33. Neogene and Quaternary Calcareous Nannofossils from the Blake Ridge, Sites 994, 995, and 9971

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Paull, C.K., Matsumoto, R., Wallace, P.J., and Dillon, W.P. (Eds.), 2000 Proceedings of the Ocean Drilling Program, Scientific Results, Vol. 164

33. NEOGENE AND QUATERNARY CALCAREOUS NANNOFOSSILS FROM THE BLAKE RIDGE, SITES 994, 995, AND 9971

Hisatake Okada2

ABSTRACT

Twenty routinely used nannofossil datums in the late Neogene and Quaternary were identified at three Blake Ridge sites drilled during Leg 164. The quantitative investigation of the nannofossil assemblages in 236 samples selected from Hole 994C provide new biostratigraphic and paleoceanographic information. Although mostly overlooked previously, Umbilicosphaera aequiscutum is an abundant component of the late Neogene flora, and its last occurrence at ~2.3 Ma is a useful new biostratigraphic event. Small Gephyrocapsa evolved within the upper part of Subzone CN11a (~4.3 Ma), and after an initial acme, it temporarily disappeared for 400 k.y., between 2.9 and 2.5 Ma. Medium-sized Gephyrocapsa evolved in the latest Pliocene ~2.2 Ma), and after two short temporary disappearances, common specimens occurred continuously just above the Pliocene/Pleis- tocene boundary. The base of Subzone CN13b should be recognized as the beginning of the continuous occurrence of medium- sized (>4 µm) Gephyrocapsa. Stratigraphic variation in abundance of the very small placoliths and Florisphaera profunda alter- nated, indicating potential of the former as a proxy for the paleoproductivity. At this site, it is likely that upwelling took place during three time periods in the late Neogene (6.0–4.6 Ma, 2.3–2.1 Ma, and 2.0–1.8 Ma) and also in the early Pleistocene (1.4– 0.9 Ma). Weak upwelling is also likely to have occurred intermittently through the late Pliocene. Due to the sharp and abrupt turnover of the nannofossils, which resulted from an evolution of very competitive species, the paleoproductivity of the late Pleistocene is not clear. The site was mostly in an oligotrophic central gyre setting during the 4.6- to 2.3-Ma interval, intermittently between 2.1 and 1.4 Ma, and continuously for the last several tens of thousand years.

INTRODUCTION

3000 Ocean Drilling Program (ODP) Leg 164 drilled 16 holes at seven 34°N Charleston sites in the northwestern Atlantic off the coast of the southeastern 4000 United States. Four cores recovered from the Carolina Ridge are 5000 short (50–60 m), and the presence of unconformities and condensed Shelf 100 500 997 sections makes these cores unsuitable for paleontological study. 2000 32°N Eight long holes were drilled at three sites (Sites, 994, 995, and 995 Continental 1000 997) on the Blake Ridge to recover the upper 700–750 m of sediments (Fig. 1). Four holes were for the spot sampling to obtain gas 994 Blake hydrates, and continuous sequences were recovered only from a sin- Ridge 30°N Blake gle hole each at Sites 994 and 995, and from the combination of two Plateau adjacent holes at Site 997. In addition to the presence of unconformities and condensed sections at Sites 995 and 997, the poor recovery 5000 of pre-Quaternary sediments caused by the expansion of interstitial 28°N gas made high-resolution stratigraphic studies impossible for the 82°W80°W78°W76°W74°W72°W Pliocene to Miocene sequences at these sites. Moreover, the relatively slow sedimentation rate and large coring gaps prevent a high- Figure 1. Locality of the three ODP sites studied in this report. Contours = resolution paleoceanographic study for the Quaternary cores. Minor mbsl. reworking of Cretaceous and Paleogene nannofossils is persistent in most of the cores studied, but as Gartner and Shyu (1996) had observed at Site 905 (Chesapeake Drift) penecontemporaneous rework- tinuous sediment record and the least reworking, stratigraphic change ing is not too severe in the drift that built the Blake Ridge. Redepos- in the total flora was analyzed for the entire 700 m sequence recov- ited Ascidian spicules (Okada, 1992) are common in many intervals. ered from this hole. The record represents the floral history of the last Calcareous nannofossils biostratigraphy was studied for all the 6 m.y. cores recovered from Holes, 994C, 995A, 997A, and 997B. The old- est sediments recovered from these sites belong to the latest Miocene METHODS AND PROCEDURES Subzone CN9c of Okada and Bukry (1980). Although the sedimenta- ry history and upward decrease in sedimentation rate are similar, the Samples for the Biostratigraphic Study presence and duration of hiatuses and/or condensed sections differ significantly between the sites. Because Hole 994C has the most con- Approximately 1500 smear slides were prepared for calcareous nannofossil biostratigraphy at the three Blake Ridge sites (Sites 994, 995, and 997). The slides were examined with a Zeiss Axioplan mi- 1 Paull, C.K., Matsumoto, R., Wallace, P.J., and Dillon, W.P. (Eds.), 2000. Proc. croscope in cross-polarized light. The occurrence of biostratigraphi- ODP, Sci. Results, 164: College Station, TX (Ocean Drilling Program). 2Department of Earth and Planetary Sciences, Graduate School of Science, cally important species was examined in phase-contrast. Sampling Hokkaido University, N10W8 Sapporo, 060-0810 Japan. [email protected] intervals vary between two samples per section for the upper Quater-

