165 Preliminary Report

Site 1002 Results

Site 1002 is located adjacent to DSDP Site 147 in the Cariaco Basin, a structural depression on the northern continental shelf of Venezuela that is the second largest anoxic marine body in the world, after the Black Sea. High sedimentation rates (300 to >1000 m/m.y.) and its location in a climatically sensitive region of the tropical ocean made the Cariaco Basin a prime drilling target for high-resolution studies of geologically recent climate change. The major objectives at Site 1002 were to recover a continuous and undisturbed late Quaternary stratigraphic section that will be used to (1) document how climate change in the southern Caribbean and northern South America relates to climatic forcing mechanisms and to global-scale change, especially to high latitude changes recorded in ice cores and high-deposition-rate marine sediment sequences, (2) study the rates and magnitudes of tropical climate change at interannual to millennial time scales over the last several glacial-interglacial cycles, (3) examine the stability of tropical climate in response to past changes in large-scale global boundary conditions, and (4) study the relationships between climate variability and processes that influence the burial of organic carbon in anoxic settings.

Five holes were drilled at Site 1002, two of which were mudline cores taken for geochemical studies; three more were taken for high-resolution paleoclimatic reconstructions. Only the cores from Hole 1002C were split open on board ship for preliminary descriptions and analysis. Time was short for inspection and discussion and only the most preliminary observations can be made at this time.

Hole 1002C recovered a total of 170.1 m of mostly mixed, or hemipelagic sediments. The presence of Emiliania huxleyi at the base of the sequence suggests that all of the sediments fall within Zone CN15, or were deposited in the past 248,000 years. This single biostratigraphic estimate is consistent with estimates based on extrapolating known sedimentation rates for the Holocene and last glacial back the length of the drilled sequence.

Sediments in Hole 1002C are generally dominated by terrigenous components with variable biogenic contributions of nannofossils, diatoms, and foraminifers. Much of the sediment is laminated, indicating deposition under largely anoxic conditions.

The sedimentary sequence at Site 1002 was assigned to one formal lithostratigraphic unit and eight subunits. Despite this degree of subdivision, there appear to be only about three major lithologies, which alternate in a semi-predictable fashion. The bulk of the sequence consists of clayey nannofossil mixed sediments, olive gray to greenish gray in color, which appear to have been deposited under both anoxic (laminated) and oxic (massive) conditions. These sediments are punctuated periodically by episodes of bluish gray and yellowish brown clay deposition, laid down under clearly oxic conditions. Generally following this, deposition of diatom-rich, distinctly laminated sediment indicates strong upwelling, such as was experienced during the early Holocene in Subunit Ib. Earlier periods of clay deposition, followed by accumulation of diatom-rich sediments, may similarly signal earlier periods of deglaciation.

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