Absolute ages of Quaternary radiolarian datum levels in the equatorial Pacific

QUATERNARY

Absolute

RESEARCH

5, 99-l 10 (1975)

Ages of Quaternary Radiolarian Equatorial Pacific

Datum

DAVID

H. KNOLL’

A. JOHNSON’

AND ANDREW

Levels

Woods Hole Oceanographic Institution, Woods Hole, Massachusetts and Department of Geological Sciences, Harvard University Cambridge, Massachusetts 02138* Received November

in the

02543’

25,1974

Radiolarian assemblages were examined in two Quaternarye>($24-58; RCll209) from the tropical Padific Ocean. Eight radiolarian datum levels were identified in each core, and “absolute” ages were estimated for these levels by interpolation between paleomagnetic reversal boundaries previously established for the cores. The tropical radiolarian zonation for the Quaternary proposed by Nigrini (1971) appears to be most useful in terms of the reliability and ease of identification of the proposed zonal boundaries. Our estimated ages for the base of each of these zones are: Buccinosphaera invaginata Zone (Zone 1) : 210,000 yr BP; Collosphaera tuberosa Zone (Zone 2) : 370,000 yr BP; Amphirhopalum ypsilon Zone (Zone 3) : 940,000 yr BP;Anthocyrtidium angulare Zone (Zone 4) : 1,700,OOO yr BP. A comparison of our age estimates with those of Quaternary radiolarian datum levels in cores from other regions suggests that significant diachroneity on a scale of up to several hundred thousand years may exist for some (and perhaps all) of these “events.” Diachroneity is most readily studied and documented in late Neogene cores where the absolute ages of the magnetic polarity reversals are known most precisely, but may also exist (though difficult to resolve) in earlier Cenozoic sediments. The existence of such diachroneity, if demonstrated through further studies, would have significant implications for our understanding of evolutionary patterns of planktonic communities in different biogeographic regions.

INTRODUCTION The value of fossil radiolarian assemblages has been demonstrated in numerous recent investigations of Quaternary paleoclimatology and biostratigraphy. Radio&a are of particular importance in the extensive oceanic regions below the carbonate compensation depth where siliceous microfossils provide the only available means for stratigraphic correlation. With the increasing interest in developing models of oceanic and atmospheric circulation during the Quatemary (e.g., Gates, 1974), the use of siliceous microfossils will become increasingly important in order that sample materials from widespread geographic areas can be used to form the necessary data base. Paleoclimatic studies using Radiolaria (e.g., Hays, 1967; Nigrini, 1970; Keany

and Kennett, 1972; Moore, 1973; Sachs, 1973a, 1973b; Johnson and Knoll, 1974) have interpreted changing species assemblages within the Quatemary to be a reflection of climatic changes and migrating biogeographic provinces. The resulting variability in the depositional record, expressed as a systematic variation in faunal composition with depth in a single core, carries great potential for reliable regional correlation. Unfortunately, climatic fluctuations in and of themselves are insufficient for uniquely establishing biostratigraphic control. An independent stratigraphic method, such as isotopic, paleomagnetic, or paleontological techniques, is required to determine an approximate “absolute” age for a given core interval before one can attempt more precise correlations within that 99

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interval. This fact is perhaps best illustrated by analogy to a sine curve. Any given location on the curve is equivalent to all others with the same “phase,” unless the location of the point relative to some origin can also be specified. Because of the widespread occurrence of unconformities in shallow piston cores (e.g., Riedel, 1971), reliable correlation within Quaternary sediments requires the use of identifiable datum planes before precise correlations can be reliably attempted using climatic data. Biostratigraphic studies (e.g., Nigrini, 1971; Hays, 1970; Kling, 1973; Sanfilippo and Riedel, 1974, Knoll and Johnson, in press) have documented radiolarian speciation during the Quaternary, with certain datum levels existing as useful stratigraphic indicators for corSeveral previous atrelation purposes. tempts have been made to subdivide the Quaternary on the basis of these radiolarian datum levels. Zonations have been proposed for high latitudes (Hays, 1965; Hays and Opdyke, 1967) and middle latitudes (Hays, 1970; Kling, 1971, 1973), and age estimates for these zonal boundaries have been made by correlating with the known paleomagnetic time scale for the late Neogene (e.g., Hays and Berggren, 1971). Nigrini (1971) has proposed a fourfold Quaternary zonation for tropical radiolarian assemblages; however, to date there have been no correlations proposed between Nigrini’s (1971) zonation and the other biostratigraphic and paleomagnetic zonations for the Quaternary. Some workers (e.g., Dinkleman, 1973; Johnson, 1974) have had difficulty in applying Nigrini’s zonation scheme because of low abundance or poor preservation of the diagnostic taxa. This difficulty prompted us to undertake a thorough reexamination of well-preserved assemblages of tropical Quaternary Radiolaria to identify and date all potentially useful stratigraphic datum levels. We have investigated two cores from

