--> ABSTRACT: Microfacies Analysis and Depositional Environments of Middle Unit of El Paso Group, Southern Hueco Mountains, Hudspeth County, Texas, by I. J. Aluka; #91040 (2010)

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Microfacies Analysis and Depositional Environments of Middle Unit of El Paso Group, Southern Hueco Mountains, Hudspeth County, Texas

I. J. Aluka

The middle unit of El Paso Group, 209 m (686 ft) thick, is predominantly a very thick-bedded to massive and nonstratified limestone with a few inclusions of chert nodules and lenses. The limestones are classified into seven standard microfacies (Smf). The standard microfacies are (from most common to least common) Smf-16, Pelsparite; Smf-9, bioclastic wackestone; Smf-18, algal grainstone; Smf-24, lithoclastic grainstone; Smf-23, nonlaminate pure micrite; Smf-15, oolite; and Smf-19, fenstral, peloidal and laminate micrite. The microfacies are further classified into 70 variations more fully and adequately to describe the middle unit rocks of the El Paso Group.

The middle unit contains Lecanospira, Hormotoma, Maclurites, brachiopods, and cephalopod siphuncles (in part assignable to Mcqueenoceras and Piloceras spp.). The presence of abundant peloids, few fossils, peloidal mudstones and wackestones, pellets, ooids, variety of textures, lack of laminations in the limestones, and terrigenous clastics intercalating with limestones indicate that the middle unit was deposited in restricted circulation in shelf, shelf lagoon with open circulation, and tidal flat environments. The microfacies also indicate deposition in shallow water (shallow undathem), near shoreline or near source of siliceous clastic sediments. The presence of fragmented fossils and sparsity of micrite indicate the presence of at least an occasional high-energy environment that subjected the sediments to winnowing and wave action.

AAPG Search and Discovery Article #91040©1987 AAPG Rocky Mountain Section Meeting, Boise, Idaho, September 13-16, 1987.