Along-Strike Variability in Sedimentology and Geomorphology of a Leeward Margin, Caicos Platform

Rankey, Eugene C.¹, Sean A. Guidry², Stacy Lynn Reeder³ (1) University of Miami, RSMAS, CSL, Miami, FL (2) ExxonMobil Upstream Research Company, Houston, TX (3) University of Miami, RSMAS, Miami, FL

Carbonate platforms are notoriously heterogeneous, but most conceptual models emphasize across-strike variability. The purpose of this study is to describe a suite of high-resolution Chirp seismic, sedimentologic, and bottom observations along a single Holocene leeward margin on Caicos Platform, B.W.I, characterizing along-strike changes. A group of University of Miami and ExxonMobil personnel cooperatively collected the field data.

In the north-west corner of the Caicos platform (near Providenciales), a shift in margin orientation is accompanied by changes in sedimentology and geomorphology. Along the ~2km wide NW-facing margin, basinward-thinning wedges of tidal sands are associated with tidal inlets, and pass laterally to a rocky bottom with thin, discontinuous skeletal sand. Discontinuous reefs occur near the shelf margin. In contrast, the ~2km wide NE-facing margin includes sheet-like Holocene sediments, with numerous patch reefs, occuring above a nearly planar Pleistocene surface. The continuous shelf-margin reef is flanked by a well-developed sand apron.

These results illustrate the nature of lateral variability on the downwind flank of the Caicos platform. The differences are interpreted to reflect changing energy flux. The NW-facing margin appears to be more tidally-influenced, with tidal deltas and discontinuous reef. In contrast, the NE-facing margin, oriented into the swells of the open Atlantic, is more wave-dominated with a continuous reef and expansive sand apron. These results illustrate the nature, scale, and causes of along-strike heterogeneity along one shelf margin, and provide information for improved conditioning of geologic models of isolated carbonate platforms.