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Sedimentological and geophysical data show that the sediments at the base of the West Florida Escarpment are flat-lying hemipelagic carbonate oozes, derived primarily from the shelf and upper slope, interbedded with massive siliciclastic Mississippi Fan sediments. Petrographic and scanning electron microscope (SEM) examination of the hemipelagic sediments indicate that bioerosion by Cliona sponges or boring clams, mussels, or barnacles is not presently a significant process on the West Florida Escarpment upslope from the core sites. However, the presence of angular limestone fragments and calcareous, glauconitic clasts within the fine-grained abyssal floor sediments suggests that an erosional process is active on the consolidated sections of the adjacent slope. The lithologies of the cores and SEM examination of the foraminifera show that the dark, grayish-brown silty clay is not the insoluable residue of the hemipelagic calcarenite after the diagenetic dissolution and removal of carbonate. INTRODUCTION The West Florida Escarpment is the steep lower portion of the slope that separates the shallow shelf carbonate platform from the deep abyssal plain of the Eastern Gulf of Mexico. The escarpment, which was formed from sediments associated with vertical reef growth during Cretaceous to Miocene times (Antoine and others, 1967; Uchupi and Emery, 1968), has been shaped by erosional processes that are responsible for its present day appearance (Freeman-Lynde, 1983). The escarpment extends from the Straits of Florida north to the DeSoto Canyon and ranges in relief from about 2500 m west of the Florida Keys to nearly 1000 m near the DeSoto Canyon. During October and November 1983, aboard the USNS LYNCH, the U.S. Geological Survey collected nine cores from the base and top of the escarpment (Figs. 1 and 2). The cores were taken to determine (1) the source of the sediments deposited at the base of the escarpment and (2) the sedimentological processes affecting this deposition. This report also includes sections of high-resolution seismic-reflection profiles that were collected aboard the USNS LYNCH along three transects made across the southwestern Florida outer shelf and slope and used for citing and morphologic information. METHODS The piston cores were collected with an Alpine Geophysical corer fitted with a 1364-kg core weight (Table 1). Plastic liners having internal diameters of 89 mm were used within the core barrels. Core sites were selected and target feature morphology was confirmed by high-resolution seismic-reflection profile data obtained using a tuned (3.5-kHz) transducer and a 30-kJ sparker. Navigation was performed using a Northstar 6000 Loran C receiver (Digital Marine Equipment Corp., Bedford, MA). The cores were later described and sampled in the laboratory. A split from each sample was mounted and x-rayed as a randomly oriented powder. The clay fraction from each sample, separated by centrifuge, was mounted on a silver filter as an oriented aggregate. Each oriented clay mount was subjected to four treatments to determine which clay minerals were present: air-drying, glycolation with ethylene glycol, heating to 400 °C, and heating

Characterization of sediments from the base and top of the West Florida Escarpment