Accommodation Space on an Isolated Carbonate Platform — Patterns and Implications

Abstract

Great Bahama Bank (GBB) is 'the' modern example of a flat-topped, isolated carbonate platform. It is a major modern location of non-skeletal carbonate deposition that stands behind much of our understanding of modern processes of carbonate sedimentation and is the basis for geological models that serve as reservoir analogs. GBB provides valuable insight into the extent and patterns of sediment fill of accommodation space across the platform top. Satellite imagery (Landsat TM and ETM+) and an extensive set of water-depth measurements (n = 5,723) were used to map bathymetry across GBB. Analysis of the resulting digital terrain model (DTM) reveals the maximum variation in depth-elevation over this vast (>100,000 sq. km) platform extends from the −30 m platform break to the highest Pleistocene eolianite ridge of 63 m on Cat Island. It is noteworthy, however, that although islands atop the GBB are numerous (n = 1,427) they occupy only 7.5%, or 7,716 sq. km, of the platform-top. Since islands represent the portion of the platform where accommodation has been overfilled, their rarity emphasizes the challenges to filling accommodation space across such a large platform despite the diverse grain factories producing carbonate detritus atop GBB (mud precipitation through whitings, ooids along the platform margins, skeletal sediments, and non-skeletal grains such as pellets, peloids and aggregate grains). It should be noted that aerial coverage of the GBB's islands is in fact an overestimate of overfilled accommodation; although many Holocene islands are built from storm ridge and eolianite deposits, the contribution of sub-tidal facies deposited during higher sea level are also important structuring components to Pleistocene islands. Considering the bathymetric variation of the GBB, the DTM brings to light the fact that only 7% (7,237 sq. km) of the awash platform has aggraded to sea level in the form of sand shoals or mud flats (<1 m water depth) and therefore the majority of available accommodation (~87,600 sq. km or > 85% of the platform top) remains under-filled with sediment. Areas of filled accommodation mostly extend platformward from the westerly coastlines of islands, which in turn are preferentially distributed along the eastern (windward) margin of the GBB. The bathymetric patterns highlight the irregular filling of accommodation space and graphically emphasize the challenges of correlating depositional cycles of variable thickness across a platform.

AAPG Datapages/Search and Discovery Article #90216 ©2015 AAPG Annual Convention and Exhibition, Denver, CO., May 31 - June 3, 2015