AND

KNOLL

the equatorial Pacific in which the radiolarian assemblages are very well preserved, and for which the magnetic stratigraphy has been previously established (Hays et al., 1969). Our principal objective was to identify Nigrini’s (1971) zonal boundaries and other stratigraphically useful Late Neogene radio&an events (Sanfilippo and Riedel, 1974), and to estimate absolute ages of these events. We anticipate that many of these events may prove useful in subsequent studies for local and for regional correlation. Our results have also allowed us to make some preliminary observations concerning the presence and significance of diachroneity in Late Neogene sediments. MATERIAL STUDIED Two piston cores from the equatorial Pacific were selected for this study: V2458 (02” 16’N; 141”4O’W) and RCll-209 (03”39’N; 140”04’W). Each of these cores apparently contains a complete record of Quaternary sedimentation in the equatorial Pacific. Radiolarian assemblages throughout the cores are very well preserved (Johnson and Knoll, 1974), and the paleomagnetic stratigraphy of the cores has been determined (Hays et al., 1969). Because of the thickness of the Quaternary section in these cores and the reliable paleomagnetic age control, excellent resolution of identifiable events can be achieved. For estimating absolute ages of radiolarian datum levels, we used as reference points three magnetic reversal boundaries: the base of the Brunhes, the base of the Jaramillo, and the base of the Olduvai. The assumed ages of these boundaries (after Opdyke, 1972) and their locations within the cores studied (after Hays et al., 1969) are summarized in Table 1 and in Fig. 1. DATUM LEVELS Eight Quaternary radiolarian datum levels were identified in the cores, including those events which define the zonal

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TABLE 1 Magnetic Stratigraphy used for Estimating Ages of Radiolarian Datum Levels in Cores V24-58 and RCll-209 Locationb Event

Age (m.y.)’

V24-58

0.69 0.92 1.86

Base of Brunhes Base of Jaramillo Base of Olduvai aAfter Opdyke (1972). bAfter Hays et al. (1969).

550 720 1020

boundaries proposed by Nigrini (1971). The locations of these levels within the cores, along with our estimated ages for these levels, are presented in Table 2. Below we discuss the reliability of each datum level, from youngest to oldest: (1) Collosphaera sp. A Buccinosphaera invaginata Nigrini (1971) defined the base of the youngest Quaternary zone (Zone 1) by the first appearance of B. inuagina ta. The use of this species has heretofore been limited by the fact that the test is very fragile, and has been identified only in

EPOCH

f&E7

DEPTH 2

4

IN CORE 6

(meters1 8

10

12

(cm)

14

FIG. 1. Paleomagnetic stratigraphy of two cores (V24-58; RCll-209) which were used in this study, modified after Hays et al. (1969). Assumed ages of magnetic boundaries (after Opdyke, 1972), and exact locations of these boundaries in the two cores studied, are indicated in Table 1. Numbers in parentheses are average sedimentation rates, in mm/lo3 yr, for each of the core intervals indicated.

