-A
73
5
2
«—
38
2
1
49
276
57
8
2
1
4
S
8
8
14
—
273
134
5
14-4
4
2
4
+
2
1
3
4-
l^-
7
14
JLJL
63
g
MINSRALOGICAL ANALYSES.
Samples
296
Lower
297
« Jacalitos".
M
taken
along Jacalitos
Jacalitos
t;
299
c
301
white sa, midd/e Stchegoin'!
Same (?)
303
296
Hornblende
Basaltic
hb,
Augite
Hypers then©
Ipidote
Black opaque
Turbid
Titanite
Zircon
Rutile
Tourmaline
Garnet
?
c
7
297
1
298
299
300
60
31
26
301
302
303
37
8
8
24-
1121+
-~2-43+2
-
28
25
4
44
.*.
1
28
50
25-551
(2
(IS)
44)
2
(7
(5)
12
61
15
)
+ 318
22
1
1
1
11
13
+42
4-4+
17
48
+
4
3
5
4
_...
~
-
—
-¦-
S
7
1
+
1
1
--
--
Creek.
Alluvium
Tutorc formation
Much ftiass'ivc blots sondsrone, marine
Erchecjoin group
*°"*
Drob sandstone
ond
sandy
shole
Santo Mora ah to formotion
Diatomite imbedded in sandstone
Tern bIor formation
Sondstone
Kreyenhagen
Avenal
("Jaoali-ros")
with calcareous "Reef Beds"
shole
sandstone
moo.
Whitish ond yellowish marine sandstone.
feet of- Cretaceous shale, sandstone
and cona/ome rote underlain by varied igneous and
metamorphic Franciscan rocks (Jurassic) .
Mony thousand
Pre -Tertiary rooks.
PI.Z. Columnar Section
or Tertiary
Formation* of the Coalinga Dsfrtcf.
PLATE IV.
Fig. 1.
Thin section of brownish, fossil iferous sandstone
found near the base of the Avenal sandstone, near
Big Tar Canyon.
Angular grains of quartz and
feldspar, with one large shall fragment, set in
Magnification 33 diameters.
calcite cement.
Fig. 2.
An assemblage
of heavy minerals typical of the
Eocene rocks in the Goalinga district. Zircon
crystals, one or tiso tourmaline grains, some
opaque minerals, and a few grains of quartz or
feldspar with very low relief.
42 diameters.
Fig. 3.
¦*"
%£}
4.
Magnification
Heavy minerals from a sandstone under a white ash
bed in the middle Itchegoin (see text for discussion).
Grains are chiefly amphiboles (common hornblende, glaucophane,
and basaltic hornblende) with a few opaque ores.
Fairly typical
of all post -Kreyenhagen formations.
42 diameters.
Thin section of an oolitic phase of a calcareous
sandstone (lower Mya zone) in the upper Stchegoin of the Kettleman Hills.
Small gastropods,
some serving as nuclei of oolites, and oolites
formed around grains of quartz, feldspar, chert,
and rock fragments.
This bed *?as deposited in
fresh or nearly fresh water, and is the only
oolitic phase of the Etchegoin yet discovered.
20 diameters.
All mierophotographs
Tickell.
were made by Professor
F. G.
PLATE IV.
A&
%
JI
S
<Sfi_
'
W :/*
\
w
•
V# *S_*
¦
-_L'¦¦¦ft*,
Fig. 1. Avenal sandstone.
Thin section
Fig. 3. Etchegoin
minerals
heavy
v
* #•'
ar** JTV
-p.-^?^
.
'
Fig. 2. Eocene heavy minerals
Fig. 4. Etchegoin oolite.