Late Pleistocene calcareous nannofossils in the caribbean and their interoceanic correlation

Palaeogeography, Palaeoclimatology, Palaeoecology l~2lsevierPublishing Company, Amsterdam-Printed in The Nethertands

LATE

PLEISTOCENE

CARIBBEAN

CALCAREOUS

AND THEIR

NANNOFOSSILS

INTEROCEANIC

IN THE

CORRELATION

S. GARTNER

Rosenstiel School of Marine and Atmospheric Science, Miami, Fla. (U.S.A.) (Accepted for publication April 25, 1972)

ABSTRACT (;artner, S., 1972. Late Pleistocene calcareous nannofossils in the Caribbean and their interoceanic correlation. Palaeogeogr., Palaeoclimatol., Palaeoecol., 12:169 - 191. Pleistocene climatic fluctuations as determined by means of oxygen isotope ratios from tile pelagic sedimentary record of the Caribbean can be recognized also by changes induced in the calcareous nannoplankton. Of 23 species tabulated from the Pleistocene fossil record two species, Ceratolithus cristatus and Umbellosphaera tenuis, are more abundant during temperature maxima. Seven species, Coccolithus pelagicus, Discoaster perplexus, Discolithina /aponica, Discosphaera tubifera, Gephyrocapsa caribbeanica, Oolithotus antillarum and Umbellosphaera irregularis, occur more abundantly during temperature minima in the Caribbean. Pseudoemiliania lacunosa, a species which becomes extinct during Pleistocene, is more abundant at times of temperature maxima during the last two temperature cycles of its existence, but prior to that appears to have been more cotnmon during temperature minima in tropical latitudes. Gephyrocapsa oceanica is the most abundant species in the Pleistocene record. It is represented by two distinct morphotypes, one more common during temperature minima and the other more common during temperature maxima. The interval examined in detail represents less than one-half million years, but contains two distinct biostratigraphic data; the Pseudoemiliania lacunosa extinction and the earliest occurrence of Emiliania huxleyi. INTRODUCTION Pleistocene climatic fluctuations have left a very obvious record in the high-latitude regions o f the world's continents. The advancing Pleistocene ice sheets were incredibly powerful erosional agents, and w h e n these glaciers m e l t e d they left behind vast till sheets and moraine deposits. The radical climatic changes, which alternately caused the formation and destruction o f the ice sheets, also left their imprint on sediments deposited in the oceans. This imprint may be obvious as in certain areas along the margin o f the continents, where streams fed by glacial melt waters deposited large volumes o f freshlyeroded material; it may be less obvious in deeper parts o f high and mid-latitude oceans where considerable a m o u n t s o f land-derived sediment were b r o u g h t to the ocean basin by icebergs. The most subtle imprint in the record p r o b a b l y was left in the ocean basins of tropical latitudes, as they are far r e m o v e d f r o m glacially-induced changes in the aspect of the sediments.

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S. GARTNER

In low-latitude oceanic sediments several methods have been used to reconstruct Pleistocene history. In one of the earliest attempts fluctuations in the calcium carbonate content in cores was related to Pleistocene climatic fluctuations (Arrhenius, 1952). Recently this technique has been applied again with considerable success (Hays et al., 1969). A second method that has been used for determining variations in paleotemperature is that of measuring the ~80/160 ratio by means of a mass spectrometer in the tests of planktonic foraminifer species which lived near the surface of the ocean. The variation in this ratio is then translated into corresponding temperature variations (see for example Emiliani, 1955, 1958, 1966). This method has been the subject of some controversy, but results obtained with it have, with very little modification, stood up well under the not inconsiderable amount of criticism and scrutiny. A third method exploits the variation in relative abundance of various planktonic foraminifer species whose modern representatives show a distinct preference for warm or cold waters. This variation in abundance is then also translated into a paleotemperature curve (Ericson et al., 1964; Ericson and Wollin, 1968; Beard, 1969; Emiliani, 1969; Kennett, 1970; Imbrie and Kipp, 1971 ; Wollin et al., 1971). The calcareous nannofossils - coccoliths, discoasters and associated forms - have proved surprisingly suitable during the past decade for high resolution biostratigraphy of calcareous pelagic sediments (Bramlette and Sullivan, 1961 ; Bramlette and Wilcoxon, 1967; Hay et al., 1967; Gartner, 1969, 1971; Roth, 1970). Their minute size, though a slight disadvantage initially, allows for study of large assemblages even in the smallest samples. More recently it has been determined also that many modern species of coccolithophores have a distinct preference for a definite temperature range, while a few species have such a sharp limit of temperature tolerance that their biogeographic boundaries essentially coincide with isotherms (McIntyre and B6, 1967). Within the latest Pleistocene the biogeography of coccolithophores has been used to determine the changes that occurred in the surface water circulation of the North Atlantic during the last glacial episode (Mclntyre, 1967). Using the pelagic sediments of the Caribbean, Emiliani (1966) determined a detailed paleotemperature curve for the past 425,000 years, based on oxygen isotope ratios. Nine major episodes of cooling were recognized within that time span. Subsequent detailed study of the planktonic foraminifers in part of this interval has clearly shown the same general variations in paleotemperature on the basis of known or inferred temperature preference of various species (Lidz, 1966). Moreover, significant morphological variations have been demonstrated within the same planktonic foraminifer species in response to the climatic changes over this interval (Emiliani, 1969). PURPOSE AND SCOPE As the calcareous nannofossils are known to be very sensitive paleoclimatic indicators in temperate latitudes, it is reasonable that the phytoplankton producing these fossils would have varied also in tropical latitudes, where the climatic changes were

IATF PLEISTOCENECALCAREOUS NANNOFOSS1LS

171

less pronounced. This study documents the variation in calcareous nannofossil assemblages in response to temperature variations over the past 425,000 years. Also, the biostratigraphy of coccolithophores is related to the cyclic temperature fluctuations. In addition, however, further refinement in the nannofossil zonation should be possible, because the remains of a number of coccolithophores living today are known only scantily from the sedimentary record, and the detailed analysis required by this study should define their stratigraphic ranges. METHODS AND TECHNIQUES

