Quaternary Erosional History of the St. Marys River, Western Virginia

Abstract

The landscape between Vesuvius and Greenville Virginia records the history of competition between the Shenandoah-Potomac and Maury-James basins. The St. Marys River is the latest in a series of stream captures that appear to have extended the South River headward from near Big Marys Creek to the present divide near Lofton. The former St Mary's River, or "Lofton River," likely flowed through the Antietam hogback in roughly the place it does today but turned north following the path of Pine Run through the crossing known as Lofton. Northwest paleocurrent directions in the fan extremity, plus remnants of the Lofton River and an igneous rock lithology unique to the St. Mary's/Spy Run basin show that drainage went north when it was approximately 70 m higher. Soils developed in the youngest deposits that we could locate in the fan remnants north of the current St. Mary's River suggest that this paleo-river no more than 300 thousand years old. Yet terraces of the modem St. Marys River suggest capture took place more than 140 thousand years ago, which implies that the incision was rapid, due to the capture event itself or a subsequent base level drop in the South River basin.