Insights into Quaternary Depositional and Diagenetic Processes on a Caribbean Atoll
Van Ee, Noelle J.; Eberli, Gregor P.; Anselmetti, Flavio; Swart, Peter; Gischler, Eberhard
The proximity of Glover's Reef, a Caribbean atoll, to the North America - Caribbean plate boundary and along a known precipitation gradient makes it an ideal candidate for studying possible controls of reef distribution and platform development. Understanding Glover's Reef can provide insights for predicting the occurrence, extent, and quality of carbonate reservoirs in reef mound - patch reef complex or isolated platform depositional systems. Because it has been exposed to multiple sea-level oscillations within the last several hundred thousand years, Glover's Reef also provides insight into the pre-burial products of overprinting diagenetic signatures.
A single-channel seismic survey of over 100 km of grid lines in conjunction with N-S and E-W rotary core transects show no evidence of faults/folds controlling patch reef locations. Rather, 93% of surveyed Holocene patch reefs are located on Pleistocene topographic highs. In situ reef facies in patch reef cores indicate that these highs are growth-induced: reefs sit on reefs.
Although modern bathymetry deepens in the south of the platform, there is no evidence to support a tilted Pleistocene surface. Maps constructed of the Pleistocene topography from the seismic grid show a relatively flat surface except for locally beneath patch reefs. These grid maps also indicate that observed modern lagoon bathymetry is caused by a wedge of Holocene sediment that is thickest in the windward, northeast corner of the lagoon.
Inconsistencies in the location of Pleistocene horizons in the cores correlate to antecedent topography and variable growth potential of facies. Patch reef cores sit on antecedent highs while windward cores contain facies with fast-growing Acropora species and early marine cementation. Satellite-based facies mapping and modern grain size analyses also provide evidence for platform development in response to a dominant northeast to southwest trade wind regime. Asymmetric facies belts are apparent on both a platform and patch reef scale.
Multiple exposures to meteoric water have left a petrographic signature of vuggy dissolution and recrystallization to blocky calcite in Pleistocene core sections. An amino acid racemization geochronology suggests that the two youngest Pleistocene sequences are relatively close in age, perhaps even sub-stages of Marine Isotope Stage 5e. This work implies that even isolated carbonate systems can build complicated architecture in relatively short time intervals.
AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013