Tertiary Paleoclimatic Trends 

in the San Joaquin Basin, 

California

GEOLOGICAL SURVEY PROFESSIONAL PAPER 644-D
Tertiary Paleoclimatic Trends 

in the San Joaquin Basin, 

California

By WARREN O. ADDICOTT

SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

GEOLOGICAL SURVEY PROFESSIONAL PAPER 644-D

Distributional patterns of shallow-water 

molluscan genera reflect Eocene and 

Miocene episodes oj warm marine climate 

separated by a middle Oligocene climatic 

deterioration

UNITED STATES GOVERNMENT PRINTING OFFICE, WASH INGTON : 1 9 7 0
UNITED STATES DEPARTMENT OF THE INTERIOR 

WALTER J. HICKEL, Secretary

GEOLOGICAL SURVEY 

William T. Pecora, Director

Library of Congress catalog-card No. 71-608675

For sale by the Superintendent of Documents, U.S. Government Printing Office 

Washington, D.C. 20402 - Price 35 cents (paper cover)
CONTENTS

Page

Abstract ___ . ___..__. _-______--____._ ___________ _.... Dl

Introduction ____ __ ______ ___ _______ ____ 1

Paleogeographic setting ___________ _____ __ __. 2

Paleoclimatic analysis _______________________ _____ ______ 4

Eocene _ _ _ _ .____ ___ _ ______ 7

Oligocene _ __.- ____________________ ____________ _________________ 7

Miocene ___._.. ___________ ________________________________________________ 8

Pliocene _-. ____________________ ____________________ 10

Discussion _ _ _ ___________________________________________ 11

Sample size _ __ .___._._..._____ ___________________________ ___. 11

Page

Discussion Continued

Gaps in the record _______ _._____ _____ _ ____________________________.__ Dll

Middle Oligocene anomaly _________________ ______________________ __. 12

Eocene amelioration ._____________ _____ _- __ _ ._._____ . 13

Climatic change and extinction .___.______________ _____._________-_ 13

Other California basins ______ -__-_ ______ . 14

Oregon and Washington __._.-_-_____.-______-_______.._____._-_______-_ 14

Paleoclimatic inferences from Foraminifera ______________ 15

Summary and conclusions __________.,_______-__-___-___-__.______-_____ - 16

References _._____ _-__ _-_-_-__- _- __ -_- _ - - 16

ILLUSTRATIONS

Page

FIGURE 1. Index map showing physiographic features of central California D2

2. Maps showing Oligocene and Miocene paleogeography of the San Joaquin basin ___ __ 3

3. Map showing modern shallow-water molluscan provinces of the marginal northeastern Pacific Ocean.... ___ . 4

4. San Joaquin basin zoogeographic profiles _ ___________._.___-______ _____ -_ 5

5. Santa Cruz basin and southern Coast Range zoogeographic profiles__.___ - 9

6. Graph showing middle Oligocene latitudinal faunal gradient __ ___ __ - _ 12

7. Idealized zoogeographic profiles for the San Joaquin basin__ __.-_____. ____ 13

TABLES

TABLE 1. Faunal data.-__---_-_-__..._____.___._.._____________.

2. Extralimital warm-water molluscan genera

Page

D6

Hi

SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

TERTIARY PALEOCLIMATIC TRENDS IN THE 

SAN JOAQUIN BASIN, CALIFORNIA

By WARREN 0. ADDICOTT

ABSTRACT

Early and middle Tertiary molluscan faunas of the middle 

latitudes of the northeastern Pacific are characterized by taxa 

now living in tropical and subtropical latitudes far to the 

south. Unusually large percentages of warm-water molluscan 

genera in Eocene and Miocene faunas of the San Joaquin 

basin, California (lat. 35°-36.5° N.), reflect episodes of Tertiary marine climate substantially warmer than at present. 

Sharp decreases in warm-water genera and in taxonomic diversity during the middle Oligocene seem to represent an 

intervening climatic deterioration. Parallel faunal trends occur in other Tertiary basins of the California Coast Ranges.

INTRODUCTION

The San Joaquin basin (fig. 1), roughly coincident 

with the southern third of the Great Valley of California (lat 35°-36.6° N.), has the most complete 

sequence of shallow-water marine molluscan faunas 

of the Pacific Coast Tertiary. These central California faunas have been the subject of intensive paleontologic study during the past 60 years. Thus, 

they are particularly well suited for zoogeographicbased study of Tertiary climatic change in the nearshore marine environment.

Lower Tertiary molluscan faunas are well developed along the west side and the south margin of the 

San Joaquin basin. Oligocene and Miocene molluscan 

assemblages occur around the south and southeast 

margin of the basin. Late Miocene and Pliocene 

faunal succession is best developed in the northwestern part of the basin near Coalinga.

Tertiary molluscan faunas of central and southern 

California include a persistent element of taxa now 

living in warm-water regimes far to the south. 

During the late Pliocene and Pleistocene this warmwater element is defined by species occurring far 

north of their modern distributional limits; during 

the Miocene and older parts of the Tertiary, it is 

identified at higher taxonomic levels because of high 

percentages of extinct species. Mollusks constituting 

the warm-water element are referred to as extralimital taxa.

The first students of west coast Tertiary marne 

climate (Arnold, 1909a; Smith, 1910) noted a decrease of warm-water elements following the diverse, 

cosmopolitan faunas of the Eocene and thereby inferred progressively cooling post-Eocene marine 

climate. Extralimital late Cenozoic molluscan taxa 

are mostly from the warm-temperate California!! 

molluscan province (lat 28°-34.5° N.), ^whereas 

early and middle Cenozoic faunas include many taxa 

now restricted to subtropical and tropical molluscan 

provinces farther to the south. This concept went 

through two stages of refinement (Smith, 1919, and 

Durham, 1950) but remained essentially unchanged 

from Arnold's original inference. Studies of marine 

climate of specific parts of the California Tertiary" 

based upon marine mollusks have been made by 

Dickerson (1913; 1917), Barbat and Galloway 

(1934), Yokes (1940), Woodring, Stewart, and Richards (1940), Woodring and Bramlette (1950), Hall 

(1960, 1962a), and Addicott and Vedder (1963). 

Other workers have commented on the climatic implications of individual molluscan faunas. Recent 

studies of mid-Tertiary San Joaquin basin faunas 

(Addicott and Vedder, 1963; Addicott, 1965, 1970; 

DeLise, 1967) and work in progress now permit 

more refined analysis of mid-Tertiary molluscan assemblages. From these new faunal data a reversal of 

the post-Eocene cooling trend, with warming during 

the beginning of the late Oligocene and a peak in the 

middle Miocene? lias been recently identified (Addicott, 1968a). The purpose of this report, then, is to 

document climatically controlled changes in middle 

and late Tertiary molluscan zoogeography of the 

San Joaquin basin. This analysis does not permit 

assignment of specific temperature values to the fossil faunas such as oxygen isotope studies do. Accordingly, emphasis is placed upon identification of relative change in the shallow-water climatic regime 

as reflected by distributional patterns of Tertiary 

mollusks.

Dl
D2

36'

35° -

122°

SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

121° 120°

<O V O

Hills

^YV- JOAQUIN

San Luis Obispo &'',, BASIN ,0°

EXPLANATION

Extent of middle Miocene 

marine deposition in the 

San Joaquin basin

FIGURE 1. Index map showing physiographic features of central California referred to in text.

PALEOGEOGRAPHIC SETTING

The San Joaquin basin, centered in the southern 

part of the Great Valley of California, is today 

separated from the Pacific Ocean by the central California Coast Ranges, which average about 40-50 

miles in width. During the Tertiary the basin was 

connected to the Pacific along much of its west margin, now approximately defined by the San Andreas 

fault. The relationship to Coast Range geology to

the west has been obscured, however, by subsequent 

diastrophic movement along the San Andreas fault, 

notably large cumulative right-lateral slip (Hill and 

Dibblee, 1953).

