Geology and mineral resources of the Goose Creek area near Roanoke, Virginia

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Virginia Polytechnic Institute


The Goose Creek area in parts of Roanoke, Botetourt, and Bedford counties, Virginia, comprises about 170 square miles of complexly folded and faulted Precambrian and Paleozoic rocks of the Blue Ridge and Great Valley physiographic provinces.

The Precambrian rocks are divided into three different types of gneisses on the basis of their textures. These are unconformably overlain by Cambrian rocks of the Unicoi formation, Hampton shale, Erwin quartzite, Rome formation, Bilbrook dolomite, and Conococheague formation. The total thickness of the Precambrian gneisses is about 7,500 feet and that of Cambrian formation is 10,000 feet. The Ordovician Bffna and Fetzer limestones are about 30 feet thick and the Liberty Hall and Martinaburg shales are about 800 feet thick. Silurian-Lower Devonian rocks represented by the Clinch, Clinton, and Helderberg formations are 15 (?) to 300 feet thick. Additional unclassified shales are of Devonian age. Locally Quaternary deposits of colluvium, older terrace gravels, and alluvium cover all of the above.

One of the major structural features of the area is the nearly flat Blue Ridge thrust which extends across most of the area. The Blue Ridge thrust plate is breached by Goose Creek in the southeast -part of the area. The displacement of the thrust is at least six miles. The Precambrian rocks of the Blue Ridge fault block are believed to be the core of a large overturned northeasterly-trending anticlinorium.

Many similar northeasterly-trending folds, which are mostly open or only slightly overturned to the northwest, are found in the frontal part of the Blue Ridge thrust plate and in the underlying rocks. A few northwesterly-trending cross folds were developed in rocks both above and below the thrust and were formed contemporaneously or slightly later than the faulting. Another major structure, probably the Pulaski thrust fault, is shown in a window cut by the Salem (?) fault at Coyner Mountain. If the correlation of the Pulaski fault is correct then the minimum displacement must bell miles. Many smaller faults and folds also indicate strong compressive forces in a northwest-southeast direction. The cross folds are believed to have been developed by differential northwesterly movement of the fault blocks. The differential movements are believed to have resulted from deflection around buttresses in the Appalachian Valley, although there is a possibility that the deforming force shifted to a more westerly direction.

The Blue Ridge province is represented by resistant parts of the uneroded Blue Ridge thrust block. The Great Valley province in the northwest part of the area is underlain by soft shales and carbonate rocks and has encroached on the edge of the Blue Ridge thrust plate. Southwestward-flowing Glade Creek and its main drainage area is similar to the Great Valley in physiography and type of bedrock. It extends northeast into a breached area of the Blue Ridge thrust where its headwaters are captured by southeast-flowing Goose Creek.

The geologic history of the Goose Creek area can be summarized as follows: (1) deposition of Late(?) Precambrian sediments; (2) folding and faulting of the Precambrian rocks accompanied by metamorphism, granitization, and intrusion that probably occurred during or prior to a sub-Cambrian orogeny which may have produced the configuration of the Appalachian geosyncline; (3) cannibalism during earliest Cambrian time, supplying the lowest Cambrian elastic sediments; (4) deepening of the Appalachian geosyncline to receive the thick carbonate sediment from Lower Cambrian to Middle Ordovician; (5) resumption of cannibalism on the elevated lands to the southeast from Middle Ordovician to Lower Mississippian time, supplying younger clastic sediments; (6) folding and faulting of the Precambrian and Paleozoic rocks during the Appalachian orogeny; (7) peneplanation of the newborn Appalachian at the summit level of the Blue Ridge mountains in Tertiary(?) time; and (8) intermittent uplifting, trenching,and tilting of the peneplain and other ero~ion surfaces from Tertiary(?) to the present.

The mineral resources include limestone, dolomite, iron and shale. Once productive low-grade iron deposits are now no longer profitable. The ground water supply is plentiful and a potential asset for industry. The beat aquifers are the unconsolidated deposits and some of the carbonate rocks of the Elbrook and Rome formations.