Dinoflagellate cyst counts and age model from sediment samples of ODP Hole 175-1085A

Sediment samples from ODP Site 1085 were investigated in order to obtain more information on the initiation and development of the Benguela upwelling system during the middle and upper Miocene. In particular, our intent was to establish the causes of the upwelling as well as the response of the upwelling regime to the development of the Antarctic Circumpolar Current. Based on changes in the calcareous dinoflagellate cyst association, we found an initial increase of the dinoflagellate cyst productivity, probably related to the initiation of upwelling about 11.8 Ma ago. Two distinct increases in cyst productivity in conjunction with temperature decreases of the upper water masses reflect upwelling pulses off Namibia and occur at the end of the Miocene cooling events Mi5 (about 11.5 Ma) and Mi6 (about 10.5 Ma). Both cooling events are associated with an ice volume increase in Antarctica and are thought to have led to an increase in southeasterly winds, possibly causing these two upwelling pulses. We demonstrate a decrease in dinoflagellate cyst productivity and enhanced terrigenous input via the Orange River after the Mi5 event. At about 11.1 Ma, the dinoflagellate cyst productivity increases again. The polar cyst species Caracomia arctica occurs here for the first time. This implies an influence of subantarctic mode water and therefore a change in the quality of the upwelling water which allowed the Benguela upwelling to develop into modern conditions. From about 10.4 Ma, C. arctica forms a permanent part of the association, pointing to an establishment of the upwelling regime.

(Table 2) Radiolaria species in nodule samples from the Clarion-Clipperton province, Pacific Ocean

Radiolaria were studied in 19 manganese nodules raised from the bottom. The nodules occurred mainly on the surface of thin Quaternary sediments covering Tertiary deposits of various ages (Middle Eocene to Early Miocene). Radiolaria in nodule cores and in inner and surface layers were studied. We found 85 radiolaria species and groups of species. Usually 1-4 to 6-19 radiolaria species were detected in each of the samples. Species belonging to Middle Eocene, Late Miocene to Early Oligocene, and Oligocene to Early Miocene were found. Rare Neogene species were revealed only in fractured surface layers. Age of the nodules is mainly Oligocene. Seismic waves cause sediment vibration, loosening disintegration, and removal of suspension by bottom currents. The vibration effect causes ancient nodules to float up to the surface of Quaternary sediment. This hypothesis suggests the reason for characteristics of the Clarion-Clipperton zone: regional stratigraphic hiatus, accumulation of residual fields of nodules, and the ''floating up'' of nodules to the surface of the Quaternary sediments.

Radiolarian biostratigraphy in the central Indian Ocean

Identifiable radiolarians of stratigraphic importance were recovered at eight of the sites drilled on Leg 115. The assemblages range in age from Holocene to middle Eocene (Dictyoprora mongolfieri Zone, about 48 Ma). Faunal preservation is particularly good in two stratigraphic intervals: the Holocene through upper Miocene (0-9 Ma), and the lowermost Oligocene to middle Eocene (35-48 Ma). Fluctuating rates of silica accumulation at these drill sites during the Cenozoic reflect changing tectonic and paleoceanographic conditions. In particular, the gradual closure of the Indonesian and Tethyan seaways and the northward migration of the Indian subcontinent severely restricted zonal circulation and silica accumulation in tropical latitudes during the late Oligocene through middle Miocene. By the late Miocene the Indian subcontinent had moved sufficiently north of the equator to allow trans-Indian zonal circulation patterns to become reestablished, and biosiliceous sedimentation resumed. The composition of the radiolarian assemblages in the tropical Indian Ocean is closely comparable with that of the 'stratotype' sequences in the equatorial Pacific. However, there are some notable exceptions in Indian Ocean assemblages: (1) the scarcity of the genera Pterocanium and Spongaster in the Neogene; (2) the absence of the stratigraphically important Podocyrtis lineage, P. diamesa -> P. phyxis -> P. ampla, in the middle Eocene; and (3) the scarcity of taxa of the genus Dorcadospyris, with the exception of D. ateuchus. The succession of radiolarian events was tabulated for those stratigraphic intervals where the assemblages were well preserved. We identified 55 events in the middle Eocene to earliest Oligocene, and 31 events in the late Miocene to Holocene. The succession of events is closely comparable with that of the tropical Pacific. However, there are exceptions that appear to be real, rather than artifacts of sample preservation, mixing, and core disturbance.