Following the broad inundation by Late Cretaceous seas, the San Joaquin basin formed a narrow, 

kidney-shaped embayment during the Palebcene and 

early part of the Eocene. During this part of the 

early Tertiary, the basin was connected to the ocean
TERTIARY PALEOCLIMATIC TRENDS, SAN JOAQUIN BASIN, CALIFORNIA D3

Oligocene Early Miocene

Fresno

\

50 MILES

Middle Miocene

Fresno

Pomt Reyes

Late Miocene

Fresno

\

\

50 MILES

FIGURE 2. Oligocene and Miocene paleogeography of the San Joaquin basin prior to lateral displacement on the San

Andreas fault. Pattern indicates area of deposition.
D4 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

by a narrow passage northwest of Coalinga, the Vallecitos Straits of Hoots, Bear, and Kleinpell (1954). 

A major marine transgression occurred in the later 

part of the Eocene; the basin was broadened and 

deepened. It presumably had a broad oceanic connection on the west margin, suggested by the marine 

upper Eocene strata which are now truncated by the 

San Andreas fault (from the Tehachapi Mountains 

northwestward to the middle part of the Diablo 

Range (Repenning, 1960) ).

The sea withdrew from most of California during 

the Oligocene, giving way to extensive nonmarine 

deposition, but a narrow marine basin remained in 

the southernmost part of the Great Valley. Seaward 

connections at the ends of the linear Oligocene depositional basin are indicated by the apparent truncation of marine Oligocene strata along the San 

Andreas fault (Addicott, 1968b). A transgressive 

cycle reinitiated during the late Oligocene foreshadowed broad expansion of Miocene seas in the southeastern part of the basin. Oceanic connections during 

this period were principally along the southwestern 

part of the basin. Lake Miocene orogeny in the Coast 

Range area gave rise to the Temblor Range, diverting the Pliocene oceanic connection northward to 

what is now the southern part of the Diablo Range 

southwest of Coalinga. The basin shoaled during the 

Pliocene; brackish water conditions that developed 

during the later part of the epoch were followed by 

nonmarine deposition during the Pleistocene.

Restoration of Oligocene and Miocene paleogeography, in keeping with postulated cumulative rightlateral slip along the San Andreas fault (Hill and 

Dibblee, 1953; Addicott, 1968b; Grantz and Dickinson, 1968), suggests that the San Joaquin basin was 

bordered on the west through most of the Tertiary 

by insular and peninsular masses (fig. 2). Nevertheless, the basin seems to have been an open deepwater 

marine embayment during the Oligocene and Miocene, according to bathymetric inferences from benthonic foraminiferal assemblages in its central and 

western parts (Bandy and Arnal, 1964, 1968, 1969). 

Adjoining basins west of the San Andreas fault were 

at least as deep as the upper part of the bathyal zone 

during the Oligocene (Brabb, 1964) as well as 

throughout most of the Miocene (Cummings and 

others, 1962). Thus, there is no reason to suspect 

that the tropical aspect of Miocene molluscan faunas 

could have been caused by abnormal warming of the 

basin owing to shallow-water or silled conditions. 

Moreover, evidence from other California basins and 

Tertiary sequences around the Pacific rim, discussed

subsequently, indicate that the Miocene warming 

was an ocean wide phenomenon.

PALEOCLIMATIC ANALYSIS

The premise of this study is that paleoclimatic inferences can be made by interpreting the composition of fossil assemblages in the light of modern 

molluscan zoogeography. The modern latitudinal 

gradient along the Pacific Coast of North America, 

expressed by a series of distinctive molluscan provinces (Valentine, 1966), provides a convenient 

frame of reference for evaluating zoo.Teographic 

change in Tertiary faunas. As indicated earlier, middle-latitude Tertiary benthic invertebrate faunas include a significant proportion of warm-v7 ater taxa 

that live today in low latitudes of the eastern Pacific. 

The object of this investigation is to quantitatively 

determine changes in the proportion of this warmwater element in successive Tertiary molluscan 

faunas.

Zoogeographic-based paleoclimatic aralyses of 

fossil assemblages necessarily assume that constituent taxa have not subsequently changed their tem130° 120° 110°

FIGURE 3. Modern shallow-water molluscan provinces of the 

marginal northeastern Pacific Ocean.
TERTIARY PALEOCLIMATIC TRENDS, SAN JOAQUIN BASIN, CALIFORNIA D5

perature tolerance. The composition of Tertiary fossil 

assemblages generally seems to bear this out 

assemblages usually can be readily categorized as of 

warmer or cooler aspect than the modern fauna of 

the same latitude. Sometimes, however, there are 

anomalous occurrences of one or more warm-water 

mollusks in assemblages composed of temperate 

mollusks, or vice versa, suggesting that some taxa 

may have had different temperature tolerances in 

the past. It is important, therefore, to utilize an 

entire fauna, rather than individual taxa, in making paleoclimatic inferences. Accordingly, a simple 

means of characterizing the composition of Tertiary 

molluscan faunas of warm-water aspect has been devised. Warm-water elements are expressed as percentages to permit comparison of faunas of differing 

size. Faunal assemblages included in this analysis 

are believed to have inhabited the higher reaches of 

the inner sublittoral zone, depths of less than 15 

fathoms.

The procedure is to classify each molluscan genus

in a fauna according to the modern zoogeographic 

province (fig. 3) in which its north end point of 

range occurs. Classification is based on range c'ata 

mainly from Burch (1944-46), Smith and Gordon 

(1948), Fitch (1953), Keen (1958; 1963), and Olsson 

(1961). From these data, percentages of genera now 

restricted to warm-water molluscan provinces 

Panamic (6°S-23°N), Surian (23°N-28°N), and 

Californian (28°~34.5° N.) are readily determined. Genera that are extinct or are no longer living in the northeastern Pacific Ocean are excluded. 

Cumulative percentages of warm-water gerera 

have been plotted on a time scale (fig. 4) based upon 

the Pacific Coast megafaunal "stages" of Weaver 

and others. (1944). Boundaries on the chart have 

been adjusted in consideration of available radionetric ages on volcanic rocks interbedded in the California marine sequence. These are mainly from 

Turner (1968a, b); other dates are from Bandy 

(1967a), Clark (1966), Ingle (1967), Obradovich 

(1968), and Yeats (1965). Plotting values as cumuDomengine" sition"' "Tejon" '"Keasey"! "Lincoln

 100 o

 50

30 20 

TIME, IN MILLIONS OF YEARS

FIGURE 4. San Joaquin basin zoogeographic profiles. Numbers refer to faunal data in table 1. The inclined dashed line 

between the "Blakeley" and "Vaqueros Stages" of Weaver and others (1944) indicates the partial age equivalence of 

these units (Addicott, 1967).
D6 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

lative percentages has the advantage of permitting 

visual combination of tropical (Panamic) and subtropical (Surian) values as well as tending to smooth 

some of the irregularities in individual curves. The 

number of genera in each fauna is indicated by vertical lines in figure 4. Faunal data from which these 

percentages were determined are listed in table 1.

TABLE 1. Zoogeographic indices for selected northeastern 

Pacific Tertiary molluscan faunas

[Genera with north end points of range in modern warm-water molluscan 

provinces indicated by cumulative percentages: P (Panamic), S (Surian), 

C (Californian). Genera no longer living in eastern Pacitic are considered 

extinct. "Stages" are of Weaver and others (1944). Formational names 

not yet adopted by the U.S. Geological Survey are indicated by an asterisk 

(*) ; usage is in the sense of the authors cited]

Number of Warm-water genera 

Formation or "Stage" and Source genera (cumulative percent)

Total Extinct P S C

San Joaquin basin, California

1. Domengine Formation, southern 

Diablo Range Yokes (1939) .112 52 20 33 47 

2. San Emigdio and Pleito Formations* ("Lincoln Stage") Wagner and Schilling (1923), DeLise 

(1967), Alex Clark (unpub.- 

paleontological reports, Calif. 