In erecting his paleotemperature curve, Emiliani used numerous cores and segments of cores. Two cores which, through detailed cross-correlation, were shown to contain an uninterrupted record throughout their length are the Caribbean cores P6304-8 (lat.14°59'N, long. 69°20'W, water depth 3,927 m) and P6304 9 Oat. 14°57'N, long. 68°55'W, water depth 4,126 m). These cores were taken in the Venezuela basin on a gentle slope, and located in such a way with respect to the sea floor topography that there is very little likelihood that slumped sediments or turbidity flows reached their locations. As the cores are essentially identical with respect to their calcareous nannofossil assemblages, only the longer one of the two, P6304-9, was studied in minute detail. This core is 1,429 cm long and consists of ten calcareous pelagic ooze throughout. Samples for isotopic determination were taken at 10-cm intervals. Samples for calcareous nannofossil study were also taken at 10-cm intervals, immediately adjacent to the samples taken previously for isotopic analysis, and from the central part of the core so as to minimize the possibility of stratigraphic contamination. Species abundances were determined with a light microscope on unprocessed samples so that the abundances of the largest and smallest species would not be altered by processing. For electron microscopic study the samples required processing as they contain substantial amounts of fine detrital silicates. McIntyre and B4 (1967) counted 300 specimens per sample with an electron microscope to determine species abundance in both plankton samples and sediment samples. This technique proved unsatisfactory. Replicas of unprocessed samples could not be used for counting because many specimens were obscured by fine debris, especially among the smaller species. As a result, the count always favored large and distinctive specimens. Replicas made from processed samples no longer could yield an unbiased count because some of the smaller and larger specimens inevitably are lost during processing. Counting specimens with the electron microscope therefore had to be abandoned. Direct counting and identifying of the first 300 specimens with the light microscope also proved unsatisfactory. In many samples a large number of specimens could not be identified to the specific level owing to the inherent resolution limit of the light optical system, and it was not possible to determine to what extent the count was skewed in favor of one species or another by this difficulty. Moreover, rare species in the sample

172

s. GARTNER

frequently did not appear in counts even though the species would be noticed quickly in a rapid scan. Eventually several different methods were used. For the genus Helicopontosphaera first 100 and later 25 specimens were counted for each sample to determine the relative abundance with respect to each other of the three morphotypes, two of which have been described as distinct species. The species Pseudoemiliania lacunosa is a particularly important taxon because its extinction during the Pleistocene marks an easily recognized datum. For this species time counts were made, i.e., scanning the slide as fast as possible, all specimens of this species encountered in a given period of time were counted. This type of count permits rapid determination of relative abundance of a species even though that species may be extremely rare, as is commonly the case with species approaching extinction. In addition to the above counts, estimates were made of all species. The method for making the estimates was modified from the method used by Hay (1970). According to this technique the abundance of a species is estimated with the light microscope at a magnification of 1500 X as being present as: >100 specimens per field 10-100 specimens per field 1 - 1 0 specimens per field 1 specimen in 1 - 1 0 fields 1 specimen in 10-100 fields. The abundance of a species can be expressed simply by using exponential values, with the lowest concentration equalling 1 and the highest concentration equalling 5. On a chart, suitable symbols are used in place of numbers. There are several advantages to using this method rather than actual counting. The estimate spans five orders of magnitude. The most abundant species are eliminated immediately and progressively less abundant species can be estimated until only very few rare species remain. Scanning for the rare species is also relatively rapid because the observer's eye can be trained quickly to look only for one or two species while overlooking the most common forms already tabulated. In actual practice only four orders of magnitude were spanned because it is quite impossible to make sensible estimates of species abundance at 1500 X in a field containing more than 100 specimens.

Climatic" variations and nannofossil species composition Variations in species composition of calcareous nannofossils was first documented by Cohen (I 964) for selected samples from Caribbean cores for which isotopic temperatures had been determined previously. Cohen's conclusions in general are borne out by this study. McIntyre and B6 (1967) and McIntyre et al. (1970) documented extensively the latitudinal variation in the Atlantic and Pacific Ocean, respectively, of living coccolithophorid assemblages, and they were able to define floral provinces distributed more or less symmetrically north and south of the equator. Also, they determined the optimum

LATE PLEISTOCENECALCAREOUS NANNOFOSSILS

173

temperature ranges as well as the maximum and minimum temperature levels for several species in the Atlantic Ocean. Subsequently, McIntyre (1967) used these same data to study the latest Pleistocene climatic shifts in the North Atlantic. In core P6304-9 several species vary in abundance in close correspondence with changes in temperature. Of the 23 species tabulated, only two species are consistently more abundant during temperature maxima, while seven are consistently more abundant during temperature minima. This is perhaps somewhat surprising because coccolithophorids are generally considered warm water phytoplankton, and, hence, it might be expected that temperature maxima would favor optimum development of the maximum number of species. In several instances, however, the abundance of any one species in a randomly picked sample is not nearly so reliable an indicator of paleotemperature as might be expected, even though overall trends can be recognized readily. In Fig.1 are plotted the isotopically-determined paleotemperature for core P6304-9 (from Emiliani, 1966) and the abundances of 23 species of calcareous nannofossils. Species that are more abundant during temperature maxima are marked with a + and species that are found most abundantly during temperature minima are marked with a - ; unmarked species show no clearly discernable trend or are ambiguous in part of the interval. Ceratolithus cristatus is one of two species which generally occur in greatest abundance during temperature maxima. Occasionally, however, this species may be notably erratic and may occur in about the same numbers at a temperature minimum and at a temperature maximum. Cohen (1964) also tabulated this species and came to the conclusion that this species does not show any clear temperature preference. Norris (1965) concluded that the genus Ceratolithus contains two living species: C. cristatus, which is tropical to temperate in its range, and C. telesmus, which is strictly a tropical form. Although both of the above forms are present in the Caribbean, their occurrences do not seem to correspond to temperature minima or maxima. By far, most of the specimens of Ceratolithus have the "cristatus" type of morphology, despite their greater abundance during temperature maxima. Umbellosphaera tenuis (Plate 1, 7) is the second species which is more abundant during temperature maxima in the Caribbean. This is in conflict with the evidence presented by Mclntyre and B6 (1967) and Mclntyre et al. (1970), who found this species to have a lower optimum temperature range than U. irreguiaris. The evidence from Caribbean Pleistocene sediments leads to the opposite conclusion. Umbellosphaera tenuis evolved relatively recently in the Pleistocene, and the species apparently has not yet reached the acme of its development. The species, therefore, may not be an entirely reliable indicator. The species whose greatest abundance coincides with temperature minima are

Coccolithus pelagicus, Discoaster perplexus, Discolithina japonica, Discosphaera tubifera, Gephyrocapsa caribbeanica, Oolithotus antillarum and Umbellosphaera irregularis. Coccolithus pelagicus is not found living in the Caribbean today, but is restricted to cooler temperate and subarctic regions. During the Pliocene and earlier Neogene this

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same species, or a very close relative, apparently lived in some abundance in the Caribbean region, and its disappearance from this area corresponds approximately to the extinction of discoasters (Boudreaux and Hay, 1969) which in deep-sea sediments closely approximate the onset of the Pleistocene. This species was recorded from only eight samples in this core, and invariably occurs as one specimen per 10 to 100 fields. Not all but most of the occurrences coincide with temperature minima. Nevertheless, the possibility that this species is represented only by reworked specimens cannot be ruled out, and the occurrences may indicate nothing more than erosion of earlier Neogene strata during low stands of sea level.

