ABSTRACT: Facies Geometries of Shallowing-Upward Sequences Associated with Leeward-Margin Sediment Wedges, Caicos Platform, British West Indies

WANLESS, H. R., University of Miami, Coral Gables, FL, L. P. TEDESCO, IUPUI, Indianapolis, IN, A. H. HINE, University of South Florida, St. Petersburg, FL, and J. D. DRAVIS, Rice University, Houston, TX

Shallow seismic profiles and island drilling on Caicos Platform record four aspects of leeward margin growth leading to several types of vertical cycles of sedimentation. (1) Seaward-prograding wedges of skeletal and oolitic sands occur at and in from leeward margins. (2) These shallowing-upward wedges may be capped by islands that quickly harden into rigid emergent topography. (3) Gaps between emergent topography may be bridged by (a) continuous, emergent, catenary sandy beach ridge and dune arcs or (b) beach ridge trends dissected by tidal passes. (4) Subsequent facies occur bankward and marginward from the emergent ridges. These include (4a) highstand reef growth on the leeward platform margin now protected from cross- and off-bank transport; (4b) prograding skeletal and oolitic st andplains on energetic interior and marginal flanks to emergent islands (producing bankward- and seaward-dipping strata respectively); and (4c) tidal flats on protected interior flanks.

Repetitive highstands through the Pleistocene have each continued the shoaling and margin progradation of the platform. In some areas, shallowing-upward sequences represent individual eustatic highstands. In others, individual shallowing-upward sequences are the result of multiple highstands. Most emergent topography persists to subsequent highstands; some is eroded or inundated.

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)