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OCR for page 31
- 3] - TERTIARY AN:D CLETAC:IOUS PALEONTOLOGY OF CALIFOP~TA BAS:~3D Off FOSSIL FISH Is bar ' Lore R. David California Institute of Techrol ogy Receding and transgressing seas have ~ eft a record of fossil fish remains in the Tertiary and late Mesozoic marine sedimentary rocks in the Coast Ranges of California. These f ormations permit a review of changing fish faunas for a long period of geologica.:L time, longer than is usually the case at any one locality. Special attention has been given to these assemblages during the last few years. Profound changes have been noted in fish faunas which are due to the progres sing age of the strata in Which they occur. Of special interest to students of marine sedimentation are the marked differences in types of assemblages represented in strata of different age; differences evidently caused bychanges of environment. Lift erences in facies, as shown by a study of fossil fish-scales, agree in general with those recorded by students of Foraminifera. In What for-1 ows the distinctive types of? ~ ish assemblages that are found in California are briefly renewed: The Upper Miocene is title only epoch in the California Tertiary from which large number of fossilized fish skeletons are known. The specimens occur generally in siliceous shales, and it is presumed that volcanism. played a role in the preservation of these fossils. Diversified faunas Cadre been described from this epoch, generally of neritic to bathyal en. vironments (see Special Paper L>,, of the Geological Society of America). Except for these faunas, which in many places contain complete skeletons, the fish remans ire California strata are represented only 'oy single bores and scales. In sore stra' a scales are distributed in flare et abundance. The Upper Miocene is likewise very rich in scale assemblages, especial- ty in its lIohnian stage. tissemolages are in general of neritic facies and forms of a warm-temperate climate are present. The asser.~hlages of the Los Angeles Basin and of the San Joaquin Valley are similar. The same types are usually abundant and are found repeatedly in a given section belonging to this period of tine. Bathyal facies are present in places, especially n the u.pper.~ost Miocene strata of the DeLnox~t fan stage e . Deepening of the sea is indicated by greater abundance of the genera Rath.~:La.~us, Lampan~yctus and C;yclothone. True deep sea types are never folded in the Los Angeles Basin; they occur occasionally in the San Joaquin Valley together with other forms,~nhabitants of water of lesser depth.

OCR for page 31
- 32 - The Lo~i";er i;,Iiocene is characterized by a. gr~at prevalence of abyssa1 assemblages esp;-cia:L:Ly in its 10~7e~nost strata, the Zemor.rian stage. Ditierer~ces have been noted among, such assemblages; I`Iacrouridae are apart in places, Bcr~rcori~orph fishes in others. This stage is also characterized by the appearance of a number of :.varrn-~vat Or loving types, as certain Sparse and B~rycomorph fishes. Eocene fish ~ arms are best preserved in the Upper Eocene and are very abur~dant in the Kreyenhagen formation of the San-Joao~u:~ V.~'ley. Eocene scales are in general distinctly diffe-f~ent from those in the Miocene, only a few of the forms loo own from the lowermost Miocene are found also in the Eocene. The uppermost strata of the :(reyenhagen shov; in prances assemblages of noetic fancies of a warm coasta:t sea. As a Ale, the strata of this formation indicate exCensi~re Marie conditions of uniform type and of a fairly deep Species. Only a few forms are present and these are found in monotonous repetition in the strata; a genus of the Po~y- m~xiidae., inhabitants of rned~ium deep water down to TOO [a3~homs9 a genus of the :Exocoetidae, members or when marry sum peachy far out into the sea' a sa:Lm~onoid ? fish of unknown relationships; and occasionally a Bregmacerotid fish, a genus most often found in neon cle3?th. ~`,Iiddle and Lover Eocene strata are usually barren of fish remains. . . . The oldest faunas thus far studied are a~raiJab:Le 3~O!Q Upper Cretaceous strata. An abundance of fish remains occult in the I;.Io-reno and Panoche formations of the Panocne Creek area., middle Coast Ravages. The great gap known to exist between -the Upper Cretaceous fish and the earliest known T~rtiar:r forms is aware- -also in Cali~o~ia. The Ca1;~or~a Cret~ceous fish are comparable to Latin Upper Senonian faunas. Different assemb:Lages are present, all of which indicate f air:Ly shal:Low coastal seas ~ The California fish scale assernb:lages as a whole seem to shove a great uniformity in composition oared Large areas at aver one stance. Great diversities may be shown 'oy assemblages that differ in age, as assemblages of different bathymetric Piracies prevail in di~ferer~t periods. It is evident that Whys call changes in the erlvirorr=~,nt and in sedimentary con- d~tions must have played all imp outact role in the selection of the fish forms that were preserved. The study of these scale assemblages therefore seems to be of special interest ~ the study of ecolO=~ca1 problems present- ed by ancient strata. i.iore detailed comparisons of fossil forms and o: flee ecological conditions uncler which they might have existed with recent types and habitats might furnish interesting results ins solving 3:roblerrls of' sedimentation. Such studies Should necessitate a r.~uch ~,~eat,er cor^:pr~hension of existing conditions and habitats in oceanic e3::vironments than is avail- ab1 e today. i ,