RESULTS ABSTRACT. Ludwig, W. J., Krasheninnikov, V. A., et al., Init. Repts. DSDP, 71: Washington (U.S. Govt. Printing Office).

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1 48. OELTION O EOENE-OLIGOENE LEOUS NNNOOSSIL SSEMBLGES OM PISTON OES TKEN NE DEEP SE DILLING SITES 5 ND 52, SOUTHWEST TLNTI OEN Sherwood W. Wise, Jr., Department of Geology, lorida State University, Tallahassee, lorida and Elena L. Mostajo, Museo rgentino de iencias Naturales "B. ivadavia," 405 Buenos ires, rgentina BSTT alcareous nannofossil assemblages recovered in four Islas Orcadas piston cores along the northern margin of the Maurice Ewing Bank on the eastern alkland Plateau are correlated with lower Oligocene and middle Eocene sections at Deep Sea Drilling Project Sites 5 and 52, respectively. esults indicate that the Paleogene section near the piston core stations is generally more calcareous and complete than at the Leg 7 drill sites and could provide a valuable highlatitude biostratigraphic reference locality if drilled at some future date. INTODUTION During pril 978, a series of Islas Orcadas ruise 6 piston cores were taken along the heavily eroded northern margin of the Maurice Ewing Bank on the eastern alkland (Malvinas) Plateau (Wise et al., 978) in order to trace the outcrop belt of older (pre-pliocene) sediments thought to be exposed there (iesielski and Wise, 977). Basal sediments of the 3 piston cores taken along the northern margin range from Paleocene to Miocene in age (Jones et al., 979) and suggest the presence of a high-latitude Paleocene to Oligocene section of mixed calcareous-siliceous oozes over 200 meters thick. It was originally hoped that DSDP Site 52 could be located at a shallow depth (about 500 m) somewhere along the steeply sloping northern margin of the Maurice Ewing Bank so that the exposed Oligocene-Paleocene section could be sampled by hydraulic piston coring. Unfortunately, there were no seismic profiles adequate to evaluate sufficiently potential hydrocarbon hazards, and the site was eventually relocated some distance to the southeast in about 850 meters of water, where the older sediment section is more abbreviated. Nevertheless, the Islas Orcadas piston cores near the initially proposed drill site do provide a valuable insight into the nature of the sediments higher up on the Maurice Ewing Bank. mong those cores are four which are closely correlative in age with the materials obtained at the Leg 7 drill sites (see ig. ). The objective of this paper is to describe and correlate the occolith assemblages from those piston cores with the assemblages described from the Leg 7 drill cores (Wise, this volume). Gombos (982) recently described three new genera of ebridians from these same cores and provided general age determinations based on diatoms. Ludwig, W. J., Krasheninnikov, V.., et al., Init. epts. DSDP, 7: Washington (U.S. Govt. Printing Office). ESULTS igure 2 shows the lithologies of the four piston cores taken along the northern Maurice Ewing Bank that can be closely correlated with the middle Eocene and lower Oligocene sections cored at DSDP Sites 52 and 5, respectively (lithologies condensed from Kaharoeddin et al., 982). The calcareous nannofossil stratigraphies are given in Tables and 2. list of species encountered is given in the ppendix. It should be borne in mind that isolated piston cores must necessarily be examined out of the context of the sections from which they were retrieved. The short intervals recovered in older piston cores (usually no more than a meter or two in length) constitute only a small fraction of the total section that would be obtained in the same locality by drill cores, and variations in species abundances may lead to false conclusions about the stratigraphies or the dates of the isolated piston core sections. Nevertheless, the general age assignments given these cores on the basis of coccoliths agree with the middle Eocene and early Oligocene ages suggested by Gombos (982), who examined the diatoms. Islas Orcadas (IO) ore 6-43 contains abundant hiasmolithus solitus and eticulofenestra umbilica, which together define the Discoaster bifax Subzone of Bukry (973a). are D. bifax were noted at the base of the core, and forms here attributed to. bisecta bisecta are few to abundant throughout. Individuals of the latter species are small, about 9 to 0 µm long (about the size of the holotype of the species) and exhibit a low-order yellow interference color in crossed polarized light. Such forms were encountered only in ores 8 and 9 at DSDP Site 52, where they were lumped under the name eticulofenestra sp. cf.. hesslandii (Wise, this volume, Table 5). Some other forms lower down in the section at Site 52 were included under that taxonomic heading, but these are smaller; they do not exhibit a yellow interference color, and are not the same species as those in Islas Orcadas ore

2 to rgentine Basin /-, v^ts, igure. Locations of DSDP Sites 5 and 52 and of Islαs Orcαdαs piston cores used in this study.

