Abstract

Stratigraphic, physical, and acoustic properties of peri-platform carbonate sediments in an 18-m-long piston core (core 2218, 655 m) from Northwest Providence Channel, Bahamas, have been investigated. The sediments range in age from recent to about 1 m.y. old. There is a close correlation between changes of compressional wave velocity and Quaternary climate as indicated by δ18O. Velocity correlates negatively to aragonite content, water content, and porosity, whereas it correlates positively to grain size, saturated bulk density, and observed degree of cementation. Changes in the degree of cementation exert a particularly strong influence on velocity variations. All parameters correlate to Quaternary climate/sea-level fluctuations. During glacial/low-sea-level stages, the aragonite content, water content, water content, and porosity decrease, but grain size, saturated bulk density, and the degree of cementation increase; all of these increase velocity.

In general, water content, porosity, and the aragonite content decrease slightly with core depth, but grain size, saturated bulk density, degree of cementation, and velocity increase slightly. Two processes may contribute to these trends: (1) shallow subsurface diagenesis upon burial and (2) variations of both the interglacial production of bank-top sediments and the intensity of glacial sea-floor diagenesis.

Major changes in velocity are associated with transitions from glacial to interglacial stages. Acoustic reflectors correlate one-to-one with the velocity changes occurring at isotopic stage boundaries 7-8, 9-10, and 11-12. At the site of core 2218, deeper reflectors have an interference origin because velocity changes are more closely spaced. The reflectors that correlate with isotopic stage boundaries can be used to study the detailed history of Quaternary peri-platform carbonate deposition and place it into the context of global climate/sea-level cycles.

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