AAPG ACE 2018

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Reconstruction of a Holocene Carbonate Strand Plain From Integration of High-Resolution GPR and Carbon-14 Dating

Abstract

Understanding modern carbonate depositional systems gives valuable insights into the interpretation of ancient carbonate systems. Ancient carbonate strand plains act as productive hydrocarbon reservoirs because of their potentially high porosity. Unfortunately, ancient strand plains are difficult to identify in the rock record because of a lack of research on modern analogs. Advances in Ground Penetrating Radar (GPR), allowing shallow high-resolution subsurface mapping, have enhanced the understanding of modern carbonate systems. San Salvador Island of the Bahamas displays a remarkably clear geomorphic expression of lateral sedimentary accretion as seen by the arcuate depositional ridges visible from satellite imagery. Sandy Hook on San Salvador Island is a Holocene strand plain, ideally situated to be used as a modern strand plain analog. Sandy Hook is about 1.5 square kilometers and consists of approximately 35 beach/dune ridges. Multiple 3D GPR surveys were conducted over some of these ridges using a 400-MHz antenna (~60 traces per meter of survey distance; ~0.3-meter survey line spacing), supplemented by 2D GPR profiles. The 3D surveys furnish detailed high-resolution images of stacked clinoforms, within a discrete sequence, dipping eastward, toward the Atlantic Ocean. 2D lines perpendicular to the dune ridges also show distinct clinoforms dipping eastward over much of the area beneath the ridges. These images are used to characterize fine-scale patterns of lateral sedimentary accretion. Integration of 3D and 2D GPR surveys with carbon-14 dating of carbonate sand deposits provides a depositional analog model for strand plain systems.