3 OELTION O EOENE-OLIGOENE LEOUS NNNOOSSILS Piston ore Piston ore IO 6-46 Latitude: 'S Longitude: 'W orr. Depth: 706 m ore Length: 88 cm Latitude: 'S Longitude: 'W orr. Depth: 693 m ore Length: 27 cm Lithology ge Lithologic Description Lithology ge Lithologic Description -iioo : 0-9 cm: Pebbly sand, light olive gray (5Y 5/2) cm: Pebbly, muddy, diatomaceous ooze, light olive brown (5Y 5/6) cm: Diatomaceous ooze, dark yellowish orange (0Y 6/6) gradationally changing to grayish orange (0Y 7/4) at 60 cm cm: Nannofossil ooze, very pale orange (0Y 8/2) with streaks of grayish orange (0Y 7/4); volcanic ash sparsely scattered throughout; 3 mm piece of chert at cm and cm, and 0 mm piece of chert at cm. Smear slide: eldspar oraminifers alcareous nannos Diatoms adiolarians Sponge spicules Silicoflagellates 37 cm at: Lithology α. ge 0 27 cm: Nannofossil ooze, white (N9); volcanic ash sparsely scattered throughout; 9 cm cast from 0 9 cm composed of pebbly, glauconitic sand, moderate olive brown (5Y 4/4); sand is medium and moderately sorted; angular pebbles up to 25 mm abundant from 6 9 cm; slightly bioturbated; moderately disturbed from cm because of removal of the core catcher. Smear slides: Quartz eldspar Heavy minerals lay Volcanic glass ock fragments Glauconite arbonate unspecified oraminifers alcareous nannos Diatoms adiolarians Sponge spicules Silicoflagellates Ebridians Piston ore IO 6-45 Latitude: 'S Longitude: 42 38'W 4 cm (cast) Lithologic Description 20 cm orr. Depth: 624 m ore Length: 74 cm 00 E f 200- Lithology ge Piston ore IO T6-44 Latitude: 'S Longitude: 'W Lithologic Description orr. Depth: 677 m ore Length: 257 cm 0 36 cm: Diatomaceous ooze, light olive brown (5Y 5/6); stringers of ooze (5 mm average width), rich in foraminifers and glauconite, abundant from 0 20 cm; sedimentary clasts up to 20 mm, composed of nannofossil ooze, yellowish gray (5Y 7/2), common from cm; moderately disturbed (washed) from 0 36 cm; sharp, inclined, wavy contact. NOTE: This unit is possibly a mixture of diatomaceous ooze and glauconitic foraminiferal ooze. The mixing is probably due to implosion of the plastic liner cm: Nannofossil ooze, very pale orange (0Y 8/2); gradational change to flow-in at 4 cm; pieces of imploded plastic liner found from 33-4 cm, 9-62 cm, and cm. T ^ 5m. 0 5 cm: Glauconitic, foraminiferal quartz sand, olive gray (5Y 3/2) cm: Diatomaceous, nannofossil ooze, very pale orange (0Y 8/2); glauconite sparsely scattered throughout; stringers composed of radiolarians and glauconite sparsely scattered from cm and cm; irregular patch, yellowish gray (5Y 8/), with higher siliceous microfossil content from cm; moderately bioturbated throughout. Smear slides: Quartz eldspar lay oraminifers alcareous nannos Diatoms adiolarians Sponge spicules Silicoflagellates 5 cm cm cm Smear slide: eldspar oraminifers alcareous nannos Diatoms adiolarians Sponge spicules Silicoflagellates 27 cm igure 2. Lithologies of Mas Orcadas (IO) ruise 6 piston cores 6-43, 6-44, 6-46, and 6-45 (from Kaharoeddin et al., 982). 73