Univ., Riverside), Schenck and 

Reinhart (1938) ........... ......... 43 10 3 9 21

3. Tumey Sandstone Zimmerman 

(1944), USGS collections.... ....... 32 5 0 7 11

4. So-called "Phacoides" reef USGS 

Iocs. 5149, M3B78, M3B79 _.. ........ 31 5 12 23 35

5. "Vaqueros Stage" southeast San 

Joaquin basin Loel and Corey 

(1932), Addicott (.1965; 1970), 

USGS collections ...... ... .. .... ...... 69 12 11 25 42

6. Lower part of the Olcese Sand, 

Kern River area Addicott (1970), 

USGS collections .... .......... ....._. 28 4 13 25 38

7. Upper part of the Olcese Sand and 

lower part of the Round Mountain 

Silt Loel and Corey (1932), Keen 

(1943), Addicott (1965; 1970),

8. Santa Margarita Formation, San 

Joaquin basin Preston (1931), 

Addicott and Vedder (1963). .... .. 66 4 11 24 42 

9. Santa Margarita Formation, 

Coalinga anticline Nomland 

(1917a), Adegoke (1967).. ...... 55 4 12 22 31

10. Etchegoin Formation, Chione elsmerensis zone Nomland (1917b).. 39 5 0 12 26 

11. Etchegoin Formation, Turritella 

nova zone Nomland (1917b)-. ... 30 3 0 7 19 

12. Etchegoin Formation, Siphonalia 

zone Woodring and others (1940) 43 3 3 10 15 

13. San Joaquin Formation, Cascajo 

Conglomerate Member Woodring 

and others (1940) . ................_.. 27 1 0 4 12

14. San Joaquin Formation, Pecten 

z o n e W oodring and others 

(1940) .............. ........ ........ 47 1 0 2 9

Southern part of the Coast Ranges, California

15. Middle member of the Gaviota 

Formation* Kleinpelland Weaver 

(1963) ... ....... _..__...._ ...... ..... 25 6 11 26 47

16. Upper member of the Gaviota 

Formation* Kleinpelland Weaver 

(1963) ......................................... 19 6 8 15 31

17. Vaqueros Formation Loel and 

Corey (1932; Iocs. UCMP A494- 

496, A499) .............. ....... .... 39 3 14 33 53

18. Temblor Formation, La Panza 

Range Anderson and Martin 

(1914) ; USGS Iocs. M3813, M3814 52 10 24 38 60 

19. Santa Margarita Formation, eastern San Luis Obispo County 

Hall (1960), Woodring (1926) .._ 30 0 10 33 43 

20. Pancho Rico Formation, Salinas 

Valley Durham and Addicott

21. Careaga Sandstone Woodring and 

Bramlette (1950) .... ... 132 5 2 8 13

Santa Cruz basin, California

22. San Juan Bautista Formation* 

Alien (1945) . ......... .... ... .... ..25 7 0 11 22

TABLE 1. Zoogeographic indices for selected northeastern 

Pacific Tertiary molluscan faunas Continued

23. Vaqueros Formation Clark (1966), 

Loel and Corey (1932), Alien 

(1945), Arnold (1908), USGS collections _..__ ....... - ._-._ ._._._ 41 7 6 29 44

24. "Temblor Stage" Clark (1966),

25. Purisima Formation, lower part 

Addicott (1969a) . ......................... 25 2 4 13 17

26. Mercedl?) Formation Addicott 

(1969a) ............................................ 34 0 0 6 9

Mount Diablo area, California

27. Sandstone member of the Kirker 

Formation* Primmer (1964) ..... 22 4 6 17 28

Western Oregon and Washington

28. Eugene Formation Vokes and 

others (1951), Hickman (1968 1...... 53 11 5 12 17 

29. Lincoln Creek Formation, Porter 

Bluffs, Washington Durham 

(1944) .. . ................................. 50 17 3 6 9

Extra-limital warm-water genera and subgenera in 

middle and late Tertiary faunas of the San Joaquin 

basin and the California Coast Ranges are listed 

according to their northernmost latitudinal occurrence within modern Zoogeographic provinces in 

table 2. 

Inspection of the Zoogeographic profiles (fig. 4) 

indicates that many genera now restricted to tropical

TABLE 2. Extralimital warm-water genera in California 

Coast Range Neogene molluscan faunas classified according 

to modern molluscan province in which their north end 

point of range occurs

[Classification based on data from Burch (1944-46), FitcV (1953), Smith 

and Gordon (1948), Keen (1958, 1963), and Olsson (1961)]

Panamic Surian Californian

Bornia Anadara s.s. Amiantis 

Anomalocardia Anadara s.l. 

dementia Area s.s. Anatina 

Miltha Crassostrea Anomia 

Pinna Chionopsis Atrina 

Tropithaca 

Arciilaria, Cunearca Crassatella 

Dosinia Florimetis 

Cirsostrema Lirophora Here 

Cymatium Lyropecten Isognomon 

P'eria 

Dispotaea Macrocallista Tellinella 

Euclia Solecurtus Agathotoma 

Ficus Antillophos Austrotrophon 

Architectonica 

Hastula Cancellaria s.s. B?sla 

Knefastia 

Melongena Catilon Bulla 

Polystira Gemmula Costoanachis 

Lithoconus 

Natica s.s. 

Ptycheulimella Nerita Claims 

Pyruclia Oliva Forreria 

Strombina 

Scalina Solenosteira 

Semicassis 

Trockita Thaisella Kelletia 

Triumphis Torcula Morula 

Turricula s.s. Neverita 

Turritella broderipiana Niso 

stock. 

Typhis Pomaulax 

Vitrinellops Strioterebrum 

Terebra
TERTIARY PALEOCLIMATIC TRENDS, SAN JOAQUIN BASIN, CALIFORNIA D7

latitudes ranged far north of their modern north 

limits during the Tertiary. The proportion of these 

warm-water genera in San Joaquin basin faunas 

increased from a low point during the Oligocene to a 

middle Miocene peak and gradually decreased thereafter. Tropical, or Panamic, molluscan genera 

dropped out of the San Joaquin basin fauna by the 

end of the Miocene and subtropical genera toward 

the end of the Pliocene. The relatively high percentages of genera now restricted to tropical and subtropical latitudes suggest water conditions much 

warmer than today; the San Joaquin basin lies inland from the southern part of the Oregonian molluscan province (southern boundary 34.5° N.), the 

climate of which is generally considered temperate 

(Hall, 1964). The post-middle Oligocene increase of 

warm-water genera, together with a sharp increase 

in faunal diversity, suggests climatic warming. 

Post-middle Mocene decrease in these parameters is 

likewise taken to indicate a more or less systematic 

decrease in marine surface-water temperatures. 

Faunal evidence upon which these inferences are 

based is discussed in the following section.

EOCENE

The tropical aspect of shallow-water Eocene molluscan faunas of the San Joaquin basin has been discussed by several paleontologists (Dickerson, 1913; 

1917; Smith, 1919; Yokes, 1940; Durham, 1950). 

Their inferences were based upon the relatively 

large number of genera that are either living or are 

represented by modern analogs in tropical seas. 

Vokes (1940), for example, listed 31 such genera 

from the middle Eocene Domengine Formation, and 

Durham (1950J listed 20 molluscan genera from the 

Eocene Tejon Formation. Clark and Vokes (1936) 

observed that, without exception, all the California 

Eocene genera that can be compared with modern 

taxa have living representatives in tropical seas.

