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Pleistocene shorelines and coastal rivers: Sensitive potential indicators of Quaternary tectonism along the Atlantic Coastal Plain of North America

By
Mervin J. Bartholomew
Mervin J. Bartholomew
Department of Earth Sciences, University of Memphis, Memphis, Tennessee 38152, USA
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Fredrick J. Rich
Fredrick J. Rich
Department of Geology and Geography, Georgia Southern University, Statesboro, Georgia 30460, USA
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Published:
January 01, 2013

Our models show patterns reflecting local fault control on both shoreline regression and river deflections along the Atlantic Coastal Plain. In these models, maximum displacement is assumed to be at the center of a fault, and both uplifts and downwarps are assumed to be of sufficient magnitude to influence surface processes. Models show regional shoreline regression: (1A) without localized uplifts; (1B) with different rates of regional uplift at either end; (1C) without any localized uplifts but with a large river-dominated delta; (2A) with a fault parallel to the shoreline with seaward side down or (2B) with seaward side up; and (3) with a fault perpendicular to the shoreline. Model 1A has consistently spaced parallel shorelines and an absence of river deflections, such as characterizes most of the late Pleistocene coastal plain across Georgia. Model 1B has divergence of shorelines toward and deflection of rivers away from the end with greater uplift. Model 1C has seaward deflections of shorelines with spacing dependent upon rates of sediment influx and removal by coastal processes. Models 2A and 2B represent interruptions of model 1 patterns. Both produce a seaward deflection and wider spacing of younger shorelines on the uplifted side of the fault with associated river deflections toward the margins of the uplift. Both also produce a landward deflection and closer spacing of younger shorelines coupled with convergence of rivers toward the downdropped basin. Model 3 produces a seaward deflection and wider spacing of older shorelines across the uplift associated with river deflections toward the margins of the uplift on one side of the fault. On the other side, there is a landward deflection and narrower spacing of younger shorelines on the downdropped side of the fault where river deflections merge toward the lowest area. In model 3, shorelines are discontinuous and may be difficult to correlate across the fault, and fault length is constrained by resumption of model 1 shorelines seaward of the fault.

Model 3 matches patterns in the vicinity of the 1886 Charleston earthquake, South Carolina, with a NW-trending fault of ~50 km length with the NE side up and uplift continuing since the early Pleistocene. Very similar patterns occur in the vicinity of Beaufort, South Carolina, and Wilmington, North Carolina, which suggest other NW-trending faults of comparable or greater length may be present near these localities. Model 2A matches patterns near the Okefenokee Swamp, which suggests that a 100-km-long, N-trending fault may border the east side of Trail Ridge near the Georgia-Florida state boundary. Model 2B was used by previous workers to explain zones of river anomalies in the Carolinas, but those anomalies do not match this model.

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GSA Special Papers

Recent Advances in North American Paleoseismology and Neotectonics East of the Rockies

Randel Tom Cox
Randel Tom Cox
Department of Earth Sciences, University of Memphis, Johnson Hall, Memphis, Tennessee 38152, USA
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Martitia P. Tuttle
Martitia P. Tuttle
M. Tuttle & Associates, 128 Tibbetts Lane, Georgetown, Maine 04548, USA
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Oliver S. Boyd
Oliver S. Boyd
U.S. Geological Survey, 3876 Central Avenue, Suite 2, Mail Stop 966, Memphis, Tennessee, 38152-3050, USA
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Jacques Locat
Jacques Locat
Département de géologie et de génie géologique, 1065 avenue de la Médecine, Québec G1V 0A6, Canada
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Geological Society of America
Volume
493
ISBN print:
9780813724935
Publication date:
January 01, 2013

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