MESOZOIC FAULTING AND CENOZOIC UPLIFT: THE LINK TO LANDFORM EVOLUTION IN THE CAROLINAS

Surface geomorphic, structural, and stratigraphic relationships in the Carolinas suggest a history of substantial (0.5-1 km) Tertiary uplift of the Southern Appalachians. Analysis of drainage patterns and local slopes shows distinct differences between the physiographic regions of the southeastern Atlantic continental margin, apparently without regard to influence of the underlying bedrock. Such relationships may owe their origin to a previously more extensive terrigeneous/marine coastal plain cover, extending up-dip of the Fall Line to the Tallapoosa-Rappahannock Lineament, and perhaps marking the pre-erosional location of the Blue Ridge Escarpment. In the absence of remnants of this former cover in the Inner Piedmont, the thickness and nature of the sedimentary cover is difficult to discern, but is believed to not have extended beyond the Blue Ridge escarpment based on drainage relationships. Mesozoic extensional faulting and basin formation provide a mechanism for escarpment formation and the lowering of the Piedmont land surface, allowing Cretaceous to Late Tertiary seas to at least partially cover the present-day Piedmont. Substantial Tertiary uplift of the margin could account for the removal of this cover and exposure of the Blue Ridge Escarpment and Piedmont. Continued uplift at a subdued rate may continue to be a driving force for the short wavelength relief of the escarpment and the southern Blue Ridge. Although the exact timing and magnitude of the uplift continues to be questionable, it is believed to have been most likely centered around the major Oligocene and Early Miocene unconformity ending by the time of deposition of the Upland Unit (Mid-Miocene) traceable from New Jersey to Georgia in various stratigraphic units. Estimates for the magnitude of uplift are highly dependent on the former extent of sea level, but are thought to be of approximately 500-1000 m in vertical crustal motion.