FACIES CHARACTERIZATION AND STRATIGRAPHIC RELATIONS OF A NEARSHORE TO OFFSHORE MUDSTONE SUCCESSION OF THE LOWER EAGLE FORD FORMATION IN THE EAST TEXAS BASIN

Studies of mudstone sedimentology have utilized sequence stratigraphic interpretations as a tool to identify areas of optimal carbon burial in ancient marine basins. However, such studies mostly occur in distal environments where the dominant sediment source is biogenic material derived from the overlying water column. Thus, the relationship of lithologies in these studies to shoreline processes are not well established. In this study we evaluate the transition from the Woodbine Formation to the lower Eagle Ford Formation from samples of the USGS Gulf Coast No. 2 Dallas Redbird core taken in Dallas County, TX. Qualitative and quantitative core analysis allows for a unique opportunity to establish a stratigraphic framework from a mudstone succession that can be directly linked to shoreline processes.

Hand samples and thin sections were evaluated for composition, texture, and fabric. Additionally, core samples were evaluated for mineralogy via x-ray diffraction and infrared spectroscopy and major and trace element concentrations via ICP analysis. Total organic carbon and programmed pyrolysis parameters including HI and OI were also collected for each sample. From these analyses 9 primary lithologies were identified: 1. Cross-bedded fine sandstone; 2. Interbedded lenticular fine sand and argillaceous mudstone; 3. Carbonaceous mudstone; 4. Bioturbated sandy mudstone; 5. Bioturbated argillaceous mudstone; 6. Carbonate cement; 7. Fossiliferous limestone; 8. Wave / current rippled calcareous mudstone; and 9. Bioturbated calcareous mudstone. Stratigraphic relations of these lithologies demonstrate an overall upward trend from deposits dominated by detrital sourced sediment to deposits of mixed detrital and biogenic sediment. Within this overall succession, five 5-20 ft coarsening upward successions were identified in the detrital dominated interval. Further work is necessary to interpret the stratigraphic variability of the biogenic dominated interval. Preliminary interpretations suggest that the study interval was deposited within a transgressive and highstand systems tract. The coarsening-upward successions may represent parasequences, but further work is necessary to determine if they are able to be widely correlated or related to local autocyclic processes.