Quantitative zoogeographic analysis at the generic 

level is not suited for early Tertiary faunas because 

of the high percentage of extinct genera. Middle and 

late Tertiary molluscan faunas have about 5-20 percent extinct genera, whereas between 45 and 50 percent of the genera of the early and middle Eocene 

"Capay" and "Domengine Stage" faunas (Vokes, 

1939) are extinct. Moreover, the composition of the 

classic late Eocene molluscan fauna of the south 

margin of the San Joaquin basin ("Tejon Stage") 

is incompletely known owing to stratigraphic lumping of middle and late Eocene assemblages in Anderson and Hanna's (1925) definitive paleontologic 

study of the Tejon Formation (Marks, 1943). Nevertheless, the thoroughly studied middle Eocene "Domengine Stage" fauna from the southern part of the 

Diablo Range (Vokes, 1939) has been tentatively incorporated in the zoogeographic chart (fig. 4) to 

indicate qualitative differences between Eocene and 

Oligocene molluscan faunas. Percentages of warmwater middle Eocene genera doubtless are much 

higher than shown because many of the extinct 

genera excluded from the analysis have closely related modern counterparts in tropical and subtropical seas.

A small pelecypod assemblage from the lower part 

of the San Emigdio Formation of Wagner and Schilling (1923) near the south margin of the San 

Joaquin basin may be of late Eocene age, judging by 

associated foraminifers. The molluscan fauna, consisting of Thyasira and lucinoid pelecypods (Wagner 

and Schilling, 1923), is too small and represents a 

habitat too deep to reflect surface water temperatures. Associated benthonic foraminifers of the 

Narizian Stage are of upper bathyal or lowermost 

neritic aspect according to DeLise (1967).

OLIGOCENE

Molluscan assemblages referable to the Oligocene 

"Lincoln Stage," the limits of which are coincident 

with the biozone of Acila shumardi, occur at scattered localities along the west side of the San 

Joaquin basin from Tumey Hills (Atwill, 1935; 

Zimmerman, 1944) to the northern Temblor Range 

(Simonson and Kreuger, 1942). The largest faunas, 

however, are from the upper part of the San Emigdio 

Formation of Wagner and Schilling (1923) and the 

lower part of the Pleito Formation of Wagner and 

Shilling (1923), near the south margin of the basin. 

Molluscan assemblages are known from many localities in the 1,500 feet of strata assigned to the Refugian Stage of Schenck and Kleinpell (1936) ( = 

"Lincoln Stage") by DeLise (1967). Although molluscan fossils are abundant, faunal diversity is 

greatly reduced from that of the Eocene: Whereas 

Clark and Vokes (1936) recognized 130 species of 

mollusks from the upper Eocene part of the Tejon 

Formation in the San Emigdio Mountains and 182 

species from the type locality of the "Domenjnne 

Stage" near Coalinga, Wagner and Shilling (1923) 

listed only 70 species from their San Emigdio and 

Pleito Formations. Moreover, less than 10 percent of 

the still-living genera from the Acila shumardi zone 

of the San Emigdio Mountains can be classified as 

tropical or subtropical (fig. 4).

The comparatively cool aspect of the middle 

Oligocene fauna of the San Joaquin basin, suggested 

by low faunal diversity and low proportion of warmwater genera (fig. 4), has not been noted in previous
D8 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

analyses of marine climate. However, an unusually 

cool middle Oligocene terrestrial climate in Oregon, 

Washington, and in southern Alaska has been postulated from paleobotanical evidence (Wolfe and 

Hopkins, 1967). Smith (1919) failed to recognize the 

Oligocene climatic deterioration because he utilized 

the fauna of the Astoria Formation of Oregon as 

his sole Oligocene control. This fauna is now regarded as middle Miocene; it is relatively warmer 

in zoogeographic aspect than the molluscan faunas 

of the middle and late Oligocene of the Pacific 

Northwest (Addicott, 1969b). Durham's (1950, fig. 

3) analysis did not include Oligocene faunas from 

California; the relationship of his Oligocene paleotemperature estimates to those of this report are 

discussed subsequently.

The late Oligocene molluscan fauna of the San 

Joaquin basin is poorly known. The only definite occurrence is in the basal part of Anderson's (1905) 

type Temblor [Formation] the so-called Phacoides sandstone of the central Temblor Range. 

Although few mollusks have been reported from the 

so-called Phacoides sandstone (Anderson, 1905, p. 

170; Kleinpell, 1938, p. 39, 106; Curran, 1943, p. 

1372), recent collections have yielded shallow-water 

assemblag'es large enough to be included in this analysis. The fauna is here referred to the lower part of 

the "Blakeley Stage" of Weaver and others (1944), 

the type section of which is in northwestern Washington, based upon its apparent position between 

faunas of the "Lincoln Stage" (Aciki shumardi 

zone) and the lower Miocene "Vaqueros Stage."

Olequahia lorenzana (Wagner and Schilling), a 

gastropod restricted to the Oligocene "Lincoln 

Stage," has been collected from the so-called Salt 

Creek shale, about 10-30 feet stratigraphically below molluscan assemblages from the so-called Phacoides sandstone (California University, Riverside, 

loc. 1106). A larger Lincoln fauna occurs in a landslide block about 12 miles to the southeast (Simonson and Kreuger, 1942, p. 1614). The so-called Phacoides sandstone contains no species restricted to 

either the "Lincoln Stage" or to the "Vaqueros 

Stage." The lowest stratigraphic occurrence of "Vaqueros" mollusks in this part of the Temblor Range 

is in the stratigraphically higher Agua Sandstone of 

Clark and Clark (1935). The Phacoides fauna occurs 

within the type section of the lower part of the Zemorrian Stage (Kleinpell, 1938) of the microfaunal 

sequence; the type section of the lower part of the 

"Blakeley Stage" on Bainbridge Island, Wash., is 

also referred to the lower part of the Zemorrian 

Stage by Kleinpell (1938).

Although somewhat smaller than the fauna of the 

"Lincoln Stage" from the southern part of the San 

Joaquin basin, the combined percentage of Panamic 

(tropical) and Surian (subtropical) gerera in the 

late Oligocene fauna is more than twice as great as 

that of the middle Oligocene. Some of th« Panamic 

and Surian genera characteristic of the late Oligocene of the San Joaquin basin are: Anadara, dementia, Cmssostrea, Dosinia, Miltha, and Ficus. All of 

these warm-water genera had pre-late Oligocene 

origins. Similar middle to late Oligocene zoogeographic trends have been observed in berthonic foraminiferal faunas of California; Kleinpe1 ! (1938, p. 

102) observed that the Refugian (= Acila shumardi 

zone) fauna contains fewer benthonic for^iaminifers 

with southern affinities than does the fauna of his 

overlying Zemorrian Stage.

Faunas of this age are also known from the upper 

part of the San Lorenzo Formation and lower part 

of the Vaqueros Formation of the Santa Cruz Mountain area west of the San Andreas fault (Cummings 

and others, 1962). Fossils are abundant in these formations (Brabb, 1964) but, like the associated benthonic foraminifers (Sullivan, 1962), are indicative 

of outermost inner sublittoral or bathyal depths and, 

therefore, are excluded from this analysis.

MIOCENE

Early Miocene faunas are known frorr only three 

areas in the San Joaquin basin the northern Temblor Range (Arnold, 1909b; Clark and Clark, 1935; 

Heikkila and McLeod, 1951), the San Emigdio Mountains at the south edge of the basin (Loel and Corey, 

1932), and the Kern River area northeast of Bakersfield (Loel and Corey, 1932; Addicott, 1965, 1970). 

Assemblages from the basal part of the Jewett Sand 

near Kern River are the only ones large enough to be 

included in this analysis.

The sharp increase of warm-water genera from 

middle to late Oligocene in the southern part of the 

San Joaquin basin did not continue into the early 

Miocene. Rather, the percentage of Panamic and 

Surian molluscan genera remained almost constant 

from the lower part of the "Blakeley Stage" to the 

"Vaqueros Stage" (the upper part of the "Blakeley 

Stage" of Washington and the "Vaqueros Stage" of 

California are considered to be contemporaneous 

(Addicott, 1967) ).

