Biostratigraphic Synthesis, Leg 108, Eastern Equatorial Atlantic

Proceedings R u d d i m a n , W . , S a r n t h e i n M . , et a l . , 1989 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIH of the Ocean Drilling Program, Scientific Results, V o l .zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQ 108 28. BIOSTRATIGRAPHIC SYNTHESIS: LEG 108, EASTERN EQUATORIAL ATLANTIC 1 P.P.E. Weaver, 2 J. Backman, 3 J. G. Baldauf,4 J. Bloemendal, 5 H. Manivit, 6 K. G. Miller,7,8 E. M. Pokras, 8 M. E. Raymo, 8 L. Tauxe, 9 J.-P. Valet,10 A. Chepstow-Lusty, 11 and G. Olafsson3 ABSTRACT Leg 108 cored 12 sites in the eastern equatorial Atlantic and along the northwest African continental margin to investigate the late Neogene and Quaternary oceanographic and climatic history of these regions. Sediments recovered during Leg 108 provide in part a high-resolution stratigraphic record for the upper Pliocene through Holocene interval. The bio- and magnetostratigraphy are intercalibrated where possible and provide a useful chronostratigraphy for paleoceanographic studies. INTRODUCTION The objective of Ocean Drilling Program (ODP) Leg 108 was to retrieve Neogene sediment using advanced hydraulic piston core/extended core barrel (APC/XCB) techniques for high-resolution paleoclimatic studies along a latitudinal transect in the eastern equatorial Atlantic. This data was required to complete the latitudinal transect of cores taken in the North Atlantic during Deep Sea Drilling Project (DSDP) Leg 94 and to investigate other questions associated with the response of surface productivity and eolian input to changing climatic and oceanographic conditions. In addition, this program was ideal for establishing biostratigraphic reference sections in undisturbed Neogene sediment cores from the low-latitude Atlantic Ocean. Another major objective was to establish a high-resolution paleomagnetic stratigraphy, thus providing the first opportunity to investigate and evaluate the chronologic properties of biostratigraphic marker events in pre-upper Pliocene sediments from the low-latitude Atlantic Ocean. Considering the substantial number of DSDP/ODP sites that have been drilled in the Atlantic Ocean and the prominence of the low-latitude Atlantic regions in the history of paleoceanography, surprisingly little sediment has been cored with the APC/XCB tools. The sediments cored during Leg 108 represent the only APC 1 Ruddiman, W., Sarnthein, M., et al., 1989. Proc. ODP, Sci. Results, 108: College Station, TX (Ocean Drilling Program). Institute of Oceanographic Sciences, Brook Road, Wormley, Godalming, Surrey GU8 5UB, United Kingdom. Department of Geology, University of Stockholm, S-10691 Stockholm, Sweden. Ocean Drilling Program, Texas A&M University, 1000 Discovery Drive, College Station, TX 77843. Graduate School of Oceanography, University of Rhode Island, Narragansett Bay Campus, Narragansett, RI 02882. CNRS-UA 319, Laboratoire de Stratigraphic des Continents et Oceans, Universite Paris IV, 4 Place Jussieu, 75230 Paris Cedex, France. Department of Geological Sciences, Rutgers University, New Brunswick, NJ 08903. Lamont-Doherty Geological Observatory, Columbia University, Palisades, NY 10964. Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA 92093. Centre des Faibles Radioactivites, Laboratoire Mixte CNRS-CEA, Pare du CNRS, B. P. 91198, Gif/Yvette Cedex, France. Godwin Laboratory, Subdepartment of Quaternary Research, University of Cambridge, Cambridge CB2 3RS, United Kingdom. material available from tropical or equatorial environments of the Atlantic Ocean. Leg 108 sailed less than a year after Berggren et al. (1985a, 1985b) published their attempt to establish a Cenozoic geochronology and a thorough compilation of correlations between Cenozoic bio- and magnetostratigraphy, encompassing most important marine microfossil groups. When the authors published their correlations, they clearly suffered from a lack of adequate magnetostratigraphic sections representing equatorial environments even in the Neogene realm. Consequently, the bio- and magnetostratigraphers on Leg 108 anticipated being able to provide this missing low-latitude bioand magnetostratigraphy. With respect to calcareous nannofossil biostratigraphy, our interest was focused on the time interval preceding the top of the Thvera Subchron (prior to about 4.6 Ma). Pleistocene and Pliocene calcareous nannofossil marker events that have occurred since then have been directly correlated