4 S. W. WISE, J., E. L. MOSTJO Table. Distribution of middle Eocene calcareous nannofossils in Islas Orcadas (IO) ores 6-43, 6-44, and ge Zone or Subzone Sample (interval in cm) bundance Preservation Blackites spinosus alcidiscus leptoporus hiasmolithus expansus. grandis. solitus lausicoccus fenestratus occolithus formosus. pelagicus. staurion. sp. cf.. pseudogammation* Discoaster barbadiensis D. bifax D. binodosus D. distinctus D. saipanensis Ellipsolithus distichus Helicosphaera carteri Markalius inversus Neococcolithes dubius Pontosphaera pectinata P. plana P. pulcheroides eticulofenestra bisecta bisecta. sp. cf.. hesslandii (small). onusta. samodurovi. umbilica eticulofenestrids (other small) Sphenolithus moriformis Zygrhablithus bijugatus middle Eocene eticulofenestra umbilica Nannotetrina quadrata Discoaster bifax occolithus staurion IO 6-43, 20 IO 6-43, 30 IO 6-43, 40 IO 6-43, 50 IO 6-43, 60 IO 6-43, 70 IO 6-43, 80 IO 6-44, 5 IO 6-44, 5 IO 6-44, 25 IO 6-44, 35 IO 6-44, 50 I IO 6-46, 5 IO 6-46, 5 IO 6-46, 25, O, O, O, O, O M, E M, E M, E M, E M, E? f V V V V V V V V V V? V V? f f fr? V V V V V H V H V H V H V?? Note: V = very abundant; H = highly abundant; = abundant; = common; = few; = rare; fr = fragment; P = poor; M = moderate; G = good; E = etched; O = overgrown; I = flow-in. bundances in lowercase denote reworked or contaminant specimens. a yclicargolithus sp. Table 2. Distribution of early Oligocene calcareous nannofossils in Islas Orcadas (IO) ore ge Zone Sample (interval in cm) bundance Preservation Blackites spinosus hiasmolithus altus. oamaruensis lausicoccus fenestratus occolithus pelagicus ylicargolithus floridanus Discoaster adamanteus D. deflandrei D. sp. Isthmolithus recurvus Lapideacassis sp. eticulofenestra bisecta bisecta. bisecta fllewiczii. daviesii. hesslandii. hillae. umbilica Sphenolithus moriformis Zygrhablithus bijugatus early Oligocene Blackites spinosus IO 6-45, 5 IO 6-45, 5 IO 6-45, 25 IO 6-45, 35 IO 6-45, 45 IO 6-45, 55 IO 6-45, 65 IO 6-45, 73, O V V V V V V V Note: V = very abundant; = abundant; = common; = few; = rare; P = poor; M = moderate; G = good; E = etched; O = overgrown. Bukry (973a) indicates that. bisecta bisecta makes its first appearance somewhere within the D. bifax Subzone. On the alkland Plateau this appears to be the case with the species first appearing in the upper portion of the section at Site 52. It is not present above ore 52-8, however, so its occurrence here may be sporadic in the lower part of its range. Its occurrence in ore IO 6-43 is quite consistent, perhaps indicating that this core represents a stratum slightly younger than the section at Site 52. ore IO 6-44 is rather badly disturbed. Pleistocene glacial marine sediments in the top 40 cm are contaminated with middle Eocene coccoliths from the nannofossil ooze below because the plastic core liner imploded during core retrieval. Most of the nannofossil ooze contained in the remainder of the core is flow-in material which was drawn into the liner during core retrieval. Pleistocene coccoliths are represented by a few alcidiscus leptoporus and Helicosphaera carteri in the top 35 cm of the core. Middle Eocene coccpliths include common to abundant hiasmolithus solitus and. umbilica but no. bisecta. The absence of the latter could mean that the core sampled a lower stratigraphic level than that of ore IO The evidence for this could be considered ambiguous, however, since. bisecta is not consistently present in the upper part of the section at Site 52. No Sphenolithus furcatolithoides or S. radians were noted. This core, therefore, probably repre- 74