331 H. OKADA nary to one sample per section for the Neogene sequence. Nannofos- sil zones employed here are those of Bukry (1973, 1975) and Okada and Bukry (1980). Supplementary nannofossil datum events summarized in Young et al. (1994) were also determined where possible. Chronology of the datum events used for this study is mostly based on Berggren et al., (1995a, 1995b). A summary of the chronological Nannofossil datums (Ma) Epochs Zones of Martini (1971) Polarity Zones of Okada and Bukry (1980) Age (Ma) Chrons data employed is illustrated in Figure 2. 0 CN15 NN21 E. huxleyi acme (0.09) E. huxleyi (0.26) Samples and Procedures for the Floral Investigation b NN20 P. lacunosa (0.46) To study the floral assemblages in Hole 994C, 236 samples were CN14 a selected representing approximately 30-k.y. time intervals. The smear 1 R. asanoi (0.83)** slides of the samples were examined under a light microscope for the 1 medium Gephyrocapsa (1.03) occurrence of all nannofossil taxa. NN19 large Gephyrocapsa (1.22-1.24) Florisphaera profunda is usually the only lower photic-zone spe- Pleistocene b large Gephyrocapsa (1.46-1.48) cies preserved in marine sediment, and it responds to environmental CN13 C. macintyrei (1.59) changes in a different manner from all other taxa that are basically medium Gephyrocapsa (1.67-1.70) a upper photic-zone dwellers (Molfino and McIntyre, 1990a, 1990b). D. brouweri (1.95) For the convenience of discussion, therefore, all taxa excluding F. 2 2 profunda will be called as upper photic-zone species. d NN18 D.triradiatus acme (2.18) Because an increase in relative abundance of one taxon automat- c NN17 D. pentaradiatus (2.46-2.56) ically results in a decline of the other taxa, relative abundance data D. surculus (2.55-2.59) b has inherent limitation for reconstructing the biosphere’s response to D. tamalis (2.78) CN12 changing environment. Selective dissolution also distorts composi- 3 tion of fossilized assemblage. To minimize the total sum problem, the NN16 a abundance change of F. profunda was expressed as its abundance ra- 2A tio against the all other coccoliths that are regarded as upper photic- zone species. Sphenolithus spp. (3.65) R. pseudoumbilica (3.75) Although the dissolution effect cannot be eliminated, the mass NN15 accumulation rate of each taxon is a better data to use to analyze the 4 Pliocene b NN14 paleo-environment. For this study, however, severe disturbance of CO D. asymmetricus (4.2) recovered cores caused by the expansion of interstitial gas prevent- CN11 Amaurolithus spp. (4.4)* ed reliable calculation of the mass accumulation rate. a NN13 For each smear slide, three separate observation were made. A. primus (4.8) 5 c 1. More than 300 randomly selected specimens of the upper photic- 3 C. rugosus (5.0) zone species were identified to species and genus or species CN10 b groups, and counted. NN12 C. acutus (5.34) a 2. The number of Florisphaera profunda specimens encountered D. quinqueramus (5.6) was recorded separately. d A. amplificus (5.9) 3. The other upper photic-zone taxa not encountered after 300 6 specimens had been counted were checked for few (1.0%– CN9 NN11 0.1%) or rare (<0.1%) occurrences. 3A Miocene c

A. amplificus (6.6) GROUPING OF SPECIES AND TAXONOMIC REMARKS First occurrence Last occurrence

Many investigation of Neogene nannofossils often ignore speci- Figure 2. Late Neogene and Quaternary calcareous nannofossil zonations mens smaller than 2.5–4.0 µm. Smaller nannofossils are sometimes and supplementary biostratigraphic events as compiled by Young et al. grouped as small placoliths. Because small placoliths often dominate (1994). The events are adopted from Berggren et al. (1995a, 1995b), except the flora in many stratigraphic intervals (e.g., the middle Pleistocene for the two events marked with asterisks. The age with single asterisk is a “small Gephyrocapsa Zone” of Gartner, 1977), they cannot be ig- new correlation of Rio et al. (1990) to the magnetostratigraphy of Cande and nored in floral assemblage studies. Kent (1995), and the age with double asterisks is adopted from Takayama Studies of living calcareous nannoplankton reveal blooms of very (1993). small (<2 µm) placoliths, Gephyrocapsa crassipons, Gephyrocapsa ericsonii, Reticulofenestra pulvula, and Reticulofenestra punctata, in upwelling regions of the tropical Pacific Ocean (Okada and Honjo, Many morphotypes or variations exist in the Gephyrocapsa lin- 1973; Okada and McIntyre, 1977). Also, a morphometric study of eage (e.g. Matsuoka and Okada, 1989, 1990), and the classification Gephyrocapsa through the Quaternary revealed the occurrence of and taxonomy of the genus Gephyrocapsa is currently in a state of very small-size clusters separable at ~2.0 µm in some time intervals confusion. Because it is not the purpose of this investigation to refine (Matsuoka and Okada, 1990). Therefore, a size of 2.0 µm was used to the classification of this genus, specimens of Gephyrocapsa are clas- separate very small and small placoliths. Because of the difficulty of sified into four size categories: very small (<2.0 µm), small (2.0–3.0 identifying the very small placoliths at species level in the light mi- µm), medium (3.0–5.0 µm), and large (>5.0 µm). As mentioned croscope, they were combined in counts. Very small nannofossils above, very small Gephyrocapsa are incorporated into the very small that are not placoliths occur only rarely and were included in the mis- placolith category. The small and large Gephyrocapsa were not sub- cellaneous category. divided, but the medium Gephyrocapsa were further divided into two

332 NEOGENE AND QUATERNARY CALCAREOUS NANNOFOSSILS categories: Gephyrocapsa caribbeanica for the medium forms with a bility that the unconformity or condensed sections observed at the very small or completely closed central opening, and Gephyrocapsa Blake Ridge sites correlate with the sequence stratigraphy in the Gulf oceanica (medium) for the forms with a relatively large central area. of Mexico. Species of genus Reticulofenestra are similar to Gephyrocapsa in coccosphere construction and size distributions throughout the late Occurrence of Datum Events and Zonal Assignment Pliocene to Quaternary. Coccoliths of the small form of the genus, Reticulofenestra minuta, and the medium form, Reticulofenestra As is common in hemipelagic settings, ceratoliths are rare in all minutura, are separated at the coccolith size of 3.0 µm (Backman, intervals, and some datum events based on the phylogeny of Cera- 1980). Because specimens of Gephyrocapsa that lost or didn’t devel- tolithaceae were difficult to identify in the upper Miocene to lower op a bridge are difficult to distinguish from specimens of Reticu- Pliocene sequence. However, the last occurrence (LO) of Amauroli- lofenestra under a light microscope, the separation of medium and thus amplificus (top of Subzone CN9c), the first occurrence (FO) of small Gephyrocapsa at 3.0 µm is a reasonable as well as practical so- Ceratolithus acutus (base of Subzone CN10b), and the FO of Cera- lution. tolithus rugosus (base of Subzone CN10c) were easy to identify. But Small specimens of Helicosphaera, including Helicosphaera the general paucity of Amaurolithus primus makes the placement of minuta, Helicosphaera pacifica, and Helicosphaera pavimentum are the CN10/CN11 boundary difficult. The LO of Amaurolithus delica- combined as small Helicosphaera. Finally, specimens of genera tus lies at 4.42 Ma. This is the youngest occurrence of Amaurolithus Acanthoica, Scyphosphaera, and Syracosphaera were not identified spp. in Hole 994C, which is concordant with the observation at Site at the species level. 905 off the New Jersey coast (Gartner and Shyu, 1996). As Young et Gartner (1967) originally described Umbilicosphaera aequis- al. (1994) reported, specimens of Amaurolithus tricorniculatus ex- cutum as Cyclicoccolithus aequiscutum from the Pliocene of Jamaica hibiting weak to moderate birefringence are fairly common in Sub- and a Pliocene core taken from the Gulf of Mexico. Cohen and Rein- zone CN11a. hardt (1968) have transferred this species to the genus Umbili- The LO of Triquetrorhabdulus rugosus and the FO of C. acutus cosphaera. Aubry (1993b) noted its consistent occurrence in the mid- are reported to correlate closely (Berggren, et al., 1985; Raffi and dle Miocene cores in the Gulf of Mexico, and by claiming invalidity Flores, 1995), but in Hole 994C, the former event lies below the latter of Cohen and Reinhardt’s transfer of this species to Umbilicosphaera (Fig. 5), a similar relationship has been observed at Site 905 (Gartner rightfully reclassified it to genus Umbilicosphaera (Aubry, 1993b). and Shyu, 1996). Zonal assignment of Subzones CN11b to CN12d The coccolith size illustrated in the original description ranges be- was straightforward. Although it is not a zonal marker, the FO of the tween 3.6 and 3.8 µm, but the specimens encountered in this investi- acme of Discoaster triradiatus (2.18 Ma) is a commonly used bio- gation range from 2.0 to 4.4 µm, with an average size of ~3.0 µm. The stratigraphic event (Berggren et al., 1995a). Because of the general relative size of the central opening varies, but most specimens found paucity of this taxon, however, this event was not detectable in Hole in this study have a much smaller central opening than the original il- 994C. Determination of the Quaternary datum events posed no prob- lustrations. The cross-polarized light image of this taxon illustrated lem, except for the base of Zone CN13 as noted below. Emiliania by Aubry (1993a) is similar to the specimens observed here, but the huxleyi is only common in the upper two sections of Core 164-994C- size of Aubry’s (1993a) specimens are larger than encountered in this 2H, but it’s abundance increased (>50%) throughout Core 164-994C- study. SEM observation of U. aequiscutum confirmed that the prox- 1H (Table 2, back-pocket foldout, this volume). Therefore, the entire imal disc is equal to or slightly larger than the distal disc, which is the Core 164-994C-1H is younger than 0.085 Ma, and a fairly large cor- key point for the classification to genus Umbilicosphaera. A review ing gap is suspected below this core. The oxygen isotope data (Oba of the taxonomy and biogeography of the species will be included in et al., Chap. 18, this volume) indicates an identical interpretation. a separate article (Okada and Hagino, pers. comm., 1998). Intermittent Occurrence of Gephyrocapsa Taxa