RCll-209

(cm)

680 920 1410

well-preserved assemblages. Recently Knoll and Johnson (in press) have identified the precursor of B. inuaginata, and have designated this form as Collosphaera sp. A. Recognition of this evolutionary event has made the Zone l/Zone 2 boundary considerably easier to identify. The age of this evolutionary transition is estimated to be 210,000 yr BP, with an uncertainty of about 20,000 yr. Both Collosphaera sp. A and B. inuaginata have been identified only in tropical assemblages, and are relatively rare taxa. (2) Last Occurrence of Axoprunum angelinum This cosmopolitan species, more commonly known as Stylatractus universus, was previously recognized to be a stratigraphically useful form in high latitude regions (Hays, 1967; Hays and Opdyke, 1967). It is fairly common and easily identified in the Neogene, and appears to decrease in abundance toward the end of the Neogene. The last appearance of this species has generally been easy to recognize, and has been dated at approximately 400,000 yr BP in the Antarctic (Hays, 1967) and in the North Pacific (Hays, 1970). In the equatorial Pacific, however, the last appearance of this form may be significantly younger. Our investigation (see Table 2), as well as the previous study by Hays et al. (1969, Table 3), identified the extinction of Axoprunum angelinum (= Stylatractus sp.) in core V24-58 at a level of approximately 250 cm. This level would correspond to an age of 320,000 yr BP, as-

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TABLE 2 Estimated Ages of Quaternary Radiolarian Datum Levels in Cores V24-58 Age Estimates are Based on Paleomagnetic Stratigraphy Summarized

and RCll-209. in Table 1

Depth (cm) Event Collosphaera sp. A + B. invaginata T Axoprunum angelinum B Collosphaera tuberosa B Collosphaem sp. A T Anthocyrtidium angulare T Lamprocyrtis neoheteroporos T. vetulum ----) T. tmchelium T Pterocanium prismatium

V24-58

RCll-209

V24-58

150-180 240-250 272-297 476-504 730-741 730-753 882-928 960-990

200-230 320-340 362-380 598-618 920-930 980-1015 1162-1200 1281-1321

0.19-0.23 0.31-0.32 0.35-0.38 0.61-0.65 0.95-0.98 0.95-1.02 1.42-1.57 1.68-1.76

Event T Axoprunum angelinum T Lamprocyrtis neoheteroporos L. neoheteroporos -+ L. haysi T Eucyrtidium matuyamai

(3) First Appearance of Collosphaera tuberosa Nigrini (1971) defined the second youngest Quaternary zone (Zone 2) by the first appearance of this species,

TABLE and Age of Radiolarian Location,

0.20-0.23 0.32-0.34 0.36-0.38 0.60-0.62 0.92-0.94 1.03-1.10 1.39-1.46 1.62-1.70

for the A. angelinum. extinction in higher latitudes. The issue of synchroneity vs diachroneity in the A. angelinum extinction can be resolved only with more precise means of core-to-core correlation, such as oxygen isotope techniques. Some preliminary investigations of Indian Ocean core material suggest to us that diachroneity in the A. angelinum extinction remains a likely possibility. In core CHAIN 100-26 (07”48’N; 56”12’E) we have identified the last appearance of A. angelinum well above the first occurrence of Buccinosphaera invaginata, in the upper third of Nigrini’s Zone 1. Consequently, it appears that diachroneity on the order of lo5 yr is required for one or both of these radiolarian events.

suming a constant sedimentation rate during the Brunhes (see Fig. 1). Since the average sedimentation rates apparently did change in both cores studied (Fig. l), we should consider the possibility that deposition rates within the Brunhes portions of the cores were also nonuniform. One interpretation of the average sedimentation rate data (see Fig. 1) would be .of an increasing rate during the Brunhes, since the average rate for the underlying Matuyama sediment was substantially lower. In this case, the age of the A. angelinum extinction would be younger than our 320,000 yr age estimate. Alternatively one could interpret the lower carbonate minima in the upper Brunhes intervals of the cores (Hays et al., 1969, Fig. 12) as indicative of decreasing sedimentation rates, in which case the age of the A. angelinum extinction in these cores would be older than 320,000 yr, and probably indistinguishable from the 400,000 yr age estimate Location

Age (m.y.) RCll-209

3 Events at DSDP Site 173

Site 173’

2-212-3 2-~~13-1 4-l/4-3 4-cc/5-1

Depth (m)

Age (m.y.)b

7-9 15-16 25-29 34-35

0.40 0.54 0.76 0.90

‘After Kling (1973, Tables 3 and 9). Numbers designate the core and section numbers between which each event occurs. bWe have used the ages given by Kling (1973) for the top and bottom of the Axoprunum angelinum Zone of 0.4 and 0.9 m.y., respectively. We then assume a constant sedimentation rate within the A. angelinum Zone to date the intermediate events.

