CENOZOIC RADIOLARIAN PALEOBIOGEOGRAPHY - Science Direct

Palaeogeography, Palaeoclimatology, Palaeoecology, 26(1979): 253--289

253

© Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands

CENOZOIC RADIOLARIAN PALEOBIOGEOGRAPHY: IMPLICATIONS CONCERNING PLATE TECTONICS AND CLIMATIC CYCLES

FLORENTIN J.-M° R. MAURRASSE

Department of Physical Sciences, Florida International University, Miami, Fla. 33199 (U.S.A.) (Received November 7, 1977; revised version accepted August 17, 1978)

ABSTRACT Maurrasse, F. J.-M. R., 1979. Cenozoic radiolarian paleobiogeography: implications concerning plate tectonics and climatic cycles. Palaeogeogr., Palaeoclimatol., Palaeoecol., 2 6 : 2 5 3 - - 2 8 9 A preliminary study of the paleobiogeographic patterns of radiolarian facies during the Paleogene and subsequent time shows that: (1) Through time radiolarian assemblages display distinct faunal provincialism reminiscent of modern faunal distributions correlated with planetary temperature gradients and surface oceanic conditions. The equatorial--tropical radiolarian fauna extended apparently unrestricted across the Pacific Ocean, the Caribbean Sea and the Atlantic Ocean through Early Miocene time. In the Caribbean Sea and the Atlantic Ocean, radiolarians reached their maximum abundance in the Eocene and Oligocene. Subsequently, they gradually declined to virtual disappearance in these areas in the early Miocene. Their Pacific counterparts remained practically undisturbed, except that post early Miocene assemblages there showed a marked trend toward decreasing test thickness. This trend has since been a worldwide characteristic of Neogene radiolarian assemblages and their modern equivalents. It is postulated that the disappearance of radiolarians in the Caribbean Sea and the Atlantic Ocean at the end of the Paleogene is related to the onset of the emergence of the isthmus of Panama which interrupted the preexisting oceanic circulation between the Pacific and Atlantic Oceans. (2) Throughout the Paleogene there have been marked sequential fluctuations in the radiolarian assemblages of the Caribbean Sea which indicate intermittent incursions of higher-latitude fauna in this area. Associated with the faunal fluctuations are cyclic variations in the total carbonate of the sediment with patterns also comparable in duration to Pleistocene carbonate cycles in the equatorial Pacific known to have been induced by climatic changes. Based on similarities with Pleistocene climatic cycles in the equatorial Pacific and elsewhere, it is surmised that the faunal and lithologic fluctuations observed in Paleogene radiolarian sediments were also induced by the biologic and physico-chemical processes associated with worldwide changes in the climatic conditions of that time. INTRODUCTION

Considerable oceanographic data gathered in the past two decades have provided excellent means for defining both present and past biogeographic distributions of various microplanktonic organisms that are useful as paleoclimatic indicators. The reliability of the fossil groups stems from modern

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29 30 31 146 149 150 151 152 153 117A 10 13 14 72 73

14°47.11'N 12°52.92'N 14°56.60'N 15°06.99'N 15°06.25'N 14°30.69'N 15°01.02'N 15°52.72'N 13°58.33'N 57°20.00PN 32°37.00tN 06°02.40'N 28°19.89'N 00°26.49'N 01°54.58'S

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14°41.00'N 14°38.30PN 14°33.40tN 14°37.30'N 20°16.00PN 14°50.00'N 67°12.00'N 33°42.00'N 11°12.00'N 28°32.00'S 31°26.00'S 41°30.00'S 51°08.00'S 47°45.00'S 19°28.00'N 07°35.00'N 04°39.00'N 44°13.00tS

70°52.70'W 70°52.20tW 70°48.60rW 70°50.30'W 81°29.00rW 76°15.00rW 06°10.00'E 62°30.00'W 48°05.00rW 29°00.00'W 00°50.00'E 56°36.00'W 54°22.00'W 57°38.00rW 140°01.00tW 178°25.00tE 144°58.00'W 179°34.00'E

