287 resultados para A. carinata
Resumo:
The Quaternary benthic foraminifers from Leg 95 Sites 612 and 613 were examined with respect to paleoceanographic trends. Data from the two sites indicate the presence of markedly different bottom-water masses, during both glacial and interglacial periods. The dominant interglacial species at Site 612 is Uvigerinct peregrina, which is barely present in corresponding intervals at Site 613. Dominant glacial species are Elphidium excavatum and Cassidulina reniforme at Site 612 and Epistominella takayanagii at Site 613.
Resumo:
During Leg 198 of the Ocean Drilling Program (ODP), Paleogene sediments were recovered form 10 holes at four sites along a bathymetric transect from the Southern High of Shatsky Rise. In terms of age, the Paleogene successions span from the Cretaceous/Paleocene boundary to the early Oligocene. Sediments are mainly composed of tan nannofossil ooze with scattered darker layers richer in clay. This data report concerns planktonic foraminiferal biostratigraphy from three holes, specifically Hole 1209A (water depth = 2387 m), Hole 1210A (water depth = 2573 m), and Hole 1211A (water depth = 2907 m). The thickness of Paleogene sediments is 105.90 m in Hole 1209A, 95.05 m in Hole 1210A, and 56.11 m in the deepest Hole 1211A. Preliminary investigations conducted on board revealed that at Site 1209 the succession was mostly complete, whereas the succession was more condensed at Site 1211.
Resumo:
Cores from Sites 1129, 1131, and 1132 (Ocean Drilling Program (ODP) Leg 182) on the uppermost slope at the edge of the continental shelf in the Great Australian Bight reveal the existence of upper Pleistocene bryozoan reef mounds, previously only detected on seismic lines. Benthic foraminiferal oxygen isotope data for the last 450,000 years indicate that bryozoan reef mounds predominantly accumulated during periods of lower sea level and colder climate since stage 8 at Sites 1129 and 1132 and since stage 4 at the deeper Site 1131. During glacials and interstadials (stages 2-8) the combination of lowered sea level, increased upwelling, and absence of the Leeuwin Current probably led to an enhanced carbon flux at the seafloor that favored prolific bryozoan growth and mound formation at Site 1132. At Site 1129, higher temperatures and downwelling appear to have inhibited the full development of bryozoan mounds during stages 2-4. During that time, favorable hydrographic conditions for the growth of bryozoan mounds shifted downslope from Site 1129 to Site 1131. Superimposed on these glacial-interglacial fluctuations is a distinct long-term paleoceanographic change. Prior to stage 8, benthic foraminiferal assemblages indicate low carbon flux to the seafloor, and bryozoan mounds, although present closer inshore, did not accumulate significantly at Sites 1129 and 1132, even during glacials. Our results show that the interplay of sea level change (eustatic and local, linked to platform progradation), glacial-interglacial carbon flux fluctuations (linked to local hydrographic variations), and possibly long-term climatic change strongly influenced the evolution of the Great Australian Bight carbonate margin during the late Pleistocene.