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herein dated as approximately 370,000 yr BP f - 10,000 yr. Collosphaera tuberosa is larger, more robust, and more common than either Buccinosphaera invaginata or Collosphaera sp. A; hence, its first appearance is relatively easy to recognize. To date this species has been identified only in tropical assemblages. (4) First Appearance of Collosphaera sp. A This taxon, which Knoll and Johnson (in press) have identified as the ancestor of Buccinosphaera invaginata, entends substantially below the base of Nigrini’s (1971) Zone 2, and appears to have evolved from a smooth-shelled collosphaerid by the increasing development of outward protuberances from the test surface. The first appearance of Collosphaera sp. A is here estimated to occur at around 610,000 yr BP (Table 2). However, this event is not as easily recognized as the others discussed in this section because Collosphaera sp. A was present only in rare amounts (one to four individuals on a strewn slide) in the intervals immediately above its first appearance in the two cores examined. Further work is required to identify more precisely the ancestral form of Collosphaera sp. A and the age of the evolutionary transition, using core material containing better preserved assemblages. (5) Last Occurrence of Anthocyrtidium angulare This species is rare to common in early Pleistocene sediments in tropical latitudes. Iti last appearance, here dated as approximately 940,000 yr BP, defines the base of Nigrini’s (1971) Zone 3. This datum level is easily recognized because of the common occurrence of A. angulare below the level, and because of the apparently abrupt extinction of this species. To date this form has not been identified in middle and high latitudes.

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(6) Last Occurrence of Lamprocyrtis neoheteroporos This species was first described by Kling (1973) in sediments from DSDP Sites 173 and 175 in the North Pacific, and was believed to be part of an evolutionary lineage beginning with Lumprocyrtis he teroporos and terminating with Lamprocyrtis haysi, the extant form. Sanfilippo and Riedel (1974) subsequently identified this lineage in the tropical Indian and Pacific oceans, and Hays (1965) identified L. heteroporos in high southern latitudes, Consequently it appears that some, and perhaps all, of the species within this late Neogene Lamprocyrtis lineage are cosmopolitan in distribution. We initially sought to identify the levels in cores V24-58 and RCll-209 where evolutionary transitions occur within the Lamprocyrtis lineage. However, we found that the ancestral and descendant morphotypes commonly had long overlapping ranges, and that morphotypes of a transitional nature or of uncertain relation to the principal lineage were uncomfortably common. Consequently, we were able to reliably identify only the last appearance of the morphotype of L. neoheteroporos, which we interpret to occur at approximately 1.03 m.y. BP (Table 2). When our data are compared with those of Kling (1973) from the North Pacific, it appears that the extinction of L. neoheteroporos is significantly diachronous between low and high latitudes. Kling (1973, Fig. 1; Table 2A) indicates that at Site 173 the evolutionary transition from L. neoheteroporos to L. haysi occurs within the A. angelinum Zone, and that the last morphotype of L. neoheteroporos occurs in the upper part of this zone. We have estimated the ages of the morphotypic and evolutionary upper limits of L. neoheteroporos using Kling’s (1973) data from site 173; our estimates for the ages of these events in the North Pacific are 0.54 and 0.76 m:y.,

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respectively (see Table 3). In the tropical Pacific, however, we have identified the last morphotype of L. neoheteroporos well below the base of the Jaramillo at around 1.03 m.y. BP (Table 2). Thus, a diachroneity of several hundred thousand years in the extinction of L. neoheteroporos is suggested. Substantially more work will be required on the Late Neogene genus Lamprocyrtis before the species within this genus can be used for precise stratigraphic correlations. (7) Theocorythium vetulum+ Theocorythium trachelium Nigrini (1971) first described the species T. vet&urn in Late Pliocene and Early Pleistocene material from the tropical Pacific, and suggested that this species was the ancestor of the common Pleistocene form T. tmchelium. Although we can tentatively identify the evolutionary transition from T. vet&urn to T. trachelium in cores V24-58 and RCll-209 (Table 2), we have some doubts that this event will prove easy to identify for purposes of correlation between cores. Theocorythium trachelium has been reported to extend substantially below the Pliocene-Pleistocene boundary in both the tropical Pacific (Dinkelman, 1973) and tropical Indian Ocean (Johnson, 1974). Nigrini (1971) found that in several cores both T. vetulum and T. trachelium occur throughout Zone 4. In other cores studied, Nigrini (1971) found no specimens of T. vetulum in either the early Pleistocene or late Pliocene intervals. Consequently, it appears that the relatively low abundance of T. uetulum may inhibit the reliable identification of the evolutionary transition to its descendant form.

