Stratigraphy of the Pennsylvanian Formations of North-Central Texas

Palo Pinto Formation

" Name and Stratigraphic Position. — At the base of the Canyon group in the Brazos River Valley and lying with apparent conformity upon the shales and sandstones of the Strawn is a bed of massive limestone which varies in thickness from 50 to 100 feet. This is named the Palo Pinto limestone from the town of Palo Pinto located on its outcrop. It may be recognized easily elsewhere in well logs and in the field because it is the lowermost thick limestone in the section above the Strawn sands.

Lithologic Character.  — The Palo Pinto limestone is a thick, crystalline, dark-gray limestone weathering white or grayish yellow. In many places the lower portion is made up of many thin beds from two to six inches thick, separated by partings of gray marl so that in weathering the rock shelves off into great piles of slabs, chips, and chunks. The upper layers are thicker, dark gray, fine-grained, even-textured, more fossiliferous, and purer than the lower beds. Upon weathering these beds break into large blocks and irregular chunks.   "

Paleontology.  — The faunal character of the Palo Pinto limestone has not been indicated satisfactorily in the course of the field work on the Texas Pennsylvanian. The collections are rather meager and for the most part contain only the more common, long-ranging Pennsylvanian types. The limestone is not on the whole very fossiliferous and there has not been opportunity for special paleontological investigation of this horizon. So far as observed the fossils are contained chiefly in the upper portion of the limestone above the parting of yellow shale which divides the formation into two main ledges.

Perhaps the chief characteristic of the Palo Pinto fossils is their robust appearance. Species which at other stratigraphic horizons have only moderate size, appear here as very large individuals which in some cases are almost twice the normal size. Most of the specimens, also, are very perfectly formed and well preserved.  "