5 OELTION O EOENE-OLIGOENE LEOUS NNNOOSSILS sents a stratum lying somewhere above Section and below ore In ore IO 6-46,. solitus is abundant, but no confirmed specimens of. umbilica have been found. Instead, the assemblage contains abundant. samodurovi, which is similar to. umbilica in appearance but is smaller. Bukry (973a) considers. samodurovi to be the progenitor of the larger. umbilica, but does not specify what size difference he uses to distinguish the two. We attribute all forms larger than 4 µm to. umbilica. In ore IO 6-46, there are rare fragments of forms which must have approached 4 µm in length, but no confirmed examples of. umbilica were found. Since. umbilica was consistently present through the section at Site 52, it would seem that ore IO 6-46 should probably be assigned to Bukry's (973a) middle Eocene occolithus staurion Subzone. One specimen of. staurion was noted in Sample 6-46, 5 cm (Table ; ig. 3). This species can also occur, however, in the D. bifax Subzone (Bukry, 973a). Nannotetrina quadrata was not observed. ore IO 6-45 is dated as early Oligocene by the presence of lausicoccus fenestratus and Isthmolithus recurvus in the absence of D. saipanensis and. oamaruensis. In this respect, the core is equivalent to the Blackites spinosus Zone cored in a long sequence at DSDP Site 5. single specimen of D. saipanensis was noted in an intermediate sample taken at 40 cm in ore IO 6-45 (not shown in Table 2). This specimen, however, is apparently reworked, Gombos (982, text-fig. ) also suspected reworking at this interval. Neither. fenestratus nor /. recurvus occur in the topmost 5 cm of the core. Because of the high sedimentation rate in this area, it is doubtful, however, that the upper boundary of the B. spinosus Zone is actually present in this core, although that remains a possibility. Strong fluctuations in the abundances of. fenestratus were noted in the equivalent section at DSDP Site 5 (Wise, this volume, Table ), and this fact may account for its apparent absence at the top of ore Scanning electron micrographs revealed exceptionally clear ultrastructural details for some of the Oligocene coccoliths of ore IO The Isthmolithus recurvus in Plate, igures -3 are composed of a paper-thin wall constructed of narrow vertical laths. In one specimen (Plate, igs. and 2), the wall is folded into a small loop at one end (right side of specimen) and then overlapped along an oblique suture just beyond that point. This wall construction is markedly different from that of Neococcolithes dubius (Plate 4, ig. 9) which has a wall composed of robust, strongly inclined elements (a characteristic eiffellithalid rim). There seems to be no reason to suppose that there is some sort of evolutionary link (or intermediate connecting form) between these two taxa as has sometimes been suggested in the literature. DISUSSION orrelation of middle Eocene piston and drill cores from the Maurice Ewing Bank suggest that the piston cores represent fragments of a broader stratigraphic interval than that sampled at Site 52. Islas Orcadas Piston ores 6-43 and 6-46 may represent, respectively, strata slightly younger and slightly older than the section at Site 52. On the basis of coccoliths the correct sequence of cores from youngest to oldest, is IO 6-43, 6-44, and M. Gombos (pers. comm., 982) reports that this sequence is in accord with his diatom data when measured against the diatom stratigraphy of Site 52 (Gombos, this volume). Based on these data, the following sequence of calcareous nannofossil datums within or bounding the Discoaster bifax Subzone of the eticulofenestra umbilica Zone can be suggested for the area of the alkland Plateau (they are listed in descending stratigraphic order): LD, hiasmolithus solitus; D, eticulofenestra bisecta bisecta; LD, Sphenolithus furcatolithoides; D,. umbilica. Since the entire D. bifax Subzone was not drilled or cored at any one locality, we cannot fully ascertain the reliability of these datums in this region. urther drilling would be required. Nor can we ascertain the duration of time encompassed by the D. bifax Subzone in this region. On the basis of Bukry's (973b) calculations, the subzone spans only about m.y. If that is correct, then the sedimentation rate at Site 5 during that igure 3. occolithus staurion Bramlette and Sullivan; Islas Orcadas Sample 6-46, 5 cm, 3200., phase contrast light; B, transmitted light;, cross-polarized light. 75

6 S. W. WISE, J., E. L. MOSTJO time would have been a phenomenal 70 m/m.y. (Wise, this volume). n alternative explanation is that the interval actually spans a greater amount of time. If. solitus persisted longer in the higher latitudes than in the tropics where Bukry's (973a) zonation is grounded, then the subzone would encompass a greater amount of section. Many of these questions could best be answered by further drilling in the vicinity of the Islas Orcadas piston cores discussed here. The section there is shallower and is far more calcareous in the Oligocene than the equivalent section at DSDP Site 5. In addition, exposure of progressively older sediments down the long northern slope of the Maurice Ewing Bank places the entire Tertiary section within sampling range of the hydraulic piston corer. The acquisition of such a section would be of great value to high-latitude biostratigraphy. KNOWLEDGMENTS The Islas Orcadas piston cores were taken during a cruise sponsored jointly by the U.S. National Science oundation, the rgentine Naval Hydrographic Office, and the rgentine ntarctic Survey. Dr. Mostajo's participation in laboratory studies at lorida State University and subsequent investigations have been supported by NS grants DPP and DPP We thank Dr. ndrew M. Gombos for re-examining his diatom data on the study material and providing us with his results. Ms. Mary Parker helped prepare the manuscript, which was typed by Ms. Pamela hymes. EEENES Bukry, D. 973a. Low-latitude occolith biostratigraphic zonation. In Edgar, N. T., Saunders, J. B., et al., Init. epts. DSDP, 5: Washington (U.S. Govt. Printing Office), , 973b. occolith stratigraphy, Eastern Equatorial Pacific, Leg 6, Deep Sea Drilling Project. In van ndel, Tj. H., Heath, G.., et al., Init. epts. DSDP, 6: Washington (U.S. Govt. Printing Office), iesielski, P.., and Wise, S. W., 977. Geologic history of the Maurice Ewing Bank of the alkland Plateau (Southwest tlantic sector of the Southern Ocean) based on piston and drill cores. Mar. Geol., 25: Gombos,. M., Jr., 982. Three new and unusual genera of ebridians from the southwest tlantic Ocean. J. Paleontol., 56: Heck, S. E., van, 979a. Bibliography