A small molluscan assemblage from near the 

lower Miocene-middle Miocene boundary (No. 6 in 

fig. 4) seems to reflect conditions essentially unchanged from the early Miocene. This control point 

is based upon meager assemblages from the lower 

part of the Olcese Sand of the Kern River area. The
TERTIARY PALEOCLIMATIC TRENDS, SAN JOAQUIN BASIN, CALIFORNIA D9

combined percentage of tropical and subtropical elements in it is unchanged from that of the early Miocene, although there is a slight drop in the percentage of warm temperate elements. This fauna has not, 

however, been intensively collected, so the zoogeographic indices (fig. 4) must be considered tentative. 

A coeval assemblage of oysters and pectinids from 

the Carneros Sandstone Member of the Temblor 

Formation of Cunningham and Barbat (1932) in the 

Temblor Range on the west side of the San Joaquin 

basin (Curran, 1943) is much too small to incorporate in this analysis.

Warm-water mollusks reached a peak during the 

middle Miocene. Assemblages of this age are diverse 

and are widely distributed along the west side of the 

San Joaquin basin in the northern Temblor Range 

and southern Diablo Range (Addicott, 1968b). By far 

the largest recorded fauna, however, is from the 

Kern River area where more than 200 species of mollusks have been identified from the Barker's Ranch 

fauna (Anderson and Martin, 1914; Loel and Corey, 

1932; Keen, 1943; Addicott, 1965, 1970). This fauna 

occurs in about 100 to 200 feet of section which includes the uppermost part of the Olcese Sand and the 

lower part of the Round Mountain Silt. Studies in 

progress indicate that the coeval fauna of the socalled Button Bed sandstone of the Temblor Range 

on the west side of the San Joaquin basin is of comparable size and diversity.

During the middle Miocene, the percentage of 

warm-water mollusks increased sharply from early 

Miocene levels. Moreover, tropical and subtropical 

genera are nearly four times as abundant as during 

the apparent climatic minimum that occurred during 

the Oligocene "Lincoln Stage." Generic diversity is 

also much higher than the following late Miocene 

and Pliocene levels.

Comparable peaks in the percentage of warmwater mollusks occur in Miocene basins of the Coast 

Ranges west of the San Andreas fault (fig. 5). 

Middle Miocene faunas of eastern San Luis Obispo 

County directly west of the fault contain the highest 

percentage of warm-water elements. Smaller faunas 

from the Santa Cruz basin to the northwest have a 

similar combined percentage of Panamic and Surian 

genera, but the proportion of subtropical (Surian) 

genera is much higher. According to recent postulates of post-middle Miocene lateral slip along the 

San Andreas fault (Addicott, 1968b; Grantz and 

Dickinson, 1968), the Santa Cruz basin lay directly 

across the fault from the southern part of the San 

Joaquin basin during the middle Miocene. The somewhat cooler aspect of the middle Miocene fauna of

60

50

- 40

30

20

10

Series

Oligocene Miocene Pliocene

Provincial stages

"Lincoln" Blakeley'.'. ,.,. , Vaaueros

/

"Temblor"

24

\\

A -

30 20 10 

TIME, IN MILLIONS OF YEARS

TIME, IN MILLIONS OF YEARS

FIGURE 5. Santa Cruz basin (A) and southern Coast 

Range (B) zoogeographic profiles. Numbers refer to 

faunal data in table 1. The inclined dash line between 

the "Blakeley" and "Vaqueros Stages" of Weaver and 

others (1944) indicates the partial age equivalence of 

these units (Addicott, 1967).

the Santa Cruz basin suggested by the lower proportion of tropical genera may be the result of its 

more seaward, less protected setting and the possible 

influence of upwelling. However, the Santa Cruz 

basin fauna is so small that intensive collecting
D10 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

could conceivably alter the percentage composition 

of warm-water elements.

Further evidence of the middle Miocene peak in 

the post-middle Oligocene warming of marine climate is apparent from diversity trends within some 

important middle and late Cenozoic warm-water 

molluscan lineages: Cancellaria, Anadara, and Turritella. Species of Cancellaria in the San Joaquin 

basin, for example, increase from six during the 

early Miocene (Clark, 1918; Loel and Corey, 1932; 

Addicott, 1970) to 18 during the middle Miocene 

(Anderson, 1905; Arnold, 1909b; Addicott, 1970) but 

decline to about seven during the late Miocene (H.R. 

Gale, in Preston, 1931; Addicott and Vedder, 1963) 

and only three during the early Pliocene (Nomland, 

1917b). Similarly, the Tnrritella stocks of Merriam 

(1941) increase from two in the California early 

Miocene to five in the middle Miocene but decline 

again to only two during the late Miocene and 

during the Pliocene. Species of Anadara (Reinhart, 

1943; Hall, 1962a) likewise rise from a low of one 

during the middle Oligocene to six during the middle 

Miocene but decline to three during the late Miocene 

and two during the Pliocene.

Late Miocene assemblages occur at scattered localities in the southern part of the Diablo Range, 

the southern Temblor Range, and along the southeast margin of the San Joaquin basin. The largest 

faunal assemblages are from the Comanche Point 

area south of Bakersfield (B. L. Clark, in Merriam, 

1916; Addicott and Vedder, 1963) and the Coalinga 

area (Nomland, 1917a), about 125 miles to the 

northwest. Both assemblages are shown in figure 4; 

the Comanche Point assemblage marks the highest 

stratigraphic occurrence of marine Tertiary in surface exposures around the southeast margin of the 

San Joaquin basin. There are subsurface records of 

Pliocene assemblages from the southern part of the 

basin (H. R. Gale, in Preston, 1931; Howard, 1935) 

and small assemblages reported from the foothills of 

the San Emigdio Mountains (Hoots, 1930), but 

faunal data are too meager to include in this analysis. Pliocene faunal analysis is based, therefore, on 

the thoroughly studied faunas of the Kreyenhagen 

Hills-Kettleman Hills area (Arnold, 1909b; Nomland, 1917b; Woodring and others, 1940) in the 

northwestern part of the basin.

Percentages of Panamic and Surian genera 

dropped sharply from the middle Miocene peak into 

the late Miocene. Cumulative percentages of warmwater late Miocene genera of the Coalinga area are 

lower than those in the southern part of the basin. 

Presumably this is due to the occurrence of a late

Miocene latitudinal faunal gradient. This gradient 

was initially inferred by Hall (1960) in his recognition of latitudinal differentiation of late Miocene 

molluscan faunas in California. Hall's inferences 

were questioned by Addicott and Vedder (1963) on 

the basis of warm-water genera from the southern 

part of the San Joaquin basin not considered in his 

paleotemperature analysis. Their argument was that 

paleotemperatures in the southern part of the San 

Joaquin basin probably were much warmer than 

those postulated by Hall and at least equally as warm 

as those west of the fault in San Luis Obispo County. 

Their reasoning was based upon the much larger 

number of tropical and subtropical genera in the late 

Miocene fauna of the southern San Joaquin basin. 

The problem of accurately comparing these faunas is 

still unresolved; much of it stems from the much 

smaller taxonomic diversity of molluscan assemblages west of the San Andreas fault which is in 

large part due to selective preservation of calciticshelled mollusks. Aragonitic-shelled mollusks are 

well represented in the much larger San Joaquin 

basin late Miocene assemblages. Although there are 

many more warm-water genera in the San Joaquin 

basin fauna, the percentage of warm-water genera is 

actually somewhat higher in the San Luis Obispo 

County faunas west of the fault (fig. 5). This relationship is in accord with postulated post-late 

Miocene lateral slip along the fault (summarized by 

Grantz and Dickinson, 1968) and the concept of temperature-controlled middle and late Tertiary latitudinal differentiation of molluscan faunas.

