Regional sequence stratigraphy and biostratigraphic correlations of the Upper Cretaceous Austin Chalk in south and central Texas: Insights into the evolution of the San Marcos Arch

Abstract

Although there is an extensive literature on the Austin Chalk, papers and theses cover portions of the study area or emphasize specific aspects, such as microfacies, paleontology, or geomechanical properties (Cooper et al., 2020; Dravis, 1980; Durham and Hall, 1991; Ewing, 2013; Jiang, 1989; Loucks et al., 2020a; Loucks et al., 2020b; Lundquist, 2015; Young and Woodruff, 1985; Zahm, 2020). The Austin Chalk lacks a regional sequence stratigraphic synthesis that provides a consistent chrono-stratigraphic framework across south and central Texas. The existing stratigraphic nomenclature differs between the outcrop and subsurface, and between the major producing fields on either side of the San Marcos Arch (Cooper et al., 2020; Durham and Hall, 1991; Ewing, 2013; Maranto, 2017; Young and Woodruff, 1985). In this study, detailed sequence stratigraphic correlations of the Austin Chalk indicate the presence of five depositional sequences. Isochore maps of these sequences show the sequential westward movement of the axis of the San Marcos Arch during Austin Chalk deposition. Cretaceous pelagic chalks extend from the Western Interior Seaway, through the Gulf Coast, and across the Atlantic. The Late Turonian-Early Campanian Austin Group in south and central Texas is unique in North America, due to the high proportion of clean carbonate and the wide range of depositional water depths, from shallow water around the Llano Uplift to deep water in the Gulf of Mexico. The Austin Chalk is also of economic importance in that it has produced 1.3 BO and 6 TCF since 1935, mainly as an unconventional fractured chalk play (Enverus_Drillinginfo, 2022).