Geotechnical stratigraphy and sedimentary microfabric of Oligocene to late Miocene pelagic sequences in the Southern Ocean: Paleoceanographic implications

The dominant geologic feature of pelagic sediment accumulation patterns at intermediate water depths in the Southern Ocean is the sequential northward migration and replacement of a calcareous ooze sedimentary facies by a siliceous ooze facies, following the Late Oligocene opening of Drake Passage and the subsequent initiation of the Antarctic Circumpolar Current.; Discrete measurements of physical properties (density, porosity and water content), continuous whole-core measurements of bulk density and compressional velocity, consolidation test results and permeability measurements, and SEM images of sedimentary microfabric are evaluated for 8 sites drilled in the Southern Ocean during Ocean Drilling Program (ODP) Legs 113 (Sites 689 and 690), 119 (Sites 738 and 744) and 120 (Sites 747, 748, 749 and 751). These sites are all located on submarine rises in open-ocean (pelagic) depositional environments south of the Polar Front, a major oceanographic and sedimentologic boundary.; High-resolution profiles derived from core measurements of bulk-density and compressional velocity are used to correlate between adjacent drill-holes on Maud Rise, where multiple overlapping sedimentary sequences were recovered using the advanced hydraulic piston core barrel (APC). Stratigraphic age models are applied to the bulk-density data to provide a temporal framework for a discussion of paleoceanographic events and to constrain future acoustic research studies. The Early to Middle Miocene intervals at Sites 689 and 690 are marked by distinct sequences of meter-scale, alternating carbonate and siliceous units separated by several proposed stratigraphic hiatuses. At least six dissolution/productivity events are identified in the Middle to Late Miocene on Maud Rise and others are noted at the ODP sites on Kerguelen Plateau.; The downhole profiles are used to identify the "density signature" and position of proposed stratigraphic hiatuses in sediment cores of late Oligocene to Quaternary age. Additional stratigraphic hiatuses are suggested by the reversals, inflections and discontinuities in the downhole bulk-density trends. The bulk-density "logs" are used to generate empirical profiles of calcium carbonate, which compare favorably with laboratory measurements of carbonate at each site.; An understanding of the possible interactions between the Antarctic Circumpolar Current system and seafloor topography, as modified by progressive plate tectonic motions and glacio-eustatic fluctuations, is used to develop a hypothesis for explaining the observed sediment accumulation patterns at intermediate water depths of the Southern Ocean during the Neogene.