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Beata Ridge Beata Ridge Beata Ridge Beata Ridge N. Cayman Is. Nicaragua Rise Norwegian Sea Bermuda Rise Equatorial Atlantic Rio Grande Rise Walvis Ridge Falkland Plateau Falkland Plateau Falkland Plateau Equatorial Pacific Equatorial Pacific Equatorial Pacific Chatham Rise

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256 global oceanic data showing that all marine microplanktonic groups display gradients in taxonomic diversity which are consistently covariant with the relative planetary temperature gradient and oceanic water masses. Since modern assemblages are practically the same as those of the Pleistocene, the paleoecologic significance of the faunal fluctuations recorded in sediments of that epoch have been ascertained with considerable accuracy. Thus, the fluctuations in various microplanktonic groups recorded in Pleistocene sediments, compared to present population distribution patterns in the ocean's surface, have been successfully equated with past climatic fluctuations with the foraminifera (Ericson et al., 1956, 1961; Emiliani, 1964; Stehli, 1965; Ericson and Wollin, 1968; Ruddiman et al., 1970; Ruddiman, 1971; Gardner, 1973; Kellogg, 1973; Prell, 1974), the Coccolithophorida (McIntyre, 1967; McIntyre et al., 1970; Caulet and Clocchiatti, 1975), the Radiolaria (Hays, 1965; Hays et al., 1969; Duncan et al., 1970; Nigrini, 1970) and the diatoms (Kanaya and Koizumi, 1966; Donahue, 1967, 1970). Similar principles have also been successfully applied using either group for paleoclimatic and paleoceanographic reconstruction of deep-sea sediments older than Pleistocene from various parts of the world (Vella, 1967; Jenkins, 1968; Hays, 1970; Casey, 1970, 1971, 1972; Margolis and Kennett, 1971; Kennett and Vella, 1974; Kennett and Watkins, 1974; Blank and Margolis, 1975; Savin et al., 1975). Although Paleogene radiolarian biostratigraphy has developed considerably in the past eight years or so through the results of the Deep Sea Drilling Project expeditions, so far there have been no ecological inferences concerning the biogeography of the species and their potential paleoecological usefulness. The main objective of this paper is to (1) present the tectonic and climatic implications of radiolarian facies during the Paleogene and subsequent periods and (2) discuss the evidence of midPaleogene radiolarian biogeography and faunal provincialism. Furthermore, sequential fluctuations of taxa that have been determined to correlate with either low- or high-latitude assemblages also provide a basis for paleoclimatic and paleoceanographic interpretation of sequential Paleogene biofacies changes observed in cores of various deep-sea areas of the world (Figs.l, 2). METHODS The samples used in this study are from a total of 32 sites (Figs.l, 2), including eighteen piston cores from the Lamont-Doherty Geological Observatory core library and fifteen from Deep Sea Drilling Project cores. Five additional DSDP sites not shown in Figs.1 and 2 were also studied: Leg 8, Equatorial Pacific sites 72 (00°29.49'N, 138 ° 52.02'W) and (01°54.02'S, 137°28.12'W); Leg 10, Gulf of Mexico sites 86 (22°52.48'N, 90°57.75'W), 94 (24°31.64'N, 88°28.16'W), 95 (24°09.00'N, 86°23.85'W) and 96 (23°44.56'N, 86°45.80'W). Complementary data have also been taken from the various Deep Sea Drilling Project Initial Reports as listed in the

257

References. The cores chosen are considered to be located in key geographic areas of the world's ocean; secondary geographic displacement due to sea-floor spreading as shown by magnetic data (Heirtzler et al., 1968; Francheteau, 1970) has also been taken in consideration in their selection. The main cores were selected primarily on the basis of their reported radiolarian content. Most of the cores were calcareous siliceous with varying a m o u n t of carbonate. Among the cores studied, nine did not have reported Radiolaria, but their locations could indirectly give further information on the extent of radiolarian sediments at various epochs within the Tertiary. 90ow