BIOSTRATIGRAPHY Various species or morphotypes of the genus Gephyrocapsa have been used in Quaternary biostratigraphy. The following Gephyrocap- Standard nannofossil datum events observed at the three Blake sa events are currently used: (1) the FO of medium-sized Gephyro- Ridge sites are summarized in Table 1. Practically all nannofossil capsa in the earliest Pleistocene, (2) the FO and LO of large Gephy- zones and subzones are present at the three sites studied, but because rocapsa within the early Pleistocene, and (3) the first common occur- of minor reworking, boundaries for some zones and subzones were rence of medium Gephyrocapsa after the “small Gephyrocapsa difficult to identify at Sites 995 and 997, (Fig. 3). The zonal correla- Zone” of Gartner (1977, 1988) in the early Pleistocene (Fig. 2). Thus tion at Hole 994C (Table 2, back-pocket foldout, this volume) is in while the sporadic occurrence of medium to large Gephyrocapsa agreement with the magnetostratigraphy (Hiroki, Chap. 39, this vol- within the Pleistocene is a well-known fact, this study revealed a sim- ume). ilar pattern of occurrence in the small to medium Gephyrocapsa in the Pliocene. Sedimentation Rate Samtleben (1980) reported FO of Gephyrocapsa species, his Ge- phyrocapsa sp. 1, within Zone NN15 of Martini (1971) (Subzone Age-depth plot graph of zonal boundaries shows the downward CN11b), but the FO of this taxon was observed at ~4.3 Ma, within trend of generally increasing sedimentation rate (Fig. 4). The sedimen- Subzone CN11a or Zone NN13 in the sites studied here (Table 2, tation rate in Hole 994C increases from an average of 5.9 cm/k.y. in back-pocket foldout, this volume). The small Gephyrocapsa (2.0–3.0 the Quaternary to 26.2 cm/k.y. in the Miocene. The sedimentation µm) became an abundant to common component of the middle curves indicate unconformities or condensed sections in Holes 995A, Pliocene flora followed by an abrupt decrease in abundance in the 997A, and 997B (Figs. 3, 4). The short unconformity or condensed 3.3- to 2.9-Ma interval. This taxon became absent between ~2.9 and section detected between 570 and 574 mbsf in Hole 995A, as well as 2.5 Ma (Fig. 5). The small Gephyrocapsa re-emerged in Sample 164- the reduced sedimentation rates observed at the similar depths in Holes 994C-16H-6, 77–79 cm, and occurs continuously to the top of core. 994C and 997B, correspond to a major condensed section (~5.7 Ma) Although it was included in the very small placolith category, the in the Gulf of Mexico (Gartner and Shyu, 1996). Moreover, the other very small forms of Gephyrocapsa (<2.0 µm) show an identical unconformity or condensed section at 310–340 mbsf (4.6–3.7 Ma) in stratigraphic distribution as the small Gephyrocapsa. Holes 995A and 997A roughly corresponds to a condensed interval in Because many researchers have ignored the small and very small the Gulf reported by Gartner and Shyu (1996). Thus, there is a possi- Gephyrocapsa in biostratigraphic studies, it is not clear whether the

