Foraminifer, coarse fraction and carbonate characteristics of sediments from ODP Leg 198 sites on Shatsky Rise

Holes 1209A and 1211A on Southern High, Shatsky Rise contain expanded, nearly continuous records of carbonate-rich sediment deposited in deep water of the equatorial Pacific Ocean during the Paleocene and Eocene. In this study, we document intervals of carbonate dissolution in these records by examining temporal changes in four parameters: carbonate content, coarse size fraction (>38 µm), benthic foraminiferal abundance, and planktonic foraminiferal fragmentation ratio. Carbonate content is not a sensitive indicator of carbonate dissolution in the studied sections, although rare intervals of low carbonate may reflect times of relatively high dissolution. The proportion of coarse size fraction does not accurately record carbonate dissolution either because the relative abundance of nannofossils largely determines the grain-size distribution. Benthic abundance and fragmentation covary (r**2 = 0.77) and are probably the best indicators for carbonate dissolution. For both holes, records of these parameters indicate two episodes of prominent dissolution. The first of these occurs in the upper Paleocene (~59-58 Ma) and the second in the middle to upper Eocene (~45-33.7 Ma). Other intervals of enhanced carbonate dissolution are located in the upper Paleocene (~56 Ma) and in the upper lower Eocene (~51 Ma). Enhanced preservation of planktonic foraminiferal assemblages marks the start of both the Paleocene and Eocene epochs.

Benthic foraminifera across the Cretaceous/Paleogene boundary in ODP Hole 198-1210A

Deep-sea benthic foraminifera show important but transient assemblage changes at the Cretaceous/Paleogene (K/Pg) boundary, when many biota suffered severe extinction. We quantitatively analyzed benthic foraminiferal assemblages from lower bathyal-upper abyssal (1500-2000 m) northwest Pacific ODP Site 1210 (Shatsky Rise) and compared the results with published data on assemblages at lower bathyal (~ 1500 m) Pacific DSDP Site 465 (Hess Rise) to gain insight in paleoecological and paleoenvironmental changes at that time. At both sites, diversity and heterogeneity rapidly decreased across the K/Pg boundary, then recovered. Species assemblages at both sites show a similar pattern of turnover from the uppermost Maastrichtian into the lowermost Danian: 1) The relative abundance of buliminids (indicative of a generally high food supply) increases towards the uppermost Cretaceous, and peaks rapidly just above the K/Pg boundary, coeval with a peak in benthic foraminiferal accumulation rate (BFAR), a proxy for food supply. 2) A peak in relative abundance of Stensioeina beccariiformis, a cosmopolitan form generally more common at the middle than at the lower bathyal sites, occurs just above the buliminid peak. 3) The relative abundance of Nuttallides truempyi, a more oligotrophic form, decreases at the boundary, then increases above the peak in Stensioeina beccariiformis. The food supply to the deep sea in the Pacific Ocean thus apparently increased rather than decreased in the earliest Danian. The low benthic diversity during a time of high food supply indicates a stressed environment. This stress might have been caused by reorganization of the planktic ecosystem: primary producer niches vacated by the mass extinction of calcifying nannoplankton may have been rapidly (<10 kyr) filled by other, possibly opportunistic, primary producers, leading to delivery of another type of food, and/or irregular food delivery through a succession of opportunistic blooms. The deep-sea benthic foraminiferal data thus are in strong disagreement with the widely accepted hypothesis that the global deep-sea floor became severely food-depleted following the K/Pg extinction due to the mass extinction of primary producers ("Strangelove Ocean Model") or to the collapse of the biotic pump ("Living Ocean Model").

Carbonate and barite content accross the Eocene/Oligocene boundary of ODP Leg 198 sites, Shatsky Rise

The barite and CaCO3 content (in weight percent) of marine sediments can be used to determine spatial and temporal changes in export production (organic and carbonate carbon flux) and/or CaCO3 preservation (inorganic carbon burial). Here we report barite and CaCO3 content in Eocene/Oligocene (E/O) boundary sediments from locations drilled on Shatsky Rise during Ocean Drilling Program Leg 198. Records of these indexes may be used along with other data to determine how the major E/O boundary climatic transition (initiation of Antarctic glaciation and resultant ocean-climate system changes) affected marine export production/preservation at Shatsky Rise. Such data are necessary to elucidate the timing and phasing of changes in the carbon cycle relative to fluctuations in oceanographic conditions across this climatically important interval.

Planktonic foraminifera stratigraphy of ODP Holes 198-1209C and 198-1211C

During Leg 198, the Cretaceous/Paleocene (K/P) boundary was recovered in a remarkable set of cores in nine separate holes at Sites 1209, 1210, 1211, and 1212 on the Southern High of Shatsky Rise. The boundary succession includes an uppermost Maastrichtian white to very pale orange, slightly indurated nannofossil ooze overlain by lowermost Paleocene grayish orange foraminiferal ooze. The boundary between the uppermost Maastrichtian and the lowermost Paleocene is clearly bioturbated. The contact surface is irregular, and pale orange burrows extend 10 cm into the white Maastrichtian ooze. Preliminary investigations conducted on board revealed that the deepest sections of these burrows yielded highly abundant, minute planktonic foraminiferal assemblages dominated by Guembelitria with rare Hedbergella holmdelensis and Hedbergella monmouthensis, possibly attributable to the lowermost Paleocene Zone P0. The substantial thickness of the uppermost Maastrichtian Micula prinsii (CC26) nannofossil Zone and the lowermost Danian Parvularugoglobigerina eugubina (Palpha) foraminiferal Zone suggested that the K/P boundary was rather expanded compared to the majority of deep-sea sites (see Bralower, Premoli Silva, Malone, et al., 2002, doi:10.2973/odp.proc.ir.198.2002). This data report concerns the planktonic foraminiferal biostratigraphy across the K/P boundary in Hole 1209C, the shallowest site (2387 m water depth), and in Hole 1211C, the deepest site (2907 m water depth), where the foraminiferal record across the boundary appeared to be best preserved.