Integrated Geochemistry and Sedimentology of the Wolfcamp B3 and B2 Intervals, Midland Basin, TX

Abstract

The Permian-aged, hydrocarbon-rich, mixed carbonate-siliciclastic mudrocks of Midland Basin Wolfcamp B2 and B3 are highly heterogeneous, making paleoenvironmental reconstruction difficult. The high-frequency lithologic and geochemical variations in the examined core often fall below a 2-inch (~ 5 cm.) vertical resolution, warranting a novel inorganic geochemical interval averaging approach for geochemical comparisons. Conventional sedimentological techniques such as core description, petrography, and ichnology allowed for a localized application of a regionally accepted 2nd order sequence-stratigraphic framework. Inorganic and organic geochemical techniques were then applied to further corroborate the paleoredox and paleoproductivity interpretation established by more sedimentologically based techniques. The influence of 2nd order eustatic sea-level fluctuations and sediment gravity flow events on paleoredox conditions was confirmed. Combined geochemical and ichnological evidence suggest that the Wolfcamp B3 and B2 mudrocks were deposited under suboxic conditions, with relatively more anoxic conditions during lowstand and progressively more oxic conditions during transgression and highstand, respectively.