--> New Data on the Palo Pinto Formation, (Missourian, Pennsylvanian) Northeastern Palo Pinto County, Texas, by L. S. Kelley and M. K. Nestell; #90903 (2001)

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New Data on the Palo Pinto Formation, (Missourian, Pennsylvanian) Northeastern Palo Pinto County, Texas

L. S. Kelley and M. K. Nestell
Department of Geology, University of Texas at Arlington

Moore and Plummer (1921) defined the Palo Pinto Formation, but the precise type section location and unit boundaries were not clearly presented. Stratigraphic terminology was further confused in later works (e.g., Plummer and Hornberger (1935), Cheney (1940)). Lateral lithofacies changes from limestone to calcareous shale within the formation have not been previously documented. The Palo Pinto Formation begins the Canyon Group representing a change from siliclastic to carbonate dominated deposition. The unit’s calcareous shale lithofacies has been miscorrelated as the upper part of the underlying siliclastic Keechi Creek Shale (Strawn Group). Defining its upper and lower boundaries is critical in placing this unit in its proper stratigraphic context.

A mappable quartzose phosphatic crinoidal packstone, informally called the Union Hill Member, defines the onset of carbonate deposition at the formation’s base. Laury’s (1962) stratigraphic scheme for the Palo Pinto and overlying Posideon formations is supported. Cheney’s elevation of the Wynn Limestone Member (lower/middle part of the formation) to formational status is rejected. This unit is dominantly limestone at the type section, but is replaced by fossiliferous calcareous shale to the northeast. The first grainstone within the upper part of the formation, informally called the Reilly Ranch Member, is a correlative bed for the shoaling upwards regressive part of the sequence. The uppermost medium bedded limestone of the formation is a foraminiferal grainstone containing distinctive fusulinaceans and algae (e.g., Triticites, Nankinella, and Epimastopora). This unit can be traced from the type section to the northeast into Wise County as the Martin Lake Limestone where the same fusulinaceans and algae are present. Fluvial deposits of the superjacent Posideon Formation overlie the carbonate grainstone at the top of the Palo Pinto Formation.

AAPG Search and Discovery Article #90903©2001 AAPG Mid-Continent Meeting, Amarillo, Texas