--> Stratigraphic Evolution of an Icehouse Strandplain System — West Caicos, BWI

AAPG Annual Convention and Exhibition

Datapages, Inc.Print this page

Stratigraphic Evolution of an Icehouse Strandplain System — West Caicos, BWI

Abstract

The development of carbonate strandplain-dune island complexes during the mid-late Pleistocene and Holocene serves as an analog for similar shallow water carbonate grainstone reservoirs in the ancient. Laterally shingled unconformity-bound Pleistocene high-frequency cycles with extensive meteoric diagenesis and karstification are an analog for icehouse reservoir accumulations like the vuggy microkarstic Canyon-Cisco grainstone reservoirs of the Horseshoe Atoll and time-equivalents on the Eastern Shelf and eastern margin of the Central Basin Platform. Pleistocene high-frequency cycles display thicknesses of several meters, lateral extents of 20-30 sq. km., and porosities that range from 20 to 30% suggesting that these deposits are embryonic stratigraphic packages that are well-suited for analog research. A unique combination of sub-meter hyperspectral integrated bathymetric-topographic airborne lidar across the entire 24 sq. km. of the island plus surrounding shelf to -50m; cm UAV-generated DEMs with integrated high-fidelity RGB imagery; more than 150 samples for petrographic and diagenetic characterization; and fracture and rock strength data was tied to the stratigraphic framework. Mapping 12 km of continuous coastal outcrop at cm resolution was key to recognizing unconformity-bound units, whereas island-wide mapping at a broader scale helped identify larger morphostratigraphic patterns that supported and augmented the coastal mapping. The combined map has led to differentiation of 6 unconformity-bound stratigraphic units: (1) an older recrystallized beach-dune system (likely MIS stage 9/11); (2) a less-well-defined dune ridge with 220ky date; (3 and 4) two distinct unconformity-bound intra-MIS 5e pulses with well-constrained paleoshoreline elevations and intra-5e fall magnitude of approximately 5 m; (5) a falling stage set of arcuate catenary dune ridges that build eastward and downstep off the NE corner of the island to below present day sea level (likely MIS 5d-a); and (6) Holocene oolitic strandplain deposits that reached an acme near 3 ky and now are partially vegetated and suffering erosion. Each of the 6 units is capped erosionally and by subaerial exposure and meteoric diagenesis, have both distinct grain types, facies assemblage, and rock-mechanical/petrophysical properties. Such a complex record of exposure-bound high-frequency cycles is a close proxy for icehouse grainstones and will guide our modeling efforts of said reservoirs.