Discoaster perplexus, which is not a true discoaster at all, is never very abundant, but seems to occur consistently. Throughout the core this species is lacking at the temperature maxima while at the same time it is present during temperature minima. Cohen (1964) also noted that this species seemingly was more c o m m o n during temperature minima. l~'scolithina japonica follows the same trend as Discoaster perplexus but to a lesser degree, as is also the case with Oolithotus antillarum. The most common species which shows a quite clear preference for temperature minima is Discosphaera tubifera. This species is sub-tropical to temperate in its distribution today, and according to Mclntyre and B6 (1967) has an optimum temperature range between 21 and 25°C, with an upper limit at 27°C.

Umbellosphaera irregularis (Plate I, 4) also shows a slight increase during temperature minima, although the trend with this species is not entirely clear. Part of the reason may be that this species also is a relatively recent addition to the nannoflora, and it does not occur throughout the length of core P 6 3 0 4 - 9 . Among the species which appear to show no preference for either temperature maxima or temperature minima are Cyclococcolithina leptopora, Cyclolithella annula, Emiliania

huxleyi, Rhabdosphaera clavigera, Scapholithus fossilis, Syracosphaera pulchra and Syracosphaera sp. But even among these species some variation is noted in relation to one or more temperature cycles. Thus, nearly all species seem to have responded negatively to the temperature maximum centered around 930 cm, and Rhabdosphaera clavigera, Scapholithus fossilis and Syracosphaera pulchra in general appear to have been more abundant during temperature minima in the lower half of the core. Syracosphaera sp. (Plate I, 1 - 3 ) shows a very strong preference for temperature minima in the lower 700 cm of the core but is relatively sporadic in the upper 700 cm.

Fig. 1. Abundance variation with depth of calcareous nannofossils in Caribbean core P6304 9. A dot (') indicates 1 specimen in 10 to 100 fields; an open circle (o) indicates 1 specimen in 1 to 10 fields; a solid circle (O) indicates 1 to 10 specimens per field; and a solid square (Ira)indicates 10 to 100 specimens of that species in every field. Geph),rocapsa spp. includes the three species Gephyrocapsa aperta, (;. ericsoniiand G. protohuxleyi. These three species cannot be clearly distinguished with a light microscope and therefore their abundance is totalled in one column. The actual occurrence of these species in this core as determined with the electron microscope is plotted on the right-hand side, but without abundance variations. On the extreme right-hand side is reproduced the isotopic paleotemperature curve (from Emiliani, 1966).

S. GARTNER

176 PLATE I

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LATE PLEISTOCENE CALCAREOUS NANNOFOSSILS

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A special case is represented by the species Pseudoemiliania laeunosa (Plate II, 3). This species first appeared during the mid-Pliocene and was the dominant placolith species throughout the Late Pliocene. During the earlier Pleistocene Pseudoemiliania lacunosa is gradually replaced by another placolith group, the various species o f Gephyrocapsa. As the latter group increases, P. lacunosa is found in smaller and smaller numbers, until finally the species disappears completely. One might expect that a species on the verge of extinction would be especially responsive to radical changes in environment, such as major fluctuations in temperature, and that the abundance o f such a species would directly reflect temperature fluctuations. Therefore some considerable effort was given to this species. After several methods were tried, time counts were chosen as probably most suitable for determining the relative abundance of this species in a sample. The species is easily recognized with a light microscope and, apart from the technique, the counts can be considered quite accurate. The time counts are made by selecting at random an area on the slide and counting the number of specimens of this species encountered during a three-minute scan. After some little practice it is possible to scan over 60 fields in three minutes, each field containing in the order of ten to fifty specimens. This technique is not as dependent on the density of nannofossils on the slide as might appear, because if the preparation is too dense a field is more difficult to scan and requires more time, whereas if the preparation is dilute fields are scanned much more rapidly. On each slide four separate counts o f three minutes each were made, each count on a different area of the slide. The four counts were totalled for the final value. For this particular core the counts were repeated three times by two different people in order to establish the reliability of the counts. For each repeated count substantially the same results were obtained. The results of one such count are plotted in Fig.2 along with the isotopicallydetermined paleotemperature for the same interval. It appears that going backwards in time from the extinction level ofPseudoemiliania lacunosa the first two temperature maxima (nos. 13 and 15) correspond to noticeable increase in abundance of this species. However, the trend in abundance reverses at the temperature minimum centered around 1,300 em and the species attains its greatest abundance yet. This reverse trend seemingly continues for the next lower temperature maximum. It may be argued that the pattern of abundance variations leading to the extinction of Pseudoemiliania lacunosa may be an artifact developed only at this particular location owing, perhaps, to the peculiar sedimentary history of this site. This possibility was PLATE l All photographs are at the same magnification. The marker on each photograph equals 1 micron. 1 3. Syracosphaera sp. Plan view; 1, 3 = 0 cm; 2 = 600 cm. 4. Umbellosphaera irregularis Paasche. Proximal view, 0 cm. 5. Gephvrocapsaoceanica Kamptner. Form A ; Distal view; 0 cm. 6. Qvch)lithella annula (Cohen). Plan view; 150 cm. 7. Umbellosphaera tenuis (Kamptner). Distal view; 0 cm.

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LATE PLEISTOCENE CALCAREOUS NANNOFOSSILS

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Fig.2. The variation in abundance ofPseudoemiliania lacunosa just preceding the extinction of that species in Caribbean core P6304 -9 is plotted at the top, and the isotopic paleotemperature curve for the same interval is plotted at the bottom. Note the correspondence of the two curves for cycle 13 and part of cycle 15, and the reversal of the trend between cycles 15 and 17. ? tested on two cores: one f r o m a nearby l o c a t i o n in the Caribbean (P6408---10) and one f i o m the eastern equatorial Pacific (P6702

6). In b o t h cores fluctuations in a b u n d a n c e

occur similar to those in core P 6 3 0 4 - 9 and in core P 6 4 0 8 - 1 0 the variations in abundance o f P . lacunosa correlate with the same isotopic t e m p e r a t u r e m a x i m a (unpublished) as in core P6304 -9. Isotopically-determined t e m p e r a t u r e s are not available for P6702 6 , but in this core fluctuations in calcium carbonate c o n t e n t can be correlated to isotopically d e t e r m i n e d p a l e o t e m p e r a t u r e variations in the Caribbean, high calcium carbonate levels corresponding to t e m p e r a t u r e m i n i m a and low calcium carbonate levels corresponding to t e m p e r a t u r e m a x i m a (Fig.3). The pattern o f a b u n d a n c e variation preceeding the e x t i n c t i o n o f P . lacunosa is identical. The e x t i n c t i o n o f P s e u d o e m i l u m i a lacunosa appears to be a synchronous event in tropical latitudes inasmuch as e x t i n c t i o n occurs during the same t e m p e r a t u r e m i n i m u m in the Caribbean and in the Pacific. The s e d i m e n t a t i o n rate in the three cores e x a m i n e d in detail is comparable and this may allow certain conclusions about vertical mixing o f calcareous nannofossils. M c l n t y r e et al. (1967) state that the zone o f mixing for calcareous nannofossils is 30 cm or more. Their conclusion is based on the e x p o n e n t i a l e x t i n c t i o n curve for discoasters above the P l i o c e n e - P l e i s t o c e n e b o u n d a r y which was c o n s t r u c t e d from counts

