| Abstract | The Lower Cenomanian Maness Shale is a mudrock unit lying between the Buda Limestone and the Woodbine sandstones in east Texas and between the Buda Limestone and Eagle Ford shales in south Texas. The Maness has been studied since the 1950’s, yet much is still unknown, such as its sediment source, depositional environment, and source rock potential. This study combined mineralogical, elemental, biostratigraphic, and organic geochemical data to refine the knowledge of the east Texas Maness and compare the data to previous studies. The mineralogical composition of the Maness in east Texas is 36% clay, 35% quartz, and 18% calcite, with traces of pyrite, phosphate, and siderite concretions. Since this study confirmed that the Maness in east Texas is age-correlative to the Maness near the San Marcos Arch based on biostratigraphy, the mineralogical data was compared to studies near the San Marcos Arch and Brazos Basin to determine that the east Texas Maness is more silica-rich and less clay-rich. Furthermore, the presence of benthic foraminifera, ostracods, and echinoids suggest relatively oxygenated bottom waters, although elemental analysis indicates there may be a shift from oxic to anoxic conditions in the Upper Maness. TOC values average 2.8% suggesting that the Maness in the type area is a potential source rock, although environmental conditions were not conducive to organic matter preservation. The thickness trend on the Maness isopach map suggests two potential deltaic sediment sources. The Maness may be sourced from the Sabine Uplift to the east, similar to the Harris delta, or it may be sourced from the northern Ouachita Uplift, similar to the Woodbine deltaic complex. In either situation, the East Texas Field is proximal to the sediment source as tempestite deposits and bottom water oxygen conditions suggest a shallow shelfal depositional environment. Conversely, the Maness in south Texas was deposited within a distal, deeper depositional environment below storm wave base. Lastly, mineralogical shifts from the Buda to the False Buda to the Upper Maness is a factor of decreasing oxygenation, which increased siliciclastic input into the system. |
