ABSTRACT

The Tuscarora Formation is a medium sandstone with a few layers of vein quartz pebbles. The lower, red portion is a subgraywacke to graywacke, and was deposited in a submerged deltaic-estuarine environment. The upper, white portion is a supermature orthoquartzite formed as a beach sand deposited during a period of declining relief. The source area lay to the southeast; during early Tuscarora deposition it consisted largely of older sediments and low-rank metamorphic rocks, but as erosion proceeded, the sedimentary cover was stripped off and the plutonic igneous sources became of increasing importance. The Rose Hill Formation consists largely of open-marine to brackish-water olive clay shale, but intercalated with this are thin layers of gray siltstone and red hematitic sandstone, rang ng from orthoquartzite to subgraywacke in composition. The hematitic sandstones were deposited in a more shallow marine oxidizing environment than the gray siltstones which are cemented with ankerite and quartz. Iron minerals are common in the Rose Hill, and hematite, chlorite pellets, ankerite, and pyrite show consistent environmental associations. The source area for the Rose Hill consisted of low-rank metamorphic plus plutonic igneous rocks. The Keefer Sandstone shows evidence of lagoon-border and beach-dune deposition and consists of immature to supermature orthoquartzite to subgraywacke sandstones. The source area had now become deeply eroded so that plutonic igneous rocks dominated, but there were still some low-rank metamorphic rocks exposed.

High rounding was accomplished in one cycle of deposition in the beach and dune environments of the upper Tuscarora and upper Keefer sandstones; rounding potency varied markedly from bed to bed. Metamorphic rock fragments, because of their low resistance to abrasion, are found to be very useful as environmental indicators.