and taxa of calcareous nannoplankton. Int. Nannoplankton ssoc. Newsl., l:bl-5, l-2, Bl-27., 979b. Bibliography and taxa of calcareous nannoplankton. Int. Nannoplankton ssoc. Newsl., :BVI, 3-28, B _, 980a. Bibliography and taxa of calcareous nannoplankton. Int. Nannoplankton ssoc. Newsl., 2:5-34. _, 980b. Bibliography and taxa of calcareous nannoplankton. Int. Nannoplankton ssoc. Newsl., 2:43-8.., 98a. Bibliography and taxa of calcareous nannoplankton. Int. Nannoplankton ssoc. Newsl, 3:4-4.., 98b. Bibliography and taxa of calcareous nannoplankton. Int. Nannoplankton ssoc. Newsl., 3:5-86. _, 982. Bibliography and taxa of calcareous nannoplankton. Int. Nannoplankton ssoc. Newsl., 4:7-50. Jones, S., Wise, S. W., Jr., Deelice, D.., Hattner, J. G., Mostajo, E. L., Gombos,. M., and Weaver,. M., 979. Basal sediment ages of Islas Orcadas cruise 6 piston cores. ntarc. J. U.S., 4: Kaharoeddin,.., Graves,. S., Bergen, J.., Eggers, M.., Harwood, D. M., Humphreys,. L., Goldstein, E. H., Jones, S., and Watkins, D. K., 982. Islas Orcadas cruise 6-78, sediment descriptions. la. State Univ. Sed. es. Lab. ontrib., 50: 72. Loeblich Jr.,.., and Tappan, H., 966. nnotated index and bibliography of the calcareous nannoplankton. Phycologia, 5:8-26., 968. nnotated index and bibliography of the calcareous nannoplankton III. /. Paleontol., 42: , 969. nnotated index and bibliography of the calcareous nannoplankton III. J. Paleontol., 43: , 970a. nnotated index and bibliography of the calcareous nannoplankton IV. /. Paleontol., 44: , 970b. nnotated index and bibliography of the calcareous nannoplankton V. Phycologia, 9:57-74., 97. nnotated index and bibliography of the calcareous nannoplankton VI. Phycologia, 0: _, 973. nnotated index and bibliography of the calcareous nannoplankton VII. /. Paleontol., 47: Wise, S. W., Jr., Jones, S., iesielski, P.., Georgi, D. T., Woodroffe, D. S., and Jacobs, S. S., 978. Islas Orcadas cruise 6. ntarct. J. U.S., 3: PPENDIX alcareous Nannofossil Species onsidered in This eport, Listed in lphabetical Order of Species Epithets The bibliographic references for these species are provided in Wise (this volume), Loeblich and Tappan (966,968,969,970a, b, 97, 973) and Heck (979a, b, 980a, b, 98a, b, 982). Discoaster adamanteus Bramlette and Wilcoxon, 967 hiasmolithus altus Bukry and Percival, 97 Discoaster barbadiensis Tan Sin Hok, 927 Discoaster bifax Bukry, 97 Zygrhablithus bijugatus (Deflandre) Deflandre, 959 Discoaster binodosus Martini, 958 eticulofenestra bisecta bisecta (Hay, Mohler, and Wade) oth, 970 eticulofenestra bisecta filewiczii Wise and Wiegand in Wise, this volume Helicosphaera carteri (Wallich) Kamptner, 954 eticulofenestra daviesii (Haq) Haq, 97 Discoaster deflandrei Bramlette and iedel, 954 Ellipsolithus distichus (Bramlette and Sullivan) Sullivan, 964 Discoaster distinctus Martini, 958 Neococcolithes dubius (Deflandre) Black, 967 hiasmolithus expansus (Bramlette and Sullivan) Gartner, 970 lausicoccus fenestratus (Deflandre and ert) Prins, 979 yclicargolithus ßoridanus (oth and Hay) Bukry, 97 occolithus formosus (Kamptner) Wise, 973 Sphenolithus furcatolithoides Locker, 967 hiasmolithus grandis (Bramlette and iedel) Gartner, 970 eticulofenestra hesslandii (Haq) oth, 970 eticulofenestra sp. cf.. hesslandii (small) (Haq) oth, 970 eticulofenestra hillae Bukry