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Sampling of the cores was systematically carried out within the various lithologies as could be deduced from color layering which was very evident in most of them. Sample intervals vary from about 50 cm in thick homogeneous sequences to less than 5 cm at boundaries of changing lithologies. Standard sample size was approximately one cubic inch (ca. 16 cm3). In order to determine state of preservation and nature of the fine matrix, a smear slide was made for every sample. Each sample was oven dried at about 100°C, weighed, disaggregated in tap water containing about two parts per thousand of calgon (sodium hexametaphosphate), then sonified for about 30 sec or less at low frequency. The sample was then washed with a weak jet of tap water in a 38-pm sieve. This process eliminated particles of medium silt and clay sizes, but ensured m a x i m u m retention of small radiolarian specimens which would otherwise have been lost. Distilled water was used for the final

258 wash. The coarse fraction was oven dried at less than 100°C for 15--30 min, then weighed. The weight was reduced to percentage of original dry sample weight. The entire coarse fraction was then examined in a foram tray under stereomicroscope for identification of total and dominant particulate elements. After this first examination, one or the other of the following steps were undertaken: (1) If the coarse fraction consisted essentially of siliceous particles, a standard radiolarian slide (Riedel, 1959) was prepared from an aliquot of the residue. (2) When calcareous components were present, the sample was treated with 2N hydrochloric acid, washed, oven dried and weighed. The noncalcareous coarse fraction was also reduced to percentage of original sample weight. The slide made from this residue was prepared following the same m e t h o d as in the preceding case. Carbonate analyses of the calcareous portions of the cores were made from dry bulk samples by use of an apparatus similar to that described by Hiilsemann (1966). Basically it involves the chemical reaction of hydrochloric acid on the carbonate fraction of the dry sample and the formation of carbon dioxide. The amount of CO2 generated is measured in a burette by the displacement of a column of mercury. Because the product of the pressure and volume of a gas is a constant which depends only upon the temperature (Boyle's law), calculations of the CO2 generated were made from this principle. Also, the total amount of gas generated is directly proportional to the amount of carbonate present in the sample. Thus, in the graphs, carbonate content is given as weight percent of the dry sample. Carbonate content for many of the Deep Sea Drilling samples was analyzed by the Scripps Institution of Oceanography for the preliminary results of Legs 4 and 15. The Scripps Laboratory used a LECO 70 Second Carbon Analyzer as described in Leg 4 (Bader et al., 1970) and Leg 9 (Hays et al., 1972). This m e t h o d uses the difference in thermal conductivity between oxygen and carbon dioxide. The Hiilsemann m e t h o d carried an absolute inaccuracy of about 1.5% whereas the LECO method as compared with the latter, gave values around 1--2% lower, particularly in results given for Leg 4.

Coarse-fraction study All particulate constituents were accounted for, and the absolute amount of benthonic and planktonic Foraminifera and ostracods (very rare) were counted and reduced to relative number per grams of sediments (Figs.6, 7). Planktonic foraminifera were generally scarce in the sites at depths below 3000 m in the present topography. Several symbols related to relative estimated frequency and state of preservation of both calcareous and siliceous microfauna are also shown in these figures.

259 -+ T R F C A D

Absent Present Present, negligible by weight or volume of total coarse fraction Rare, less than 1/100 of total coarse fraction Few, less than 1/10 of total coarse fraction Common, greater than 1/10 and less than 1/3 of total coarse fraction Between 1/3 and 1/2 of total coarse fraction Dominant, greater than 1/2 total coarse fraction, or nominal when more than two elements are equally abundant 1 Slight or no obvious dissolution effect. Planktonic foraminifera are represented by whole tests, and fragments represent less than 1/10 of the estimated total planktonic foraminifera present in the total coarse fraction larger than 38 pm. 2 Obvious etching of tests. Planktonic foraminifera fragments represent between 1/2 and 2/3 of total estimated planktonic foraminifera present in total coarse fraction larger than 38 pm. 3 Strong etching of tests. Planktonic foraminifera or radiolarian fragments predominate in their respective assemblages. 4 Whole tests very scarce or absent. Fragments dominate. The absence of a numerical subscript beside the lettered symbols indicates very good preservation of the corresponding fauna.

Smear slide study Smear slides were checked mainly for relative preservation of the calcareous nannoplanktons. They were examined with a Leitz (Wetzlar) petrographic microscope and a Wild (M20) microscope.

