Ocean Drilling Program (ODP) Site 1002 is located in the Cariaco Basin, a structural depression on the northern continental shelf of Venezuela which, after the Black Sea, is the largest anoxic marine basin in the world. Since recovery of the first sediment cores from this basin in the late 1950s, it has been known that laminated deposits that accumulate in its depths are nearly undisturbed by bioturbation and contain well-preserved assemblages of both calcareous and siliceous microfossils (Heezen et al., 1958, 1959). High sedimentation rates (300 to >1000 m/m.y.) and location in a climatically sensitive region of the tropical ocean made the Cariaco Basin a prime drilling target on Leg 165 for high-resolution studies of geologically recent climate change.
The major objectives at Site 1002 were to recover a continuous and undisturbed upper Quaternary stratigraphic section that could 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 in other 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. The recovery objectives were successfully achieved with the drilling of five holes at Site 1002, two of which were single mudline cores taken for geochemical studies, and three that were taken for high-resolution paleoclimatic reconstructions and that together penetrated to a maximum depth of 170.1 meters below seafloor (mbsf).
Site 1002 came at the very end of Leg 165, with only 2 days allocated for drilling, followed by a short transit (~1.5 days) to the final port of San Juan, Puerto Rico. Given the advance realization that normal shipboard processing of Site 1002 cores would be impossible in the available time, special provisions were made whereby only cores from the first of the long holes, Hole 1002C, were opened on board ship for initial description and preliminary sampling. The limited time for sampling and the general scarcity of biostratigraphic datums within the hemipelagic sediments of late Quaternary age resulted in a very poorly defined age model for Site 1002 as reported in the Leg 165 Initial Reports volume of the Proceedings of the Ocean Drilling Program (Sigurdsson, Leckie, Acton, et al., 1997). The tentative shipboard identification of Emiliania huxleyi at the base of the sequence initially indicated that all of the sediments recovered at Site 1002 lie within calcareous nannofossil Zone CN15 of Okada and Bukry (1980), suggesting a basal age of the site of no more than 248 ka. Our shore-based studies have subsequently shown this estimate to be in error and have led to a new integrated stratigraphy based on the standard of late Quaternary oxygen-isotope variations linked to a refined biostratigraphic framework. The purpose of this paper is to formally present the revised stratigraphy for this site and to tie in and discuss temporal changes in the sediment lithologies in the context of late Quaternary climate cycles.