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Detailed studies of carbonate mineralogy and geochemistry using samples recovered by deep-sea drilling in the northern Bahamas document shallow-burial (<250 mbsf) diagenetic trends that occur in two stages. Stage 1 diagenesis (0-10 meters below the seafloor, mbsf) results in rapid, extensive calcitization and local dolomitization in marine-derived pore fluids. Stable oxygen isotopes are quickly enriched, while carbon values are depleted. Aragonite undergoes dissolution and high-magnesian calcite exsolves to low-magnesian calcite. Below 10 to at least 185 mbsf, stage 2 diagenesis continues to alter primary components, leading to ooze-chalk and chalk-limestone transformations and low amounts of dolomite, while rates and amplitudes of change are considerably less than in stage 1. Oxygenand carbon-isotope ratios indicate that diagenesis still occurs in marine-derived pore fluids. Overall, shallow-burial diagenesis of periplatform carbonates proceeds much more readily than diagenesis of deepsea pelagic ooze. This is because of higher diagenetic potential related to the influx of metastable shallow-water-derived components in a deep-marine realm. Subsurface calcitization and lithification of periplatform sediments occurs rapidly with depth in regions of moderate accumulation rates (20-60 m/m.y.; north of Little Bahama Bank). This is a result of an interpreted greater rate of diagenetic alteration with burial, and in deep (3000 m) water is related to seawater saturation levels relative to carbonate mineralogy. Calcitization and local dolomitization may occur at or near the sediment/ water interface during formation of disconformities. In contrast, metastable aragonite and high-magnesian calcite are present in significant amounts at depth in regions with high accumulation rates (>90 m/m.y., Exuma Sound), despite lithification that produces chalk and limestone. The presence of metastable components in porous limestones in Exuma Sound underscores the current high diagenetic potential for these rocks and the development of reservoir potential in periplatform deep-water limestones at shallow sub-bottom depths. DEDICATION This paper is dedicated to the memory of H. Mark Van Buren, who, at the age of 36, died because of medical complications from an automobile accident on January 16, 1986 in San Jose, California. Mark's 1984 Master's thesis—"Seismic Stratigraphy of a Modern Carbonate Slope: Northern Little Bahama Bank"—was the basis for many of the objectives of Leg 101, Sites 627 through 630. Mark's work focused on the now widely cited bathymetry of the deep bank margin north of Little Bahama Bank, as well as on 3.5-kHz echo-character studies and seismic sequence analysis. Mark also discovered Walkers Cay Fault, a prominent northeast-southwest striking fault zone normally oriented to the bank margin of Little Bahama Bank. All these studies influenced both the design and execution of Leg 101 drilling north of Little Bahama Bank.

A Regional Perspective of Shallow-Burial Diagenesis of Deep-Water Periplatform Carbonates from the Northern Bahamas