Environment Analysis of a Silurian Patch Reef, Lockport Dolomite of West Virginia
A coral-stromatoporoid reef has been recognized from a core in the Lockport Dolomite of West Virginia, and interreef dolomite was recovered in a second core from a nearby well. Submerged topographic highs on the sea floor, a relic of sand bars in the underlying Keefer Sandstone, provided an optimum site for Lockport organic growth. Local relief protected the reef community from being smothered by terrigenous material. Simultaneously, argillaceous interreef sediments accumulated in deeper water between topographic highs. The reef, though small, consists of three vertical biofacies. The buildup began as a thicket of current-baffling crinoids. They colonized the muddy, shallow-subtidal sea floor after an initial transgression. Skeletal debris of this bafflestone facies gradually changed the consistency of the sea floor; the substrate became firmer and the crinoids were supplanted by a community of stick corals. The substrate coarsened with the admixture of coral skeletons, and the reef was eventually capped by a frame-building stromatoporoid community. In contrast to other Niagaran reefs, the vertical succession of biofacies was not due to upward reef growth above wave base. The patch reef in the Lockport Dolomite developed in a quiet, protected shelf setting, and community succession was controlled intrinsically resulting from continual alteration of the sea floor by the reef organisms themselves.
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Carbonate buildups have long been a focus of intense geological study. An underlying reason is the importance of carbonate buildups as significant hydrocarbon reservoirs. This core workshop is intended to provide a “hands on” look at the subsurface geologic record created by carbonate buildups with emphasis on lithofacies, stratigraphy of buildups and their surrounding deposits, geometry, “reef”-building and sediment-producing organisms, and diagenesis and porosity evolution