Synthesis of Geochronologic Research on Late Pliocene to Holocene Emergent Shorelines in the Lower Savannah River Area of Southeastern Georgia, USA

Open-File Report 2021-1015
By: , and 

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Abstract

Emergent late Pliocene and Pleistocene shoreline deposits, morphologically identifiable Pleistocene shoreline units, and seaward-facing scarps characterize the easternmost Atlantic Coastal Plain (ACP) of the United States of America. In some areas of the ACP, these deposits, units, and scarps have been studied in detail. Within these areas, temporal and spatial data are sufficient for time-depositional frameworks for shoreline-evolution to have been developed and published. For other areas, such as the southeastern Atlantic Coastal Plain (SEACP), available data are conflicting and (or) insufficient to develop such a framework, or to make shoreline correlations. Differential epeirogenic uplift and shoreline deformation, resulting from mantle-flow and climate-induced isostatic adjustments, complicate regional shoreline correlations. In the SEACP, the topographically prominent Orangeburg Scarp (hereafter, the Scarp) rises tens of meters in elevation from southeastern Georgia to southeastern North Carolina. The degree to which the Scarp and shoreline units seaward of the Scarp are deformed continues to be debated, but there is general agreement that the lower Savannah River area (LSRA) of Georgia and South Carolina is the least deformed area of the SEACP.

This paper synthesizes published and previously unpublished numerical age and stratigraphic data for emergent Pliocene and younger shoreline deposits in the LSRA in Georgia. Age data are applied to these shoreline deposits as they are delineated (map units) on the 1976 geologic map of Georgia by Lawton and others. Age assignments are based on stratigraphic position, fossil content, soil and weathering diagnostic properties, and numerical ages as determined by meteoric Beryllium‑10 paleosol residence time (10BePRT), optically stimulated luminescence (OSL), uranium disequilibrium series (U-series), amino acid racemization (AAR), and radiocarbon (14C) analyses. These data provide a preliminary Pliocene-Pleistocene geochronology for the Orangeburg Scarp and shoreline deposits seaward of the Scarp in the LSRA of Georgia. Minimum ages and age ranges indicate the following:

  • the Orangeburg Scarp formed sometime in the late Pliocene and early Pleistocene, between 3 Ma and 1 Ma;
  • three, and possibly four, shoreline complexes were deposited in the middle Pleistocene;
  • two shoreline complexes were deposited in the late middle and the late Pleistocene;
  • deposition of the youngest shoreline complex began in the late Pleistocene and continues to the present;
  • each shoreline complex was modified by multiple sea level highstands over time periods that lasted tens of thousands to hundreds of thousands of years; and
  • Pleistocene shoreline chronology differs in part from modeled global sea level highstands.

Suggested Citation

Markewich, H.W., Pavich, M.J., Mahan, S.A., Bierman, P.R., Alemán‑González, W.B., and Schultz, A.P., 2021, Synthesis of geochronologic research on Late Pliocene to Holocene emergent shorelines in the lower Savannah River area of southeastern Georgia, USA: U.S. Geological Survey Open-File Report 2021–1015, 48 p., https://doi.org/10.3133/ofr20211015.

ISSN: 2331-1258 (online)

Study Area

Table of Contents

  • Acknowledgments
  • Abstract
  • Introduction
  • LSRA Shoreline Deposits and Shoreline Complexes—Stratigraphy and Age
  • Details for Previously Unpublished Age and Stratigraphic Data
  • Summary of Age Data
  • General Observations Based on the Age Data
  • Concluding Comment
  • References Cited
  • Glossary
  • Appendix 1. Methods Used for Sampling and Analyses
Publication type Report
Publication Subtype USGS Numbered Series
Title Synthesis of geochronologic research on Late Pliocene to Holocene emergent shorelines in the lower Savannah River area of southeastern Georgia, USA
Series title Open-File Report
Series number 2021-1015
DOI 10.3133/ofr20211015
Year Published 2021
Language English
Publisher U.S. Geological Survey
Publisher location Reston, VA
Contributing office(s) Florence Bascom Geoscience Center
Description viii, 48 p.
Country United States
State Georgia, South Carolina
Other Geospatial Lower Savannah River
Online Only (Y/N) Y
Additional Online Files (Y/N) N
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