165 Preliminary Report


The Caribbean region poses a wide array of geologic questions, owing to its relatively uncertain plate tectonic evolution, the nature of its largely unsampled oceanic crust or basement, and its important role in global ocean circulation. With the exception of DSDP Site 502, the Caribbean had not been targeted by the Ocean Drilling Program or Deep Sea Drilling Project for more than two decades. A fresh impetus to Caribbean drilling was provided by the recent discovery of a strewn field of unaltered impact glass spherules or tektites in Haiti and Mexico at the Cretaceous/Tertiary boundary, and the identification of their source in the 180 to 300 km-wide Chicxulub impact crater in the Yucatan. Leg 165 drilling was intended to address two major themes: the nature of the Cretaceous/Tertiary boundary (65 Ma) and the influence of tropical seas on global ocean history and climate evolution. In addition, several of the proposed deeper holes held the prospect of reaching basement and, hence, providing new clues to the early formation of the Caribbean Plate. Drilling at five ODP sites (998, 999, 1000, 1001, and 1002; Fig. 1) has provided an excellent marine record representing nearly 80 m.y. of Earth history, but it has also led to the unexpected discovery of several major episodes of explosive volcanism in the Caribbean region, and the recovery of an important succession of submarine basaltic lava flows of the Caribbean Oceanic Plateau.

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