(8) Last Occurrence of Pterocanium prismatium This extinction has long been recognized as a useful stratigraphic indicator.

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KNOLL

It occurs near the top of the Olduvai magnetic event and is here dated as approximately 1.70 m.y. BP. Go11 (1972a) has suggested that this event is diachronous in the equatorial Pacific; verification of such diachroneity will require more extensive biostratigraphic and paleomagnetic investigations. DISCUSSION There are three principal sources of uncertainty in estimating absolute ages for the datum levels which we have discussed: (a) the reliability of the ages assigned to the paleomagnetic time scale; (b) possible effects of postdepositional reworking; (c) the validity of the assumption of constant sedimentation rates for given core intervals. The first of these factors is not likely to be a major source of error. The paleomagnetic time scale for the Late Neogene has been refined considerably during the past decade (Watkins, 1972; Opdyke, 1972), and the Quaternary portion in particular has been extensively documented in a large number of cores and terrestrial samples. Consequently, the estimated ages of the Quaternary polarity reversals are likely to be in error by no more than a few percent (C. Denham, personal communication). Postdepositional reworking can fiequently cause the blurring of biostratigraphic boundaries, particularly extinctions; one should therefore evaluate the possible influence of reworking in any material studied. We examined radiolarian and nannofossil assemblages at lo- to 30-cm intervals in both cores studied, and found no evidence for contamination of any of the assemblages by Tertiary species. Consequently we feel that reworking processes were not significant in blurring any of the datum levels which were used in this study. The assumption of constant sedimentation rates between identified polarity reversals is far more uncertain. Episodic depositional processes and erosional

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events have been well documented in deep ocean sediments; therefore, criteria are needed for evaluating the extent to which either of these processes has affected a given sedimentary unit to a degree which would yield a nonuniform average accumulation rate. In the two cores studied for this report, additional data indicate that the assumption of uniform deposition rates may indeed be justified for the intervals considered. The close similarity between the two cores in their carbonate content (Hays et al., 1969) and in their radiolarian paleoclimatic indices (Johnson and Knoll, 1974) suggests that there are no missing intervals on the order of 10’ yr or longer. The paleoclimatic data for cores V24-58 and RCll-209 also show a striking periodicity on the order of 90,000 yr during the Brunhes (Hays et al., 1969; Johnson and Knoll, 1974). This periodicity, and the close core-to-core correspondence, suggests either uniform deposition rates during the Brunhes, or rates which varied similarly in the two cores. In the upper Matuyama epoch there is good core-to-core agreement in the carbonate content (Hays et al., 1969, Fig. 12), but the periodicity of the carbonate data is less obvious than in the overlying Brunhes material. Consequently the assumption of uniform sedimentation below the Brunhes in the two cores studied is more open to question. A more precise method of identifying and quantifying nonuniform sedimentation rates during the Brunhes has been proposed by Shackleton and Opdyke (1973). They argue persuasively that isotopic changes in the ocean should occur essentially synchronously, and have proposed a chronolo,q for oxygen isotope stages 1 through 22 by assuming a constant sedimentation rate in core V28238 (Shackleton and Opdyke, 1973, Fig. 9, Table 3). If one then assumes a oneto-one relationship between the oxygen isotope stages and the Pacific carbonate variations of Hays et al. (1969), one can

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then estimate an age for Brunhes sediments within which the carbonate cycles have been identified. For example, the A. angelinum extinction in cores V2458 and RCll-209 occurs approximately at the B9/BlO carbonate transition of Hays et al. (1969). If the B9/BlO carbonate transition is equivalent to the stage ll/stage 12 transition on the oxygen isotope curve, then the age of the A. angelinum extinction in the two cores studied would be around 440,000 yr BP. This age is virtually indistinguishable from the 400,000 yr BP age estimate for the A. angelinum extinction in One would therefore higher latitudes. interpret synchroneity in the A. angehum extinction by assuming nonuniform Brunhes sedimentation rates in V24-58 and RCIl-209. Clearly the problem of synchroneity vs diachroneity in microfossil datum levels can be resolved only with the use of a precise correlation technique, such as oxygen isotopic analysis, in all material studied. Of the eight datum levels which we have discussed in this report (Fig. 2), six