to oxygen isotope stratigraphy (e.g., Thierstein et al., 1977) or to magnetostratigraphy (e.g., Backman and Shackleton, 1983) in numerous piston cores from low-latitude regions. Therefore, we saw little reason to expect substantial revision, on the order of 5%-10% or more, in the age estimates of PliocenePleistocene calcareous nannofossil markers, as viewed within the frame of the marine magnetic anomaly time scale of Berggren et al. (1985a, 1985b). In many early DSDP legs, planktonic foraminifers were regarded as more important than calcareous nannofossils for biostratigraphy. Recent investigations, such as those of Weaver and Clement (1987) and Hodell and Kennett (1986), however, have shown that many late Neogene species have diachronous first and last occurrences, and it has become important to test the accuracy of these datums against the paleomagnetic record in as many areas as possible. Because many of the original data were collected in tropical regions, we hoped that Leg 108 would provide important additional data, particularly from sites lying in the tropics but under the influence of cool surface currents. The ages of datum levels below the Miocene/Pliocene boundary are less well defined; thus, all additional data from Paleomagnetically dated cores in this interval are of importance. Considerable problems were encountered in obtaining good paleomagnetic records during Leg 108. These included the combined effects of low magnetic intensities, the occurrence of slumps and turbidites, the recovery of condensed sequences, improperly functioning core-orienting devices, 455 P.P.E. WEAVER ET AL. and magnetic overprinting. In fact, we were only able to define data were not available, we were forced to rely on the and identify magnetostratigraphic polarity zones in the biostratigraphy alone. Pliocene-Pleistocene interval. These Paleomagnetically dated Calcareous nannofossil ages are well established throughintervals strengthen our interpretation of Pliocene-Pleistocene out the Pliocene and Quaternary, but there are several probstratigraphy by adding Atlantic tropical sites to the relatively lems in pre-Pliocene sediments. Unfortunately, we did not small number of DSDP and ODP sites with independent age identify any paleomagnetic boundaries below the Pliocene and control. The lack of paleomagnetic signals in pre-Pliocene so these biostratigraphic problems could not be resolved. The sediments, however, does little to improve the dating of planktonic foraminiferal datum levels are also unreliable in biostratigraphic datum levels in these older sequences. zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA pre-Pliocene sediments, and our accumulation rate curves are therefore based on best-fit criteria. RESULTS Since the pre-Pliocene accumulation rates may be subject The biostratigraphic results, together with some previously to error, it is difficult to use them to assess the accuracy of unpublished Leg 108 data, have been compiled into tables biostratigraphic datum levels. It is generally accepted, howshowing first or last occurrences of biostratigraphic marker ever, that calcareous nannofossils give more reliable age species, and the sub-bottom depth intervals assigned for these information than planktonic foraminifers, and the accumulamarker events (Tables 1-3). In thezyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Proceedings of the Ocean tion rate curves do fit more calcareous nannofossil datum Drilling Program, Initial Results volume (Ruddiman, Sarnpoints than planktonic foraminiferal ones. Therefore, we have thein, et al., 1988), we outline the stratigraphic scheme used to given age estimates throughout of the planktonic foraminifers determine stratigraphic ages in these sites. For calcareous derived from the accumulation rate curves (Table 3). A nannofossils, planktonic foraminifers, and paleomagnetics, comparison between Tables 1 and 3 will indicate where this largely follows Berggren et al. (1985a, 1985b). Departures paleomagnetic control of this data existed. from the Berggren dates are discussed in the "Introduction" OCCURRENCE OF MAJOR GROUPS chapter of the Initial Results volume. Where paleomagnetic data were available, it has been possible to assess the accuOf the 12 sites cored during Leg 108 (Fig. 1), 8 did not racy of the microfossil datum levels. Where paleomagnetic penetrate below the upper Miocene; the deepest site, however, penetrated into the Upper Cretaceous. Figures 2 and 3 Table 1. Stratigraphic placement in meters (to the nearest decimeter) of the Leg 108 chron and subchron boundaries. 