Abstract

The utility of outcrops to geoscientists working the subsurface is typically limited by provincial nomenclature, outcrop-based lithostratigraphic subdivisions, which commonly differ in name and numbers among researchers, and often a basic indifference to the subsurface stratigraphy. In the subsurface of South Texas, the Eagle Ford Group is commonly divided into an organic-rich Lower Eagle Formation and a carbonate-rich Upper Eagle Ford Formation. In contrast, coeval strata that crop out nearby in West Texas are traditionally referred to as the Boquillas Formation. Adding further complexity to the outcrop stratigraphy is that previous workers divided the Boquillas into two to five informal lithostratigraphic units whose names and boundaries differ among researchers. By convolving information from a handheld gamma ray spectrometer, outcrop geochemical data and sequence stratigraphy, the Lower and Upper Eagle formations, as defined in the subsurface of South Texas, can now be defined in the coeval Eagle Ford Group outcrops of West Texas. Integrating basic geochemical and petrophysical data to the updated stratigraphy on these outcrops was transformative. By doing this, these West Texas exposures became portals to examine, as well as explain and predict, the distribution and thickness variations of specific chronostratigraphic units that are critical to the economic success of exploiting the Eagle Group across the unconventional source rock play fairway in South Texas.