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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 69 (1985)

Issue: 2. (February)

First Page: 297

Last Page: 297

Title: Early Diagenetic History of Late Pennsylvanian Calclithite Beds, Hueco Mountains, El Paso County, Texas: ABSTRACT

Author(s): James C. Pol

Article Type: Meeting abstract


Calclithite beds exposed on the western escarpment of the Hueco Mountains were deposited in a fan-delta system featuring fluvial channels, marine bars or beach sands, shallow-marine shale and limestone, and tidal flats and lagoons. Two distinct calclithite types occur. One is a coarse, poorly sorted gravelly sand with angular to subrounded grains. This type occurs in discontinuous or channel-shaped beds. Sedimentary structures include fining-upward sets, imbrication, and trough cross-bedding. These characteristics indicate sporadic unidirectional flow, as would be expected in ephemeral streams. The second calclithite type is fine to medium-grained well-sorted sand with very well-rounded grains. This type crops out as thin, relatively continuous units. Sedimentary structur s include ripples, small-scale cross-beds, low-angle and horizontal or planar bedding.

The early diagenetic history of the calclithites reflects their depositional environment. The coarse calclithite was deposited in undersaturated freshwater conditions, shown by the absence of early cement. Early compaction of the coarse calclithite, indicated by intergranular microstylolitization and shale-clast deformation, is the most commonly observed texture. The fine-grained calclithite exhibits a markedly different diagenetic history. The first recognizable "diagenetic" event is micritization of marine-derived fossils and calclithite grains. Early cementation in the marine phreatic environment resulted in isopachous rims of fibrous aragonite and bladed Mg-calcite cement. Pore centers contain a later equant calcite cement. Little or no early compaction occurred in the fine calcli hite. Freshwater flushing is indicated by the replacement of former aragonite cement rims by finely crystalline equant calcite.

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