Radiolarian slide study These slides were studied under natural transmitted light with the same microscopes previously mentioned. Because of the scarcity of certain groups, such as Lithomitra, Bathropyramis, Peripyramis, Cornutella, the cannobotryids (Plate I, 1--7) and the diatoms referred to as Triceratium (Plate I, 8), Hemiaulus (Plate I, 14), and Pyxidicula (Plate I, 9), which appeared to be good paleoecological markers, many of the slides, particularly all those of the Caribbean samples, were studied in their full content, instead of by random count across the slide. Relative percentages were estimated for species whose abundance exceeds 5% of the total assemblage by counting 600 individuals per slide. These estimates were often double-checked by supplementary examination of the coarse fraction under stereomicroscope. In general, apart from the very rare species numbering less than one per thousand, there was good agreement b e t w e e n the assemblage represented in the slide and that of the total coarse fraction examined under the stereomicroscope. FA CTO R S I NF LUENC I N G THE OCCURRENCE OF MODERN R A D I O L A R I A N SEDIMENTS AND COMMUNITIES

Because of similarities between the Cenozoic sediments studied and present

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Artostrobium g r o u p 1. DSDP 1 5 2 - - 2 - - 2 / 6 6 - - 6 7 cm.

Lithomitra g r o u p 2. D S D P 1 5 2 - - 1 - - 2 / 1 2 8 - - 1 2 9 cm. 3. C a n n o b o t r y i d R C 9 - - - 5 8 / 4 8 8 - - 4 9 0 cm. Theocampe armadillo g r o u p 4. R C 9 - - 5 8 / 2 7 0 - - 2 7 2 cm. 5. R C 9 5 8 / 2 9 0 - - 2 9 2 cm. Peripyramis g r o u p 6. V 2 8 - - 4 3 / 3 2 0 cm. Cornutella g r o u p 7. R C 8 - - 2 1 6 8 9 - - 6 9 1 cm. 8. D i a t o m r e f e r r e d t o as Triceratium V 2 8 - - 1 2 0 / 3 9 5 - - 2 9 6 cm. 9. A s s e m b l a g e o f c o l d - w a t e r d i a t o m s r e f e r r e d to in t e x t as Pyxidicula R C 1 2 - - 2 3 7 / 2 9 2 - - 2 9 3 cm. Lophophaena cf. L. auriculaleporis g r o u p 10. V 2 8 - - 4 3 / 1 8 0 cm. 11. R C 9 - - 5 5 / 1 0 2 0 cm. Lophocyrtis biaurita g r o u p 12. R C 9 - - 1 0 7 1 4 6 6 - - 4 6 8 cm. 13. D S D P 1 0 - - 9 - - 3 1 1 4 6 - - 1 4 7 cm. 14. Stylotrochus charlestonensis V 2 8 - - 4 3 1 4 0 0 - - 4 0 2 cm. ( A r r o w at u p p e r r i g h t c o r n e r p o i n t s at d i a t o m r e f e r r e d t o in t e x t as Hemiaulus). 15. Calocyclas semipolita V 1 7 - - 1 0 7 / 4 0 0 cm. 16. Theocotyle cryptocephala nigrinae DSDP 1 0 - - 9 - - 3 / 1 4 6 - - 1 4 7 cm. 1 7 Phormocyrtis striata striata DSDP 1 0 - - 9 - - 3 / 1 4 6 - - 1 4 7 cm. 1 8 Theocampe mongolfieri R C l 1 - - 1 9 9 1 1 1 7 5 - - 1 1 7 8 cm. 19 Spongodiscus cf. S. americanus R C 9 - - 5 5 / 8 5 0 cm. 2 0 Podocyrtis chalara DSDP 1 3 - - 3 - - 1 / 9 7 - - 9 8 cm. 2 1 Podocyrtis sinuosa D S D P - - 1 4 9 - - 3 2 - - 4 1 1 0 0 - - 1 0 1 cm. 2 2 Thyrsocyrtis rhizodon D S D P 1 4 9 - - 3 2 - - 2 / 2 6 - - 2 7 cm. 23 Podocyrtis papalis DSDP 1 4 9 - - 2 2 - - 2 / 2 6 - - 2 7 cm. 24 Thyrsocyrtis triacantha R C l 1 - - 1 9 9 / 1 1 7 5 - - 1 1 7 6 cm. 25 Podocyrtis mitra DSDP 1 4 9 - - 3 3 - - 1 / 4 4 - - 4 5 cm. 26 Thyrsocyrtis tetracantha R C 9 - - 5 8 / 4 8 8 - - 4 9 0 cm. 27 C o l d - w a t e r assemblage ( L a t e E o c e n e ? ) including very large s p o n g o d i s c i d s a n d a b u n d a n t d i a t o m s o f t h e Triceratium a n d Hemiaulus groups.