The last significantly large occurrence of 

Panamic (tropical) molluscan genera in the San 

Joaquin basin occurred during the late Miocene. Only 

two Panamic genera are recorded from the Pliocene. An occurrence of Euclid as Cancellaria fernandoensis tribulis (Nomland, 1917b, p. 238), from an 

isolated lower Pliocene locality on Warthan Creek 

southwest of Coalinga was not assigned to either of 

the Pliocene zones by Nomland (1917b) and is, 

therefore, not represented in figure 4. An unnamed 

turritellid genus, commonly known as the Turritella 

broderipiana stock (Merriam, 1941), that seems to 

be restricted to the modern Panamic fauna is represented by a species in the lower part of the 

Etchegoin Formation (Woodring and others, 1940).

PLIOCENE

Pliocene faunas of the San Joaquin basir are less 

diverse than those of the Miocene and are characterized by greatly reduced percentages of warmwater genera. Cumulative curves (fig. 4) depict a 

progressive decrease in the percentage of Surian and
TERTIARY PALEOCLIMATIC TRENDS, SAN JOAQUIN BASIN, CALIFORNIA Dll

Californian genera although individual percentages 

of these are subject to variation. The Pliocene curves 

are based upon five faunas: two each from the 

Jacalitos and Etchegoin Formations and one from 

the San Joaquin Formation. These have received intensive study (Arnold, 1909b; Nomland, 1916,1917b; 

Woodring and others, 1940). Tropical genera are all 

but missing from the San Joaquin basin Pliocene as 

indicated above. Subtropical (Surian) genera systematically decrease from 12 percent in the early Pliocene to only 2 percent in the late Pliocene. The 

smaller percentage, based upon the pelecypod 

Anadara s.s., probably represents a relict population. 

This seems to be a case in which a single genus that 

is now restricted to a distant warm-water province 

probably does not indicate temperature fully as 

warm as those in which it now lives (the northernmost occurrence of Anadara s.s. is in the Surian molluscan province). By the end of the Pliocene, only a 

few extralimital genera remained in the San Joaquin 

basin. These are warm temperate genera referable to 

the California molluscan province, the north 

boundary of which is today less than 200 miles south 

of the Kettleman Hills area.

Barbat and Galloway (1934) inferred an abrupt 

late Pliocene cooling, based upon the occurrence of 

abundant My a (Arenomya) in the fauna of the San 

Joaquin Formation. With the exception of brief 

warm-water phases represented by their PectenMytilus-Scalez and Pecten coalingensis faunal zones 

near the base and the middle parts of the formation, 

they considered the marine climate to be significantly cooler than the modern climate of this latitude. However, a fairly large, self-sustaining population of M. (A.) arenana inhabits Elkhorn Slough 

in nearby Monterey Bay (Fitch, 1953); it seems 

doubtful therefore, that this taxon reflects significantly cooler marine temperatures. Zoogeographic 

analysis of the Pecten coalingensis zone fauna of 

Woodring, Stewart and Richrads (1940) and qualitative evaluation of the much smaller assemblages 

from their other San Joaquin faunal zones suggest 

that marine surface-water temperatures were comparable to those occuring in the southernmost part 

of the modern Oregonian molluscan province off 

central California. In other words, the marine climate was as warm as or perhaps slightly warmer 

than occurs at this latitude today.

The present analysis is in accord with Barbat and 

Galloway's (1934) belief that the succession of Jacalitos and Etchegoin faunas evidence progressive 

cooling and with Durham's (1950) similar conclusion 

on the relationship of Etchegoin to San Joaquin

faunas. The slight late Pliocene climatic warming 

inferred by Durham (1950, p. 1259, fig. 3) based 

upon mollusk and coral identifications from northern 

California, was negated after reidentification of the 

supposed warm-water taxa and a zoogeographic 

analysis of the associated fauna indicated that the 

fauna as a whole suggested somewhat cooler temperatures than occur at that latitude today (A llison 

and others, 1962). Stanton and Dodd (1969) seem to 

hold a contrasting view that there were no significant climatic trends or fluctuations during the later 

part of the Pliocene in the Kettleman Hills area of 

the San Joaquin basin. Their faunal analysis and 

strontium paleotemperature estimates based upon 

the bivalve Crenomytilus did, however, indicate that 

water temperatures were warmer than occur ?.t this 

latitude today.

DISCUSSION

SAMPLE SIZE

Although the molluscan sequence of the San 

Joaquin basin is much more complete than in other 

California Tertiary basins, zoogeographic analysis is 

hampered by gaps in the fossil record and rparse 

assemblages in parts of the sequence. Faunal size for 

example, varies from less than 30 to nearly 150 

genera. These differences may be in part the result 

of inadequate sampling (Durham, 1967); the Miocene fauna of the lower part of the Olcese Sand, for 

example, has not been thoroughly sampled. Most of 

the faunas utilized in the analysis, however, have 

been rather intensively collected suggesting that the 

apparent relationship of low Oligocene and Pliocene 

generic diversity to much higher middle Miocene 

levels probably is real. Species diversity trerds in 

Oligocene to Pliocene molluscan faunas of California 

exhibit similar relationships (Keen and Bentson, 

1944, fig. 3). Changes in generic diversity in San 

Joaquin basin faunas presumably reflect climatic 

change, judging by the occurrence of high levels of 

taxonomic diversity in modern warm-water eauatorial seas (Fischer, 1960; Stehli and others, 1967). 

Similar trends in diversity of molluscan genera and 

subgenera occur in the western Atlantic part of the 

Tertiary Caribbean faunal province; the numHr of 

taxa increases dramatically from a low point during 

the Oligocene to a peak during the middle Miocene 

and then declines (Woodring, 1966).

GAPS IN THE RECORD

Biostratigraphic control is adequate to discern 

only general faunal trends. Climatic maximums suggested by peaks at 40 to 50 and 10 to 20 irillion 

years in the San Joaquin basin zoogeographic profile 

(fig. 4) appear to agree well with the 30-millior-year
D12 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

Mesozoic and Cenozoic climatic cycle advanced by 

Dorman (1968). Clearly, the existence of subsidiary 

cycles, or changes associated with minor climatic 

fluctuations, cannot be ruled out with presently 

available control. The spacing of faunal control is 

better for the Pliocene five faunas in approximately 7 million years than for the Oligocene and 

Miocene only six faunas during a span of about 25 

million years. Furthermore, one of the mid-Tertiary 

faunas, as previously mentioned, is inadequately 

known. Biostratigraphic study of the type Tejon 

Formation of the south margin of the San Joaquin 

basin must be completed before the Eocene climatic 

peak can be accurately identified.

Shallow-water molluscan faunas occur in many of 

the apparent stratigraphic gaps on the chart. Potential stratigraphic control is at least twice as dense as 

shown, but, unfortunately, many of the faunas are 

too small for quantitative analysis. Oxygen isotope 

study of the faunal sequence could provide much 

denser control, in addition to a better indication of 

actual marine temperatures.

MIDDLE OLIGOCENE ANOMALY

Zoogeographic indices from middle Oligocene molluscan faunas of the Pacific coast indicate that the 

climatic minimum suggested by low percentages of 

warm-water middle Oligocene genera of the San 

Joaquin basin may not have been as much lower than 

late Oligocene and early Miocene values as is shown 

in figure 4. Percentages of warm-water genera between latitude 34° and 48° N. are plotted in figure 

6; data from the Santa Ynez Mountains west of the 

San Andreas fault are adjusted for post-Oligocene 

lateral slip in keeping with recent postulates of Addicott (1968b). Although the faunas of the Gaviota 

Formation of Kleinpell and Weaver (1963) and the 

sandstone member of the Kirker Formation of Primmer (1964) were the subject of recent taxonomic 

study, the much larger middle Oligocene faunas of 

Oregon, Washington, and the San Joaquin basin suggest that these key faunas may still be incompletely 

known. The zoogeographic indices from them are 

based, in both cases, on less than 25 genera. Accordingly, the middle Oligocene latitudinal graph should 

be considered tentative. The data are sufficient, however, to suggest latitudinal organization of middle 

Oligocene molluscan faunas of the eastern Pacific. 

