Morphology, paleogeographic setting, and origin of the Middle Wilcox Yoakum Canyon, Texas Coastal Plain



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The Yoakum Canyon is the largest of the Gulf Coast Eocene erosional gorges and is interpreted as a buried submarine channel. It can be traced for 67 miles from the Wilcox fault zone, which defines the position of the early Eocene shelf edge, nearly to present outcrop. This paper expands on previously published descriptions of the canyon using a more extensive subsurface data base. Decompaction of the canyon shale-fill reveals that original depths of the canyon exceeded 3500 ft (1067 m). Apparent canyon wall slump scarps and a peripheral chaotic zone, interpreted as an incipient slump feature, are comparable to similar features of the late Quaternary Mississippi submarine canyon. The Yoakum canyon formed within the Garwood subembayment to the west of and adjacent to the Middle Wilcox continuation of the Rockdale delta system. Quantitative mapping of facies adjacent to the Yoakum shale indicate the following sequence of events: 1) Muddy, distal deltaic and shelf facies of the lower Middle Wilcox were deposited during a retrogradation. 2) A resurgence of progradation deposited the upper Middle Wilcox deltaic sands atop the unconsolidated, lower Middle Wilcox continental margin muds creating a density inversion which initiated slump failure of the continental margin sediments. 3) Headward erosion of the canyon across the shelf occurred contemporaneously with a subsidence-induced transgression caused by a decrease in the sediment supply. The Yoakum canyon was excavated by a combination of slumping and current scour. 4) The canyon was filled with hemipelagic and prodelta muds. 5) Progradation of the Upper Wilcox (Carrizo) deltaic sands capped the sequence.