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Palaeogeography, Palaeoclimatology, Palaeoecology, 14 (1973): 277-291 © Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands

LATE MIOCENE-EARLY PLIOCENE PALEOTEMPERATURES FOR CALIFORNIA FROM MARINE DIATOM EVIDENCE JOHN A. BARRON Department of Geology, University of California, Los Angeles, Calif. [U.S.A.) (Accepted for publication September 24, 1973)

ABSTRACT Barron, J. A., 1973. Late Miocene-Early Pliocene paleotemperatures for California from marine diatom evidence. Palaeogeogr., Palaeoclimatol., Palaeoecol., 14: 277-291. Paleotemperatures have been interpreted from the evidence of the diatom flora for an Upper Miocene section of marine diatomaceous sediment near Lompoc, California. The diatom flora has been compared with the distribution of modern diatoms in surface sediments of the North Pacific Ocean to propose a Miocene sea paleotemperature curve for this area of California. Temperatures declined sharply in the Late-Mohnian (Upper Miocene) to a winter minimum of about 10°C. Thereafter, a gradual and fluctuating rise in temperature ~haracterized the latest Miocene (Delmontian); minimum seasonal temperatures approached 17°C by the Early Pliocene. This diatom assemblage paleotemperature curve is supported by other evidence. Independent studies of particular diatom temperature indicator species show the same trends, as do the paleotemperature indications of a fossil fish fauna and the foraminiferal fauna in the section. Furthermore, the curve shows a marked correspondence to paleotemperature curves based on planktonic foraminifers and on radiolarians for the Upper Miocene of southern California, providing an additional tool for paleotemperature reconstruction. INTRODUCTION Superficially, diatoms appear to provide ideal evidence for paleoecologic interpretation. They occur in large numbers in diatomaceous sediments, so that statistically valid sample sizes are readily obtained for study. In contrast to other plankton groups, many diatom species are relatively long ranging. Therefore, the known ecologic distribution of living, long-ranging species may be used to interpret past environments for much of the Tertiary. Finally, diatoms are found in virtually every aquatic environment within the photic zone, and thousands of distinctive species are available to classify such habitats. Nevertheless, until recently little work of a paleoecologic nature has been carried out on diatoms. Lohman (1941) and others have pointed out that the death assemblages of diatoms in sediments are likely to be quite different from living assemblages found in the overlying surface waters. Lightly silicified species of Rhizosolenia and Chaetoceros, which dominate in the oceanic plankton, are selectively dissolved at depth, so that the sediments are relatively enriched in the more heavily silicified species (IAsitzin, 1971). In addition, measured settling rates of empty diatom frustules (10 cm/h) and the deep-sea nature of diatomaceous sediments suggest that the frustules may have been carried far from their life habitats by surface currents (Lohman, 1941). Thus, it may seem that the death

