Controls of Depositional Facies Patterns on a Modern Carbonate Platform: Guidelines for Stratigraphic Correlations in Ancient Systems

Abstract

Our recent studies of Holocene sediments across the top of Great Bahama Bank (GBB) have focused on platform-wide mapping of sediment distribution, an analysis of the variable filling of accommodation space, a comparison between key ooid sand bodies, and an examination of whitings occurrences and mud production. Collectively, these quantitative-based studies were aimed to provide new insight into the variability of depositional facies that challenge subsurface interpretations. Missing from these analyses, however, has been a scrutiny of the physical controls over platform-top deposition, which, coupled with the enhanced mapping may provide even more robust quantitative comparative sedimentology and stratigraphy guidelines.

To explore these fundamental controls, we developed a hydrodynamic model for the GBB forced by prevailing ocean hydrodynamics surrounding the platform, including the Florida Current, and tides, winds, and atmospheric pressure. Current intensity and direction can be examined through high-resolution time steps, and the platform can be partitioned into zones of mean annual hydrodynamic energy. Areas of vigorous tidal exchange in the model correspond to localities where high-energy ooid shoal systems have developed along the platform-margin. There is a predictive relationship between increasing peak current velocity and increasing area of the sand body for the Cat Cays, Joulter Cays, Schooners Cays and TOTO areas. A connection between platform-top hydrodynamics and the formation/suppression of whitings is evidenced in the portion of GBB west of Andros Island suggesting a relationship between the production/deposition of platform-top lime muds and off-platform circulation patterns. Accommodation filling is related to platform topography and hydrodynamic flow. For instance, accommodation filling locally along the platform margin by grainstones in areas of high tidal exchange versus mud accumulation leeward of islands, or the development of hiatal areas in areas unsheltered by abundant islands, such as observed in the southern GBB.

A broader understanding of platform-top currents and their diverse controls can aid interpretation of the rock record, including the type and distribution of sediments accumulating on the platform top, the distribution of extensive hiatal surfaces (sites of non-deposition), and therefore identification of locations which have the potential to host the most complete depositional cycles.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018