PLATE 11 All photograpbs are at the same magnification. The marker on each photograph equals 1 m icron. 1. (;ephyrocapsa oceanica Kamptner. Form A ; proximal view: 600 cm. 2. Gephyrocapsa oceanica Kamptner. Form B; proximal and distal views: 500 cm. 3. Pseudoemiliania lacunosa (Kamptner). Proximal view; 1,300 cm. 4. Gephyrocapsa ericsonii Mclntyre and B6. Proximal view; 1,300 cm. 5. Helicopontosphaera wallichi (Lohmann). Distal oblique view; 550 cm. 6. tfelicopontosphaera kamptneri lfay and Mohler. Proximal view: 50 cm.

180

S. GARTNER

750

800

900

I000

I I00

808590

15 aoo

15 900

17 rooo

~loo

izoo

Fig.3. The variation in abundance ofPseudoemiliania lacunosa just preceding the extinction of that species in Pacific core P6703-6 is plotted at the top, and the calcium carbonate percentage curve for the same interval is plotted below. Note again the approximate correspondence of the two curves for cycle l 3 and part of cycle 15, and the reversal of the trend between cycles 15 and 17. made at 20-cm intervals. This being so the extinction ofPseudoemiliania lacunosa also should follow a similar exponential curve when determinations are made at 10-cm intervals. In none o f the three cores is that the case. Instead P. lacunosa varies in abundance for the last two climatic cycles o f its life in response to temperature variations, then quickly disappears from the record at the temperature minimum between maxima 11 and 13. The disappearance is so striking, in fact, that in Caribbean core P 6 3 0 4 - 8 , which terminates at this temperature minimum, probably within 10 cm o f the extinction point ofP. lacunosa, this species is not present at all. The zone o f upward mixing o f calcareous nannofossils therefore must be considerably less than the 30 cm or more indicated by Mclntyre et al. (1967), and, in fact, appears to be less than 10 cm. Berger and Heath (1968) considered the problem o f vertical mixing from a theoretical point o f view, and determined that the true extinction level of a species is that point at which it has been reduced to 37% o f its maximum value below. Strictly speaking Berger and Heath's criteria are not applicable in this case. It can be argued further that the formula cannot be applied to any species whose abundance fluctuates over a time interval preservable in the fossil record, because it is not possible to determine whether a fluctuation in abundance was in process immediately preceding extinction. That is to say, it is not possible to determine what level corresponds to the "maximum concentration below". Moreover Berger and Heath assume that there is no significant decline o f a species' abundance prior to its becoming extinct, which probably is not correct. If we assume that the last peak in abundance corresponds to the level of maximum abundance below, we can determine the upper limit for the distance over which reworking occurs. In core P 6 3 0 4 - 9 the last peak for Pseudoemiliania lacunosa is at 990 cm. At

[ATE PLHSTOCI,~NV CALCARI'OUS NANNOFOSSILS

181

980 cm this species is no longer present. Thus the reference level corresponding to no dilution by upward reworking, the 37% level, and the level o f complete absence are all contained within 10 cm o f sediment, and upward reworking could not have exceeded 10 cm. In the Pacific core P 6 7 0 2 - 6 Pseudoemiliania lacunosa is reduced from a peak abundance to zero within 20 cm. However, the three points along this curve, at 800 cm, 810 cm, and 820 cm do not fall on an extinction curve as they form a convex curve, while an extinction curve must be concave. Thus in this case also vertical mixing could not have exceeded 10 cm.

The Helicopon tosphaera complex The genus Helicopontosphaera is represented by three species, 11. kamptneri (Plate I1, 6) and H. wallichi (Plate II, 5), and a third form which is relatively rare and as yet unnamed. The above species all appear to have developed from a common ancestor sometime during the kate Neogene but generally they are found in the same environment. Intuitively it seems unlikely that three closely-related species would have identical ecological requirements. It would be reasonable to assume, therefore, that profound lemperature changes may have had a notable effect on the abundance of one o f the species of this genus. In order to test this possibility the relative abundances o f the above species were determined by identifying from 25 to 100 specimens belonging to this genus and tabulating their numbers. Initially it was thought that H. wallichi and H. sp. were identical and these two species are counted together. This should not effect the count very much as H. sp. is always quite rare. The results are plotted in Fig.4. !i: ! .

.

.

.

/

~:"[. . . . t"ig.4. Helicopontosphaera wallichi plus/4, sp. are plotted as a percentage of all specimens of Heffcopontosphaera along with the isotopic paleotemperature curve. Some correspondence of the curves may be noted for the upper 400 cm of the core but below this level apparently no correspondence can be recognized by this technique. For the latest Pleistocene there appears to be some correspondence between the relative abundances of Helicopontosphaera wallichi plus H. sp. and the isotopicallydetermined temperature variations. But beyond temperature maximum 5 this apparent correspondence no longer exists. On Fig.l, which shows relative abundances of all species as determined by scan rather than counl, 11. wallichi plus H. sp. seemingly occur ill greater abundance during isotopic temperature maxima, but only towards the b o t t o m of the core.