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J.A. BARRON

assemblage present in sediments cannot be used to interpret the past environment of a given area. Recently, workers such as Kanaya and Koizumi (1966) and J ous6 e t al., (1969, 1971) have circumvented these problems. These workers have documented modern diatom distributions in the surface sediment of the Pacific Ocean. Biogeographic diatom zones have been defined by the thanatocoenoses present on the sea floor of a given latitude rather than by the living assemblage in the plankton, thereby removing the problem of selective dissolution during settling. In addition, large-scale postmortem transportation has been discounted (Kanaya and Koizumi, 1966) by detailed comparison of diatom assemblages present in sea-floor sediments with those in the overlying surface waters (Kozlova and Muhina, 1967). Mechanisms such as rapid settling of diatoms in aggregates (Kanaya and Koizumi, 1966) and cancellation of lateral transport by differentially moving currents in vertical water masses (Jous6, 1957) have been suggested in explanation of the lack of significant lateral transport of diatom frustules. Furthermore, recent experiments on settling have been inconclusive; diatom frustules may settle anywhere from a few millimeters per day to tens of meters per day (Lewin and Guillard, 1963; Smayda and Boleyn, 1965). Kanaya and Koizumi (1966) and Jous6 (I 971) have successfully used their diatom data to interpret Quaternary glacial cycles in the North Pacific. Furthermore, Kanaya (1971) and Jous6 et al. (1971) have indicated their use for earlier Tertiary periods. In the present study, paleotemperature interpretations laave been made for a section of Upper Miocene diatomaceous sediment near Lompoc, California, on the basis of the contained diatom assemblages. MATERIAL The area around Lompoc, California, is well known for its thick accumulations of Miocene and Pliocene diatomaceous sediment (Dibblee, 1950). The Johns-Manville Quarry south of Lompoc is the largest, purest deposit of diatomite actively mined in the world (Mulryan, 1936). Over 500 m of section from the quarry itself and from rocks below that stratigraphic level were measured and collected for study (Fig. 1). Dibblee (1950) assigned the upper half of the section to the Sisquoc Formation and the lower half to the Monterey Formation. The Monterey Formation contains laminated diatomite interbedded with chert and porcelaneous shales which probably were secondarily derived from the diatomites (Bramlette, 1946), whereas the Sisquoc generally consists of pure laminated diatomite throughout the section. A small local unconformity is marked by a thin chert cobble conglomerate bed near the top of the Sisquoc section. Above this conglomerate there are 24 m of diatomaceous mudstone of Early Pliocene age (Wornardt, 1967). The only foraminiferal fauna present in the section is from the middle portion of the

LATE MIOCENE - EARLY PLIOCENEPALEOTEMPERATURES FOR CALIFORNIA

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Bolivina hughesi Zone of the Upper Mohnian Stage (Upper Miocene). The present investigations of the foraminifers agree with this conclusion. The placement of the Upper Mohnian-Delmontian Stage boundary in the Sisquoc Formation is based herein on a correlation of diatom evidence with the Upper Newport Bay section south of Los Angeles. The stage boundary at Newport utilized herein is that of Ingle (t967) and Warren (1972). Previous investigations of diatom floras of the Lompoc Quarry have been made by Yermoloff (1920) and Mann (1921). Wornardt (1967) has extensively covered a Pliocene flora in the Sisquoc Formation just north of Lompoc. METHOD OF STUDY Fifty samples were selected for study at roughly equal stratigraphic intervals from the section. They were prepared following the standard preparation for siliceous microfossils:

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approximately 5 g of diatomaceous material was broken into centimeter-sized piece's and treated in 30% hydrogen peroxide and sodium pyrophosphate. After disintegration, the material was boiled in 50 cc of 37% hydrochloric acid and 30 cc of 70% nitric acid. The acid was then removed, and the material was stored in distilled water. Strewn slides were made by mixing the material into suspension, withdrawing the suspension by a capillary tube, and mounting the material in a Hyrax medium on a standard microscope slide. At least three slides per sample were examined to determine the species present. Following Koizumi (1968) and Mandra (1968), 200 diatom frustules were counted per sample by mechanically traversing a microscope slide. This sample size of 200 was found to be statistically reliable through the calculation of a coefficient of reliability from the Brown "prophesy" formula, as outlined by Barkley (1934). Modern diatom distribution

The modern diatom biogeographical zones for the North Pacific Ocean as determined by Jous~ et al. (1969, 1971) are shown in Fig.2. These zones closely match the surface water masses of the North Pacific, and it seems apparent that the water masses exert control over them. Each zone is dominated by a characteristic diatom flora (Table I); and narrow transitional zones, which contain a mixture of floras, exist between the zones. For example, the subtropical zone flora, which is present off California today, is composed of 55-60% individuals of species representing the subtropical diatom complex (Table II).