+ -

T Anthocyrtidium T Lomprocyrtis

an(lulare neoheteroporos

-

Theocorythium T . trachalium

vetulum

+

T ___~ Pterocanium

prismatium

+

FIG. 2. Estimated absolute ages of Quaternary radiolarian zonal boundaries, and other identifiable radiolarian events in the two cores Uncertainties associated with dating studied. these events are discussed in the text.

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JOHNSON

appear to be sufficiently reliable and easily recognizable to be presently useful as stratigraphic indicators, and two should be regarded as tentative and requiring further work. The evolution of the form which we have designated Collosphaera sp. A needs to be documented more precisely, and further work is also required in establishing the ranges of the morphotypes of Theocorythium vetulum and T. trachelium. During this study we attempted without success to identify and use the Tholospyris taxa which Go11 (1972b) recognized as useful Late Neogene stratigraphic indicators. We were able to identify in several samples many of the extant taxa recently investigated by Renz (1973), but were unsuccessful in attempting to establish stratigraphic ranges for any of these forms. The Quatemary radio&an zonation of Nigrini (1971) appears to have utilized the most reliable and easily recognized stratigraphic indicators, and consequently we see no need to recommend any changes or further subdivisions at this time. Two principal disadvantages remain in the application of this zonation. One is that Zone 3 is defined totally on the basis of negative evidence, with a first appearance defining the top of the zone and a last occurrence defining the base of the zone. The second is that Zone 4 is nearly as long as the remaining zones combined, and consequently a further subdivision of Zone 4 would be desirable. Both of these difficulties can perhaps be overcome through a more thorough investigation of the Lamprocyrtis lineage to identify more precisely the morphotypic and evolutionary limits of the various taxa. It would be inappropriate to end this discussion without at least briefly mentioning the subject of diachroneity in biostratigraphic correlation. No microfossil “event,” be it extinction, evolutionary transition, or morphologic first occurs appearance, simultaneously

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throughout the entirety of a species’ geographic range. Thus, it would seem that radio&an biostratigraphy is built upon a shaky framework of inherently diachronous phenomena. Fortunately, most datum levels may be considered isochronous in a practical sense because the time differences involved are in many cases too small to be resolvable in the sedimentary record. In the Late Neogene, however, our greater chronological resolution demands that we consider diachroneity, its causes, and its implications. Two causes for time-transgressive biostratigraphic events seem likely. One factor is the climatic deterioration and subsequent glacial/interglacial climatic oscillations during the Late Neogene. Extinction and migration due to changing environmental conditions would be time-transgressive along the oceanic climatic gradient. Such diachroniety has been well documented in North Atlantic foraminiferal assemblages (Ruddiman and McIntyre, 1973). Also, within a given latitudinal zone, local populations might persist in some areas after members of a species had vanished in other areas This is apparently the (Blow, 1970). case with A. angelinum which can be found in equatorial Indian Ocean sediments containing I?. inuaginata, a species which did not evolve until after A. angelinum had become extinct in equatorial Pacific waters. The second causative factor involved in diachroniety is migration of adaptive mutations through oceans. The time required for a newly evolved species to migrate from its place of origin to another favorable region is dependent on both biological factors such as Darwinian fitness (Dobzhansky, 1970, p. 101) and on physical parameters, principally the motion of ocean currents. Synchroneity, or the lack thereof, can be investigated via several lines of evidence. One is a comparison of absolute age estimates based on interpolation

