Reef, Lagoon and Off-Reef Facies James Atoll Reef (Lower Cretaceous) Fairway Field, Texas
The hydrocarbon-productive James reef at Fairway field, trending nearly at a right angle to the Lower Cretaceous strandline, has been proven by detailed facies mapping and key well control to have an atoll reef configuration. Facies of the atoll are differentiated into: (I) two northwest trending reefs of algal stromatolite-hydrozoan boundstone (lowermost zone), Chondrodonta wackestone (middle zone), and rudistid boundstone and wackestone (uppermost zone); (2) lenticular bodies of reef-derived skeletal grainstone that flank the reefs; and (3) lagoonal limestones characterized by interbedded miliolid-peloidal grainstone, algal nodule wackestone, and biostromes of rudistid wackestone and Chondrodonta wackestone. The thickest sections of the lagoonal facies lie between the reefs, and the reef facies appear to partially enclose the lagoonal facies. The off-reef facies, which developed contemporaneously with reef growth, consist of argillaceous, skeletal packstone, wackestone, and mudstone.
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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