Proposed Type Sections for Upper Silurian and Lower Devonian Subsurface Units in Permian Basin, West Texas: GEOLOGIC NOTES

Abstract

The name Wristen Formation is proposed for the formation in the Permian basin known as the shale, Upper Silurian, or Green with a type section in Ward County, Texas. Two members are designated in the Wristen Formation--the Wink and Frame Members. The lower, Wink Member, consists principally of gray limestone, and the upper, Frame Member, consists principally of greenish-gray shale and limestone. These members grade into a thick carbonate facies in Andrews County, Texas. The Wristen Formation is assumed to be of late Middle and Late Silurian age, and correlative with part of both the Hunton Group of Oklahoma and perhaps the Caballos Novaculite of the Marathon region. The name Thirtyone Formation is proposed for the unit known as the Lower Devonian cherty in the subsurface of the Permian basin. The type section is in Crane County, Texas. The three lithofacies of the Thirtyone are: (1) a chert facies in the southwest; (2) a carbonate facies in the north; and (3) a siliceous limestone facies in the center of the study area. The Thirtyone is of Early and Middle Devonian age, and is also correlative with part of both the Hunton Group of Oklahoma and the Caballos Novaculite of the Marathon region.