262

deep-sea deposits, the factors controlling the faunal composition of m o d e m radiolarian sediments are of critical importance in the understanding of the mechanisms involved in the occurrences of the ancient analogs. A survey of the literature on modern deep-sea sediments shows that opaline silica in the form of Radiolaria occur in significant abundance in modern abyssopelagic sediments only on the floor of certain specific areas of the world oceans, mainly in the northwest and equatorial Pacific, the equatorial Indian Ocean, and around Antarctica (Fig.4). The surface waters of these areas are also known to be the sites o f dynamic divergence {Fig.l); hence, they are constantly replaced by ascending waters from intermediate depths. This upwelling mechanism, which is associated with the major wind systems and the Coriolis effect, thus leads also to a constant return of nutrients to the surface waters. Consequently, waters of upwelling areas that are greatly enriched in nutrients such as phosphate, nitrates, silica, etc., are characteristically colder and are the most productive of Radiolaria. Therefore, the distribution pattern of radiolarian sediments reflects the ecological conditions of surface waters at these locations which are conducive to greater biogenic silica productivity. These conditions are primarily dependent upon the velocity of regional wind systems which are critical in determining the magnitude of upwelling in a given area at a given time. The general relationships between atmospheric and oceanic circulations on the one hand, and oceanic circulation and upwelling on the other, are very evident in the equatorial--tropical zones. These regions are indeed well known to show remarkable seasonal changes in their circulation pattern and intensity of upwelling as a result of concomitant shifting of the major atmospheric pressure cells. Thus, n o t only does the local wind field affect the ocean currents, but changes of the general atmospheric circulation over large oceanic regions, comprising the whole hemisphere or more, also seem to affect the oceanic circulation (Neumann and Pierson, 1966). Modern distribution patterns of radiolarian sediments not only show their close relationship with upwelling areas related to dynamic divergence, but they also show distinct faunal provincialism covariant with planetary temperature gradients and water masses (Popofsky, 1908; Riedel, 1958; Hays, 1965; Petrushevskaya, 1968; Nigrini, 1967, 1970; Goll and BjCrklund, 1971). Among the various radiolarian taxa, it appears that spumellarians such as the spongodiscids, and nassellarians of the Superfamily Archipilliceae (Haeckel, 1882, amended Campbell, 1954) provide species that are often characteristic of cold-water communities. Nassellarians that show cold-water affinities include, among other taxa, the following genera: Bathropyramis, Peripyramis, Cornutella, Lophophaena, Lophocyrtis, the artostrobiids and cannobotryids (Plate I), of which some species are also cosmopolitan (Petrushevskaya, 1968). The most characteristic taxa that show warm-water affinities in modern assemblages seem to belong to the Theoperidae (Haeckel, 1881, amended