182

S. GARTNER

The relative abundance determinations ofHelicopontosphaera wallichi made by the two methods, i.e., absolute counts and rapid scan estimates, offers a test of the sensitivity of the two techniques. Near the top of the core the scan technique shows no significant variations in relative abundance although an absolute count does indicate some percentage variations. In the lower part of the core H. wallichi is much less common relative to H. kamptneri, so much so, in fact, that it is rarely encountered in a count of less than 25 specimens of the genus. Yet by the scan technique H. wallichi consistently appears, though in much reduced numbers. It would seem, therefore, that while the scan technique is relatively inaccurate for measuring relative abundances of species which occur in approximately the same concentration, it is, as one would expect, quite sensitive for species occurring in very small numbers relative to the dominant forms in an assemblage. THE Gephyrocapsa COMPLEX The genus Gephyrocapsa is restricted entirely to post-Pliocene sediments, and the first occurrence of the genus closely corresponds to the extinction of discoasters. Eight species have been described in this genus, some of which may be junior synonyms. It is not likely that all of these species appeared simultaneously in the record, and there is a distinct possibility that some are now extinct. However, there is very little reliable stratigraphic documentation for the genus, and, because of the small size of several of the species, this potentially useful taxon could not be adequately exploited in this study. Gephyrocapsa aperta, G. ericsonii, G. kamptneri and G. protohuxleyi all are too small to be identified with the light microscope. Also, G. ericsonii may grade into G. protohuxleyi as indicated by Mclntyre (1970) and separating the two with a light microscope is impractical. In order to establish which of the above species are present, species of Gephyrocapsa were determined with the electron microscope every 50 cm. Only one, G. kampmerL was not encountered in any sample, and the species thus does not figure any further in this study. The remaining three species were lumped together under G. sp. in abundance estimates made with the light microscope, and it is doubtful, therefore, that this estimate is particularly meaningful. Ranges for these species, however, are given from the electron microscopic examination. The electron microscopic and light microscopic studies both indicate an absence of the small species of Gephyrocapsa from the top of the core. Below about 100 cm some specimens of the three species were noted with the light microscope, and below 200 cm they may occur in some abundance, although their abundance seems to bear no particular relationship to temperature. Between 1,050 cm and 1,130 cm all small species of Gephyrocapsa seem to be anomalously lacking, although all three species are present at various levels between 1,130 cm and the bottom of the core. Of the three species, only G. ericsonii (Plate II, 4) is known to be extant, but according to Mclntyre et al. (1970) the preferred temperature range of the species today is between 15 ° and 19°C. G. protohuxleyi is merely a transitional form between the genus Gephyro-

LATE PLEISTOCENE CALCAREOUS NANNOFOSSILS

183

capsa and the dominant modern and Late Pleistocene coccolith species Emiliania huxleyi. Fhis form apparently evolved out of existence. G. aperta is not known as a living form, but it is not known whether its disappearance from the Caribbean is a true extinction or whether the species migrated to higher latitudes as did several other species of this genus. Gephyrocapsa caribbeanica was first described from the fossil record in the Caribbean. Fhe species has been found living, but only at much higher latitudes (Geitzenauer, 196c); McIntyre et al., 1970), and the preferential abundance during isotopic temperature minima agrees well with its present geographic preference. Gephyrocapsa oceaniea presents a special problem. This species was originally described and characterized by Kamptner (1943) from light microscopic observations, and a quick perusal of the literature shows a rather bewildering array of forms that have been assigned to it. For light microscopic work a broad concept of this species is entirely satisfactory, indeed necessary. Such a broad concept was used for the light microscopic tabulations of Fig.l. For electron microscopic study, further discrimination is possible. however. Kamptner's circumscription of this species lacks the precision attainable with electron micrographs. Moreover, Kamptner did not illustrate the species. The next citation is by Deflandre and Fert (1954) who presented several electron micrographs, but their specimens are smaller than the smallest diinension given by Kamptner. Also, the illustrations are of poor quality and the specimens are, therefore, a poor standard of reference. Halldal and Markali (1955) published some very good transmission electron micrographs of specimens of this species from the North Atlantic, and although they used whole specimens rather than replicas, nrost of the essential features are readily discernible. The number of elements is 37 to about 48, the bridge angle is between 60 ° and 70 ° in their specimens, and the maximum diameter is 3.4 and 4.5 ~. It is also noteworthy that one of the specimens illustrated by Halldal and Markali has an appreciably larger central area than do the other two. Among other specimens assigned to this species in the literature the bridge angle varies from about 40 ° to 70 ° , with most values clustered between 55 ° and 60 ° . The lowest and highest reliable measurements recorded for the bridge angle are 33 ° and 75 °, respectively. The element cotint similarly varies from a low of about 35 to a maximum of about 70. For most specimens the elenrent count is between 40 and 60. In most assemblages from the Caribbean there is a mixture of specimens with a relatively large central area (Plate II, 2) and specimens with a relatively small central area (Plate I, 5; Plate II, I). As there is also considerable variation in size within the G. oceanica group, the above feature is best expressed as the ratio (R) of the maximum outer diaineter divided by the maximum inner diameter. The maximum inner diameter is measured on the distal side from the "shoulder" of the central tube or collar, i.e., the point where the opening is largest on the distal side. The value R is commonly between 1.50 and 2.50 or more. If specJanens are separated qualitatively into, say form A (small center) and form B (large center), then the values of R for form A are usually greater than 1.90, while for form B values of R commonly are less than 1.90. Moreover, form

184

S. GARTNER

A (small center) is associated, though not exclusively, with lower temperature, while form B (large center) is associated most frequently with higher temperature. The number o f shield elements and the bridge angle seemingly are not related consistently to the size o f the central opening. On Fig.5 electron microscope photographs o f specimens o f Gephyrocapsa oceanica from 0, 50 and 100 cm have been separated subjectively into form A (x) (Plate I, 5; Plate II, 1) and form B (o) (Plate II, 2) morphotypes. On the upper graph the specimens have been plotted according to criteria used traditionally to characterize species o f Gephyrocapsa, i.e., number o f shield elements and crossbar angle. Both forms have approximately the same distribution on the graph according to these criteria. x = FORM A1 o = FORM B]'SPECIMENS

FROM O, SO AND IOOcm

9

x

o

o

o

o

x

~

o

XX

,.=,

0

x

x

o o

x

o

o

o

o° x x o

ox

40

4o. 5bo ~?o° ~" ANGLEOF DIAGONALCROSSBARTO MAJORAXIS

r.6o"

,to

18o

19o

zoo

Z'.lO

z:zo

zi3o

zl,o

eiso

FREQUENCY DISTRIBUTION OF R RATIO (R) = MAXIMUM OUTER DIAMETER / M A X I M U M INNER DIAMETER

Fig.5. Two morphotypes of Gephyrocapsa oceanica separated subjectively are plotted; on top according to conventionally used parameters for distinguishing species in this genus, i.e., number of shield elements and the angle which the crossbars make with the long axis of the elliptical placolith; on the bottom as a frequency distribution of R, the ratio of maximum outer diameter of the placolith to maximum inner diameter of the central tube. The same specimens were used for both plots. All specimens in this plot are from 0-, 50- and 100-cm levels in Caribbean core P6304-9. Note the sharp separation of the two morphotypes on the lower plot. On the lower graph the same specimens are plotted as a frequency distribution of R, the ratio of m a x i m u m outer diameter divided by the maximum inner diameter. The separation o f the two groups is obvious when this criterion is used. On Fig.6 two assemblages were treated according to the same criteria. One o f the assemblages (750 cm = o) is from a temperature maximum, and the second assemblage (1,299 cm = x) is from a temperature minimum. The specimens were not divided subjectively into form A and form B morphotypes. On the upper graph there appears to be some separation by crossbar angle, i.e., the specimens from the temperature maximum have, on the average, a smaller crossbar angle than do specimens from the temperature