456 Site and time zone Age (Ma) Depth (mbsf) 108-657BBrunhes/Matuyama Jaramillo (upper) Jaramillo (lower) Matuyama/Gauss 0.73 .0.91 0.98 2.47 29.0 30.7-34.7 36.2 72.1-73.7 108-658AOlduvai (upper) Olduvai (lower) 1.66 1.88 109.2-109.8 124.1-129.7 108-658BOlduvai (upper) Olduvai (lower) 1.66 1.88 108.2 126.2 108-659ABrunhes/Matuyama Jaramillo (upper) Jaramillo (lower) 0.73 0.91 0.98 22.8 28.6 31.0 108-659BJaramillo (upper) Jaramillo (lower) Olduvai (upper) Olduvai (lower) Matuyama/Gauss 0.91 0.98 1.66 1.88 2.47 26.4 29.3 47.8 52.4 74.7 108-660ABrunhes/Matuyama Jaramillo (upper) Jaramillo (lower) Olduvai (upper) Olduvai (lower) 0.73 0.91 0.98 1.66 1.88 18.5 22.9 24.6 36.4 28.4 108-661ABrunhes/Matuyama Jaramillo (upper) Jaramillo (lower) Olduvai (upper) Matuyama/Gauss 0.73 0.91 0.98 1.66 2.47 10.5-12.7 14.8 16.0 26.1-26.7 36.8 108-661BBrunhes/Matuyama Jaramillo (upper) Jaramillo (lower) Olduvai (upper) 0.73 0.91 0.98 1.66 13.1-15.7 — — 25.4 Table 1 (continued). Site and time zone Age (Ma) Depth (mbsf) Olduvai (lower) Matuyama/Gauss Gauss/Gilbert 1.88 2.47 3.40 30.2 36.2 52.5 108-664BBrunhes/Matuyama Jaramillo (upper) 0.73 0.91 27.0 35.5 108-664CBrunhes/Matuyama Jaramillo (upper) Jaramillo (lower) 0.73 0.91 0.98 25.9 34.5 37.6 108-664DBrunhes/Matuyama Jaramillo (upper) Jaramillo (lower) 0.73 0.91 0.98 27.9 35.8 38.2 108-665ABrunhes/Matuyama Jaramillo (upper) Jaramillo (lower) Olduvai (upper) Olduvai (lower) Matuyama/Gauss 0.73 0.91 0.98 1.66 1.88 2.47 14.8 19.3 21.0 33.2 36.4 49.1 108-665BBrunhes/Matuyama Jaramillo (upper) Jaramillo (lower) Olduvai (upper) Olduvai (lower) Matuyama/Gauss 0.73 0.91 0.98 1.66 1.88 2.47 13.8 16.9 18.7 32.6 34.3-35.0 49.1 108-666ABrunhes/Matuyama Olduvai (upper) Olduvai (lower) Matuyama/Gauss 0.73 0.91 0.98 2.47 18.4 34.4-37.1 45.0 77.6 108-668BBrunhes/Matuyama Olduvai (upper) Olduvai (lower) 0.73 0.91 0.98 12.1-15.3 27.6 29.8 BIOSTRATIGRAPHIC SYNTHESIS: LEG 108, EASTERN EQUATORIAL ATLANTIC Table 2. Stratigraphic placement in meters of calcareous nannofossil events from Leg 108 sites and their assigned ages. Species Age (Ma) Table 2 (continued). Depth (mbsf) Species 108-657ALO Discoaster brouweri FOzyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Emiliania huxleyi FO acme Discoaster triradiatus 0.9-3.3 0.27 LO Pseudoemiliania lacunosa 0.46 LO Discoaster pentaradiatus 0.9-3.3 LO Calcidiscus macintyrei 1.45 LO Discoaster surculus 50.2-51.0 LO Discoaster brouweri LO Discoaster tamalis 55.2-61.2 1.89 FO acme Discoaster triradiatus 61.9-62.8 2.07 LO Sphenolithus spp. LO Discoaster pentaradiatus 59.7-68.5 2.35 LO Reticulofenestra pseudoumbilica LO Discoaster surculus 2.45 LO Amaurolithus spp. — LO Discoaster tamalis FO Ceratolithus rugosus 69.2-78.8 2.65 LO Sphenolithus spp. 88.2-97.7 FO Ceratolithus acutus 3.45 LO Reticulofenestra pseudoumbilica 98.1-98.9 LO Discoaster quinqueramus 3.56 LO Amaurolithus spp. 3.7 97.9-103.6 LO Amaurolithus amplificus FO Ceratolithus rugosus 4.6 135.7-146.0 FO Amaurolithus amplificus FO Ceratolithus acutus 5.0 135.7-146.0 FO Amaurolithus primus LO Discoaster quinqueramus 5.6 135.7-146.0 FO Discoaster quinqueramus LO Amaurolithus amplificus 5.6 145.2-146.0 LO Discoaster hamatus FO Amaurolithus amplificus 148.1-150.0 5.9 FO Catinaster calyculus FO Amaurolithus primus 6.5 150.0-154.8 FO Micula prinsii FO Discoaster quinqueramus 8.2 150.0-154.8 FO Micula murus LO Quadrum trifidum 108-658 AFO Emiliania huxleyi 34.2-43.7 0.27 108-662ALO Pseudoemiliania lacunosa 68.7-70.2 0.46 FO Emiliania huxleyi LO Calcidiscus macintyrei 99.1-99.4 1.45 LO Pseudoemiliania lacunosa LO Discoaster brouweri 124.7-126.9 1.89 LO Calcidiscus macintyrei FO acme Discoaster triradiatus 135.0-145.0 2.07 LO Discoaster brouweri LO Discoaster pentaradiatus 165.3-165.7 2.35 FO acme Discoaster triradiatus LO Discoaster surculus 2.45 165.8-166.2 LO Discoaster pentaradiatus LO Discoaster tamalis 197.7-201.3 2.65 LO Discoaster surculus LO Sphenolithus spp. 281.4-290.9 3.45 LO Discoaster tamalis LO Sphenolithus spp. 108-659BLO Reticulofenestra pseudoumbilica LO Pseudoemiliania lacunosa 7.8-8.1 0.46 LO Calcidiscus macintyrei 45.8-55.3 1.45 108-663 ALO Discoaster brouweri 54.7-55.9 1.89 FO Emiliania huxleyi FO acme Discoaster triradiatus 59.8-61.3 2.07 LO Pseudoemiliania lacunosa LO Discoaster pentaradiatus 70.6-70.8 2.35 LO Calcidiscus macintyrei LO Discoaster surculus 70.9-71.1 2.45 LO