Integrated Chirp, Remote Sensing and Sedimentologic Characterization of Geomorphic Variability Along a Shelf Margin, Northwest Caicos Platform

Eugene C. Rankey¹, Sean A. Guidry³, Stacy L. Reeder², Rodrigo Garza-Perez⁴, and Humberto Guarin^5
1RSMAS/University of Miami, Miami, FL
²Schlumberger-Doll Research, Cambridge, MA
³ExxonMobil Development Co., Houston, TX
⁴UMDI Sisal, UNAM, Merida, Mexico
⁵Bert Instruments, Inc., Hollywood, FL

Carbonate platforms are notoriously heterogeneous, especially across depositional strike. In contrast, changes along strike have been less systematically explored. The purpose of this study is to describe along-strike changes of the north-western margin of Caicos Platform, B.W.I. (near Providenciales). A group of University of Miami and ExxonMobil personnel cooperatively collected the field data, including sediment and bottom descriptions and Chirp subbottom profile data.

The northwest-facing margin with discontinuous reefs and coarse skeletal sands passes to a mid-shelf rocky (Pleistocene) bottom with patchy fine-medium skeletal-peloid sands. Nearshore areas include laterally discontinuous peloid-skeletal tidal delta sands and islands with beaches of fine peloid sands. Above the seaward-dipping surface of the top Pleistocene, the most pronounced bathymetric changes occur around reefs and tidal deltas. In contrast, the northeast-facing margin includes a continuous aggraded reef associated with coarse skeletal sands. These sands gradually fine away from the reefs and concomitantly include more abundant peloids. Nearshore sediments are well-sorted fine peloid-skeletal sands with few ooids. Because the top Pleistocene surface is gently dipping seaward, Holocene sediment thicknesses vary with changes in bathymetry.

These results illustrate variability around this part of the Caicos platform margin, interpreted to reflect changing nature of energy. The tidal deltas and discontinuous reef on the NW-facing margin suggest this margin is more tidally-influenced. In contrast, the NE-facing margin with continuous reef and expansive sand apron suggest it is more wave-dominated. These results illustrate the nature, scale, and causes of along-strike heterogeneity along one shelf margin, and likely will have ancient analogs.

AAPG Search and Discover Article #90078©2008 AAPG Annual Convention, San Antonio, Texas