Geology of the Hanover Academy and Ashland quadrangles, Virginia

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Virginia Polytechnic Institute and State University

The Ashland and Hanover Academy quadrangles in east-central Virginia lie astride the Fall Line. Metamorphic and granitic rocks of the Piedmont Province to the west of the Fall Line are pre-Triassic in age. Biotite gneiss, granite gneiss, muscovite-biotite schist, amphibolite, and Petersburg Granite are represented. Along the eastern margin of the Piedmont a northeast trending half-graben, the Taylorsville Basin, bordered on the northwest by the Fork Church fault, contains rocks of Triassic age. These rocks are divided in this report into four successive conformable formations. Unconsolidated Coastal Plain sediments east of the Fall Line are Cretaceous, Tertiary, and Quaternary in age. This province includes the Patuxent Formation (Cretaceous), the Aquia Formation (Paleocene), and the Marlboro Clay (Eocene), the St. Marys Formation (Miocene), the Brandywine Formation (Miocene), and the Sunderland, Wicomico, and Talbot terraces (?Pilocene·Pleistocene), as well as Recent alluvium.

The Hylas Zone, a linear zone of cataclastic rocks which trends northeast-southwest across the Piedmont portion of the mapped area, is interpreted as a fault zone that has disrupted the Piedmont rocks. The zone also served as a locus for faultlng in Triassic time and has affected at least indirectly the thicknesses and attitudes of Coastal Plain strata at least as young as Paleocene.