Abstract
The Moodys Branch Formation (Eocene) is a rock unit in the Gulf Coastal Plain which exhibits remarkable strike-persistence along 600 miles of outcrop from East Texas to Alabama. The average thickness of this unit is only about 10 feet. This transgressive marine unit was deposited on a shallow-shelf, and the lithology is generally glauconitic, sandy limestone (greater than 50 percent calcium carbonate). Unconformably underlying the Moodys Branch, with an Ophiomorpha-burrowed contact, are deltaic and beach sands, while conformably overlying the Moodys Branch are neritic clays and carbonates. Vertical variations in mineral composition within the Moodys Branch, based on point-count data of 48 thin-sections representing 21 localities from East Texas to Alabama are: upward increase in matrix, and upward decrease in quartz, mica, feldspar, glauconite, and fossil fragments. Mean percentage values for mineral composition in the study area are matrix, 50; quartz, 24; fossil fragments, 16; and glauconite, 6.5. Mica, feldspar, chert and rock fragments combined form less than 4 percent of the mineral composition. Significant vertical trends in textural properties, based on study of 100 samples, are upward increase in clay and silt; and upward decrease in mean grain size. Mean percentage values for the Moodys Branch are: clay, 21; silt, 21; sand, 58; and mean value for sand-size quartz is 0.286 mm. The above trends are interpreted to represent a decrease in the influence of terrigenous sources in the vertical sequence. This implies increasing water depth, reflecting an open-marine transgression of the Moodys Branch over the underlying non-marine sediments, and is confirmed by study of the microfauna.
Anderson, Don Randolph (1971). Moodys Branch Formation (Eocene) in Gulf Coastal Plain: a model for transgressive marine sedimentation. Texas A&M University. Texas A&M University. Libraries. Available electronically from
https : / /hdl .handle .net /1969 .1 /DISSERTATIONS -213319.