333 H. OKADA (mbsf) Interval 6.29-7.04 13.54-14.29 34.04-34.79 45.04-45.79 46.54-47.29 55.54-56.39 64.04-64.89 72.04-72.79 80.40-80.89 108.90-110.37 121.04-123.39 154.37-155.22 304.80-306.25 326.48-327.70 331.27-337.31 331.27-337.31 414.13-423.99 494.13-495.90 545.43-560.20 581.90-583.40 . µm Hole 997A (cm) Range larger than 4.0 larger 10H-CC to 11H-1-49 41X-CC to 42X-1-30 42X-CC to 43X-1-30 42X-CC to 43X-1-30 20X-CC to 22X-1-40 2H-3, 39 to 2H-3-114 3H-1, 114 to 3H-2-39 5H-2, 114 to 5H-3-39 6H-3, 114 to 6H-4-39 6H-4, 114 to 6H-5-39 9H-2, 114 to 9H-3-49 38X-5, 30 to 38-CC 14X-3, 31 to 14X-4-29 26X-3, 30 to 26X-4-30 8H-2, -114 to 8H-3-49 13H-CC, 1 to 14H-2-114 52X-CC, 1 to 54X-1-28 10H-1, 114 to 10H-2-49 15H-2, 114 to 15H-4-49 19H-5, 114 to 19H-6-49 Gephyrocapsa (mbsf) Interval 9.90-10.96 79.47-80.09 84.28-85.78 89.67-91.21 19.00-20.00 40.00-41.00 47.00-48.00 61.28-62.78 106.88-107.84 128.28-129.75 135.78-135.78 155.66-155.78 295.28-296.19 310.22-319.? 319.70-322.60 322.60-329.60 456.09-457.09 569.91-570.08 573.86-580.68 629.62-637.48 Hole 995A (cm) Range inuous occurrence of themedium akayama (1993); ** = Rio et al. (1990). FO = first occurrence, LO = last occurrence, RE = re- (1993);akayama RE = last occurrence, LO occurrence, et al. ** = Rio (1990). FO = first T 2H-6-70 to 2H-CC-41 3H-6-20 to 3H-6-120 6H-1-30 to 6H-1-130 13H-7-8 to 13H-CC-15 16H-2-8 to 16H-4-5 16H-8-8 to 17H-1-8 35X-4-8 to 35X-CC-19 56X-2-9 to 56X-2-109 6H-5-130 to 6H-6-80 8H-2-108 to 8H-3-108 38X-1-22 to 38X-6? 39X-1-10 to 39X-CC-57 11H-4-108 to 11H-5-108 12H-2-104 to 12H-3-108 19H-7-108 to 20H-1-8 10H-CC-36 to 11H-2-69 39X-CC-57 to 40X-1-30 68X-CC-27 to 69X-1-8 69X-CC-22 to 71X-1-8 76X-CC-30 to 77X-1-18 (mbsf) Interval 8.05-9.05 19.04-20.04 33.04-34.04 49.04-50.04 63.14-63.64 81.40-81.84 86.34-87.84 91.54-93.05 105.34-106.84 137.17-138.67 146.39-147.89 164.80-165.57 261.67-263.36 280.42-289.80 330.30-338.67 347.06-349.87 428.61-435.87 541.88-546.21 579.27-580.77 603.63-608.16 Hole 994C (cm) Range 2H-3, 65 to 2H-4, 15 3H-4, 64 to 3H-5, 14 5H-1, 14 to 5H-1, 114 6H-5, 94 to 6H-6, 44 8H-2, 24 to 8H-2, 74 11H-4, 44 to 11H-5, 44 12H-1, 64 to 12H-2, 65 13H-4, 44 to 13H-5, 44 16H-6, 77 to 16H-7, 77 17H-6, 50 to 17H-7, 50 32X-1, 77 to 32X-CC, 30 67X-1, 78 to 67X-4, 76 72X-1, 77 to 72X-2, 77 34X-CC, 0 to 35X-1, 0 10H-CC, 40 to 11H-1, 44 20X-CC, 20 to 21X-1, 77 40X-CC, 20 to 41X-1, 77 41X-CC, 22 to 42X-2, 77 52X-CC, 27 to 54X-1, 77 74X-CC, 17 to 75X-1, 76 0.26 0.46 0.83* 1.03 1.59 1.95 2.78 3.65 3.75 4.2 4.4** 5.0 5.34 5.6 5.9 Age (Ma) Table 1. Biostratigraphicevents datum observedthree at the Blake RidgeTable Sites 994,995, and 997. 1.22-1.24 1.46-1.48 1.67-1.70 2.46-2.56 2.55-2.59 = as noted in the text, this event is now identified as the FO of theasFOof common identifiedand the cont now is thistext, = event noted as in the † Zonal boundary CN15/CN14b CN9d/CN9c CN10c/CN10b CN14b/CN14a CN14a/CN13b CN13b/CN13a CN13a/CN12d CN12d/CN12c CN12c/CN12b CN12b/CN12a CN12a/CN11b CN11b/CN11a CN10b/CN10a CN10a/CN9d † spp. spp.

Gephyrocapsa Gephyrocapsa event Gephyrocapsa Gephyrocapsa Nannofossil D. asymmetricus P. lacunosa P. R. asaoi macintyrei C. brouweri D. pentaradiatus D. surculus D. tamalisD. Sphenolithus R. pseudoumibilica Amaurolithus quinqueramus D. A. amplificus E. huxleyi C. rugosus C. acutus FO FO LO LO RE medium large LO large FO LO FO medium LO LO LO LO LO LO FCO LO FO FO LO LO entrance, FCO = first common occurrence. occurrence. common first = FCO entrance, Notes: The estimated ages are adopted from Berggren et al. (1995a, 1995b) except for the two events marked with marked asterisks; * = estimatedNotes: adopted The are (1995a, from et al. ages Berggren for the two events 1995b) except

334 NEOGENE AND QUATERNARY CALCAREOUS NANNOFOSSILS

Hole 994C Hole 995A Holes 997A & 997B A g e A g e Nanno- fossil Zone A g e Nanno- fossil Zone Nanno- fossil Zone Core Core Core Recovery Recovery 0 0 0 Recovery CN15 CN15 CN15 2H 2H 2H CN14b CN14b CN14b 3H 3H 3H late late 4H late 4H 4H CN14a CN14a 5H CN14a 5H 5H 6H 6H 50 6H 50 50

7H 7H 8H Pleistocene

CN13b early 8H 8H CN13b CN13b 9H 10H 10H Pleistocene 10H CN13a early Pleistocene 11H early 11H 11H 12H 12H 12H CN12d 100 CN13a 100 CN13a 100 13H 13H 13H 14H 14H 14H CN12d CN12c 15H CN12d 15H 15H 16H 16H CN12c 16H 17H CN12b 17H CN12c CN12b 17H 150 150 150 19H 19H 19H CN12b 20X 20H 20H 21X 21X 21X 22X 22X 22X

23X 23X 23X late 24X 24X 24X 200 late 200 200

25X 25X late 26X 26X CN12a 26X 27X 28X 28X 28X CN12a 29X 29X 30X CN12a 30X 30X 31X 250 250 250 31X 31X 32X 32X 32X 34X 33X 33X 35X Pliocene 34X 34X 36X Pliocene 35X 35X 37X 300 300 300 37X 38X CN11b 37X 38X 38X 39X CN11b Pliocene 39X 39X 41X 40X 40X 42X CN11b 41X 41X 43X 350 42X 350 350 44X CN11a Depth (mbsf) 42X CN11a 43X CN11a 43X 45X 44X 44X 46X 46X 46X 47X

47X early 48X 47X CN10c early 400 49X 400 49X 400 50X 50X 50X 52X 51X CN10c 51X 4X 52X 5X 53X CN10c 54X 54X early 7X 450 55X 450 55X 450 8X 56X 56X 9X CN10b 57X 57X 11X 58X 58X 12X 59X CN10b 59X 13X 61X 14X 500 500 61X 500 62X 62X 16X 63X 63X CN10b 17X 64X 64X 18X CN10a 65X 65X 19X 67X 66X 20X 550 550 550 68X 67X 22X 69X CN10a 68X 23X CN9d 71X 69X CN10a 24X 72X 71X 26X 73X CN9d 72X 27X 600 600 600 74X 73X CN9d 28X 75X late 74X 29X late 76X Miocene 75X 30X

77X 31X Miocene

76X late 78X 77X 33X Miocene 650 79X 650 650 34X CN9c 78X 35X 80X 79X CN9c 81X 80X CN9c 37X 82X 81X 38X 83X 82X 39X 700 84X 700 83X 700 41X 42X 43X 45X 46X 47X 750

Figure 3. Comparison of calcareous nannofossil zonal assignments at Blake Ridge Sites 994, 995, and 997. Black zones in the recovery column show the stratigraphic intervals where cores were recovered.

