GEOLEX

Summary of Citation: Thirtyone

Publication:
Hills, J.M. and Hoenig, M.A., 1979, Proposed type sections for
   Upper Silurian and Lower Devonian stratigraphic units in
   Permian basin, West Texas: American Association of Petroleum
   Geologists Bulletin, v. 63, no. 9, p. 1510-1521

Usage in Publication:
Thirtyone Formation

Modifications:	Geologic Province:	Dominant Lithology:
Named	Permian basin	Limestone Chert

Summary:
Name applied to some rocks known only in the subsurface of West TX formerly designated "Devonian cherty limestone," "Devonian limestone," and "Lower Devonian." Type section designated in Champlin Refining Co. 1 Crane University well, sec 40, Blk 31, University Lands Survey, Crane Co, TX between 9,050 and 8,040 ft where it consists of white, brown to gray limestone and white to gray chert. The limestone may be siliceous, tripolitic, cherty, or dolomitic. Has 3 regional facies: 1) in southwest part of basin--chert carbonate with some gray crystalline cherty dolomite; 2) central part of basin--a lower chert, calcareous tripolite, and siliceous limestone, and an upper gray siliceous limestone; 3) northeast part of basin--white to gray limestone with traces of white to gray chert. Base of formation not easy to recognize where chert is missing. Is thickest at type. Deposition probably contemporaneous with Caballos Novaculite. Fossils: inarticulate brachiopods, bivalves, nautiloids, bryozoans, crinoids, corals. Early Devonian age indicated. Correlation chart. Cross section. E-logs. Overlies newly named Frame Member of newly named Wristen Formation. Underlies Woodford Formation. Upper contact erosional. Present in Winkler, Andrews, Ward, Ector, Pecos, Crane, and Upton Cos, TX in the Permian basin.