Discoaster brouweri LO Discoaster tamalis 78.5-80.0 2.65 FO acme Discoaster triradiatus LO Sphenolithus spp. 104.1-112.4 3.45 LO Discoaster pentaradiatus LO Reticulofenestra pseudoumbilica 104.1-112.4 3.56 LO Discoaster surculus LO Amaurolithus spp. 3.7 123.3-124.8 LO Discoaster tamalis FO Ceratolithus rugosus 136.4-143.1 4.6 FO Ceratolithus acutus 5.0 148.8-151.1 108-664DLO Discoaster quinqueramus 148.8-151.1 5.6 LO Pseudoemiliania lacunosa FO Amaurolithus primus 6.5 159.8-178.8 LO Calcidiscus macintyrei FO Discoaster quinqueramus 8.2 182.6-184.8 LO Discoaster brouweri LO Discoaster hamatus 8.9 188.3-191.7 FO acme Discoaster triradiatus FO Catinaster calyculus 10.0 191.7-199.1 LO Discoaster pentaradiatus FO Discoaster hamatus 191.7-199.1 10.0 LO Discoaster surculus FO Catinaster coalitus 10.8 199.1-200.7 LO Discoaster tamalis LO Cyclicargolithus floridanus 11.6 211.7-212.9 LO Sphenolithus spp. FO Triquetrorhabdulus rugosus 211.7-212.9 14.0 LO Reticulofenestra pseudoumbilica LO Sphenolithus heteromorphus 14.4 212.9-214.4 LO Amaurolithus spp. LO Helicosphaera ampliaperta 16.0 229.1-232.3 FO Ceratolithus rugosus FO Sphenolithus heteromorphus 17.1 235.8-245.3 FO Ceratolithus acutus LO Sphenolithus belemnos 17.4 235.8-245.3 LO Discoaster quinqueramus FO Sphenolithus belemnos 21.5 245.3-246.7 LO Amaurolithus amplificus LO Triquetrorhabdulus carinatus ? 245.3-246.7 FO Amaurolithus amplificus FO Discoaster druggii 23.2 246.7-248.6 FO Amaurolithus primus LO Sphenolithus ciperoensis 252.1-254.8 25.2 FO Discoaster quinqueramus 108-660ALO Pseudoemiliania lacunosa LO Calcidiscus macintyrei LO Discoaster brouweri FO acme Discoaster triradiatus LO Discoaster pentaradiatus LO Discoaster surculus LO Discoaster tamalis LO Sphenolithus spp. LO Reticulofenestra pseudoumbilica FO Ceratolithus rugosus LO Discoaster quinqueramus 0.46 1.45 1.89 2.07 2.35 2.45 2.65 3.45 3.56 4.6 5.6 11.3-16.5 32.3-33.1 39.8-40.9 41.6-42.7 45.7-47.2 47.2-48.7 53.0-54.5 61.9-63.4 63.4-64.9 71.9-74.5 74.5-76.5 108-661ALO Pseudoemiliania lacunosa LO Calcidiscus macintyrei 0.46 1.45 5.3-8.5 21.4-22.9 LO Discoaster FO Catinaster FO Discoaster hamatus calyculus hamatus 108-665ALO Pseudoemiliania lacunosa LO Calcidiscus macintyrei LO Discoaster brouweri FO acme Discoaster triradiatus LO Discoaster pentaradiatus LO Discoaster surculus LO Discoaster tamalis LO Sphenolithus spp. LO Reticulofenestra pseudoumbilica LO Amaurolithus spp. FO Ceratolithus rugosus Age (Ma) Depth (mbsf) 1.89 2.07 2.35 2.45 2.65 3.45 3.56 3.7 4.6 5.0 5.6 5.6 5.9 6.5 8.2 8.9 10.0 66.6 68.7 72.3 27.7-28.9 30.0-30.9 33.9-35.4 35.4-36.9 40.5-41.6 51.5-52.4 53.0-54.5 54.6-56.0 65.1-67.0 67.0-69.0 68.2-69.0 69.0-71.6 71.6-73.1 73.1-77.6 78.3-78.7 81.9-82.1 82.6-? 107.1-107.5 114.5-115.6 124.0-124.9 0.27 0.46 1.45 1.89 2.07 2.35 2.45 2.65 3.45 3.56 4.1-4.8 21.7-22.2 106.8-108.5 122.2-123.2 130.4-133.5 148.3-152.1 151.3-151.5 159.5-160.5 189.7-193.9 193.9-196.7 0.27 0.46 1.45 1.89 2.07 2.35 2.45 2.65 4.3-5.8 14.5-15.8 48.2-61.9 103.1-103.7 109.8-111.7 133.0-135.0 135.0-138.6 141.6-143.2 0.46 1.45 1.89 2.07 2.35 2.45 2.65 3.45 3.56 3.7 4.6 5.0 5.6 5.6 5.9 6.5 8.2 8.9 10.0 10.0 14.9-16.4 59.3-68.8 68.8-78.3 89.6-92.6 99.4-102.4 97.3-106.8 116.3-125.8 157.0-160.0 163.0-163.8 7-192.3 203.4-207.9 222.6-227.1 227.1-231.9 231.9-236.2 250.9-255.6 260.4-263.4 282.5-285.5 294.4-295.9 296.8-? 294.4-295.9 0.46 1.45 1.89 2.07 2.35 2.45 2.65 3.45 3.56 3.7 4.6 8.9-9.5 29.9-30.7 35.6-36.8 39.6-39.8 45.5-47.0 47.0-48.5 50.7-51.2 63.8-64.4 65.0-65.4 67.1-69.9 72.7-73.8 457 zyxwvutsrqp P.P.E. WEAVER ET AL. zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA discoasters survive longer and frequently provide stratigraphic information in strongly dissolved intervals. Calcareous nannofossils were completely absent below the uppermost Age Depth Species (Ma) (mbsf) part of the upper Miocene at Site 660, from the middle Miocene to the lowermost Pliocene at Site 661, and below the lower Pliocene at Site 665. 