Atoka Series in North Central Texas: ABSTRACT

Abstract

During the Mississippian and Pennsylvanian periods in North Texas, the area of thickest accumulation shifted westward and the tectonic activity, as shown by the character of the sediments and their rate of thickening, decreased. In the sequence of gradually changing depositional environments from linear geosynclinal type to continental basin type, the Atoka and Des Moines epochs are transitional. The depositional pattern of Atoka sedimentation suggests a modified geosynclinal environment. Sediments of early Atoka time indicate that the Atoka basin formed under conditions of considerable crustal mobility. Thousands of feet of interspersed shale and dirty sandstones attest the rapid burial of the geosynclinal sediments. The Atoka series thins rapidly across a hinge area, where the sediments are predominantly shales with some interbedded sandstones, to the shelf area, where limestones and dark shale were deposited. The different sedimentary types, controlled by environment, were deposited contemporaneously. The marked divergence of time and lithologic units makes it advisable to apply terminology only to facies types. The Marble Falls formation in North Central Texas, as generally considered, includes the Pennsylvanian-Mississippian unconformity. Although the Muenster Arch was not uplifted until post-Atoka-pre-Des Moines time, conditions existed in the general area which inhibited the rate of downwarping relative to the surrounding area. The thinner Atoka sediments, which were deposited over the Arch, were later removed by erosion. End_of_Article - Last_Page 1673------------