The straight-line profiles also disclose anomalously 

low values for San Joaquin basin faunas. Accordingly, smoothed curves utilizing interpolated values 

from figure 6 have been constructed for the San 

Joaquin basin Tertiary (fig. 7). Much stronger contrasts between Miocene faunas of California and the

10 20

EXTANT GENERA, IN PERCENT

30

FIGURE 6. Middle Oligocene latitudinal faunal gradient. 

Numbers refer to faunal data in table 1. The fauna of 

the upper member of Kleinpell and Weaver's (1963) 

Gaviota Formation (no. 16) west of the Sar Andreas 

fault (lat 34° N.) is adjusted for post-Oligocene lateral 

slip (Grantz and Dickinson, 1968).
TERTIARY PALEOCLIMATIC TRENDS, SAN JOAQUIN BASIN, CALIFORNIA D13

Series

Eocene

60

50

40

§ 30

20

10

Oligocene Miocene Pliocene Pleisto 

cene

EXPLANATION

yN

Panamic, Surian, and 

Californian genera

o

Panamic and Surian 

genera

\

\

\

\

Panamic genera

a

Genera no longer 

in northeast Pacific/ 

5

\X

X,

X

>

50 40 30 20 

TIME. IN MILLIONS OF YEARS

10

FIGURE 7. Idealized zoogeographic profiles for the San Joaquin basin utilizing interpolated middle Oligocene 

values from figure 6. Single dashed curve shows changes in the percentage of genera no longer living in 

the eastern Pacific Ocean, herein considered to be extinct. Numbers refer to faunal data in table 1.

Pacific Northwest (Addicott, 1969b) are indicative of 

more distinct latitudinal gradients; there is no evidence of a Miocene continuation of unusually low 

middle Oligocene zoogeographic indices in San 

Joaquin basin molluscan faunas.

Reasons for the San Joaquin basin anomalies in 

the middle Oligocene latitudinal faunal gradient are 

not readily apparent. They could be the result of 

inadequate sampling or local upwelling of cold 

water. The possibility of upwelling at this time but 

not in later stages of deposition, in the San Joaquin 

basin seems favored by the high Oligocene relief, 

evidenced by extensive deposition of nonmarine 

strata in California and by the fact that the basin 

was more open to the Pacific than during subsequent 

stages (fig. 2). It is notable that the faunas of the 

San Juan Bautista Formation of Alien (1945) near 

Monterey Bay, west of the San Andreas fault, and 

the San Emigdio and Pleito Formations of Wagner 

and Schilling (1923) of the southern San Joaquin 

basin have almost identical percentages of warmwater genera (table 1). The two faunas initially 

lived at the same latitude and in proximity according

to recent postulates of cumulative right-lateral slip 

along the San Andreas fault (Addicott, 1968b; 

Grantz and Dickinson, 1968).

EOCENE AMELIORATION

Although the relationship of middle Oligocene to 

later Tertiary values is perhaps better portrayed by 

the adjusted curves, the dramatic late Eocene or 

early Oligocene climatic deterioration is minimized. 

Moreover, its configuration cannot be defined because of inadequate biostratigraphic control. As 

stressed earlier, the Eocene peak doubtless was much 

higher than shown because of the many extinct Eocene genera of warm-water affinities not included in 

the analysis. Many of the excluded gastropod genera, 

for example, are spinose forms suggestive of warmwater conditions. The Eocene peak was probably 

much higher than the middle Miocene peak.

CLIMATIC CHANGE AND EXTINCTION

Increased rates of extinction at the generic level 

during the Oligocene and the Pliocene in the San 

Joaquin basin seem to be related to the climatic 

deterioration that followed the principal Eocene and
D14 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

Miocene warm pulses. The close correlation between 

zoogeographic evidence of warming climate and a 

slowing of the apparent rate of extinction is indicated by curves in figure 7. Eocene and Oligocene data 

are scant; in the much better controlled Neogene 

faunal sequence, however, a plateau in the extinction 

curve occurs during the Miocene. It is followed by a 

sharp decline during the Pliocene. In this study, extinct genera are defined as those no longer living in 

the eastern Pacific Ocean.

OTHER CALIFORNIA BASINS

Zoogeographic profiles from Tertiary basins in 

the central California Coast Ranges west of the San 

Andreas fault (fig. 5) are similar to the San Joaquin 

basin profile although based on sparse faunal control. Of these, the southern Coast Range profile (fig. 

55) assembled from faunal data in San Luis Obispo 

and Santa Barbara Counties has better stratigraphic 

control. Oligocene faunas of the Gaviota Formation 

of Effinger (1935) of the Santa Ynez Mountains 

(Kleinpell and Weaver, 1963) seem to define the 

mid-Tertiary climatic deterioration much better 

than the San Joaquin basin faunas. Unfortunately, 

the late Oligocene fauna of the Alegria Formation of 

Dibblee (1950) in the Santa Ynez Mountains (Kleinpell and Weaver, 1963) is too small to be included in 

this analysis. Late Oligocene control is also lacking 

in the Santa Cruz basin profile to the north.

Both the southern Coast Range and the Santa 

Cruz basin (= La Honda basin of Cummings and 

others, 1962) profiles have prominent middle Miocene peaks which correspond to a similar peak in the 

San Joaquin basin profile. The Santa Cruz basin 

peak differs from the southern Coast Range peak, 

however, in having a much smaller percentage of 

Panamic (tropical) genera and a relatively larger 

percentage of Surian (subtropical) genera. Presumably this is a reflection of the Santa Cruz basin's 

more northern position in relation to the middle Miocene latitudinal faunal gradient.

OREGON AND WASHINGTON

The Miocene climatic peak is further reflected by a 

northward migration of many warm-water genera 

along the Pacific Coast during the middle Miocene 

(Addicott, 1968b). Several genera now restricted to 

the Panamic, Surian, and Calif ornian molluscan provinces advanced northward from early Miocene distributional limits in central California to Oregon and 

Washington during the middle Miocene. All of these 

tropical, subtropical, and warm temperate genera, 

except Anadam s.s., disappeared from Oregon and 

Washington by the end of the middle Miocene, their

northermost late Miocene limits occurring once more 

in California.

Durham's (1950) Oligocene paleoclimatic curves 

for Washington differ from the California zoogeographic profiles (fig. 4 and 5) in picturing a gradual transition from near-tropical early Oligocene climate to subtropical late Oligocene climate. The 

middle Oligocene climatic deterioration evident in 

the California profiles and from palecbotanical 

evidence in Oregon and Washington (Wolfe and Hopkins, 1967) probably occurred between Durham's two 

Oligocene faunas. Presumably the intervening middle Oligocene fauna of the upper part of the "Lincoln 

Stage" in Washington was excluded from his diagram because of its "slightly deeper fades" (Durham, 1942). That the late Oligocene fauna of western 

Washington was relatively cooler than the early 

Oligocene fauna seems perfectly clear, but the zoogeographic relationship to California faunas, which 

have much larger proportions of tropical and subtropical mulluscan genera, suggests that the initial 

estimates of marine climate were too warn. In the 

context of this analysis, mollusks of the lower part of 

the "Lincoln Stage" (Durham, 1950J, p. 12^5) would 

be classified as marginally subtropical to warm temperate and those of the lower part of the "Blakeley 

Stage," warm temperate. Durham (1940) initially 

considered corals from the lower part of the 

"Blakeley" to be of "a decided warm temperate 

aspect."

More than half of the molluscan genera from the 

lower part of the "Lincoln Stage" in Washington, 

once regarded as indicative of near-tropical condition 

(Durham, 1950, p. 1255), are now known to range 

northward into the temperate Oregonian molluscan 

province (lat 34.5°-48° N.); several other genera 

are not represented in modern easteri Pacific 

faunas. None of the remaining genera are today restricted to the tropical Panamic molluscan province, 

and the three that today live in subtropical latitudes 

Gemmula, Nerita, and Macrocallista constitute 

an even smaller percentage of warm-water elements 

than occurs in the middle Oligocene fauna of California Coast Range basins.

