Upper Pennsylvanian Limestone Banks, North-Central Texas

Nelson and others (1962) define a bank as " ... a skeletal deposit formed by organisms which do not have the ecologic potential to erect a rigid wave-resistant structure." They explain that a bank may have any geometry. The principal types or end members are biostromes which are thin, flat to lenticular deposits, or bioherms which are mounds. The American Geological Institute Glossary of Geology, (1972) accepts this definition and adds "It is thinner than, and lacks the structural framework of, an organic reef." It is this kind of limestone bank which is the subject of the following report. The purpose of this report is twofold: (1) to describe the regional distribution of upper Pennsylvanian, especially Missourian (Canyon), limestone banks in the subsurface of North-Central Texas, and (2) to relate the different calcareous facies observed in outcrops of Missourian limestone banks to modern calcareous environments. There have been numerous, recent papers about the Missourian terrigenous elastic rocks in North-Central Texas but few describing limestone facies. Brown and Goodson (1972), Brown and others (1973), Erxleben (1974), Galloway and Brown (1972, 1973), and Wermund and Jenkins (1970) have shown extensive deltaic deposition during Missourian and Virgilian times. Galloway and Brown (1972, 1973) have also shown how elastic slope deposits infill the basins in the same region. Although there have been several studies of outcrops of Missourian calcareous facies, this research does not appear in the literature. Unfortunately, work by Pollard (1970) in the Possum Kingdom area of Palo Pinto County, Raish (1964) in the Chico Ridge Bank of Wise County, and Roepke (1970) in the Colorado River valley has not been published. I have previously describe some aspects of the limestones in the Possum Kingdom Bank of Palo Pinto County (Wermund, 1966, 1969) but never demonstrated entirely the regional significance of the Pennsylvanian calcareous rocks. Modem calcareous environments have been described in depth in the recent literature, but no analogs of modern and Missourian calcareous sediments have been suggested. Both the regional distribution and modem analogs of Missourian limestones are emphasized here. Analogs of modern sedimentation are interpreted from outcrop studies. Locations of significant outcrops are listed in an appendix and are intended as potential field trip stops