Subsurface Stratigraphy Of The Strawn And Canyon Groups Of West Central Texas

Author : John W. Shelton
Publisher :
ISBN 13 :
Total Pages : 298 pages
Book Rating : 4.:/5 (31 download)

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Download or read book Studies of the Strawn-Canyon Boundary, Pennsylvanian, in North-central Texas written by John W. Shelton and published by . This book was released on 1953 with total page 298 pages. Available in PDF, EPUB and Kindle. Book excerpt: The Strawn-Canyon boundary is traced from the Colorado River valley of Texas to the Brazos River valley. Equivalent beds of the Capps limestone, uppermost Strawn unit of the Colorado River valley, are mapped in the Pennsylvanian inlier in Comanche County and in Eastland and Palo Pinto counties. In Eastland County the Strawn-Canyon boundary is placed at the top of the "boulder bed," which lies 15 feet above the limestone equivalent of the Capps limestone. The equivalent of the "boulder bed" in Palo Pinto County is the lenticular Village Bend limestone, but the top of the Strawn series is drawn at the base of the overlying Lake Pinto sandstone. The best criterion for establishment of the Strawn-Canyon boundary is paleontologic change. The series of the Pennsylvanian are established primarily on the basis of fusulinid zones. Strawn series is characterized by the genus Fusulina; Canyon series, by Triticites. The brachiopod Mesolobus and bryozoan Prismopora, occurring in pre-Canyon beds, serve as supplementary evidence in establishing the boundary. Upper Strawn and lower Canyon stratigraphic units are typically irregular and heterogeneous. Exceptionally, the Capps limestone equivalent of Eastland and Comanche counties and the Dog Bend limestone of Palo Pinto and Parker counties are rather uniform in lithology and thickness. Upper Strawn and lower Canyon sandstones are orthoquartzites, of the "washed-graywacke" type. The sandstones are characterized by a fair percentage of chert and by simple heavy mineral suites. The limestones are composed largely of detrital material. The Capps limestone, in part, and its equivalents are calcarenites; the Village Bend and Dog Bend limestones, calcilutites. Partial chemical analyses and differential thermal analyses of the carbonate rocks reveal that the predominant carbonate mineral is calcite. As suggested by the orthoquartzite and total thickness of Pennsylvanian beds, the exogeosyncline of north-central Texas during the Pennsylvanian period subsided at a rather slow rate. The irregularity of upper Strawn and lower Canyon strata is typical of sediments deposited near the strand line. The sandstones and shales were deposited in both nonmarine and marine environments. Cycles or rhythms in sedimentation during late Strawn and early Canyon time are somewhat obscured by the influx of sediments from the nearby source, which lay to the east and southeast.