Co‐existence of skeletal and ooid shoals as a result of antecedent topography—Cat cay shoal complex, Bahamas

Abstract

High‐resolution seismic data reveal an unexpected Pleistocene topography underneath the Cat Cay shoal complex along the western margin of Great Bahama Bank, illustrating how Pleistocene topography focuses tidal flow to create different types of grainstone shoals. The 1–3 km wide and 35 km long shoal complex is composed of the Cat Cay ooid shoal that is a laterally continuous 8 m thick ooid shoal and a sequence of 300–600 m wide and less than 6 m thick skeletal‐dominated tidal deltas south of Ocean Cay. The skeletal tidal deltas overlie an irregular Pleistocene surface, while the Cat Cay ooid shoal is situated on a flat Pleistocene surface east of a Pleistocene rock ridge. This finding challenges the assumption that an antecedent high is needed for ooid shoal initiation. The base of the Cat Cay ooid shoal is an up to 4 m thick skeletal‐peloidal unit that is similar in composition to the skeletal tidal deltas south of Ocean Cay but their deposition was followed by an up to 4 m thick accumulation of ooids. The Pleistocene ridge west of the Cat Cay ooid shoal allowed accumulation of mud and peloids (the nucleus source), while to the south, muddy sediment was winnowed away and no ooids formed. The evolution of the two shoal types is ultimately the result of the presence and absence of antecedent topography adjacent to the shoal system, resulting in variations of mud accumulations and the formation of the nucleus in the ooid shoal. The coeval occurrence of ooid and skeletal shoals in the same complex implies that in the rock record, a vertical succession from oolitic to skeletal shoals does not indicate an environmental change such as climate or an anoxic event but rather a change in flow conditions created by antecedent topography.

Impact of facies and diagenetic variability on permeability and fluid flow in an oolitic grainstone—Pleistocene Miami Oolite

“…Variation in ooid‐rich sediments has been documented on outcrops and in cores between the subenvironments of the MO (Evans, ; Usdun, ), similar to the variability documented by coring in Joulters and other modern sand shoal equivalents (Dravis, ; Harris, ; Sparks and Rankey, ; Cruz and Eberli, ). For example, cross‐bedded and relict‐bedded (cross‐bedding discernable but texture nearly obliterated by burrowing) oolitic–peloidal grainstones typify the shoals of the MO and burrow‐mottled ooid–peloid packstones to grainstones occur in the channels (Figure ).…”

Preface: Celebration of the Career of Robert Nathan Ginsburg

“…For decades, these studies remained the only ones available. Three papers in this compilation revisit sediments from the Bahamas (Cruz & Eberli, ; Harris, ; Purkis, Harris, & Cavalcante, ; Weij, Reijmer, Eberli, & Swart, ) building on his fundamental contributions and describing the distribution of sediments on Great Bahama Bank. The accretion of such sediments and their manifestation in the geological record was a logical extension of the study of Modern sediments.…”