335 H. OKADA

Age (Ma) 0 1 2345 6 7

Quaternary Pliocene Miocene late early late early late 0 and Bukry (1980) Epochs Martini (1971) Age (Ma) Chrons Zones of Okada Polarity 0 0 21 15 b 20 100 a CN14

1 E. huxleyi 1 1 Pleistocene Pleistocene 200 NN19 b CN13 Gepyrocapsa a capsa

2 small 2 300 2 d NN18 R. asanoi Gephyro H. sellii

997A c b large

Depth (mbsf) 400 (medium) 3 CN12 3 994C 997B a NN16 995A 2A G. caribbeanica

500 997A + 997B G. oceanica Pliocene Pliocene 4 b 4 14-15 CN11

600 a NN13 c 5 3 5

700 b CN10 NN12 a D.triradiatus D. asymmetricus C. macintyrei P. lacunosa S. abies D. tamalis

R. pseudoumbilica D. brouweri D. pentaradiatus D. surculus Umbilicosphaera aequiscutum A. amplificus d C. rugosus Figure 4. Age-depth relationships of biostratigraphic markers of calcareous 6 C. acutus 6 nannofossils at Sites 994, 995, and 997. Two horizontal bars at the bottom of c Miocene 3A Miocene CN9 the figure (6.6–5.9 Ma) indicate the range of Amaurolithus amplificus. NN11 b T. rugosus D. quinqueramus A. delicatus A. primus A. tricorniculatus 7 7 temporary disappearance in the upper Pliocene in Hole 994C is a glo- Figure 5. Range chart of important species for the late Neogene to Quater- bal event. Because age-diagnostic discoasters are often absent in nary biostratigraphy. The arrows indicate biostratigraphic events used for the hemipelagic sequences, the disappearance and reappearance of com- zonation of Okada and Bukry (1980), and the areas with a horizontal short mon to abundant small Gephyrocapsa in the upper Pliocene provide bar indicate the supplementary events used for the age calibration. The solid a useful biostratigraphic marker. lines indicate consistent occurrences, and the dashed lines indicate sporadic The FO of Gephyrocapsa caribbeanica was originally used to de- occurrences. fine the base of Subzone CN13b (Bukry, 1973; Okada and Bukry, 1980). Because of the taxonomic confusion of Gephyrocapsa spe- A New Biostratigraphic Event cies, however, this boundary event has recently been revised as the FO of medium Gephyrocapsa (Berggren et al., 1995a). In Hole 994C, Umbilicosphaera aequiscutum is a major component of the nan- early specimens of G. caribbeanica occurs with Gephyrocapsa oce- noflora in the upper Miocene and Pliocene in all the Blake Ridge sites anica (medium; Table 2, back-pocket foldout, this volume). Actual- studied, and this taxon is particularly abundant in the upper Pliocene ly, these two taxa co-occur discontinuously in the uppermost (Fig. 6). This species also occurs commonly in the lower upper Mio- Pliocene (Fig. 5). Most of the medium Gephyrocapsa observed in the cene (Zones CN 7 and CN8) of Carolina Ridge Sites 992 and 993. Be- upper Pliocene range from ~3.0 to 4.0 µm in coccolith size, but very cause its occurrence is so prevalent, the fact that this taxon has not rare specimens, slightly larger than 4.0 µm, were also observed. been recorded in previous studies of ODP cores is surprising. The Above the two temporal disappearances in the upper Pliocene, G. species was first described from the Pliocene of Jamaica (Gartner, caribbeanica and G. oceanica (medium) occur continuously in the 1967), and Aubry (1993b) reported its early occurrence in the lower lower Pleistocene upward from Sample 164-994C-12H-1, 64–66 cm middle Miocene Zone CN4 (NN5) in the Gulf of Mexico. This spe- (Table 2, back-pocket foldout, this volume; Fig. 6), and specimens of cies appears to have been ignored in the previous studies because of G. oceanica larger than 4.0 µm are common. The base of Subzone its small size. However, because U. aequiscutum is so abundant and CN13b, therefore, should be defined by the base of the continuous easily recognizable under a cross-polarized microscope, it should not occurrence of the larger medium-sized Gephyrocapsa (larger than be overlooked in future calcareous nannofossil studies. Moreover, 4.0 µm). the sharp decline in the abundance of the taxon in the middle part of Thus, the sporadic occurrence is a common feature for all sizes of the uppermost Pliocene Subzone CN12d is obviously its LO, and rare Gephyrocapsa, and the “small Gephyrocapsa Zone” of Gartner to few specimens found above Sample 164-994C-15H-5, 45–47 cm, (1977) represents just one example of the temporary disappearances are likely to be reworked. Because Subzone CN12d has a long dura- of medium to large Gephyrocapsa (Fig. 5). As Matsuoka and Okada tion (~0.5 m.y.) and the only biostratigraphic event in this subzone, (1989, 1990) demonstrated, the younger forms emerging after the the base of the acme of Discoaster triradiatus (2.18 Ma) is hard to de- temporal disappearances are likely to be new morphotypes that tect in hemipelagic sediments; the LO of U. aequiscutum at ~2.3 Ma evolved from the base stock of small forms. is a useful biostratigraphic event.

336 NEOGENE AND QUATERNARY CALCAREOUS NANNOFOSSILS

MAJOR ALTERATION OF THE FLORA ia huxleyi. Some of these new taxa possibly were opportunists that could successively compete with the very small placoliths in a condition of moderately strong upwelling. Small and very small placoliths dominate the upper photic-zone The abrupt dominance of Gephyrocapsa caribbeanica and Ge- flora in most intervals (Fig. 6). Following the gradual decrease in the phyrocapsa oceanica (medium) at ~0.55–0.25 Ma is well document- abundance of medium to large specimens of Reticulofenestra and ed in the other oceans, including the central Pacific (Erba, 1995), Sphenolithus, which is possibly due to a global cooling, Reticu- Philippine Sea (Matsuoka and Okada, 1989), and the eastern Indian lofenestra minuta and small specimens of Gephyrocapsa dominated Ocean (Okada and Wells, 1997). Therefore, the nannofossil indica- the flora. Their dominance was temporarily reduced in the early late tors of upwelling, an increased abundance of the very small pla- and middle late Pliocene because of the increased abundance of me- coliths, will not be detected in upper Pleistocene sequence unless the dium placoliths such as Pseudoemiliania lacunosa, Reticulofenestra studied core came from particular hemipelagic settings, where a fluc- minutula, and Umbilicosphaera aequiscutum. From the uppermost tuation in upwelling strength or the influence of coastal waters has Pliocene upward, the small and very small placoliths dominate the occurred. In such areas the very small placoliths may be able to com- flora except in two short intervals in the upper Pleistocene, where the pete with the newcomers for the ecological superiority. flora is mostly composed of medium Gephyrocapsa and Emiliania Emiliania huxleyi evolved only at 0.26 Ma (Berggren et al., 1995b) huxleyi (Fig. 6). and has been the most dominant component of the flora in a large part During the late Pleistocene, rapid evolution and abrupt alteration of the world oceans for the last 85 to 73 k.y. (Thierstein et al., 1977). of the flora occurred. The taxa that dominate this interval include The fact that E. huxleyi produces big spring blooms in nutrient-rich, small and medium forms of Gephyrocapsa and Emiliania such as, high-latitude waters is proof of its high potential as an opportunist. In Gephyrocapsa protohuxleyi, Gephyrocapsa muellerae, and Emilian- Hole 994C, E. huxleyi dominated the upper photic-zone flora in Core

