Sedimentology and Geomorphology of Holocene Carbonate Systems from the Reef-Rimmed Shelf of Crooked-Acklins Platform, Southern Bahamas

Hakiki, Fikril ¹; Rankey, Eugene C.²; Reeder, Stacy L.^3
1 Marine Geology and Geophysics, Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, FL.
² Department of Geology, University of Kansas, Lawrence, KS.
³ Schlumberger-Doll Research Center, Schlumberger, Cambridge, MA.

Reef-rimmed shelves are common geomorphic elements in both modern and ancient carbonate systems. Understanding the facies heterogeneity of sediments in Holocene analogs can play an important role for developing more geologically realistic reservoir models. However, the quantitative details of facies distributions and spatial geomorphic and sedimentologic patterns of reef-rimmed shelves have not been widely documented. By integrating sedimentologic and remote sensing data, this study aims to evaluate the depositional patterns and processes that influence sedimentary and geomorphic patterns on a reef-rimmed shelf on the northern margin of Crooked-Acklins Platform in the southern Bahamas.

Facies along the narrow (1-3 km wide) shelf margin include reef crest, reef apron, backreef sands with blowouts, and nearshore sands. The best sorted and coarsest (mean size 1200 μm) sediment with low mud content (< 1%) is associated with the high energy environment just platformward of the breaks in the shelf-margin reef. Sediments of the backreef shelf are dominated by skeletal grains such as Halimeda, foraminifera, mollusks and corals; peloids are predominant in areas with decreased hydrodynamic activity, and they tend to increase in abundance away from the reef. Sediments here are finer than near the shelf margin reefs (mean size 980 μm). In shoreline re-entrants, nearshore areas include red algal-sponge-coral biostromes, and beaches are well-developed; rocky shorelines dominate elsewhere. Overall, sediment properties such as grain size are not correlated with water depth (R² = 0.006).

These sedimentologic data will be integrated with remote sensing analyses to further assess the influence of spatial context and geomorphology on sediment properties. These results provide testable models that could be used for prediction of sedimentologic and geomorphic heterogeneity in subsurface analogs.

AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009