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LATE MIOCENE-EARLY PLIOCENE PALEOTEMPERATURES FOR CALIFORNIA

281

TABLE I Modern diatom complexes of the North Pacific Ocean ''2 North-boreal diatom complex C. wailesei Gran et Angst * A ctinocyclus c h o l n o k y i Van Landingham Nitzschia bicapitata Cleve A. curvatulus Janisch N. interrupta Heiden et Kolbe A. ochotensis Jous6 N. kolaiczeckii Grunow Asteromphalus robustus Castracane N. sicula (Castracane) Hustedt * Biddulphia aurita (Lyngbye) Br6bisson et Godey Pseudoeunotia doliolus (Wallich) Grunow * Coscinodiscus curvatulus Grunow * (Nitzschia fossilis (Frenguelli) emend. Kanaya) 3 * C. excentricus Ehrenberg * C. marginatus Ehrenberg * Rhizosolenia styliformis Brightwell Denticula seminae Simonsen et Kanaya Roperia tesselata (Roper) Grunow * (Denticula hustedtii Simonsen et Kanaya) 3 * Thalassionema nitzschioides Grunow * Melosira sulcata (Ehrenberg) Kiitzing * Thalassiosira deeipiens (Grunow) J6rgensen Rhizosolenia alata Brightwell T. faponiea Kisselev * R. hebetata Barley (f. hiemalis) Gran T. lineata Jous~ S t e p h a n o p y x i s nipponica Gran et Yendo Thalassiothrix laneeolata Hustedt Thalassiosira gravida Cleve * Thalassiothrix longissima Cleve et Grunow Tropical diatom complex 4 * Coscinodiscus lineatus Ehrenberg Subtropical diatom complex * Hemidiscus cuneiformis Wallich * A e t i n o c y c l u s ehrenbergii Ralfs * Coscinodiscus nodulifer Schmidt A c t i n o p t y c h u s bipunctatus Lohman * Coscinodiscus asteromphalus Ehrenberg Equatorial diatom complex * C. radiatus Ehrenberg * Actinocyclus ellipticus Grunow C. stellaris Roper * Asterolampra marylandica Ehrenber~ LAfter Jous6 et al., 1969, 1971; 2 arcto-boreal complex is not listed; a extinct ancestral species; 4only species present in the Lompoc section for the tropical and equatorial complexes are listed; * indicates presence in the Lompoc section.

TABLE II North Pacific diatom biogeographical zones ~ Diatom zone

Location

Characteristics

Arcto boreal

neritic off Alaska and the Soviet Union

neritic, cold-loving species

North boreal

north of 38°N in NW; north of 54°N in NE

north-boreal species reach 90-94% of flora

Transitional (north borealsubtropical)

2 - 4 ° zone along southern boundary of north boreal

north-boreal species decline to 50%

Subtropical

approximately between 40°N and 23°N

55-60% subtropical species; in north: 30-40% northboreal; in south: 5% northboreal, 26% tropical

Tropical

5°N to about 20°N

tropical species

Equatorial

4°S to 5°N

After Jous6 et al. (1969, 1971).

PLATE I Diatom species common to the Lompoc section and to the modern north-boreal diatom complex of Jous6 et al. (1971). All scales indicate 20 v unless otherwise labeled. 1. Actinocyclus cholnokyi Van Landingham. 6. Dentieula hustedtii Simonsen et Kanaya. 2. Coscinodiscus rnarginatus Ehrenberg. 7. Coscinodiscus curvatulus Grunow. 3. Melosira sulcata (Ehrenberg) Kiitzing. 8. Denticula hustedtii Simonsen et Kanaya. 4. Coscinodiscus excentricus Ehrenberg. 9. a,b. Thalassiothrix longissima Cleve et Grunow. 5. Biddulphia aurita (Lyngbye) Br~bisson et Godey.