60 very small placoliths ( < 2.0 µm ) 40

80 small placoliths ( 2.0 - 3.0 µm )

20 R. minuta smallGephyrocapsa 0

40 Emiliania huxleyi

20 P lacunosa 0 80

60 G caribbeanica

40 G. oceanica (medium) Umbilicosphaera aequiscutum

20 Percentage Abundance

0 large Reticulofenestra (R.gelida + R. pseudoumbilica) large Gephyrocapsa 20

60 R. perplexa

40 R. producta

R. minutura 20

0 Discoaster spp. 10 Syracosphera spp. Sphenolithus spp.

0 15 CN14 CN13 CN12 CN11 CN10 CN9 Figure 6. Stratigraphic variations in percentage abun- b aab dcb a b a cab d c dance of the major components of the flora observed in Pleistocene Pliocene Miocene Hole 994C. Abundances are percentage abundance of

0 1 2 3 4 56 Ma each entity within the upper-photic flora.

337 H. OKADA

1H, where the abundance of F. profunda is also high (Table 2, back- posite directions when the nutrient profile changes in the euphotic pocket foldout, this volume; Figs. 6, 7). This observation illustrates E. zone. huxleyi’s ecological success even in normally mesotrophic to olig- Actually, in Hole 994C, the abundance of F. profunda expressed otrophic stratified waters. Perhaps temporal eutrophication is respon- as the ratio against the total upper-photic taxa (Fig. 7B) and the abun- sible for the co-abundance of F. profunda and E. huxleyi. dance of very small placoliths within the upper photic-zone flora (Fig. 7C) show generally reversed stratigraphic trends except in the upper Pleistocene. The stratigraphic trend for the small placoliths, PALEOCEANOGRAPHY INFERRED meanwhile, shows no clear relationship with that of the F. profunda FROM NANNOFLORA ratio (Fig. 7). These observations demonstrated that an increased Nannofossil Taxa Indicating Environmental Change abundance of the very small placoliths can be interpreted as an indi- cation of increased nutrient supply into the upper-photic water. Be- Pujos (1992) suggested four genera and species as the most useful cause the location of Site 994 is at the periphery of the subtropical nannofossils for interpretation of Pliocene-Pleistocene paleoecology: central gyre, such a condition could have occurred when the Gulf Coccolithus pelagicus, Helicosphaera spp., Rhabdosphaera spp., Stream shifted its course eastward and brought an increased influence and Syracosphaera spp. Because they constitute only a small portion of the gyre margin water, or possibly of the Gulf Stream itself, to the of the upper photic-zone flora, stratigraphic variations within them site. are not easily identified (Table 2, back-pocket foldout, this volume). To re-examine their usefulness for paleoceanography, the other dom- Environmental Change Inferred inant components of the flora should be excluded from counting, but from Nannofossil Assemblage such a study is not within the scope of this investigation. Instead, this study examines the usefulness of more abundant components of the Quantitative study of nannofossils in Pacific surface sediments flora for paleoceanographic interpretations. show that the modern central gyre flora is characterized by F. profun- Modern, very small placoliths thrive in tropical upwelling settings da abundance higher than 50% of the total flora (Tanaka, 1991), (Okada and Honjo, 1973), and they are very abundant components of equivalent to F. profunda ratio of 1.0. A preliminary study at Deep hemipelagic Quaternary nannoflora (e.g., Biekart, 1989; Okada and Sea Drilling Project (DSDP) Site 445 (Philippine Sea) indicated that Wells, 1997). On the other hand, Molfino and McIntyre (1990a, an F. profunda ratio of >1.0 has prevailed since ~2.5 Ma (Okada, 1990b) demonstrated that the abundance of Florisphaera profunda, a 1983). In Hole 994C, the F. profunda ratio remains below 1.0 for the lower photic-zone dweller, declined when the nutricline rose as a re- entire period, and mostly lies between 0.8 and 0.2 (percentage abun- sult of intensified trade winds. A recent study confirmed the useful- dance of 45% and 17%, respectively; Fig. 7). These data indicate that ness of F. profunda abundance as an indicator of primary production the waters overlying Site 994 have fluctuated between oligotrophic (Beaufort et al., 1997). These data suggest a new hypothesis: the rel- gyre waters whose stratification is strong and mesotrophic gyre mar- ative abundance of very small placoliths and F. profunda move in op- gin waters in which moderate upwelling occurs. The change in the F.

S-W Function Ratio Percentage Abundance

1.0 0.6 0.2 0 Chrons Epochs Polarity Age (Ma) Nannofossil Zones gyre margin 1.2 1.6 2.0 2.4 20 40 0 2040 60 80 gyre water 0 0 15 b ?? a

1 CN14 1 1 Pleistocene b CN13 a 2 2 2 d c b

3 CN12 3

2A a Pliocene m ) m ) b µ 4 µ 4 Figure 7. Stratigraphic trend observed in Hole 994C in the (1) diversity of upper-photic nannoflora expressed CN11 a in Shannon-Wiener (S-W) Function (DH), (2) relative

c abundance of F. profunda expressed as a ratio against 5 3 5

b the total upper-photic taxa, (3) percentage abundance / upper-photic taxa

CN10 of the very small placoliths, and (4) percentage abun- a dance of the small placoliths. To make comparison eas- d

6 small placoliths ( 2.0 - 3.0 6 ier, the F. profunda ratio is plotted in a reversed F. profunda very small placoliths ( < 2.0

c manner. The vertical bars at the right side of the figure Miocene 3A CN9 indicate the time intervals when the site was mostly occupied by the gyre margin water or by the gyre water. b (a) (b) (c) (d) 7 7

