BOARDMAN, DARWIN R., II, Oklahoma State University, Stillwater, OK
been identified and analyzed for Upper Pennsylvanian and Lower Permian rocks exposed on the Eastern shelf of the Midland basin. Based on the vertical distribution of marine condensed sections along with the interpreted magnitude of each sea level rise, a preliminary seal level curve has been generated.
Two different types of marine condensed sections have been identified. Type A is gray to black clay (core shales) with abundant pyrite, non-skeletal phosphate, along with an offshore, pelagic dominated fauna consisting primarily of ammonoids and conodonts, Type B is green to gray limestones characterized by glauconite, pyrite, along with a fauna characterized by abundant phosphatized mollusks, along with high numbers of moderately offshore conodonts.
Type A marine condensed sections are interpreted to represent deposition in a low-oxygen outer shelf (50-100 m depth) characterized by sediment dilution associated with condensed pelagic fauna. Since these type A marine condensed sections represent deposition in water depths below the euphotic zone and are located on the high inner shelf, they are interpreted to represent major marine transgressions caused by glacial-eustatic sea level rises. Type B marine condensed sections are interpreted to have formed under similar sediment dilution and condensation conditions as type A, but in fully oxygenated bottom water within the euphotic zone (25-50 m depth). The type B marine condensed sections are therefore interpreted to represent intermediate glacial-eustatic sea level rises.
AAPG Search and Discovery Article #90994©1993 AAPG Southwest Section Meeting, Fort Worth, Texas, February 21-23, 1993.