263 Riedel, 1967). Genus groups of these families, which are most typical of the warm-water realm, are usually of large size, with smooth, elongated to bellshaped abdomen, large basal opening and apical horn of varying length, but more reduced in warmer water (Plate I, 20--26). Ecophenes of these taxa which occur in cooler water seem to develop more ornamental spines on the outer surface of the shells, and often show also much greater development of apical horns. As for all other living organisms, species diversity in modern radiolarian assemblages also increases systematically toward low-latitude regions. Similarly, the n u m b e r of specimens in the assemblages, or species dominancy, increases toward high-latitude environments and vice versa toward low~ latitude environments (Hays, 1965; Petrushevskaya, 1968). Thus cold-water assemblages are significantly impoverished in number of species in comparison with those of low-latitude regions. PALEOGENE RADIOLARIAN DISTRIBUTION PATTERNS The t a x o n o m y used in this section is partly after Campbell (1954) and mostly based upon recent works by Riedel and Sanfilippo (1970, 1971), Sanfilippo and Riedel (1973), and Foreman (1973). The radiolarian biostratigraphic zonation used as time framework (Fig.3) is after Riedel and Sanfilippo (1970) subsequently completed and amended by Sanfilippo and Riedel (1973), Moore (1971), Foreman (1973), Dinkelman (1973) and Maurrasse (1973). These radiolarian zones are based essentially on tropical assemblages because they were predominant in the time range considered in this study. They would, therefore, have been of little use for most high-latitude areas if climatic fluctuations did not allow migrations of the temperate species into these regions, and vice versa. In either case further caution was exercised as it appears that the range of certain species that occur in both high- and lowlatitude cores discussed in this study may actually be diachronous, due to adaptation or permanent migration with changing environmental conditions through their time range (Maurrasse, in preparation). Fig.3 is a synoptic representation of eighty-six selected species considered to be the most reliable, biostratigraphically and paleoecologically. The great majority of the species shown at the left side of this figure does not occur in most of the high-latitude cores. Few exceptions are Calocyclas semipolita semipolita (Plate I, 15), Theocotyle cryptocephala nigrinae (Plate I, 16), and Phormocyrtis striata striata (Plate I, 17) which are cosmopolitan species. They reach their optimum abundance in the middle-latitude areas. Theocampe mongolfieri (Plate I, 18) is also cosmopolitan throughout most of its range, but it does not appear in the Late Eocene radiolarian sediments of high-latitude cores studied. In contrast to the species shown at the left side of Fig.3, most of the taxa shown at the right side (Nos. 63 to 86), for instance the spongodiscids,

264 usually reach their o p t i m u m development and abundance essentially in highlatitude sites. Their occurrence is often very sporadic in the low-latitude areas. An exception among the spongodiscids is Spongodiscus americanum {Plate I, 19) which shows significant increase in size and abundance within levels of higher-carbonate sediments of the low-latitude sites. Among the taxa represented in Fig.3, twenty-two genus and species groups have been f o u n d to characterize faunal assemblages with distribution patterns reminiscent of modern faunal provincialism correlated with planetary temperature gradients arid surface oceanic conditions.

Selected radiolaria representative o f the different paleogene faunal provinces (cf. Plate I) Group 1. Warm-water species

Podocyrtis chalara Riedel and Sanfilippo Podocyrtis mitra Ehrenberg Podocyrtis papalis Ehrenberg Podocyrtis sinuosa Ehrenberg Thyrsocyrtids: Thyrsocyrtis rhizodon Ehrenberg Thyrsocyrtis tetracantha (Ehrenberg) Thyrsocyrtis triacantha (Ehrenberg) Theocampe mongolfieri (Ehrenberg) Podocyrtids:

Group 2. Cooler-water species

Spongodiscids:

Artostrobium spp. Calocyclas semipolita semipolita Clark and Campbell Phormocyrtis striata striata Brandt Amphicraspedum murrayanum Haeckel Amphicraspedum prolixum Sanfilippo and Riedel Spongodiscus americanus Kozlova Xiphospira circularis Clark and Campbell

Group 3. Cold-water species

Bathropyramis spp. Peripyramis spp. Cornutella spp. Lopophaena spp. Lophocyrtis biaurita (Ehrenberg) group Spongodiscids: Prunopyle occidentalis Clark and Campbell Spongodiseus phrix Sanfilippo and Riedel Stylotrochus nitidus Sanfilippo and Riedel Spongodiscus cruciferus Clark and Campbell L ychnocanoma amphitrite Foreman The distribution and diversity patterns of modern and Paleogene radiolarian sediments and communities summarized herein have been used as a basic framework for paleoecological interpretations. Assuming t h a t the distribution of mid-Paleogene radiolarian productivity, and their assemblages as well,

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