I.ATE PLEISTOCENE CALCAREOUS NANNOFOSSILS o = 750

185

crn { W A R M )

x =~300 crn (COLD)

60

x x

o°

50

o o

o

8080

40-

30

ANGLE

xo

x

x x

x x

x

o

x

x

40 0 5100 ~'0 ~ iO* OF DIAGONAL cRoSSBAR TO MAJOR AXIS

~b 0

~160 170 180 1.90 200 2.lO 2 5'0 FREQUENCY DISTRIBUTION OF R R = MAXIMUM OUTER D I A M E T E R / M A X I M U M INNER DIAMETER

230

2'40

Fig.6. Specimens of Geph3,rocapsa oceanica iron] two different depths, and corresponding to opposite extremes of climatic fluctuation, are plotted; on top according to conventional parameters of number of shield elements and angle between crossbars and the major axis of the elliptical plaeolith; on the bottom as a frequency distribution of R, the ratio of maximum outer diameter of the placolitb to the maximum inner diameter of the central tube. Note the smaller average R value for the specimens from 750 em (warm), and the larger R values for the specimens from 1,300 cm (cold). The specimens were not separated subjectively into the two morphotypes, as m] Fig.5.

m i n i m u m . The two assemblages are separated by an interval o f about 2 0 0 , 0 0 0 years, and it is not clear to what e x t e n t this has influenced the distribution. On Fig.5 the three assemblages are one from a t e m p e r a t u r e m a x i m u m (0 cm), one from a near t e m p e r a t u r e m i n i m u m (50 cm), and one f r o m an intermediate t e m p e r a t u r e level ( 1 0 0 cm). In these three assemblages no significant separation is noticeable according to crossbar angle. Hence the clustering effect n o t e d for the assemblages from 750 cm and 1,299 cm is thought to be time d e p e n d e n t , as the two are separated by a significant time interval. In the f r e q u e n c y distribution plot o f R a clear clustering o f R-values again is apparent; R-values o f the specimens f r o m 750 cm are, on the average, less than are R-values o f specimens f r o m 1,299 cm. It is not entirely clear w h e t h e r the two m o r p h o t y p e s represent two distinct species, but certainly one m o r p h o t y p e is m o r e c o m m o n during t e m p e r a t u r e m a x i m a while the other m o r p h o t y p e favors t e m p e r a t u r e m i n i m a in the Caribbean. BIOSTRATIGRAPHY OF THE LATE PLEISTOCENE IN Tilt" CARIBBEAN Above the discoaster e x t i n c t i o n datum, which is c o m m o n l y accepted as a p p r o x i m a t i n g the Plio-Pleistocene b o u n d a r y in deep sea sediments, three additional nannofossil zones

186

S. GARTNER

are recognized (Hay et al., 1967; Gartner, 1969; Geitzenauer, 1969). From oldest to youngest these zones are the Pseudoemiliania lacunosa Zone, the Gephyrocapsa Zone, and the Emiliania huxleyi Zone. The P. lacunosa Zone extends from the last occurrence of Discoaster brouweri to the last occurrence of the nominal species. The upper part of this zone is contained within core P6304-9, extending from the base of the core to 980 cm. The top of this zone corresponds to the temperature minimum between stages 11 and 13 of Emiliani's usage. The next higher zone, the Gephyrocapsa Zone, extends from 980 cm to the first occurrence of Emiliania huxleyi at 620 cm. Apparently the oligothermic cosmopolitan species E. huxleyi first invaded the Caribbean during the temperature minimum at 620 cm but did not become well established there until the next temperature minimum at 470 cm, and reached its present dominant position during the temperature minimum at 250 cm. Thus, the Pleistocene interval preceeding the temperature minimum at 980 cm is assignable to the P. lacunosa Zone. The interval from 980 cm to 620 cm correlates with the Gephyrocapsa Zone, while the interval above 620 cm is the Emiliania huxleyi Zone. Additional markers are present also to aid in the identification of the above zones. Umbellosphaera irregularis first appears sporadically at 1,120 cm, but is found consistently only above 1,050 cm, less than 100 cm below the extinction ofP. lacunosa, and the co-occurrence of the above two species marks temperature maximum 13. Similarly, the first occurrence of Umbellosphaera tenuis is during temperature maximum 7, immediately following the earliest occurrence of Emiliania huxleyi. Three small species of Gephyrocapsa, G. protohuxleyi, G. aperta and G. ericsonii, disappear from the Caribbean at about the level at which E. huxleyi assumes a dominant position. One of the above, G. ericsonii, is extant but lives only at higher latitudes than the Caribbean. G. protohuxleyi probably is extinct as may be the case also for

G. aperta. ABSOLUTE AGES OF PLEISTOCENEDATUMLEVELS The above biostratigraphic datum levels are readily related to an absolute time scale. The time scale for the climatic fluctuations has been developed over a period of about 15 years by Emiliani and others (Emiliani, 1955, 1958; Rosholt et al., 1961; Rona and Emiliani, 1968) and is based on ~4C dates for the youngest portion of the cores and 230 Th/231 Pa ratios back to about 170,000 years ago. Beyond that point, ages are largely extrapolated from sedimentation rates as the interval is, for the most part, beyond the reach of reliable absolute dating techniques. The most important nannofossil datum level is the extinction of Pseudoemiliania lacunosa at the temperature minimum between stages 11 and 13, or approximately 275,000 years ago. Geitzenauer (1969), by means of an indirect correlation, gave an estimated age of 700,000 for this datum in sub-Antarctic-Pacific cores. Even if allowance is made for equatorward compression of this species' geographic range prior to its becoming extinct, the discrepancy in ages is still far too large.

l A T E PLEISTOCENE CALCAREOUS NANNOFOSSILS

I hi7

K e n n e t t ' s (1970) study o f the p l a n k t o n i c Foraminifera f r o m some o f the cores used by Geitzenauer aids s o m e w h a t in fixing this datum. The e x t i n c t i o n level o f Umbilicosp-

haera cricota (= Pseudoemiliania lacunosa) as d e t e r m i n e d by Geitzenauer (1969) in cores E 2 1 - 1 7 and E 1 5 - 1 6 corresponds to warm cycle 6 of K e n n e t t ' s usage (see K e n n e t t , 1970, Fig.6 and 8). It is interesting to note that if Emiliani's warm cycle 3 is not c o u n t e d , ',as is c o m m o n l y done w h e n the climatic cyles are d e t e r m i n e d by the less sensitive paleontological (e.g., p l a n k t o n i c foraminifers) or geochemical (e.g., calcium carbonate percentage) methods, then Emiliani's t e m p e r a t u r e m a x i m u m 13 (= the last a b u n d a n t occurrence o f Pseudoemiliania lacunosa in the Caribbean) corresponds to K e n n e t t ' s temperature m a x i m u m 6 (= the e x t i n c t i o n level ofPseudoemiliania lacunosa in the subAntarctic Pacific Ocean (Fig.7)). Thus the e x t i n c t i o n o f this species appears to have KENNETT. 1970

EMILIANI. 1966 ~ 0 ~i (%.)