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from paleomagnetic data. A legitimate SPECIES LIST argument against this approach is that The following is an abbreviated syssedimentation rates during a given polartematics section, listing all radiolarian ity interval may have varied in one core species which have been used in this rerelative to another. A second, more de- port for defining datum levels. For each finitive line of reasoning is to compare species, two or three recent references the sequence of useful levels among dif- are given which contain appropriate speferent cores (Sanfilippo and Riedel, cies descriptions and illustrations, thereby 1974). Thus the fact that the extinction enabling the reader to determine the criof A. angelinum is stratigraphically be- teria which we have applied in identifylow the evolution of B. inuaginata in the ing the taxa used in this study. Pacific Ocean but above it in the Indian Ocean demands that at least one of these events be time-transgressive. Sanfilippo Anthocyrtidium angulare Nigrini (Plate 1, and Riedel (1974, Table 12, Fig. 2) have Fig. 3) illustrated graphically a number of other Anthocyrtidium angulare Nigrini, 1971, sequence differences between Late Cenop. 445, pl. 34.1, Figs. 3a, 3b; Dinkelzoic radiolarian events in Indian Ocean man, 1973, pl. 10, Fig. 5. and Pacific Ocean cores. Axoprunum angelinum (Campbell and Recognition of diachroneity in QuaterClark) (Plate 1, Fig. 5) nary microfossil datum levels has impliStylatractus uniuersus Hays, 1970, p. cations for both radiolarian biostratig215, pl. 1, Figs. 1, 2; Kling, 1971, raphy and evolutionary biology. Care p. 1086, pl. 1, Fig. 7; Dinkelman, must be exercised in the use of fauna1 1973, pl. 10, Figs. 6,7. events for precise long-range correlation Axoprunum angelinum (Campbell and in the Late Neogene. In such correlaClark); Kling, 1973, p. 634, pl. 1, tions, maximum advantage should be Figs. 13-16; pl. 6, Figs. 14-18. invagina ta Haeckel (Plate taken of paleomagnetic stratigraphy, of Buccinosphaera sequences of events, and of climatically 1, Fig. 2) Buccinosphaera invaginata Haeckel, induced variations in cores recognizable 1887, p. 99, pl. 5, Fig. 11; Nigrini, as changes in carbonate content, isotopic 1971, p. 445, pl. 34.1, Fig. 2; Dinkelcomposition, and fauna1 composition. man, 1973, pl. 10, Fig. 3; Knoll and Knowledge of the rates of migration of Johnson, in press, pl. 1, Figs. 3-6. evolutionary transitions will add substantuberosa Haeckel (Plate 1, tially to a growing understanding of Collosphaera Fig. 4) plankton evolution. Detailed stratiCollosphaera tuberosa Haeckel, 1887, graphic investigations of many well-dated p. 97; Nigrini, 1971, p. 445, pl. 34.1, Late Neogene cores, coupled with inforFig. 1; Dinkelman, 1973, pl. 10, Figs. mation on the movement of ocean cur1, 2; Knoll and Johnson, in press, rents, will provide a picture of the rate pl. 2, Figs. l-3. of migration of phenotypic adaptations through the oceans. Such studies are less Collosphaera sp. A. (Plate 1, Fig. 1) Collosphaera (?), Riedel and Sanfilippo, practical in plankton groups for which 1971, pl. lA, Fig. 1. relatively few Late Neogene extinctions Collosphaera irregularis Haeckel; Knoll and speciations have been recognized and Johnson, 1973, p. 11, pl. 1, (e.g., the planktonic Foraminifera). NevFig. 1; pl. 2, Figs. 4-7. ertheless, advances in the evolutionary Collosphaeru sp. A, Knoll and Johnson, biology of the Radiolaria will be applicain press, pl. 1, Figs. 1, 2; pl. 2, Figs. able to the larger problem of oceanic plankton evolution as a whole. 4-6.

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QUATERNARY

Lamprocyrtis

neoheteroporos

RADIOLARIANS

Kling

(Plate 1, Fig. 6)

