Historical analysis and reinterpretation of the lower part of the Canyon Group (Missourian, Upper Pennsylvanian), Wise County, Texas: A fine can of worms
Authors: Nestell Merlynd K. , Kimball Rustin A. 
Published: December 2023

Late Pennsylvanian (Early Missourian) age limestone strata exposed in several isolated outcrops in the Trinity River Valley in southwest Wise County, Texas were last described by Bose (1917), and Scott and Armstrong (1932). These strata can be correlated with the Upper Pennsylvanian Palo Pinto and Posideon formations of Laury (1962) in the lower part of the Canyon Group in the Brazos River Valley. The two reports were stratigraphically inconsistent concerning the seven limestone units of the Palo Pinto Formation as named by Scott and Armstrong (1932), and both included many poorly located type sections. The Bose (1917) report included no map and many key geographic references were to 1914 ranch names. Wise County records have helped to pinpoint these locations and allowed the reconciliation of the Bose (1917) Palo Pinto limestone localities to those of Scott and Armstrong (1932). Examination of exposures of these strata, and their associated fusulinid and conodont faunas has demonstrated that the following correlations to the Canyon Group in the type area in the Brazos River Valley in Palo Pinto County can be made (in descending order): (i) a conodont-rich black mudstone (indicating maximum transgression and a deep basin environment) at the base of the Wolf Mountain Shale and just above the Wiles Limestone correlates to a similar interval just above the Willow Point Limestone, well exposed in the area around the southwest shore of Lake Bridgeport; (ii) the Willow Point Limestone (= Bridgeport Limestone of Bose) correlates to the Wiles Limestone (top of the Posideon Formation); (iii) strata in the Martin Lake area just south of Bridgeport correlate to equivalent age conodont-rich black mudstones present in the middle part of the Posideon Formation; (iv) the Martin Lake Limestone is a fusulinid/algal grainstone containing a distinctive nankinellid fusulinacean at all outcrops and indicates very shallow marine deposition. It correlates with the top part (= Wynn Limestone) of the Palo Pinto Formation; (v) the Hudson Bridge Limestone correlates with the lower part of the Palo Pinto Formation. A black shale interval a few centimeters thick found in a core taken in an abandoned quarry in the Palo Pinto Formation in southwestern Wise County is correlated to a crinoid - conodont-rich 10-25cm unit that marks the base of the Palo Pinto Formation on top of the Keechi Creek Shale in much of Palo Pinto County. The new correlation of the Willow Point Limestone, the uppermost member that Scott and Armstrong (1932) reported as being in the Palo Pinto Formation, and its placement into the overlying Posideon Formation, leaves six limestone members in the Palo Pinto Formation identified in Wise County. Its top and bottom members, the Martin Lake Limestone and the Hudson Bridge Limestone, respectively, now are firmly correlated to the top and bottom, respectively, of the Palo Pinto Formation in the type area. A 1937 revision of the geologic map of Wise County raised the lower boundary of the Palo Pinto Formation, placing its lowest two members into the older Mineral Wells Formation of the Strawn Group (Armstrong 1937).