Gl~lger/na ~chyden~ cm

100%

50%

0%

cm+~

or •

I

PLAYSet ol, 1969 % C,~RBONATE

0

-I

cm 100%

,

,

or_ BI

90%

60%

113o

2oo ~

IOO

\

3o,:),

150

5oo i

B5

II ./ / i o

f~

Fig.7. Correlation of paleotemperature curves in three cores from three different areas. Kennett's curve, redrawn here, is based on the per cent of Globigerina pachMerma in subantarctic core Et5 16; Emiliani's curve is based on oxygen isotope ratios in Caribbean core P6304-9; the redrawn curve from Hays et al. is for core V24 58 from the equatorial Pacific and is based on the percent carbonate in the sediment. The cycles in the cores are correlated on the extinction level of Pseudoemiliania lacunosa. In core E 15-16 the predicted extinction level of P. laeunosa is at about 530 cm. The actual extinction level (from Geitzenauer, 1969) is half of a cycle further down in the core.

188

S. GARTNER

occurred during the same temperature cycle in the Caribbean and in the sub-Antarctic Pacific. Kennett (1970) dates his warm cycle number 6, i.e., the extinction datum of Pseudoemiliania lacunosa, at just under 600,000 years B.P. It appears, therefore, that either one or both of these time scales are incorrect. A check on the age of this datum for low latitudes is afforded by the equatorial Pacific core V 2 4 - 5 9 (Lamont-Doherty Geological Observatory) in which the highest occurrence ofP. lacunosa is at 160 cm, which corresponds to the high carbonate level (= glacial) between interglacials B9 and B11 in the terminology of Hays et al., (1969). This level is dated at 350,000 years by the latter authors. The age is based on correlation with a nearby core (RC11-209) for which a time scale was devised from a 14C date and interpolated dates from the Brunhes-Matuyama boundary. It is noteworthy that Hays et al. (1969) arrived at the correct correlation of their paleot~mperature curve based on carbonate percentage, with Emiliani's oxygen isotopic paleotemperature curve, and the extinction datum ofP. lacunosa merely confirms their correlation (Fig.7). In any case, whether the correct age ultimately turns out to be closer to 275,000 or to 350,000 years for equatorial latitudes, this datum is much younger than the 600,000-700,000 year estimates of Kennett and of Geitzenauer for the Pacific Antarctic. The second important datum is at the earliest occurrence ofEmiliania huxleyi. In core P6304-9 this species first appears, though sporadically, during the temperature minimum centered around 600 cm, which according to the time scale of Rona and Emiliani (1969) is about 170,000 years B.P. Geitzenauer (1969) estimated a 150,000 year age for this datum based on interpolation from the 300,000-year isochron in subAntarctic-Pacific Ocean cores. Mclntyre (1970) gives an age estimate for this same datum of 250,000-270,000 years. However, this is inconsistent with the occurrence of this species at 360 cm in core V12-122 (Mclntyre, 1970 p.188) which level, according to Ericson and Wollin (1968), has an age of 128,000 years, and according to the expanded time scale dates at 150,000 years B.P. (see Hays et al., 1969, fig. 16). In any case, the 360-cm level in V12-122 is correlated by Hays et al. (1969) with the temperature minimum occurring at 400 cm in P6304-9, which in the latter core is one full cycle younger than the earliest occurrence orE. huxleyi, and corresponds to the first abundant occurrence of the species in this core. SUMMARY AND CONCLUSION A number of species of calcareous nannofossils show marked variations in abundance in response to Pleistocene climatic variation in the Caribbean region. Two species, Ceratolithus cristatus and Umbellosphaera tenuis, are more abundant during temperature maxima. Seven species, Coccolithus pelagicus, Discoaster perplexus, Discolithina japonica, Discosphaera tubifera, Gephyrocapsa caribbeanica, Oolithotus antillarum and Umbellosphaera irregularis are distinctly more abundant during temperature minima. This greater diversity of calcareous nannofossils during Pleistocene temperature minima in the

LATE PLEISTOCENE CALCAREOUS NANNOFOSSILS

189

Caribbean suggests that most coccolithophores thrive in sub-tropical and temperate latitudes, and that relatively fewer species prefer the torrid tropical belts. The coccolith Pseudoemiliania lacunosa undergoes similar abundance variations both in the Caribbean and in the Pacific just prior to becoming extinct in the Late Pleistocene. The genus Helicopontosphaera is represented by three closely-related species in the Pleistocene, which, however, do not seem to have significantly different temperature preferences. Gephyrocapsa oceanica is represented by two distinct m o r p h o t y p e s of which one is encountered more frequently during temperature minima, the other during temperature maxima in Late Pleistocene Caribbean sediments. Two distinct nannofossil datum levels can be recognized in the Late Pleistocene: the extinction ofPseudoemiliania lacunosa and the earliest occurrence of Emiliania huxleyi. Both datums are readily correlated in low-latitude pelagic sediments in the Atlantic and Pacific Oceans, but correlation with high-latitude pelagic sediments is not so clear. The chronology of Pleistocene climatic fluctuations is the same for the Caribbean and for the equatorial Pacific, and is confirmed by correlating temperature-dependent cyclic variations recorded in the sediment, as well as by correlating biostratigraphic datum levels. ACKNOWLEDGEMENT Calcium carbonate analyses on Pacific core P6702 6 were made available by Drs. K. Bostrom and E. Bonatti. Samples ot" core V24 59 were obtained through the courtesy o f Mr. R. Capo and Dr. J. D. Hays from Lamont-Doherty Geological Observatory Dr. C. Emiliani made available unpublished data on Caribbean core P6408 10. This research was supported by National Science Foundation Grant G A - 1 2 9 4 3 . Contribution number 1540, School of Marine and Atmospheric Sciences. REFERENCES Arrhenius, G., 1952. Sediment cores from the East Pacific. Swed. Deep-Sea Exped. {1947 1948) Rep.. 5 (1): 1 89. Beard, L H., 1969. Pleistocene paleotemperature record based on planktonic formninifers. Gulf of Mexico. Trans. Gulf Coast Assoc. Geol. Soc., 19: 535-553. Berger. W. 1t. and Heath, G. R., 1968. Vertical mixing in pelagic sediments. Mar. Rcs., 26 (21: 134- 143. Boudreaux, J. E. and Hay, W. W., 1969. Calcareous nannoplankton biostratigraphy of the Late Pliocene Pleistocene Recent sediments in the SUBMAREX cores. Rev. Esp. Micropah'ontoL, 1 (3): 249 292. Bramlette, M. N. and Sullivan, F. R., 1961. Coccolithophorids and related nannoplankton of the Early Tertiary in California. Mieropaleontology, 7 (2): 129-188. Bramlette, M. N. and Wilcoxon, J. A., 1967. Middle Tertiary calcareous nannoplankton of tlle Cipero section, Trinidad, W.I. Tulane Stud. Geol., 5 (3): 93- 131. Broecker, W. S. and Ku, T. L., 1969. Caribbean cores P6304 8 and P6304-9: New analysis of absolute chronolog. Science, 166:404 406.

