Structural Geology of Southeastern Virginia

Abstract

New data are presented that alter somewhat the basic concepts of the geology of the Coastal Plain in Virginia. These may be summarized as follows: Upper Cretaceous deposits have a rather wide range of distribution south of the James River but are apparently lacking immediately north of the James River; Eocene sediments, generally less than 100 feet thick south of the James River, are known to be several hundred feet thick throughout most of the Coastal Plain north of the James River and thicknesses up to about 800 feet are known at Fort Monroe. A structural contour map on the Eocene-Miocene contact shows that that boundary is gently but definitely warped. Interpretations based on these data are as follows. The lack of Upper Cretaceous sediments at Newport News and Fort Monroe is ascribed to pre-Eocene channeling rather than to relative uplift of that area with respect to Norfolk. Post-Upper Cretaceous channel filling is not the complete explanation for all the thickening of sediments north of the James River and that area is believed to have subsided throughout Eocene time. Subsidence is accounted for by faulting of the basement rock. The fault is thought to trend westward along the James River and approach the Fall Zone; the maximum displacement along the postulated fault, from 300 to 600 feet, occurs in the Hampton Roads area. In post-Miocene time the area was gently folded as a result of settling movements along a pre-existing fault or series of faults. Geophysical data are drawn upon to substantiate the interpretations presented and to show the probable similarity of the Cape Fear region in North Carolina to the Hampton Roads region in Virginia.