108-666A0.46 9.1-10.6 LOzyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Pseudoemiliania lacunosa Manivit (this vol.) has provided a site-by-site description of 1.45 32.9-33.3 LO Calcidiscus macintyrei the calcareous nannofossil biostratigraphy, including range LO Discoaster brouweri 1.89 46.0-48.6 charts that show the stratigraphic distribution of the total 2.07 51.6-54.5 FO acme Discoaster triradiatus assemblages and the critical marker species. She also dis2.35 67.0-68.3 LO Discoaster pentaradiatus 2.45 70.0-75.7 LO Discoaster surculus cussed the general character of preservation, abundance, and LO Discoaster tamalis 2.65 75.7-86.9 diversity of the nannofossil assemblages, with respect to the 3.45 123.1-126.3 LO Sphenolithus spp. environmental setting of the individual sites. LO Reticulofenestra pseudoumbilica 3.56 123.1-126.3 Chepstow-Lusty et al. (this vol.) and Olafsson (this vol.) LO Amaurolithus spp. 3.7 126.3-131.5 4.6 144.9-150.5 FO Ceratolithus rugosus provided quantitative studies of calcareous nannofossils from 5.0 FO Ceratolithus acutus 150.5-? the late Pliocene of Sites 658, 659, and 662 and the Oligocene to middle Miocene of Site 667, respectively. These studies 108-667 A6.6-6.9 0.46 LO Pseudoemiliania lacunosa have in common (1) the adoption of an identical counting 1.45 16.5-29.8 LO Calcidiscus macintyrei technique, (2) the use of closely spaced sample intervals, and 16.5-29.8 1.89 LO Discoaster brouweri (3) resolved biostratigraphic information—in the case of Olafs2.07 16.5-29.9 FO acme Discoaster triradiatus son, as a main focus in the Oligocene through middle Miocene 2.35 32.2-33.8 LO Discoaster pentaradiatus 35.1-37.0 2.45 LO Discoaster surculus interval from Site 667, and in the case of Chepstow-Lusty and 40.5-41.7 2.65 LO Discoaster tamalis others, as a by-product of their interest in the significance of 48.8-49.6 3.45 LO Sphenolithus spp. late Pliocene discoaster abundance fluctuations from Sites 49.6-54.2 3.56 LO Reticulofenestra pseudoumbilica 658, 659, and 662. 58.3-67.8 3.7 LO Amaurolithus spp. 4.6 75.8-78.3 FO Ceratolithus rugosus Planktonic and benthic foraminifers have similar strati79.7-85.1 5.0 FO Ceratolithus acutus graphic distributions at Leg 108 sites and are absent when 84.2-85.1 5.6 LO Discoaster quinqueramus there is strong dissolution. They are present in all sites 106.8-108.3 6.5 FO Amaurolithus primus throughout the Quaternary and upper Pliocene, but they 118.3-120.0 8.2 FO Discoaster quinqueramus 157.9-158.3 11.6 LO Cyclicargolithus floridanus become poorly represented in the deeper water sites through 157.6-158.0 14.0 FO Triquetrorhabdulus rugosus the early Pliocene and Miocene. Sites 659 and 667 contain 160.3-160.9 14.4 LO Sphenolithus heteromorphus foraminifers from the middle Oligocene to Holocene. The 166.2-166.6 16.0 LO Helicosphaera ampliaperta planktonic foraminiferal fauna from the upper Miocene to 207.7-208.0 17.1 FO Sphenolithus heteromorphus 211.3-211.7 17.4 LO Sphenolithus belemnos Holocene has been discussed by Weaver and Raymo (this 244.7-229.8 21.5 FO Sphenolithus belemnos vol.), and the Oligocene to middle Miocene fauna has been 9 251.4-251.8 LO Triquetrorhabdulus carinatus described by Miller et al. (this vol.). The former study was 250.4-257.8 FO Discoaster druggii 23.2 limited to core-catcher samples augmented by extra samples 293.0-293.4 25.2 LO Sphenolithus ciperoensis 343.3-352.2 28.2 LO Sphenolithus distentus from around zonal boundaries. The study by Miller et al. (this 364.8-376.0 30.2 FO Sphenolithus ciperoensis vol.) was based on a more detailed examination of 1-6 samples per core and included a comparison of Site 667 with 108-668BLO Pseudoemiliania lacunosa 0.46 8.5-10.0 Site 366, which was also drilled on the Sierra Leone Rise LO Calcidiscus macintyrei 1.45 22.8-24.6 during DSDP Leg 41. LO Discoaster brouweri 1.89 29.6-30.1 The quality of the diatom assemblage in the upper FO acme Discoaster triradiatus 2.07 31.2-? Pliocene to Holocene varied greatly among the Leg 108 Note: Ages are as presented in Ruddiman, Sarnthein, et al., 1988. sites. Preservation and abundances were relatively good at FO = first occurrence and LO = last occurrence. sites underlying the waters with the highest primary productivity, specifically Sites 658, 662, and 663. Abundances and preservation were moderate at Site 664. Sites underlying show the intervals that were cored at each site and indicate the unproductive waters, such as Sites 657, 659-661, and stratigraphic occurrence of the major microfossil groups (cal665-668, were generally very poor in diatoms. Diatoms only careous nannofossils, planktonic and benthic foraminifers, occur sporadically in sediments older than Pliocene in age. and diatoms), together with the intervals in which paleomagThe marine diatom flora is described by Baldauf and Pokras netic results can be regarded as reliable. One can see from the (this vol.). distributions that the paleomagnetic signals were only detected between 0 and 2.5 or 3 Ma in most