Southwest Section AAPG Annual Convention

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Late Pennsylvanian (Virgilian) to Early Permian (Leonardian) conodont biostratigraphy of the “Wolfcamp Shale”, northern Midland Basin, Texas.

Abstract

Analysis of Late Pennsylvanian (Virgilian) to Early Permian (Leonardian) conodonts from the northern Midland Basin, west Texas, has produced a biostratigraphic framework that enables correlation to surrounding regions, such as the Eastern Shelf and Midcontinent. Conodont specimens were obtained from organic-rich basinal shales from three cored intervals (8836–9020 ft, 9200–9502 ft, 9660–9840 ft) of the Shell Stephens L 1V well (Lynn County, Texas). The presence of conodonts within the deep-water basinal shale facies suggests that the specimens were deposited in situ, rather than transported by turbidite or debris flow. Core 1 was age-dated as latest Wolfcampian to early Leonardian based on the occurrence of species of Neostreptognathodus and Sweetognathus. Core 2 was age-dated as latest Virgilian to early-mid Wolfcampian based on occurrences of species of Streptognathodus and Sweetognathus. The Virgilian-Wolfcampian boundary was placed at 9740′ within Core 2 based on the presence of Streptognathodus wabaunsensis, S. conjunctus, and S. invaginatus. Core 3 was age-dated as Virgilian based on the occurrence of Streptognathodus virgilicus and S. pawhuskaensis. Barren to nearly barren intervals are present towards the mid to upper portion of Core 2 (9200′ – 9300′), and towards the base of Core 3 (below 9800′), while diverse clusters of conodonts occurred at the top of Core 1 (8841′–8970′), bottom half of Core 2 (9330′–9502′), and middle of Core 3 (9670′ – 9715′). Delineation of cyclothems using the gamma ray logs and core lithologies were used in association with the constructed conodont framework to aide in correlation to adjacent regions and wells. The success of this study will allow for conodonts to be utilized alongside the established fusulinid zonation to strengthen Pennsylvanian-Permian correlations throughout the Permian Basin and Midcontinent region, as well as globally.