283

Near the northern boundary of the subtropical zone, north-boreal species comprise 3 0 40% of the flora. As the southern boundary is approached, however, 26% tropical species and only about 5% north-boreal species are found in the flora. Kanaya and Koizumi (1966) list very similar diatom zones both in terms of species composition and distribution. The zones of Jous~ et al. (1971) are used here, however, since they have been defined in terms of percentage composition. RESULTS Examination of Lompoc material reveals that many of the modern diatom species described by Jous6 et al. (1971) are present throughout the section (Table I). The extinct ancestral species Denticula hustedtii Simonsen et Kanaya and Nitzschia fossilis (Frenguelli) emend. Kanaya (see Plate I) are listed here as Miocene analogues of living species, following Kanaya ( 1971) and Koizumi (1973). The species belonging to Jous~'s diatom complexes constitute a significant percentage of the total flora of the Lompoc rocks (Fig.3). North-boreal and subtropical diatom species dominate the assemblage by number and fluctuate relative to each other throughout the section. This fluctuating relationship has been interpreted in the paleotemperature curve shown in Fig.4A. Following Kanaya and Koizumi (1966), the character of the curve was determined by the ratio of warm-water species to total warm- and cold-water species. Diatoms of Jous~'s subtropical, tropical, and equatorial complexes were regarded herein as warmwater species, whereas north-boreal species were regarded as cold-water species. The curve was then smoothed by averaging over 100-ft stratigraphic intervals with a 50-ft overlap. Winter temperatures have been assigned to the resulting curve by comparison of the criteria of Jous6 et al. (Table II) with the diatom zone map superimposed on a map of winter isotherms in the North Pacific (Fig.2) and with Fig.3. Winter temperatures were used because they correspond closely to the diatom zones and because minimum seasonal temperatures probably are more limiting to phytoplankton (Smayda, 1958). The curve indicates a sharp decline in winter temperatures to about 10°C during the Late Mohnian. A gradual, fluctuating rise in temperature began thereafter and continued through the Delmontian and into the Early Pliocene, where temperatures of about 17°C are proposed. In terms of Jous~'s classification, the flora was subtropical in character during the deposition of most of the Lompoc section; however, the portions of the curve corresponding to 9 - 1 I°C minimum seasonal temperature may be interpreted as transitional between the north-boreal and the subtropical diatom zones. (See Plate II for subtropical diatom species.) ADDITIONALEVIDENCE The diatom paleotemperature curve constructed for the Lompoc section is supported by other evidence from diatom distributions. In a separate series of counts, the ratio of

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PLATE II Diatom species common to the Lompoc section and to the modern subtropical diatom complex of Jous~ et al. (1971). All scales indicate 20#. 1. Coscinodiscus radiatus Ehrenberg. 2. Coscinodiscus asteromphalus Ehrenberg. 3. Coscinodiscus stellaris Roper 4. Thalassiosira decipiens (Grunow) J~Srgensen. 5. Actinocyclus ehrenbergii Ralfs. 6. Thalassionema nitzschioides Grunow. 7. Nitzschia fossilis (Frenguelli) emend. Kanaya.

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LATE MIOCENE-EARLYPLIOCENEPALEOTEMPERATURESFOR CALIFORNIA

287

Coscinodiscus argus Ehrenberg, a warm-water neritic diatom species (Lohman, 1941), to Melosira sulcata (Ehrenberg) Kiitzing, a cold-water neritic species, was determined to rise and fall with the previous paleotemperature curve. Values of this ratio greater than two correspond to the warmer temperatures of the curve, whereas the ratio is less than one where cooler temperatures are found. Furthermore, the occurrence in the section of the rare warm-water species Coscinodiscus gigas vat. diorama (Schmidt) Grunow and C. nodulifer Schmidt (see Plate III) generally matches the warmer portions of the curve (Fig.4B). Other faunal evidence corroborates this paleotemperature curve. The Sisquoc Formation of the quarry contains a large fossil fish fauna, which has been documented by Jordan (1921) and David (1943). The fauna is especially abundant in the stratigraphic interval shown on the temperature curve (Fig.4A). David reports that this fauna is subtropical to warm temperate in character, and that conditions were warmer than those present today off Lompoc. This evidence agrees quite well with the diatom curve for that interval. The foraminiferal fauna from the middle portion of the Monterey Formation (Fig.4A) contains a small number of Globorotalia (Turborotalia) pachyderma, all of which are sinistrally coiled. According to Ingle (1967), Bandy (1972), and others, sinistral G. pachyderma is indicative of conditions cooler than those off southern California today. These data, therefore, also are in agreement with the diatom-based temperature curve. By itself, the diatom temperature curve would not be conclusive paleoclimatic evidence for all of California. The temperature changes indicated by the curve may reflect either a widespread climatic warming in the latest Miocene or fluctuations in the cold-water California Current as proposed by Ingle (1967) for this period, or they may merely reflect local variations due to features of the coastal configuration or to local currents. Some evidence, however, suggests that these are more than just local temperature trends. Surprisingly similar temperature curves for sections throughout southern California have been obtained for planktonic foraminifers (Ingle, 1967; Bandy, 1972) and for radiolarians (Casey, 1972). These data support a temperature minimum (about 10°C) during the Late Mohnian and increasing temperatures during the latest Miocene (Delmontian) (about

