Thesis (M.S.)--Brigham Young University. Dept. of Geological Sciences, 2008. / Includes bibliographical references (p. 29-34).

The nose of the Eastern shelf of the Midland Basin is a prominent structural and depositional feature present in Glasscock, Sterling, and Howard counties, Texas. This feature has been expressed in many regional maps and mentioned in some literature, but has not otherwise been studied significantly. This study looks at the viability of using an acoustic impedance seismic inversion to interpret the 2nd and 3rd order sequence stratigraphy of the southern portion of the nose of the Eastern shelf along with its shelf to basin transition in Glasscock, Sterling, and Reagan counties during the Wolfcampian (Asselian-Sakmarian) time (Early Permian). The Wolfcamp Formation (Wolfcampian-Leonardian) was subdivided into six units based on regionally mapped shale markers that correlate with 3rd order sequence boundaries. These horizons were mapped throughout the study area utilizing 3D seismic data and well logs. Analysis of seismic amplitude and inversion (acoustic impedance) volumes, along with well logs were then used to create a 2nd and 3rd order sequence stratigraphic framework in the study area. Six 3rd order sequences and two 2nd order sequences were identified in the study area during the Wolfcampian. From this framework a 2nd order sea-level curve was developed. The oldest Wolfcampian 3rd order sequence is marked by sediment bypass of the shelf and slope into the basin during a 3rd order sea level fall. Shelfal deposition resumed during subsequent sequences as sea-level rose and carbonate production resumed. Carbonate production increased during sequences four through six as part of a 2nd order sea-level highstand. During this highstand the nose of the Eastern shelf grew vertically increasing the gradient of the slope from less than 1° to 3.5°. The end of Wolfcampian deposition is marked by a large number of gravity flows into the basin resulting from subaerial exposure and erosion after a second order sea-level fall.

The Late Paleozoic Ice Age represents a dynamic period in Earth system history recording a shift from icehouse to greenhouse conditions. Concomitant with this change was a series high-frequency, high-amplitude sea level fluctuations leading to the deposition of “Kansas type” cyclothems in the Mid-Continent, and a similar rhythmic expression of interbedded shales and carbonates in the Midland Basin. Stable isotope geochemistry is a particularly powerful tool when examining these mud-rich successions because changes in organic matter partitioning may be recorded first in δ13CDIC of sea-water and consequently in δ13Ccarb of marine rocks. The δ13Ccarb record may also illuminate early and late-stage diagenetic processes and associated destruction of organic matter. This study used high-resolution x-ray fluorescence (XRF) and δ13Ccarb measurements to analyze paleo-environmental conditions in two cores within the Midland Basin Wolfcamp Formation. Using this approach, the combination of more positive δ13Ccarb measurements and enrichment of redox-sensitive elements reflect conditions more favorable for organic matter enrichment in the distal core. Additionally, four (< 6 in.) early-diagenetic intervals have been identified representing prolonged periods of reduced or non-deposition based on sharp negative δ13Ccarb excursions. These horizons are proposed as potential chronostratigraphic tie-points between the two core localities.