Geology of the Adwolf-Thomas Bridge area, Virginia

Abstract

The Adwolf-Thomas.Bridge area of Smyth County, Virginia is underlain by Paleozoic rocks that crop out in northwest-trending belts. The formations that are considered in this study include in ascending stratigraphic order, the Erwin Formation, Shady Dolomite, Rome Formation, Elbrook Formation and Conococheague of Cambrian age and the uppermost Knox Dolomite, Tumbez Formation, Mosheim Formation, Giesler Limestone, Arline Limestone and Rich Valley Formation of Ordovician age.

The area is structurally complex. The southeast dipping Seven Springs thrust brings Late Cambrian rocks of the hanging wall into contact with rocks as young as Middle Ordovician age in the Saltville thrust block.

The Holston River syncline and the Glade-Pond Mountain anticlinorium form the area southeast of the Seven Springs fault. The Holston River syncline is an asymmetrical, southweat-plunging syncline in rocks of Cambrian age. The Glade-Pond Mountain anticlinorium is also confined to rocks of Cambrian age and is complicated by a series of small anticlines which have been broken on their northeast limbs by southeast dipping reverse faults.

Sands and carbonates were the predominant sediments deposited in Cambrian and Early Ordovician time. In Middle Ordovician time, both carbonates and clayey muds were deposited. As no Silurian or younger Pal~ozoic sediments are present, it is not known when sedimentation ended.

Deformation, perhaps in part contemporaneous with sedimentation, appears to have been' climaxed in Mississippian time after sediments of this age were deposited in the area considerably to the north of the area discussed in this report (Butts 1940).