PLATE III Diatom species common to the Lompoc section and to the modern tropical and equatorial diatom complexes of Jous~ et al. (1971). All scales indicate 20 ~t. 1, 2. Coscinodiscus lineatus Ehrenberg. 3. Hemidiscus cuneiformis Wallich. 4. Coscinodiscus nodulifer Schmidt. Equatorial species 5. Actinocyclus ellipticus Grunow. 6. Asterolampra marylandica Ehrenberg. Other warm-water species mentioned in the text 7. Coscinodiscus argus Ehrenberg. 8. Coscinodiscus gigas vat. diorama (Schmidt) Grunow.

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J.A. BARRON

15°-20°C). (In comparing these values to the diatom curve, it should be remembered that the diatom curve portrays winter minimum temperatures.) Bandy (1972) also states that the Late Mohnian cold cycle is consistent with the cooler cycle of the northwestern U.S.A., as recorded by the paleobotanical evidence of Wolfe and Hopkins (1967). It should be mentioned that these results are in disagreement with Durham (1950) and Addicott (1970) who interpret the molluscan data as showing a major cooling trend extending through the Late Miocene and Pliocene of the Pacific coast of North America. The author, however, concurs with Bandy (1972), who suggests that the molluscan data may reflect either a lack of information in appropriate sections or local variations in shallow water areas. Certainly, other diatomites in the circum-Pacific area should be investigated in this manner. Temperature curves may reveal widespread trends which can be used as a check of correlation. Preliminary work on a section of Upper Miocene diatomaceous sediment at Upper Newport Bay south of Los Angeles suggests that its paleotemperature curve parallels that of the Lompoc section. SUMMARY AND CONCLUSIONS (1) The work of Jousd et al. (1969, 1971) on the modern distribution of diatoms in the surface sediment of the Pacific Ocean provides a basis for making paleotemperature interpretations from the diatomites for the Tertiary of the circum-Pacific area. (2) These distributions have been utilized for paleotemperature interpretation for a 515-m thick Upper Miocene section of diatomaceous rock near Lompoc, California. Temperature declined sharply during the Late Mohnian (Late Miocene) to a winter minimum of about 10°C. A gradual and fluctuating rise in temperature occurred thereafter during the latest Miocene, until winter temperatures of about 17°C were reached by the Early Pliocene. (3) Independent studies of individual diatom species distribution support this trend, as do the paleotemperature indications of fish and foraminiferal faunas present in the Lompoc section. (4) The paleotemperature curve agrees well with curves published for planktonic foraminifers (Ingle, 1967; Bandy, 1972) and for radiolarians (Casey, 1972) of the Late Miocene of southern California. (5) Diatoms from the widespread Tertiary diatomite facies may provide a useful tool for paleoclimatic interpretations of the circum-Pacific area. ACKNOWLEDGEMENTS The samples used in this study were collected by A. R. Loeblich of U.C.L.A. and John Ruth of Chevron Oil Field Research Company, La Habra, California. Appreciation is due to R. G. Hendy and the Johns-Manville Corporation for permission to collect on quarry property.