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Cohen, C. L. D,, 1964. Coccolithophorids from two Caribbean deep-sea cores. Micropaleontology, 10 (2): 231-250. Deflandre, G. and Fert, C., 1954. Observations sur les coccolithophorides actuels et fossiles en microscopie ordinaire et electronique. Ann. Pal~ontologie, 40: l 15-176. Emiliani, C., 1955. Pleistocene temperatures. J. Geol., 63 (6): 5 3 8 - 5 7 8 . Emiliani, C., 1958. Paleotemperature analysis of core 280 and Pleistocene correlations. J. Geol., 66 (3): 2 6 4 - 2 7 5 . Emiliani, C., 1966. Paleotemperature analysis of Caribbean cores P 6 3 0 4 - 8 and P6304 9 and a generalized temperature curve for the past 425,000 years. J. Geol., 74 (2): 109-124. Emiliani, C., 1969. A new paleontology. Micropaleontology, 15 (3): 265-300. Emiliani, C. and Rona, E., 1969. Caribbean cores P6304 8 and P6304-9: New analysis of absolute chronolog. A reply. Science, 166: 1551-1552. Ericson, D. B. and Wollin, G., 1968. Pleistocene climates and chronology in deep-sea sediments, Science, 162: 1227-1234. Ericson, D. B., Ewing, M. and Wollin, G., 1964. The Pleistocene epoch in deep-sea sediments. Science, 146: 723-732. Gartner, S., 1969. Correlation of Neogene planktonic foraminifer and calcareous nannofossil zones. Trans. Gulf Coast Assoc. Geol. Soc., 19: 5 8 5 - 5 9 9 . Gartner, S., 1971. Calcareous nannofossils from the JOIDES Blake Plateau cores, and revision of Paleogene nannofossil zonations. Tulane Stud. Geol. Paleontol., 8 (3): 101-121. Geitzenauer, K. R., 1969. The Pleistocene Calcareous Nannoplankton o f the Sub-Antarctic Pacific Ocean. Thesis Dept. Geol., Florida State University, Tallahassee, Fla., 115 pp. Halldal, P. and Markali, J., 1955. Electron microscope studies on coccolithophorids from the Norwegian Sea, the Gulf Stream and the Mediterranean. A vh. Nor. Vidensk.-Akad. Oslo, Mat. -Naturvidensk. KI., 1 : 1 - 3 0 + 27 pl. Hay, W. W., 1970. Calcareous nannofossils from cores recovered on leg 4. In: R. G. Bader et al., Initial Reports o f the Deep Sea Drilling Profect, 4: 4 5 5 - 5 0 3 . Hay, W. W., Mohler, H. P., Roth, P. H., Schmidt, R. R. and Boudreaux, J. E., 1967. Calcareous nannoplankton zonation of the Cenozoic of the Gulf Coast and Caribbean-Antillean area, and transoceanic correlation. Trans., Gulf Coast Assoc. Geol. Soc., 17: 4 2 8 - 4 8 0 . Hays, J. D., Saito, T., Opdyke, N. D. and Burckle, L. H., 1969. Pliocene- Pleistocene sediments of the Equatorial Pacific: Their paleomagnetic, biostratigraphic and climatic record. Geol. Soc. A m. Bull., 80 (8): 1481-1514. Imbrie, J. and Kipp, N. G., 1971. A new micropaleontological method for quantitative paleoclimatology: Application to a Late Pleistocene Caribbean core. In: K. K. Turekian (Editor), Late Cenozoic GlacialAges. Yale University Press, New Haven, Conn., pp. 7 1 - 1 8 1 . Kamptner, E., 1943. Zur Revision der Coccolithineen Species Pontosphaera huxleyi Lohm. Akad. Wiss. Wien, Math. - Naturwiss. Kl. A nz., 80 (l 1): 4 3 - 4 9 . Kennett., J. P., 1970. Pleistocene paleoclimates and foraminiferal biostratigraphy in sub-Antarctic deep-sea cores. Deep-SeaRes., 17: 125-140. Lidz, L., 1966. Deep-sea Pleistocene biostratigraphy. Science, 154: 1448-1452. Mclntyre, A., 1967. Coccoliths as paleoclimatic indicators of Pleistocene glaciation. Science, 158: 1314-1317. Mclntyre, A., 1970. Gephyrocapsa protohuxleyi sp.n. a possible phyletic link and index fossil for the Pleistocene. Deep-SeaRes., 17: 187-190. Mclntyre, A. and B6, A. W. H., 1967. Modern Coccolithophoridae of the Atlantic Ocean - I. Placoliths and cyrtoliths. Deep-Sea Res., 14:561 597. Mclntyre, A., B6, A. W. H. and Preikstas, R., 1967. Coccoliths and the Plio-Pleistocene boundary. Progress in Oceanography, Pergamon, New York, N.Y., 4: 3 - 2 5 . Melntyre, A., B6, A. W. H. and Roche, M. B., 1970. Modern Pacific Coccolithophorida: A paleontological thermometer. Trans. N. Y. Acad. Sci., Ser. 11, 32 (6): 720 731. Norris, R. E., 1965. Living ceils of Ceratolithus cristatus (Coccolithophorineae). Arch. Protistenkd., 108: 19-24.

I.ATE PLEISTOCENE CALCAREOUS NANNOFOSSILS Rona, E. and Emiliani, C., 1969. Absolute dating of Caribbean cores P6304 8 and P6304 9. Science, 163:66 68. Rosholt, J. N., Emiliani, C., Geiss, J., Koczy, F. F. and Wangersky, P. J., 1961. Absolute dating of deep-sea cores by Pa TM/Th23°'method.J. Geol., 69 (2): 162 185. Roth, P. H., 1970. Oligocene calcareous nannoplankton biostratigraphy. Eclogae (;eol. Helv.. 63 (3): 799 88l. Wollin, G., Ericson, D. B. and Ewing, M., 1971. Late Pleistocene climates recorded in Atlantic and Pacific deep-sea sediments. In: K. K. Turekian (Editor), Late Cenozoic Glacial Ages. Yale University Press, New Haven, Conn., pp. 199 214.

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