Abstract Reef-rimmed margins on carbonate platforms are notably heterogeneous. To explore 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 field data, including sediment and bottom descriptions as well as Chirp subbottom profile data. The results illustrate the nature of sedimentologic and geomorphic variability along this part of the Caicos platform margin, and these changes are interpreted to reflect the 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 a continuous reef and expansive sand apron is more wave-dominated and influenced by swells from the open Atlantic. These results illustrate the nature, scale, and causes of along-strike heterogeneity along one shelf margin, and likely will have ancient analogs.

Abstract Ambergris ooid shoal, on the southeastern Caicos platform, is an elongate, asymmetric, 20 km long spit-like feature to the west of Ambergris Cays. The purpose of this study is to describe the sedimentology and morphology of the Ambergris complex, commonly held as the type example of a wind-influenced ooid shoal. The Ambergris shoal crest is bare well-sorted coarse sand-sized ooids, partly exposed at low tide and ornamented by low-amplitude sand waves with variable but systematically changing orientations. Flanking the shoal crest on the north side is a ~2 m deep rubbly shoulder of Holocene hardground and a deeper (~3 m), rippled sandy bottom which deepens to a burrowed bare sandy bottom (>4 m) with scattered reefs. The southern flank passes from the shoal crest to a slightly deeper (2-4 m) sandy bottom with abundant ooids and common clasts before passing to the burrowed sandy facies. The shoal is influenced by tidal and wave energy; the geometry of sand waves suggests it is not simply a wind-generated spit in the lee of the islands, however. Our on-going work continues to evaluate and quantify the roles of waves and currents on the geomorphic character of the system.

Abstract Although the general aspects of oolitic depositional systems are well-documented, their landscape-scale patterns (geobodies) are not well enough understood to offer quantitative, predictive insights for reservoir characterization. To begin to fill this basic gap in understanding, this study describes the morphology, hydrodynamics, and process sedimentology of several modern tidally dominated Bahamian ooid shoal complexes and compares the patterns with patterns in Kansas Pennsylvanian analogs. A companion paper explores linkages further, documenting petrophysical, geophysical, and production characteristics of these Pennsylvanian oolitic reservoirs. Integrating remote sensing imagery with quantitative bathymetric, fluid flow, and granulometric data in a GIS , we document geomorphic and sedimentologic patterns and processes in several active tidally-dominated shoals. Results reveal that parabolic bars form a common morphologic motif, although there is considerable variation on that general theme. Different processes can lead to varying depositional geometries and sedimentologic patterns. Nonetheless, the landscape-scale configuration of bars and superimposed sand waves is linked closely to patterns of tidal flows. Bars are not homogenous bodies, however, and granulometric parameters such as sorting and mud percentage vary systematically and predictably within the hydrogeomorphic framework. Through exploring modern oolitic shoals, this study provides new insights on details of their morphology and dynamics as well as links between geomorphic framework and grain size and sorting; some patterns are similar to those within geobodies in Pennsylvanian reservoir analogs. These insights provide quantitative predictive information on facies geometries, on grain characteristics, and depositional porosity in analogous ancient ooid shoals.