289

Scanning electron micrographs were taken by E. Reed Wicander on the JEM 2 SEM in the Paleobiological Laboratory, Department of Geology, U.C.L.A. Support for this work came from NSF Grant GA 23741 and NASA Grant NGR 05-007-292. Illustrations were drafted by Julie Guenther and Jeanie Martinez of U.C.L.A. The manuscript was typed by Vicki Doyle o f U.C.L.A. Helen Tappan Loeblich reviewed the manuscript and offered many helpful suggestions. Support for this study was provided by the Oceanography Section, National Science Foundation, NSF Grant GA-28756. FLORAL REFERENCE LIST FOR THE LOMPOC SECTION Actinocyclus cholnokyi Van Landingham, 1967, nom. nov. pro A. divisus (Grun.) Hustedt, 1958,

p.129, pl.8, fig.81; Koizumi, 1968, pl.32, fig.3. Actinocyclus ehrenbergii Ralfs, in Pritch., 1861. Hustedt, 1929, Teil I, p.525, fig.298; Wornardt,

1967, p.33, fig.49. Actinocyclus ellipticus Grunow, 1881. Hustedt, 1929, Teil I, p.533, fig.303; Koizumi, 1968, pl.32,

fig.4. Asterolampra marylandica Ehrenberg, 1845. Hustedt, 1929, Teil I, p.485, fig.271. Biddulphia aurita (Lyngbye) Br~bisson et Godey, 1838. Hustedt, 1930, Teil I, p.846, fig.501;

Wornardt, 1967, p.60, fig.113. Coscinodiscus argus Ehrenberg, 1838. Hustedt, 1928, Teil I, p.422, fig.226; Lohman, 1941, p.70,

pl.13, fig.l, 3. Coscinodiscus asteromphalus Ehrenberg, 1844. Hustedt, 1928, Tell I, p.452, fig.250; Koizumi, 1968,

pl.33, fig.2. Coscinodiscus curvatulus Grunow, in Schmidt, 1878. Hustedt, 1928, Teil I, p.406, fig.214. Coscinodiscus excentricus Ehrenberg, 1839. Hustedt, 1928, Teil I, p.388, fig.201 ; Koizumi, 1968,

pl.32, fig.23, 24. Coscinodiscus gigas var. diorama (Schmidt) Grunow, 1884. Wornardt, 1967, p.24, fig 25; Kanaya,

1971, p,555, pl.40.1, fig.1. Coscinodiscus lineatus Ehrenberg, 1838. Hustedt, 1928, Teil I, p.292, fig.204; Koizumi, 1968, pl.32,

fig.26, 27. Cogcinodiscus marginatus Ehrenberg, 1843. Hustedt, 1928, Teil I, p.416, fig.223; Wornardt, 1967,

p.26, fig.27, 28. Coscinodiscus nodulifer Schmidt, 1878. Hustedt, 1928, Teil I, p.426, fig.229; Lohman, 1941, p.72,

pl.14, fig.3, 5. Coscinodiscus radiatus Ehrenberg, 1839. Hustedt, 1928, Teil I, p.420, fig.225; Koizumi, 1968, pl.33,

fig.9. Coscinodiscus stellaris Roper, 1858. Hustedt, 1928, Teil I, p.396, fig.207; Koizumi, 1968, pl.33, fig.9. Denticula hustedtii Simonsen et Kanaya, 1961, Koizumi, 1968, pl.34, fig.4,5,6; Kanaya, 1971, p.555,

pl.40.5, fig.13, 14. Hemidiscus cuneiformis Wallich, 1860. Hustedt, 1930, Teil I, p.904, fig.542; Koizumi, 1968, pl.34,

fig.17, 18. Melosira sulcata (Ehrenberg) Kiitzing, 1844. Hustedt, 1928, Teil I, p.276, fig.119; Lohman, 1941,

p.64, pl.12, fig.1. Nitzschia fossilis (Frenguelli) emend. Kanaya in Kanaya and Koizumi (1970); = Fragilariopsis pliocena (Brun) Sheshukova, 1959, of Kanaya, 1971, p.556, pl.40.3, fig.7, 8. Rhizosolenia hebetata f. hiemalis Gran, 1904. Hustedt, 1929, Teil I, p.590, fig.337; Jous6, 1971,

pl.31.1, fig.13. Rhizosolenia styliformis Brightwell, 1858. Jous~ et al., 1969, pl.8, fig.13; Jo.u~, 1971, pl.31.3, fig.11. Thalassionema nitzschioides Grunow, 1881. Hustedt, 1932, Teil II, p.244, fig.723, Koizumi, 1968,

pl.35, fig.9, 10.

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