338 NEOGENE AND QUATERNARY CALCAREOUS NANNOFOSSILS profunda ratio indicates that the site was mostly under the central 2. Unconformities or condensed sections exist at Sites 995 and gyre influence between 4.6 and 2.3 Ma, intermittently during 2.1 and 997. There is a possibility that sedimentation at the Blake 1.3 Ma, and continuously for the last several tens of thousand years. Ridge has some relationship with the sequence stratigraphy Very small placoliths shows four distinctive intervals of increased observed in the Gulf of Mexico. abundance at, 6.0–4.6 Ma, 2.3–2.1 Ma, 2.0–1.8 Ma, and 1.4–0.9 Ma. 3. Umbilicosphaera aequiscutum, a species that has scarcely Moderately strong upwelling is suspected for these time periods (Fig. been described in previous studies, is an abundant component 7). The small fluctuations observable in the lower upper and middle of the late Pliocene nannoflora, and its LO at ~2.3 Ma (middle upper Pleistocene may indicate intermittent weak upwelling. The part of Subzone CN12d) is a useful datum event for the Neo- short time interval at around 1.15 Ma when the abundance peaked at gene biostratigraphy. 55% may be a time of particularly strong upwelling (Table 2, back- 4. Small Gephyrocapsa first occurred at ~4.3 Ma (within the up- pocket foldout, this volume). This short interval coincides with the per part of Subzone CN 11a and Zone NN13), slightly older temporary disappearance of medium-sized Gephyrocapsa that oc- than had been previously reported. Its abrupt decline (3.3–2.9 curred as a result of phylogenetic evolution (Matsuoka and Okada, Ma) and its temporal disappearance (2.9–2.5 Ma) can be a use- 1990). The high abundance of the very small placoliths, therefore, ful datum in hemipelagic sequences in which key discoasters may partly be the result of the phylogenetic evolution of Gephyro- are often rare. capsa. 5. Medium-size Gephyrocapsa (coccolith size of 3.0–5.0 µm) occurred intermittently in the uppermost Pliocene sequence, but Comparison of the Nannofossil Data with Other Faunal/ occurs continuously above the base of Pleistocene. The com- Floral Data for the Paleoceanographic Interpretation monly used biostratigraphic event defining the base of Sub- zone CN13b, the FO of medium Gephyrocapsa, therefore Nannofossil data indicate an almost continuous upwelling in the should be considered as the beginning of the common and con- latest Miocene to earliest Pliocene interval (6.0–4.6 Ma; Fig. 7). This tinuous occurrence of medium-sized Gephyrocapsa with coc- coincides with the high productivity interval suggested by diatom flo- colith size larger than 4.0 µm. ra at Site 997 (Ikeda et al., Chap. 35, this volume). The early Pleis- 6. The Florisphaera profunda abundance has previously been tocene interval (1.4–0.9 Ma), in which a fairly strong upwelling is used as a proxy for the water-column stability in studies of suggested by the abundance of very small placoliths, also agrees with Quaternary paleoceanography. This abundance can also be abundance of diatom. utilized for the late Neogene paleoceanography. At Site 994, a The climatic interpretation inferred from the study of the Quater- higher abundance of this taxon indicates increased influence nary and latest Pliocene planktonic foraminifers in Hole 997A (Nishi, of oligotrophic central gyre waters. et al., Chap. 34, this volume) also supports the paleoceanographic in- 7. The abundance of very small placoliths (<2.0 µm) shows a terpretation of the nannofossil assemblage data. The foraminifer data generally reversed stratigraphic trend with that of F. profunda, indicate an oscillation of cool and warm periods of short durations for indicating its usefulness as an indicator of the paleoproductiv- the latest Pliocene (2.2–1.7 Ma), and a stable, cool period for the 1.2- ity. The small placoliths (2.0–3.0 µm), however, do not show to 0.95-Ma time interval when the very small placoliths registered a clear relationship with the two nannofossil indicators of en- sharp abundance increases (Fig. 7). The cool foraminifer assemblage vironmental change. resulted from increased upwelling associated with the gyre margin 8. The Blake Ridge was under gyre water during most of the waters. Pliocene (4.6–2.4 Ma), intermittently during 2.1–1.4 Ma, and continuously for the last several tens of thousand years. On the Species Diversity and Environmental Change other hand, upwelling associated with gyre margin waters was moderately strong during four time intervals: 6.0–4.6 Ma, 2.3– The stratigraphic trend in species diversity expressed as the Shan- 2.1 Ma, 2.0–1.8 Ma, and 1.4–0.9 Ma. Also, diminished upwelling may have taken place repeatedly during the late non-Wiener Function (DH) shows no meaningful relationship with that of the F. profunda ratio (Fig. 7). Therefore, this function is not a Pliocene. useful paleoceanographic proxy in the Blake Ridge area. This result 9. The paleoceanographic interpretations based upon the strati- suggests, however, that the abundance of F. profunda has no signifi- graphic variations of F. profunda and very small placoliths are cant relationship with the assemblage diversity of the upper photic- in agreement with the diatom and foraminifer data from Site zone nannoplankton. The generally reversed trend observable be- 997. tween the function and the relative abundance of very small to small placoliths can be easily explained by the fact that: (1) the function is strongly controlled by the relative abundance of dominant taxa, and ACKNOWLEDGMENTS (2) the upper photic-zone flora is dominated in most intervals by the very small and small placoliths. I would like to thank R. Matsumoto, C. Paull, and the Ocean Drill- ing Program for inviting me to participate on Leg 164. H.R. Thier- stein and T.J. Bralower critically reviewed the manuscript. I am truly SUMMARY grateful for their constructive suggestions. My special thanks is also given to K. Hagino, Hokkaido University, for helping me in the SEM Biostratigraphic and floral analysis of nannofossils in the four observation. cores recovered at the Blake Ridge Sites 994, 995, and 997 revealed new information on biostratigraphy and paleoceanographic interpre- REFERENCES tation. 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Backman, J., 1980. Miocene-Pliocene nannofossils and sedimentation rates Okada, H., and Bukry, D., 1980. Supplementary modification and introduc- in the Hatton-Rockall Basin, NE Atlantic Ocean. Stockholm Contrib. tion of code numbers to the low-latitude coccolith biostratigraphic zona- Geol., 36:1–91. tion (Bukry, 1973; 1975). Mar. Micropaleontol., 5:321–325. Beaufort, L., Lancelot, Y., Camberlin, P., Cayre, O., Vincent, E., Bassinot, F., Okada, H., and Honjo, S., 1973. The distribution of oceanic coccolitho- and Labeyrie, L., 1997. Insolation cycles as a major control of Equatorial phorids in the Pacific. Deep-Sea Res. Part A, 20:355–374. Indian Ocean primary production. Science, 278:1451–1454. Okada, H., and McIntyre, A., 1977. Modern coccolithophores of the Pacific Berggren, W.A., Hilgen, F.J., Langereis, C.G., Kent, D.V., Obradovich, J.D., and North Atlantic Oceans. Micropaleontology, 23:1–55. Raffi, I., Raymo, M.E., and Shackleton, N.J., 1995a. 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A summary chart of Neogene 3–20. nannofossil magnetobiostratigraphy. J. Nannoplankton Res., 16:21–27. Gartner, S., 1967. Calcareous nannofossils from Neogene of Trinidad, Jamaica, and Gulf of Mexico. Univ. Kansas Paleontol. Contrib., 29:1–7. ————, 1977. Calcareous nannofossil biostratigraphy and revised zona- Date of initial receipt: 15 April 1998 tion of the Pleistocene. Mar. Micropaleontol., 2:1–25. ————, 1988. Paleoceanography of the Mid-Pleistocene. Mar. Micropale- Date of acceptance: 10 March 1999 ontol., 13:23–46. Ms 164SR-232 Gartner, S., and Shyu, J.-P., 1996. Aspects of calcareous nannofossil biostratigraphy and abundance in the Pliocene and late Miocene of Site 905. APPENDIX In Mountain, G.S., Miller, K.G., Blum, P., Poag, C.W., and Twichell, D.C. (Eds.), Proc. ODP, Sci. Results, 150: College Station, TX (Ocean List of Species Considered in This Report Drilling Program), 53–63. Martini, E., 1971. Standard Tertiary and Quaternary calcareous nannoplank- Amaurolithus amplificus (Bukry and Percival, 1971) Gartner and Bukry, 1975 ton zonation. In Farinacci, A. (Ed.), Proc. 2nd Int. Conf. Planktonic Amaurolithus delicatus Gartner and Bukry, 1975 Amaurolithus primus (Bukry and Percival, 1971) Gartner and Bukry, 1975 Microfossils Roma: Rome (Ed. Tecnosci.), 2:739–785. Amaurolithus tricorniculatus (Gartner, 1967) Gartner and Bukry, 1975 Matsuoka, H., and Okada, H., 1989. Quantitative analysis of Quaternary nan- Braarudosphaera bigelowii (Gran and Braarud, 1935) Deflandre, 1947 noplankton in the subtropical northwestern Pacific Ocean. Mar. Micropa- Calcidiscus leptoporus (Murray and Blackman, 1898) Loeblich and Tappan, leontol., 14:97–118. 1978 ————, 1990. Time-progressive morphometric changes of the genus Calcidiscus macintyrei (Bukry and Bramlette, 1969) Loeblich and Tappan, Gephyrocapsa in the Quaternary sequence of the tropical Indian Ocean, 1978 Site 709. In Duncan, R.A., Backman, J., Peterson, L.C., et al., Proc. ODP, Calciosolenia murrayi Gran in Murray and Hjort, 1912 Sci. Results, 115: College Station, TX (Ocean Drilling Program), 255– Ceratolithus acutus Gartner and Bukry, 1974 Ceratolithus armatus Müller, 1974 270. Ceratolithus atlanticus Perch-Nielsen, 1977 Molfino, B., and McIntyre, A., 1990a. Nutricline variations in the equatorial Ceratolithus cristatus Kamptner, 1950 Atlantic coincident with the Younger Dryas. Paleoceanography, 5:997– Ceratolithus rugosus Bukry and Bramlette, 1968 1008. Ceratolithus separatus Bukry, 1979 Molfino, B., and McIntyre, A., 1990b. Precessional forcing of nutricline Coccolithus pelagicus (Wallich, 1877) Schiller, 1930 dynamics in the Equatorial Atlantic. Science, 249:766–769. Discoaster asymmetricus Gartner, 1969 Okada, H., 1983. Modern nannofossil assemblages in sediments of coastal Discoaster berggrenii Bukry, 1971 and marginal seas along the western Pacific Ocean. In Meulenkamp, J.E. Discoaster blackstockae Bukry, 1973 Discoaster brouweri Tan (1927) emend. Bramlette and Riedel, 1954 Reconstruction of Marine Paleoenvironments. (Ed.), Utrecht Micropale- Discoaster intercalaris Bukry, 1971 ontol. Bull., 30:171–1187. Discoaster pentaradiatus Tan (1927) emend. Bramlette and Riedel, 1954 ————, 1992. Biogeographic control of modern nannofossil assemblages Discoaster quinqueramus Gartner, 1969 in surface sediments of Ise Bay, Mikawa Bay and Kumano-nada, off Discoaster surculus Martini and Bramlette, 1963 coast of Central Japan. Mem. Sci. Geol., 43:431–449. Discoaster tamalis Kamptner, 1967