and Percival, 97 Markalius inversus (Deflandre) Bramlette and Martini, 964 alcidiscus leptoporus (Murray and Blackman) Loeblich and Tappan, 978 Sphenolithus moriformis (Brönnimann and Stradner) Bramlette and Wilcoxon, 967 yclicargolithus sp. cf.. pseudogammation (Bouche) Bukry, 973 hiasmolithus oamaruensis (Deflandre) Hay, Molhler and Wade, 966 eticulofenestra oamaruensis (Deflandre) Stradner and Edwards, 968 eticulofenestra onusta (Perch-Nielsen) Wise, n. comb. Pontosphaera pectinata (Bramlette and Sullivan) Proto Decima, oth, and Todesco, 975 occolithus pelagicus (Wallich) Schiller, 930 Pontosphaera plana (Bramlette and Sullivan) Haq, 97 Pontosphaera pulcheroides (Sullivan) omein, 979 Nannotetrina quadrata (Bramlette and Sullivan) Bukry, 973 Isthmolithus recurvus Deflandre in Deflandre and ert, 954 Discoaster saipanensis Bramlette and iedel, 954 eticulofenestra samodurovi (Hay, Mohler, and Wade) Bukry and Percival, 97 hiasmolithus solitus var. inversus Wise and Weigand in Wise, this volume Blackites spinosus (Deflandre and ert) Hay and Towe, 962 occolithus staurion Bramlette and Sullivan, 96 eticulofenestra umbilica (Levin) Martini and itzkowski,

7 OELTION O EOENE-OLIGOENE LEOUS NNNOOSSILS Plate. Lower Oligocene calcareous nannofossils, SEM. -4. Isthmolithus recurvus Deflandre (-2) 0,500, Sample IO 6-45, 20 cm, (3) 7500, Sample IO 6-45, 60 cm, (4) 8000, Sample IO 6-45, 20 cm. 5-6, 8. eticulofenestra bisecta filewiczii Wise and Wiegand, Sample IO 6-45, 40 cm, (5-6) (5, distal views, 4400; 6, 7000), (8) proximal view, 55OO. 7. eticulofenestra umbilica (Levin) Martini and itzkowski; distal view, X32OO, Sample IO 6-45, 40 cm. 77

8 S. W. WISE, J., E. L. MOSTJO Plate 2. Lower Oligocene calcareous nannofossils, SEM.. yclicargolithusfloridanns (oth and Hay) Bukry; proximal view, x 9000, Sample IO 6-45, 40 cm lausicoccus fenestratus (Deflandre and ert) Prins, distal views, (2) 8000, Sample IO 6-45, 20 cm, (3),000, Sample IO 6-45, 40 cm, (4) 9500, Sample IO 6-45, 20 cm, (5-6) Sample IO 6-45, 60 cm (5, 9000; 6, 0,000) occolithus pelagicus (Wallich) Schiller, (7) coccosphere, 400, Sample IO 45-6, 20 cm, (8) distal view, 5000, Sample IO 6-45, 40 cm, (9) proximal view, 7000, Sample IO 6-45, 60 cm. 78

9 OELTION O EOENE-OLIGOENE LEOUS NNNOOSSILS Plate 3. Lower Oligocene and middle Eocene calcareous nannofossils, SEM. -6. hiasmolithus altus Bukry and Percival, Lower Oligocene, (- 3) distal views (, 4200, Sample IO 6-45, 20 cm; 2, 400, Sample IO 6-45, 40 cm; 3, 4400, Sample IO 6-45, 40 cm), (4-5) proximal views (4, 4800, Sample IO 6-45, 40 cm; 5, 55OO, IO 6-45, 60 cm, (6) distal view, 55OO, Sample IO 6-45, 20 cm hiasmolithus solitus (Bramlette and Sullivan) Locker, middle Eocene, distal view, Sample IO 6-44, 40 cm, (7) 400, (8) hiasmolithus expansus (Bramlette and Sullivan) Gartner, middle Eocene, proximal view, 400, Sample IO 6-45, 40 cm. 79

10 S. W. WISE, J., E. L. MOSTJO Plate 4. Middle Eocene calcareous nannofossils, SEM, Sample IO 6-44, 40 cm.. hiasmolithus expansus (Bramlette and Sullivan) Gartner, distal view, 35OO. 2. Discoaster sp., Discoaster barbadiensis Tan Sin Hok, 65OO. 4. Discoaster distinctus Martini, Discoaster binodosus Martini, 33OO. 6. Discoaster sp., Discoaster saipanensis Bramlette and iedel, (7) 65OO, (8) Neococcolithes dubius (Deflandre) Black, distal view, 0,