Stratigraphy and Depositional Age of the Upper Lynchburg Group in the Schuyler 7.5’ Quadrangle, Virginia
The purpose of this research is to use updated geologic mapping in the Schuyler 7.5’ quadrangle to resolve the depositional environment, age, and stratigraphy of the Upper Lynchburg Group and its contact with the overlying Catoctin Formation. The Lynchburg Group is part of the Neoproterozoic metasedimentary cover sequence exposed across the eastern limb of the Blue Ridge in central Virginia. It overlies the Grenvillian basement complex and underlies the Catoctin Formation a unit of metamorphosed basalts dated to 550-570 Ma, marking the opening of the Iapetus Ocean. The upper units of the Lynchburg Group were given multiple names and descriptions by different researchers, each accompanied by its own set of interpretations and implications for each unit’s age, depositional environment, and the geologic history of the Blue Ridge, requiring further investigation to resolve these stratigraphic disputes.
The Swift Run Formation is a potential, siliciclastic Upper Lynchburg unit containing meta-arkose, phyllite, laminated metasiltstone and pebble-to-cobble meta-conglomerate. This unit is described as interfingered with the overlying Catoctin meta-basalts, forming a stratigraphic contact. The Biscuit Run Formation is another potential Upper Lynchburg unit, containing coarse-grained arkosic metasandstone and fine-grained metaquartzite unconformably overlain by the Catoctin Formation.
This study geologically mapped of the Schuyler 7.5” Quadrangle in collaboration with other student researchers. During our mapping efforts, we found locations where the Upper Lynchburg layers thin out showing Catoctin Greenstone truncating Lynchburg layers. The outcrops that we found and interpreted to be Upper Lynchburg within the Schuyler 7.5” Quadrangle are fine-grained micaceous metasandstones, mostly very coarse- but some fine-grained meta-arkose and quartzite samples. These samples are concurrent with the interpretation of the Biscuit Run Formation, as the Upper Lynchburg Group. underlying the Catoctin Formation unconformably and having noncontinuous depositional history leading to the opening of the Iapetus Ocean.
Meyrowitz, Haley E., "Stratigraphy and Depositional Age of the Upper Lynchburg Group in the Schuyler 7.5’ Quadrangle, Virginia" (2022). Geology Senior Theses. William & Mary. Paper 25.
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