Journal of the Graduate Research Center


The strata of Pennsylvanian age in north-central Texas dip gently and uniformly to the northwest. They are subdivided, in ascending order, into the Strawn, Canyon and Cisco Groups. The study area was limited to the upper part of the Canyon Group in Stephens and Palo Pinto counties. Four formations were mapped and the petrology described; they are, in ascending order, the Placid Shale, Ranger Limestone, Colony Creek Shale and Home Creek Limestone; also mapped were outliers of the Trinity Group (Cretaceous). All the formations show lateral and vertical lithologic changes; therefore detailed field tracing was necessary to insure accurate stratigraphic correlations. A detailed petrographic study of the carbonates showed that the limestones are composed almost entirely of comminuted organic material and have undergone little recrystallization. Much of the original sediment was mechanically deposited, and most lateral and vertical lithologic changes are believed to be related to variations in the physical environment. The limestone members are not characterized by a single rock type, but are divisible into distinct lithologies that generally can be traced throughout the area. The units vary from calcilutites to limestone conglomerates and appear to occur in rhythmic vertical succession.

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