| dc.description.abstract | Whole-rock elemental data is a useful tool for sub-dividing and characterizing mudrock variability across a shale basin. The chemostratigraphy of the Cenomanian-Turonian the Woodbine and Eagle Ford Groups in the Brazos basin—a western sub-basin of the East Texas basin—contains five distinct chemofacies within five regionally correlative chemozones, EB 1 through EB 5. Chemozones are characterized by variations in geochemical data and coincide with major sequence stratigraphic surfaces determined from gamma-ray and deep-resistivity wireline logs. Chemostratigraphic correlations of high-resolution XRF measurements (1.2 to 2.4-inch spacing; 12,282 total data points), integrated with 623 XRD mineralogy and 708 core-derived TOC measurements, highlight significant vertical and lateral elemental heterogeneities in a shale that otherwise appears to be homogenous.
In the Woodbine and Eagle Ford Groups, several key elements are identified and correlated to depositional conditions: Ca concentrations indicate carbonate input; Si, Al, K, and Ti concentrations indicate clay input; Mo and Mn concentrations indicate redox conditions; and Ni enrichment indicates paleoproductivity. These key elemental proxies characterize chemofacies and chemozones. Average concentrations of key elements were mapped across chemozones to quantify their regional variability across the basin. This chemostratigraphic framework highlights major changes in: sedimentation type (i.e. siliclastic versus carbonate), sea level, redox conditions, paleoproductivity, and organic-matter enrichment in source rock plays. This assessment ultimately aids identifying horizontal landing zones and understanding their spatial variation in source rock plays. | en |