cases and only reach the Gauss/Gilbert boundary in Hole 661B. CONCLUSION The most complete biostratigraphic records are also The stratigraphic resolution obtained in the Pliocenelimited to the Pliocene to Holocene interval, although there Pleistocene interval of all the Leg 108 sites was excellent and is some information from the Miocene and Oligocene, parusually backed up by paleomagnetic data. Therefore, these ticularly from Sites 659 and 667. The Eocene was cored at sites will provide considerable insight into previous oceanSite 660. Although no calcareous microfossils were found in ographic and climatic conditions that prevailed in the eastthese cores, middle Eocene diatoms and radiolarians do ern equatorial Atlantic Ocean during the latest Neogene. occur. Site 661 drilled through to the Upper Cretaceous, Below the Pliocene, numerous biostratigraphic problems which was recognized on the basis of its calcareous nannostill remain; and, although we cored significant thicknesses fossil flora. of these sediments, we did not obtain the vital paleomagCalcareous nannofossils are the most widely distributed netic results that could have improved the stratigraphic group in Leg 108 sites. Although this group suffers dissolution resolution. and the placoliths disappear along with the foraminifers, the Table 2 (continued). 458 BIOSTRATIGRAPHIC SYNTHESIS: LEG 108, EASTERN EQUATORIAL ATLANTIC Table 3. Stratigraphic placement in meters of planktonic foraminifer events from Leg 108 sites and their assigned ages. Species Age a Depth Age c Table 3 (continued). Species Age a Depth Age c 3.80-4.00 3.9 108-657A59.9-62.5 LO Globigerina nepenthes 3.80-4.00 59.9-62.5 1.9 4.15 FOzyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Globorotalia truncatulinoides 54.7-60.6 1.7-1.95 FO Globorotalia puncticulata 3.18-3.74 3.4 49.1-58.6 1.8 LO Globigerinoides obliquus 54.7-60.6 1.7-1.95 FO Globorotalia miocenica 4.60-5.38 5.6 FO Globorotalia inflata 65.1-68.1 2.1 2.15-2.25 64.2-65.9 FO Globorotalia margaritae 4.60-5.38 2.2 LO Globorotalia miocenica 65.1-68.1 5.3 LO Globoquadrina dehiscens 2.15-2.25 64.2-65.9 Reapp. Pulleniatina spp. 2.2 2.15-2.25 64.2-65.9 108-662ALO Globorotalia puncticulata 2.3 2.25-2.35 65.9-68.2 1.73-1.94 117.2-126.7 1.8 LO Globigerinoides obliquus extremus LO Dentogloboquadrina altispira 2.9 2.97-3.05 83.2-84.5 1.52 82.4-107.7 1.9 FO Globorotalia truncatulinoides LO Sphaeroidinellopsis seminulina 3.0 83.2-84.5 2.97-3.05 1.94-2.14 2.1 FO Globorotalia inflata 126.7-136 Disapp. Pulleniatina spp. 3.3 4.18-4.28 130.7-131.6 2.24-2.36 140.5-145.7 2.1 LO Globorotalia exilis LO Globorotalia margaritae 3.4 92.7-130.7 3.35-4.18 2.18-2.24 137.5-140.5 LO Globorotalia miocenica 2.2 FO Globorotalia crassaformis 4.15 4.28-4.55 131.6-134.6 2.18-2.24 137.5-140.5 Reapp. Pulleniatina spp. 2.2 LO Globigerina nepenthes 3.9 4.18-4.28 130.7-131.6 2.18-2.24 137.5-140.5 LO Globorotalia puncticulata 2.3 FO Globorotalia puncticulata 4.15 c 131.6-134.6 4.28-4.55 2.86-2.90 LO Dentogloboquadrina altispira 166.8-168.4 2.9 FO Globorotalia miocenica 3.4 92.7-130.7 3.35-4.18 2.90-3.04 LO Sphaeroidinellopsis seminulina 168.4-174.2 3.0 FO Globorotalia margaritae 5.6 5.40-5.55 144.3-146.1 Disapp. Pulleniatina spp. 3.26-3.49 183.7-193.2 3.3 108-658ALO Globorotalia margaritae 3.59-3.66 3.4 197.5-200.5 FO Globorotalia truncatulinoides 1.9 1.75-1.90 119.7-129.2 FO Globorotalia miocenica 3.26-3.49 183.7-193.2 3.4 LO Globigerinoides obliquus 1.8 91.2-100.7 0.62-1.46 LO Globorotalia miocenica 2.2 2.30-2.36 108-664D155.3-157.7 FO Globorotalia inflata 1.20-1.40 2.1 138.7-148.2 49.8-59.3 1.8 2.04-2.19 LO Globigerinoides obliquus extremus LO Globorotalia puncticulata 1.80-1.95 2.3 78.3-87.8 2.36-2.48 FO Globorotalia truncatulinoides 157.7-167.4 1.9 LO Dentogloboquadrina altispira 1.80-1.95 2.9 FO Globorotalia inflata 214.9-224.9 78.3-87.8 2.1 2.90-3.00 LO Sphaeroidinellopsis seminulina 1.95-2.2 3.0 LO Globorotalia exilis 87.8-97.3 2.1 3.00-3.08 224.4-233.9 LO Globorotalia margaritae 2.20-2.4 3.4 97.3-106.8 LO Globorotalia miocenica 290.9-300.4 2.2 3.60-3.69 2.20-2.4 Reapp. Pulleniatina spp. 97.3-106.8 2.2 108-659ALO Globorotalia puncticulata 106.8-125.8 2.40-2.8 2.3 1.9 FO Globorotalia truncatulinoides 36.3-45.8 1.25-1.60 LO Dentogloboquadrina altispira 2.80-3.0 125.8-135.3 2.9 1.8 LO Globigerinoides obliquus 45.8-64.8 1.60-2.20 LO Sphaeroidinellopsis seminulina 2.80-3.0 125.8-135.3 3.0 FO Globorotalia inflata 2.1 1.60-2.20 45.8-64.8 Disapp. Pulleniatina spp. 3.38-3.57 