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Biofacies and development and differential occlusion of porosity in a lower Cretaceous (Edwards) reef

A. D. Jacka and J. P. Brand
Biofacies and development and differential occlusion of porosity in a lower Cretaceous (Edwards) reef
Journal of Sedimentary Petrology (March 1977) 47 (1): 366-381


An Edwards reef, exposed in a large quarry in Scurry County, Texas, exhibits the following biofacies, outward from the reef core: 1) caprinid - Chondrodonta zone (reef core), 2) Eoradiolites - Chondrodonta zone (upper forereef), 3) Toucasia - Eoradiolites - Chondrodonta zone (middle forereef), 4) Cladophyllia zone (lower forereef). Beyond the forereef and below the reef are tabular biostromes in which Eoradiolites, Toucasia, Chondrodonta and Cladophyllia are dominant. The Edwards reef was subaerially exposed soon after deposition, and stabilization of carbonate mineralogy, lithification, solution, of aragonite fossils and differential cementation occurred in a fresh water diagenetic environment. Microcavernous porosity developed in the upper Edwards from solution of aragonitic caprinid and corm shells of the reef core. Adjacent to large caprinid molds former body cavities of Eoradiolites are filled by coarse calcispar cement which initiated as overgrowths on large crystals of inverted (from aragonite) calcite of the inner shell layer. Primary porosity (body cavities of calcitic pelecypods) became occluded by calcite cement, while secondary porosity (molds of aragonitic fossils) was preserved. A sharp boundary, representing a paleo-groundwater table, separates the upper paleovadose zone of microcavernous porosity from a lower paleophreatic zone wherein all former voids, including caprinid molds, became occluded by calcispar cement. A heavy concentration of vadose internal sediment terminates at the palco-groundwater table. Coarse aggrading recrystallization of micrite matrix to pseudospar is well developed in the paleophreatic zone, but is lacking in the paleovadose zone. Differential porosity occlusion was largely controlled by vadose-phreatic groundwater dynamics.

ISSN: 0022-4472
Serial Title: Journal of Sedimentary Petrology
Serial Volume: 47
Serial Issue: 1
Title: Biofacies and development and differential occlusion of porosity in a lower Cretaceous (Edwards) reef
Affiliation: Tex. Tech. Univ., Geosci. Dep., Lubbock, Tex., United States
Pages: 366-381
Published: 197703
Text Language: English
Publisher: Society of Economic Paleontologists and Mineralogists, Tulsa, OK, United States
References: 28
Accession Number: 1977-030845
Categories: Sedimentary petrology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. plates, strat. col., sketch maps
N32°30'00" - N32°55'00", W101°10'00" - W100°34'60"
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute.
Update Code: 1977
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