Benthic foraminifera of cores from ODP Leg 117

The relative abundances of benthic foraminifers from the Oman margin have been analyzed from ODP Sites 725 and 726 near the upper boundary of the oxygen-minimum zone (OMZ) and 728 near the lower boundary. The relative abundance pattern of the benthic foraminiferal species in the two shallow sites show synchronous changes, which, together with variations in the faunal composition, may be attributed to changes in the location of the upper boundary of the OMZ during the last 7 million years. At the deeper site, the relative abundance pattern shows considerable variation in the faunal composition during the last 8 million years. The strong dominance of the shallow-water species Ammonia beccarii during the early Pliocene at Site 728 suggests a water depth less than 400 m during the early Pliocene and subsequent subsidence during the middle and late Pliocene to the present > 1400 m water depth.

Occurrence and abundance of late Early Cretaceous radiolarians at DSDP Leg 62 Holes

Well-preserved Mesozoic radiolarian faunas have been recovered at four sites of Deep Sea Drilling Project Leg 62. Late Early Cretaceous assemblages, which occur always with foraminifers or calcareous nannoplankton, allow the description of 21 new species, the introduction of a new zone scheme, and calibration of the radiolarian zones with the geochronological scale.

Calcareous dinoflagellates in Cretaceous to Recent sediments of DSDP Hole 39-356

Calcareous dinoflagellates often dominate the dinoflagellate cyst assemblage in Cretaceous to Recent oceanic sediments. However, their distribution in Paleogene sediments has scarcely been studied. The investigation of samples from DSDP Site 356 for their calcareous dinoflagellate content revealed 35 mainly long-ranging taxa. The associations and characteristic wall types (pithonelloid, oblique, radial, tangential) fluctuate quantitatively and qualitatively in distinct stratigraphic patterns. Significant shifts, primarily at the K/T boundary and the Paleocene/Eocene boundary, reflect changes in environmental conditions. Certain dinoflagellates forming calcareous cysts, such as Operculodinella operculata, were well adapted to the relatively rapid change of environmental conditions at the K/T boundary, thus blooming to dominate the carbonate flux to the ocean floor. In contrast to the stable Paleocene associations, Eocene calcareous dinoflagellates show fluctuations in relative abundances. These fluctuations can possibly be attributed to redeposition related to increased seaward transport of specimens, due to strengthened western boundary currents. The flora includes two new genera, one new species, and two new forms: Retesphaera diadema Hildebrand-Habel, Willems et Versteegh, gen. et. sp. nov., Cervisiella saxea (Stradner, 1961) Hildebrand-Habel, Willems et Versteegh, gen. et comb. nov., Sphaerodinella? tuberosa forma elongata Hildebrand-Habel, Willems et Versteegh, comb. et forma nov., Sphaerodinella? tuberosa forma variospinosa Hildebrand-Habel, Willems et Versteegh, comb. et forma nov. Three new combinations are proposed: Cervisiella saxea (Stradner, 1961) Hildebrand-Habel, Willems et Versteegh, gen. et comb. nov., Operculodinella operculata (Bramlette et Martini, 1964) Hildebrand-Habel, Willems et Versteegh, comb. nov., and Sphaerodinella? tuberosa (Kamptner, 1963) Hildebrand-Habel, Willems et Versteegh, comb. nov. The genus Operculodinella Kienel, 1994 is emended.

Quaternary radiolarians and plamktonic foraminifera from the mouth of the Gulf of California

I recovered well-preserved radiolarian assemblages from the Quaternary sediments drilled at all four sites at the mouth of the Gulf of California during Leg 65. The sites, with positions and water depths averaged for all hole locations per site, are Site 482 - 22°47.4'N, 107°59.6'W; water depth, 3022 meters. Site 483 - 22°53.0'N, 108°44.8' W; water depth, 3070 meters. Site 484 - 23°11.2'N, 108°23.6'W; water depth, 2887 meters. Site 485 - 22°44.9'N, 107°54.2'W; water depth, 2981 meters. The nearly 200 taxa I identified are listed alphabetically in the systematic reference list. The only reliable radiolarian biostratigraphic datum determined for the Quaternary sedimentary section is the highest occurrence of Axoprunum angelinum (Hays) at Sites 483, 484, and 485.