Geodiversity Atlas—Mid-Atlantic I&M Network Index

Paleogene rocks are exposed in three of the Civil War battlefield parks in Virginia: FRSP, PETE, and RICH. The late Paleocene Aquia Formation is mapped in all three of these parks. At RICH the Pamunkey Group includes a sequence of late Paleocene–middle Eocene units including the Aquia Formation, Marlboro Clay, Nanjemoy Formation, and Piney Point Formation.

The Neogene is well-represented at FRSP, PETE, and RICH by formations associated with the Chesapeake Group. The oldest strata of the Chesapeake Group occur in RICH and consists of the 14 Oligocene–Miocene Old Church Formation. The early–middle Miocene Calvert Formation is mapped in portions of FRSP and RICH, and the late Miocene Eastover Formation is distributed across PETE and RICH. Other Miocene units that underlie RICH include the Choptank Formation and St. Mary’s Formation. At VAFO the Miocene Bryn Mawr Formation and late Miocene–Pliocene Pensauken Formation are mapped. Unnamed sand and gravel deposits of the Miocene and Pliocene are distributed across the Chancellorsville, Fredericksburg, and Spotsylvania Courthouse battlefield sites in FRSP. The Pliocene is also exposed in three of the Civil War battlefield parks in Virginia including FRSP, PETE, and RICH. This includes the early–late Pliocene Yorktown Formation mapped in all three of these parks, along with the late Pliocene Bacon Castle Formation. The late Pliocene Moorings Unit also occurs at FRSP.

Several Pleistocene units occur within the park units of the MIDN. The early Pleistocene Windsor Formation and Charles City Alloformation are mapped in both FRSP and RICH. The Chuckatuck Formation is a middle Pleistocene unit present at FRSP, PETE, and RICH where it is overlain by the Shirley Alloformation. At FRSP the late Pleistocene is represented by the Tabb Formation.

Late Triassic rocks are mapped within three park units of the MIDN in portions of GETT, HOFU, and SHEN. The Gettysburg Shale and York Haven Diabase are the predominant bedrock at GETT. Rocks of the Late Triassic Stockton Formation and Hammer Creek Conglomerate underlie HOFU. The Stockton Formation also occurs at VAFO. Late Triassic–Early Jurassic diabase dikes are documented at SHEN. Strata of the Cretaceous Potomac Group/Formation are present at three of the Virginia MIDN parks: FRSP, PETE, and RICH. The Cretaceous Patapsco Formation is present at VAFO.

Cambrian strata are widespread throughout the MIDN parks. The early Cambrian Chickies Formation is mapped at HOFU and VAFO in Pennsylvania. At SHEN a thick sequence of early Cambrian rocks includes the Weverton, Harpers Ferry, Antietam, Tomstown, and Waynesboro Formations. The Antietam Formation is also present in VAFO, overlain by the middle Cambrian Ledger and Elbrook Formations. The Elbrook Formation is also mapped at SHEN where it is overlain by the Beekmantown Group. The Cambrian is represented at APCO by the Fork Mountain Formation and sequences of greenstone, gneiss, metavolcanics, and other high grade metamorphic rocks.

The Ordovician Period is well-represented at CEBE and includes rocks of the Rockdale Run Formation, Pinesburg Station Dolomite, New Market Limestone, Lincolnshire Limestone, Edinburg Formation, Martinsburg Formation, and Oswego Sandstone. Additional Ordovician strata underlie FRSP and consist of the Ta River Metamorphic Suite, Chopawamsic Formation, Quantico Formation, Plagiogranite of Richland Run pluton, and Mine Run Complex (mélange). At FRSP the Ordovician metasedimentary rocks and the Quantico Formation are overlain by the Silurian Falls Run Granite. The Petersburg Granite is a Pennsylvanian–Permian unit at PETE.

Some of the oldest rocks in the MIDN include Mesoproterozoic banded mafic (silicate minerals containing iron and magnesium, typically dark) and graphitic felsic (feldspar- and/or quartz-rich) gneiss exposed at HOFU. Various igneous and metamorphosed igneous rocks of Mesoproterozoic to Neoproterozoic age are documented at SHEN, including the Neoproterozoic Swift Run Formation and Catoctin Formation. At BOWA, the Neoproterozoic is represented by the Ashe Formation, a metagraywacke, and amphibolite. Rocks of the Po River Metamorphic Suite span from the Neoproterozoic into the Paleozoic at FRSP, as does the Fork Mountain Formation at APCO.