Calcareous microfossil isotopes and Miocene datum events of ODP Holes 189-1170A and 189-1172A

Downcore oxygen and carbon stable isotope records of planktonic and benthic foraminifers and fine-fraction carbonate from the southern high latitudes provide critical paleohydrographic constraints on the evolution of the Southern Ocean climate. In particular, the potential effects of an intensified Antarctic Circumpolar Current on the thermal isolation and cooling of the southern high latitudes, production of cold deep waters, and, ultimately, accumulation of continental ice on Antarctica in the middle Miocene are matters of interest. Using sediment materials from Ocean Drilling Program Leg 189 Sites 1170 and 1172 off Tasmania, Ennyu and Arthur (2004, doi:10.1029/151GM13) established the surface- and deepwater stable isotope records in the Southern Ocean across the middle Miocene event of the east Antarctic ice sheet expansion and discussed the paleoclimate proxy records in terms of the thermal evolution of the southern high latitudes and its effect on deepwater circulation. This report provides data tables and other supporting information relevant to discussions presented in Ennyu and Arthur (2004, doi:10.1029/151GM13). Items included in this report are (1) the oxygen and carbon stable isotope data measured on the Miocene bulk fine-fraction (i.e., <63 µm, primarily polyspecific nannofossil assemblage) carbonate and planktonic and benthic foraminifers from Holes 1170A and 1172A and (2) the Miocene depth-age models for the two sites

Planktonic foraminiferal zonation in the Cretaceous Yezo Group, Central Hokkaido, Japan

The mudstone of the Yezo Group exposed in Central Hokkaido yields abundant microfossils of calcareous nannofossils, foraminifers, radiolarians and dinoflagellates. Benthic foraminifers consisting of both agglutinated and calcareous species occur abundantly and consistently throughout the sequence, while specimens of planktonic foraminifers are generally fewer than benthics in all samples. We recognized the following 13 planktonic foraminiferal zones assigned to the late Aptian to early Campanian in the Oyubari and Haboro–Kotanbetsu areas; (1) Globigerinelloides spp., (2) Ticinella primula, (3) Biticinella breggiensis, (4) Rotalipora subicinensis–Rotalipora ticinensis, (5) Rotalipora appenninica, (6) Rotalipora globotruncanoides, (7) Rotalipora cushmani (8), Whiteinella archaeocretacea (9) Helvetoglobotruncana helvetica, (10) Marginotruncana pseudolinneiana, (11) Marginotruncana sinuosa, (12) Contusotruncana fornicata, (13) Globotruncana arca. The Globigerinelloides spp. to H. helvetica Zones (late Aptian to early Turonian) can be correlated with standard zones in the Tethyan regions, whereas the assemblages from the M. pseudolinneiana to G. arca zones lack tropical zonal markers of Dicarinella concavata, D. asymetrica and Globotruncanita elevata in many studied sections. The scarcity or lack of tropical zonal species during the late Turonian to early Campanian suggests that the Oyubari and Haboro–Kotanbetsu regions in Hokkaido were located in the Transitional to Boreal biogeographical provinces

Drilling Reveals Climatic Consequences of Tasmanian Gateway Opening

One of the great stories of geoscience is how Gondwana broke up and the other southern continents drifted northward from Antarctica, which led to major changes in global climate. The recent drilling of Ocean Drilling Project (ODP) Leg 189 addressed in detail what happened as Australia drifted away from Antarctica and the Tasmanian Gateway opened. The drifting contributed to the change in global climate, from relatively warm early Cenozoic “greenhouse” conditions to late Cenozoic “icehouse” conditions. It isolated Antarctica from warm gyral surface currents from the north and provided the critical deepwater conduits that eventually led to ocean conveyor circulation between the Atlantic and Pacific Oceans

L'ouverture océanique au sud de la Tasmanie durant le Paléogène et ses conséquences paléocéanographiques : résultats préliminaires de la minéralogie des argiles (leg ODP 189) = Palaeogene ocean opening south of Tasmania, and palaeoceanographic implications: preliminary results of clay mineral analyses (ODP Leg 189)

ODP Leg 189 was designed to test the hypothesis that opening of the Tasmanian Seaway and initiation of circumpolar circulation contributed to the thermal isolation of Antarctica, leading to the development of initial ice-sheet and oceanic thermohaline circulation. The clay assemblages of the Tasmanian region contain the traces of two tectonic stages associated with ocean opening south of the south Tasman Rise near the Palaeocene–Eocene boundary and strike-slip activity between the western Tasmanian land-bridge and Antarctica during the Late Eocene. Earliest Oligocene clays indicate that cooling of Antarctic margins and activity of western boundary circulation progressed with the regional subsidence