154.3-163.8 3.3 LO Globorotalia exilis 2.1 2.20-2.25 64.8-65.7 LO Globorotalia margaritae 3.78-3.97 173.3-182.8 3.4 LO Globorotalia miocenica 2.2 64.8-65.7 2.20-2.25 FO Globorotalia miocenica 4.60-4.80 211.3-220.8 3.4 Reapp. Pulleniatina spp. 2.2 64.8-65.7 2.20-2.25 LO Globigerina nepenthes 182.8-192.3 3.97-4.18 3.9 LO Globorotalia puncticulata 2.3 2.25-2.50 65.7-74.3 FO Globorotalia crassaformis 3.97-4.18 4.15 182.8-192.3 LO Dentogloboquadrina altispira 2.9 83.8-84.8 2.85-2.90 FO Globorotalia puncticulata 4.18-4.38 192.3-201.8 4.15 LO Sphaeroidinellopsis seminulina 3.0 2.95-3.05 87.5-90.5 FO Globorotalia margaritae 5.72-6.22 230.3-239.8 5.6 Disapp. Pulleniatina spp. 3.3 3.15-3.45 93.3-102.8 LO Globoquadrina dehiscens 5.72-6.22 230.3-239.8 5.3 LO Globorotalia margaritae 3.4 3.45-3.72 102.8-112.3 FO Neogloboquadrina humerosa 5.72-6.22 230.3-239.8 7.5 FO Globorotalia crassaformis 4.15 4.20-4.40 125.5-131.3 LO Globigerina nepenthes 3.9 125.5-131.3 4.20-4.40 108-665AFO Globorotalia puncticulata 4.15 4.20-4.40 125.5-131.3 2.28-2.57 46.1-50.4 1.8 LO Globigerinoides obliquus extremus FO Globorotalia miocenica 3.4 112.3-116.0 3.72-3.85 1.03-1.52 21.9-31.4 1.9 FO Globorotalia truncatulinoides FO Globorotalia margaritae 5.6 6.20-8.10 159.8-182.8 2.09-2.28 40.9-46.1 2.1 FO Globorotalia inflata LO Globoquadrina dehiscens 5.3 8.20-10.50 188.3-197.8 2.09-2.28 40.9-46.1 2.1 LO Globorotalia exilis FO Neogloboquadrina humerosa 7.5 159.8-182.8 8.20-10.50 2.09-2.28 2.2 40.9-46.1 LO Globorotalia miocenica FO Neogloboquadrina acostaensis 10.2 159.8-182.8 8.20-10.50 2.09-2.28 2.2 40.9-46.1 Reapp. Pulleniatina spp. 2.09-2.28 40.9-46.1 2.3 LO Globorotalia puncticulata 108-660A2.67-2.92 52.6-55.7 LO Dentogloboquadrina altispira 2.9 FO Globorotalia truncatulinoides 1.9 39.8-44.0 1.95-2.25 2.92-3.13 55.7-58.9 LO Sphaeroidinellopsis seminulina 3.0 d LO Globigerinoides obliquus 1.8 20.8-30.3 0.80-1.30 3.82-3.86 Disapp. Pulleniatina spp. 3.3 69.4-69.9 FO Globorotalia inflata 2.1 1.95-2.25 39.8-44.0 LO Globorotalia exilis 2.1 2.25-2.42 44.0-46.7 108-667ALO Globorotalia miocenica 2.2 2.25-2.42 44.0-46.7 1.1-2.00 18.1-27.4 LO Globigerinoides obliquus extremus 1.8 Reapp. Pulleniatina spp. 2.2 1.90-2.07 39.8-41.6 1.48-2.00 18.1-27.4 FO Globorotalia truncatulinoides 1.9 LO Globorotalia puncticulata 2.3 2.25-2.42 44.0-46.7 0.76-1.05 FO Globorotalia inflata 2.1 10.8-14.9 LO Dentogloboquadrina altispira 53.8-56.6 2.9 2.87-3.08 LO Globorotalia exilis 2.00-2.18 27.4-29.8 2.1 LO Sphaeroidinellopsis seminulina 3.0 3.08-3.24 56.6-58.8 LO Globorotalia miocenica 2.00-2.18 27.4-29.8 2.2 FO Globorotalia crassula 3.08-3.24 56.6-58.8 Reapp. Pulleniatina spp. 2.18-2.68 29.8-39.3 2.2 Disapp. Pulleniatina spp. 58.8-68.3 3.3 3.24-3.84 LO Globorotalia puncticulata 2.00-2.18 27.4-29.8 2.3 FO Globorotalia miocenica 3.4 3.08-3.24 56.6-58.8 LO Dentogloboquadrina altispira 2.72-2.85 40.6-43.6 2.9 LO Globorotalia margaritae 3.4 68.3-69.4 3.84-3.90 LO Sphaeroidinellopsis seminulina 2.72-2.85 40.6-43.6 3.0 FO Globorotalia crassaformis 4.15 69.4-72.1 3.90-4.55 Disapp. Pulleniatina spp. 3.32-3.50 52.9-55.9 3.3 LO Globigerina nepenthes 69.4-72.1 3.9 3.90-4.55 LO Globorotalia margaritae 3.32-3.50 3.4 52.9-55.9 LO Neogloboquadrina pachyderma (s) 69.4-72.1 3.90-4.55 FO Globorotalia miocenica 4.56-5.70 77.3-86.8 3.4 FO Globorotalia puncticulata 4.15 58.8-68.3 3.24-3.84 LO Globigerina nepenthes 3.80-3.98 62.3-65.3 3.9 FO Globorotalia crassaformis 4.12-4.56 68.8-77.3 4.15 108-661AFO Globorotalia puncticulata 4.12-4.56 68.8-77.3 4.15 FO Globorotalia truncatulinoides 1.9 1.6-11.1 0.1-0.67 FO Globorotalia margaritae 5.50-6.34 96.3-105.8 5.6 LO Globigerinoides obliquus 1.8 11.1-20.6 0.67-1.30 LO Globoquadrina dehiscens 4.56-5.70 77.3-86.8 5.3 LO Globorotalia exilis 2.1 31.5-34.5 1.96-2.24 LO Neogloboquadrina humerosa 6.34-7.80 7.5 105.8-115.3 FO Globorotalia inflata 2.1 30.1-31.5 1.85-1.96 LO Neogloboquadrina acostaensis 8.60-10.30 124.8-134.3 10.2 LO Globorotalia miocenica 2.2 31.5-34.5 1.96-2.24 Reapp. Pulleniatina spp. 1.96-2.24 2.2 31.5-34.5 Note: FO = first occurrence, LO = last occurrence, and Disapp. = disappearLO Globorotalia puncticulata 31.5-34.5 1.96-2.24 2.3 ance. a LO Dentogloboquadrina altispira 2.9 2.70-2.87 41.0-44.0 Ages as presented in Ruddiman, Sarnthein, et al., 1988. b LO Sphaeroidinellopsis seminulina 3.0 44.0-47.0 2.87-3.05 Revised ages interpolated from the sedimentation curves presented in Ruddiman, Disapp. Pulleniatina spp. 3.3 49.1-58.6 3.20-3.75 Sarnthein, et al., 1988. c LO Globorotalia margaritae 3.4 3.74-3.80 58.6-59.9 Interval occurs in a slump. FO Globorotalia crassaformis 4.15 59.9-62.5 3.80-4.00 Probably reworked. 