PLEISTOCENE SHORELINES AND COASTAL RIVERS: SENSITIVE POTENTIAL INDICATORS OF QUATERNARY TECTONISM ALONG THE ATLANTIC COASTAL PLAIN OF NORTH AMERICA

Models (with maximum displacement at the center of a fault and displacements assumed to influence surface processes) show patterns reflecting local fault-control on both shoreline regression and river deflections along the Atlantic Coastal Plain. Model 1A (no localized uplifts) with consistently spaced parallel shorelines and an absence of river deflections characterizes most of the Late Pleistocene Coastal Plain across Georgia. Model 1B (different rates of regional uplift at either end) with divergence of shorelines toward and deflection of rivers away from the end with greater uplift characterizes the Middle Pleistocene Coastal Plain along the Virginia/North Carolina border. Models 2A (shoreline-parallel fault; seaward side down) and 2B (seaward side up) both produce seaward deflections and wider spacing of younger shorelines (on uplifted side of fault) and river deflections toward uplift-margins. Both also produce landward deflection and closer spacing of younger shorelines with convergence of rivers toward the down-dropped basin. Model 3 (shoreline-perpendicular fault) uplifts produce seaward deflection and wider spacing of older shorelines and river deflections toward margins; down-warps produce landward deflection and narrower spacing of younger shorelines and rivers merging toward the lowest area. Shorelines are discontinuous and difficult to correlate across fault. Model 3 matches patterns of epicentral area of the 1886 Charleston earthquake with a 50km-long, NW-trending fault (NE-side-up) and uplift continuing since Early Pleistocene. Model 2A matches patterns near the Okefenokee Swamp, with a 100km-long, N-trending fault (W-side-up) along Trail Ridge (Georgia/Florida border). Model 2B was used previously to explain river-anomalies in the Carolinas, but is inconsistent with these anomalies.