340 NEOGENE AND QUATERNARY CALCAREOUS NANNOFOSSILS

Discoaster triradiatus Tan, 1927 Reticulofenestra asanoi Sato and Takayama, 1992 Discoaster variabilis Martini and Bramlette, 1963 Reticulofenestra gelida (Geitzenauer, 1972) Backman, 1978 Discosphaera tubifera (Murray and Blackman, 1898) Ostenfeld, 1900 Reticulofenestra haqii Backman, 1978 Emiliania huxleyi (Lohmann, 1902) Hay and Mohler in Hay et al., 1967 Reticulofenestra minuta Roth, 1970 Florisphaera profunda Okada and Honjo, 1973 Reticulofenestra minutula (Gartner, 1967) Haq and Berggren, 1978 Gephyrocapsa caribbeanica Boudreaux and Hay, 1967 Reticulofenestra parvula (Okada and McIntyre, 1977) Biekart Gephyrocapsa crassipons Okada and McIntyre, 1977 Reticulofenestra perplexa (Burns, 1975) Wise, 1983 Gephyrocapsa ericsonii McIntyre and Bé, 1967 Reticulofenestra producta (Kamptner, 1963) Wise, 1983 Gephyrocapsa margerelii Bréhéret, 1978a Reticulofenestra pseudoumbilica (Gartner, 1967) Gartner, 1969 Gephyrocapsa muellerae Bréhéret (1978) Reticulofenestra punctata (Okada and McIntyre, 1977) Jordan & Young, Gephyrocapsa oceanica Kamptner, 1943 1990 Gephyrocapsa protohuxleyi McIntyre, 1970 Rhabdosphaera clavigera Murray and Blackman, 1898 Helicosphaera carteri (Wallich, 1877) Kamptner, 1954 Sphenolithus abies Deflandre in Deflandre and Fert, 1954 Helicosphaera euphratis Haq, 1966 Sphenolithus neoabies Bukry and Bramlette, 1969 Helicosphaera inversa Gartner, 1980 Tetralithoides quadrilaminata (Okada and McIntyre, 1977) Jordan, Kleine Helicosphaera minuta Müller, 1981 and Heimdal, 1993 Helicosphaera pacifica Müller and Bronnimann, 1974 Triquetrorhabdulus rugosus Bramlette and Wilcoxon, 1967 Helicosphaera pavimentum Okada and McIntyre, 1977 Umbellosphaera tenuis (Kamptner, 1937) Paasche in Markali and Paasche, 1955 Helicosphaera sellii (Bukry and Bramlette, 1969) Jafar and Martini, 1975 Umbilicosphaera aequiscutum (Gartner, 1976) Aubry, 1993 Neosphaera coccolithomorpha Lecal-Schlauder, 1950 Umbilicosphaera cricota (Gartner, 1976) Aubry, 1993 Oolithotus fragilis (Lohmann, 1912) Martini and Müller, 1972 Umbilicosphaera hulburtiana Gaarder, 1970 Pontosphaera discopora Schiller, 1925 Umbilicosphaera sibogae var. foliosa (Kamptner, 1963) Okada and McIntyre, Pontosphaera japonica (Takayama, 1967) Nishida, 1971 1977 Pontosphaera multipora (Kamptner, 1948) Roth, 1970 Umbilicosphaera sibogae var. sibogae (Weber-van Bosses, 1901) Gaarder, Pseudoemiliania lacunosa (Kamptner, 1963) Gartner, 1969 1970

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