Lamprocyrtis

neoheteroporos

Kling, 1973, p. 639, pl. 5, Figs. 17, 19; pl. 15, Figs. 4, 5; Sanfilippo and Riedel, 1974, pl. 3, Fig. 11. Pterocanium prismatium Riedel (Plate 1, Fig. 9) Pterocanium prismatium Riedel, 1957, p. 87, pl. 3, Figs. 4, 5; Riedel and Sanfilippo, 1970, p. 529; Riedel and Sanfilippo, 1971, pl. 8, Fig. 1; Nigrini, 1971, pl. 34.1, Fig. 4. Theocorythium trachelium (Ehrenberg) (Plate 1, Fig. 7) Theocory thium trachelium (Ehrenberg); Nigrini, 1967, p. 79, pl. 8, Fig. 2, pl. 9, Fig. 2; Nigrini, 1971, pl. 34.1, Fig. 5; Dinkelman, 1973, pl. 10, Fig. 9. Theocorythium uetulum Nigrini (Plate 1, Fig. 8) Theocorythium vetulum Nigrini, 1971, p. 447, pl. 34.1, Fig. 6a, 6b; Dinkelman, 1973, pl. 10, Figs. 11,12; Sanfilippo and Riedel, 1974, pl. 4, Figs. 6, 7. ACKNOWLEDGMENTS We thank Mr. Roy Capo of Lamont-Doherty Geological Observatory for enabling us to sample the cores used in this study. The Lamont core laboratory is supported under ONR Contract N00014-16-A-0108-0004 and NSF Grant GA-29460. We thank W. Riedel, C. Nigrini, J. Hays, and N. Shackleton for profitable discussions during the course of this investigation. The manuscript was critically reviewed by G. Lohmann and B. Haq. This research was supported under NSF Grant GA-36825. Knoll is currently supported under an NSF Graduate Fellowship at Harvard University. This is contribution No. 3466 of the Woods Hole Oceanographic Institution. PLATE

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REFERENCES Blow, W. H. (1970). Validity of biostratigraphic correlations based on the Globigerinacea. Micropaleontology 16, 257-268. Dinkelman, M. G. (1973). Radiolarian stratigraphy: Leg 16, Deep Sea Drilling Project. In Initial Reports of the Deep Sea Drilling Project, Vol. 16, pp. 747-813, U. S. Government Printing Office, Washington. Dobzhansky, T. (1970). Genetics of the Euolutionary Process, Columbia University Press, New York, 505 pp. Gates, W. L. (1974). Numerical simulation of ice-age climate. EOS Transactions of the American Geophysical Union 55, 259. Goll, R. M. (1972). Leg 9 synthesis radiolaria. In Initial Reports of the Deep Sea Drilling Project, Vol. 9, pp. 947-1058. U. S. Government Printing Office, Washington. Goll, R. M. (1972b). Systematics of eight Tholospyris taxa (Trissocyclidae, Radiolaria). Micropaleontology 18. 443-475. Haeckel, E. (1887). Report on the Radiolaria collected by H.M.S. Challenger during the years 1873-1876. Reports on the Voyage of “Challenger, ” Zool. Vol. 18, clxxxviii + 1803 p., 140 pls., 1 map. Hays, J. D. (1965). Radiolaria and late Tertiary and Quaternary history of Antarctic seas. In Biology of Antarctic Seas II, pp. 125-184. American Geophysical Union, Antarctic Research Series 5. Hays, J. D. (1967). Quaternary sediments of the Antarctic Ocean. In Progress in Oceanography, Vol. 4, pp. 117-131. Pergamon Press, New York. Hays, J. D. (1970). Stratigraphy and evolutionary trends of Radiolaria in North Pacific deepsea sediments. In Geological Investigations of the North Pacific (Hays, J. D., ed.), pp. 185218. Geological Society of America Memoir 126, Geological Society of America, New York. Hays, J. D. and Opdyke, N. D. (1967). Antarctic Radiolaria, magnetic reversals and climatic change. Science 158, 1001-1011. Hays, J. D., Saito, T., Opdyke, N. D., and Burckle, L. H. (1969). Pliocene-Pleistocene sediments of the equatorial Pacific: their

1. l-collosphaera sp. A, V24-58, 170 cm, sl. A, F36/4; 2-Buccinosphaera invaginata, 30 cm, sl. B, Q38/3; 3-Anthocyrtidium angulare, V24-58, 777 cm, sl. B, 03013. (a) focused on near surface of test; (b) focused on perimeter of test; 4-Collosphaem tuberosa, V2458, 159 cm, sl. A, C27/3; 5-Axoprunum angelinum, V24-58,109O cm, sl. B, C53/2; 6-Lamprocyrtis neoheteroporos, V24-58,lllO cm, sl. B, M36/2; 7-Theocorythium trachelium, RCll-209, 677 cm, sl. A, B44/3; 8-Theocorythium vetulum, RCll-209, 1333 cm, sl. A, S29/0; 9-Pterocanium prismatium, V24-58, 1050 cm, sl. B, T48/0. V24-58,

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