Journal of the Graduate Research Center


E. G. Wermund


The uppermost Keechie Creek, the Palo Pinto, the Wolf Mountain, and the Winchell Formations of the Missourian Series were mapped in the Possum Kingdom vicinity, Palo Pinto County, Texas. The Keechie Creek and Wolf Mountain Formations are dominantly terrigenous facies. The Palo Pinto Formation is an off-bank facies which crops out immediately updip of an equivalent subsurface limestone bank. Both the bank and off-bank facies of the Winchell Limestone crop out in the study area. Typical Missourian terrigenous facies includes mostly unfossiliferous silty clay shales intercalated with a small volume of fine-grained sandstones. Away from equivalent limestone banks the shales contain abundant clay-ironstone concretions. Near gradational contacts with limestone banks the silty clays become fossiliferous. Rarely, the terrigenous sandstones grade laterally into limestones. Limestone banks grade laterally into terrigenous and calcareous facies that are different from the bank facies itself. Typical bank facies consist of 2/3 limestone with a micritic matrix and 1/3 limestone with sparry matrix; only thin shale partings are present. The primary bank builders are platy algae in micritic limestones, osagiid-like algae in sparry limestones, and fenestrate bryozoans in both micritic and sparry limestones. Normal to the sedimentary strike of the algal-bryozoan banks the typical bank limestones grade into limestone-types which usually have a micritic matrix and contain increasing amounts of clay. In the same direction the volume of terrigenous facies increases. As much as 75 feet of bank limestones grade laterally into entirely terrigenous facies in one-quarter mile. The depositional environment of bank facies is inferred to have included: (1) slightly higher topography than surrounding terrigenous environments, (2) firm bottom sediments, (3) low turbidity in shallow marine water, and (4) abundant, loose faunal remains.

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