459 zyxwvutsrqp P.P.E. WEAVER ET AL. 20°W 10° 0° Figure 1. Location of sites cored during Leg 108. Arrows mark current systems; stippled areas indicate regions of strong Pliocene-Pleistocene up welling and divergence. 460 BIOSTRATIGRAPHIC SYNTHESIS: LEG 108, EASTERN EQUATORIAL ATLANTIC 659 series Epoch 1.66 5.3 MNFD 660 MNFD 661 MNFD zyxwvutsrq 667 MNFD zyxwvutsrqponmlkjihg Quaternary late Pliocene early Pliocene late Miocene zA middle Miocene early Miocene t 23.7 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA late Oligocene early Oligocene 37 late Eocene CU middle Eocene < early Eocene 57.8 late Paleocene early Paleocene 66.4 late Cretaceous zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA 95.5 Figure 2. Representation of cored intervals (thick lines) and distribution of major fossil groups in the deeper Leg 108 sites. Diagonal shading = hiatuses, M = paleomagnetic record, N = calcareous nannofossil distribution, F = planktonic and benthic foraminifer distribution, and D = diatom distribution. 461 P.P.E. WEAVER ET AL. 657 EpOCh 658 MNFD MNFD 662 MNFD 663 MNFD 664 MNFD 665 MNFD 666 MNFD 668 MNFD Quaternary 1.66 late Pliocene 3.4 early Pliocene 03 ^ zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA 5.3 late Miocene 10.2 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Figure 3. Representation of cored intervals (thick lines) and distribution of major fossil groups in the shallower Leg 108 sites. Diagonal lines = hiatuses, M = paleomagnetic record, N = calcareous nannofossil distribution, F = planktonic and benthic foraminifer distribution, and D = diatom distribution. zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA from the Atlantic, Indian and Pacific Oceans. Mar. Micropaleontol, 8:141-170. Baldauf, J., 1987. Diatom biostratigraphy of the middle- and highlatitude North Atlantic Ocean, Deep Sea Drilling Project Leg 94. In Ruddiman, W. F., Kidd, R. B., Thomas, E., et al., Init. Repts. Depth Age DSDP, 94, Pt. 2: Washington (U.S. Govt. Printing Office), (Ma) Species (mbsQ 729-763. Berggren, W. A., Kent, D. V., and Flynn, J. J., 1985a. Jurassic to 108-658A/658BPaleogene: Part 2, Geochronology and chronostratigraphy. In 60.2-64.7 LOzyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Nitzschia reinholdii "0.65(0.44) 126.4-132.9 1.8 FO Pseudoeunotia doliolus Snelling, N. J. (Ed.), The Chronology of the Geological Record. 163.1 Occ. Thalassiosira convexa >2.2 Geol. Soc. Mem. (London), 10:141-195. Berggren, W. A., Kent, D. V., and Van Couvering, J. A., 1985b. The 108-662Aa Neogene: Part 2, Neogene geochronology and chronostratigraphy. 22.2-31.7 0.65(0.44) LO Nitzschia reinholdii In Snelling, N. J. (Ed.), The Chronology of the Geological Record. FO Pseudoeunotia doliolus 126.7-131.2 1.8 Geol. Soc. Mem. (London), 10:211-260. Occ. Nitzschia jouseae 162.31 >2.6 Hodell, D. A., and Kennett, J. P., 1986. Late Miocene-early Pliocene 108-663A/663Bstratigraphy and paleoceanography of the south Atlantic and 99.7-109.2 FO Pseudoeunotia doliolus 1.8 southwest Pacific oceans: a synthesis. Paleoceanography, 1: 133.0 Occ. Thalassiosira convexa >2.2 285-311. 108-664DRuddiman, W., Sarnthein, M., et al., 1988. Proc. ODP, Init. Repts., 78.3-87.8 FO Pseudoeunotia doliolus 1.8 108: College Station, TX (Ocean Drilling Program). 125.8 LO Nitzschia jouseae >2.6 Thierstein, H. R., Geitzenauer, K. R., Molfino, B., and Shackleton, N. J., 1977. Global synchroneity of late Quaternary coccolith Note: Ages are as presented in Ruddiman, Sarnthein, et al., datum levels: validation by oxygen isotopes. Geology, 5:400-404. 1988. FO = first occurrence, LO = last occurrence, and Weaver, P.P.E., and Clement, B. M., 1987. Magnetobiostratigraphy Occ. = occurrence. a of planktonic foraminiferal datums: Deep Sea Drilling Project Leg Age assigned to this event by Baldauf, 1987. 94, North Atlantic. In Ruddiman, W. F., Kidd, R. B., Thomas, E., et al., Init. Repts. DSDP, 94, Pt. 2: Washington (U.S. Govt. Printing Office.), 815-829. Table 4. Stratigraphic placement in meters of diatom events from Sites 658, 662, 663, and 664 and their assigned ages. REFERENCES Backman, J., and Shackleton, N. J., 1983. Quantitative biochronology of Pliocene and early Pleistocene calcareous nannofossils 462 Date of initial receipt: 8 February 1989 Date of acceptance: 26 May 1989 Ms 108B-171 z