Paleoclimatic inferences from the late Oligocene 

molluscan fauna of Washington, the Echinophoria 

rex zone of Durham (1944), are conflicting. Late 

Oligocene marine climate was considered temperate 

by Dickerson (1917) and Bentson (1940), temperate 

to warm temperate by Addicott (1967), and subtropical by Tegland (1933) and Durham (1942, 

1950). Molluscan evidence suggests that the late 

Oligocene climate was more likely warm temperate
TERTIARY PALEOCLIMATIC TRENDS, SAN JOAQUIN BASIN, CALIFORNIA D15

than subtropical, as less than 5 percent of the molluscan general are now restricted to subtropical or 

tropical provinces.

The significance of one or two taxa of hermatypic 

(reef-building) corals upon which Durham (1942, 

1950) based his interpretation of subtropical conditions for the upper part of the Oligocene (type 

Blakeley Formation of Tegland, 1933) and lowermost 

part of the Miocene (upper part of the Twin River 

Formation) is of critical importance. Because of the 

absence of vigorous coral growth (reefs) and low 

taxonomic diversity, it has been postulated (Addicott, 1967) that the two hermatypic genera in the 

"Blakeley Stage" may have been acclimated to a 

cooler environment than the subtropical 18°-18.5° C 

minimum for vigorous growth cited by Vaughan and 

Wells (1943, p. 55).

PALEOCLIMATIC INFERENCES FROM FORAMINIFERA

Whereas a similar warming trend seems apparent 

from reported abundance and diversity of planktonic 

Foraminifera during the California Oligocene and 

Miocene, Pliocene planktonic foraminifers seem to 

indicate an entirely different picture.

Planktonics are characterized by low species diversity and are of relatively rare occurrence during the 

Oligocene to early Miocene Refugian to Saucesian 

foraminiferal stages (Smith, 1956; DeLise, 1967; 

Bandy and Arnal, 1968). They become diverse and 

relatively abundant during the middle Miocene 

(Lipps, 1967a; Bandy and Arnal, 1969). During the 

late Miocene they are apparently less diverse and 

constitute the coolest water assemblages of the California Miocene (Lipps, 1967a; b). A simple diversity 

curve fitted to these observations closely parallels 

molluscan data and would seemingly have similar 

paleoclimatic significance. A similar peak in the diversity of planktonic Foraminifera occurred during 

the middle Miocene in New Zealand (Jenkins, 1968). 

Berggren (1968) has also noted the striking similarities between taxonomic diversity in planktonic 

Foraminifera and climatic fluctuations during the 

Tertiary (Devereux, 1967), but his diversity peak is 

somewhat later in the Miocene than Jenkins'.

The paleoclimatic significance of Miocene benthonic foraminifers has been interpreted in a much different manner, closely paralleling Smith's (1919) 

concept of progressively cooling surface-water temperatures during the Tertiary. Kleinpell (1938, p. 

104-134) described a more or less gradual withdrawal of tropical and subtropical foraminiferal elements from California basins during his Zemorrian 

to Delmontian Stages. Recently Ingle (1967) postulated systematic cooling of bottom waters during the

Miocene based upon similar observations of progressive latitudinal restriction of tropical and subtropical benthonic foraminiferal elements during successive Miocene stages.

A contrasting interpretation closely alined with 

paleoclimatic inferences from San Joaquin basin 

molluscan faunas seems to be'indicated by middle 

Tertiary species diversity trends in San Joaquin 

basin foraminiferal faunas. Bandy and Arnal (1969, 

fig. 26) indicate significantly higher levels of species 

diversity in the early and middle Miocene Saucesian, 

Relizian, and Luisian Stages than in the late Oligocene to early Miocene Zemorrian Stage and the late 

Miocene Mohnian Stage. The shape of their curve is 

generally similar to the middle Tertiary zoogeographic profiles and generic diversity of San Joaquin 

basin molluscan faunas (fig. 4).

The relationship to paleoclimatic inferences from 

Pliocene planktonic foraminifers is less clear. Bandy 

(1967c, 1968) and Ingle (1967) picture early and late 

Pliocene surface-water temperatures off California 

as having been much warmer than at present and 

middle Pliocene temperatures much cooler, based 

principally upon changes in the coiling direction of 

the plaktonic foraminifer Globigerina pachyderma. 

Their interpretations differ markedly from the repeated inferences of progressively cooling Pliocene 

marine climate of the San Joaquin basin based on 

shallow water mollusks (Smith 1919; Barbft and 

Galloway, 1934; Durham, 1950; Addicott, 1969b; 

Stanton and Dodd, 1969). Molluscan evidence presented herein points to Pliocene water temperatures 

consistently warmer than at present. There is,- however, a slight suggestion of a middle Pliocene warming (fig. 7). The inferences from foraminifers cannot 

be directly related to the molluscan sequence of the 

San Joaquin basin because planktonics are found 

only in deeper water sediments. Globigerina pachyderma, for example, lives today suspended in the 

water column below depths of 100 meters (Casey, 

1963; Lidz, 1966; Bandy, 1967b; Ingle, 1967), a 

much cooler and deeper environment than nearshore 

inner sublittoral environment represented t^ the 

Pliocene mollusks.

Both the molluscan and foraminiferal evidence are 

equivocal. The shallow-water climatic regime of 

coastal sites might not have been reflected in the San 

Joaquin basin during the Pliocene because of shallow 

depths and the protection afforded by its deeply 

embayed configuration. The planktonic foraminifers, 

on the other hand, clearly do not reflect surfacewater temperatures. The relatively deep-water 

habitat of Globigerina pachyderma normally ex-
DIG SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

eludes it from all but the outermost shelf sediments. 

Although evidence from other basins (fig. 5) supports the inference of progressively cooling shallowwater temperatures during the Pliocene, detailed 

study of other California faunal sequences, including oxygen isotope studies, is needed to better evaluate this discrepancy.

SUMMARY AND CONCLUSIONS

The Oligocene and Pliocene distributional profile 

of San Joaquin basin molluscan faunas is based upon 

a more detailed faunal succession than was previously available for the northeastern Pacific. Zoogeographic trends and their inferred paleoclimatic 

significance are mirrored not only in other California Tertiary basins but also, more significantly, by 

recent paleoclimatic studies from other areas around 

the Pacific margin. Paleontologic studies of corals 

and other invertebrates from New Zealand (Squires, 

1958; Hornibrook, 1967), land floras and various 

marine paleontologic data from Japan (Tanai and 

Huzioka, 1967; Kobayashi and Shikama, 1961), and 

leaf floras from southern Alaska (Wolfe and Hopkins, 1967) and the Western United States (Dorf, 

1955) all show parallel trends. Moreover, paleotemperature curves inferred from recent oxygen isotope 

studies of New Zealand and Australian marine invertebrates have remarkable similarities (Dorman, 

1966; Devereux, 1967) to paleoclimatic inferences 

from California. The succession of climatic peaks in 

the Eocene and the Miocene seem to support Dorman's (1968) 30-million-year Mesozoic and Cenozoic 

climatic cycle. Comparable studies of marine mollusks have not been made in other Tertiary sequences around the Pacific rim, although qualitative 

analysis of the Tertiary of Japan by Saburo Kanno 

(oral commun., 1968) indicates similar trends.

This simple analysis should prove useful in defining paleoclimatic trends in similar Tertiary sequences around the Pacific rim. Requirements are: 

(1) Adequate sequences of shallow-water Tertiary 

molluscan faunas, and (2) the frame of reference 

provided by a north-south segment of coast where 

modern molluscan faunas exhibit temperaturerelated latitudinal differentiation similar to that of 

the northeastern Pacific.

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