REGIONAL STRUCTURAL AND STRATIGRAPHIC EVIDENCE FOR DATING CENOZOIC UPLIFT OF SOUTHERN APPALACHIAN HIGHLANDS

The Southern Appalachian Highlands are a deeply incised, high-elevation, metasedimentary and igneous terrain eroding in a temperate, very moist climate. Geomorphically the region should be experiencing rapid erosion, so its high elevation suggests a relatively recent uplift of a regional dome, but early enough to develop into high relief: probably tens of millions of years. Regional geologic maps suggest the time of uplift. If the arc of Cretaceous-Tertiary strata around the Alabama terminus of the Appalachians is considered a fold rather than a depositional margin, maps show that the folding was post-late Eocene, possibly during Oligocene, and definitely pre-Miocene. Similarly, a view of the Carolinas indicates a southeastward plunging arch largely buried beneath the Neogene and centered slightly south of the Cape Fear River. Stratigraphic evidence indicates folding after Oligocene deposition and before Miocene strata. The general axial trends of these two plunging arches intersect at the Southern Appalachian Highlands. We propose that gradual regional uplift of the Highlands centered at about 25 Ma. The system of trench valleys we have mapped centering on the Southern Appalachian Highlands, but extending into the Piedmont and Valley and Ridge, is etched into a post-Alleghanian complex of fractures chiefly formed during this uplift. Timing is so interpreted because the trench valley system is centered in the Highlands. These trench valleys have three orientations: the most prominent is slightly north of east, northwest, and other fainter trenches slightly west of north, agreeing with Gay (2000). The lesser lineaments generally do not cross the easterly lineaments, and therefore the easterly trends are probably the oldest. Minor faults adjacent to the due-east Laurel Creek trench trend about 120° and locally show left-lateral movement. Cenozoic denudation may have found a post-Alleghanian or Alleghanian fracture zone and etched it to a lower-elevation trench valley.