Genetic stratigraphy and geochronology of last interglacial shorelines on the central coast of South Carolina

Abstract

This study investigated the shallow subsurface of the Lower Coastal Plain of South Carolina in order to determine the sea-level history and stratigraphic architecture preserved within several emergent shoreline complexes. The absolute age of each shoreline complex was estimated using single-aliquot regenerative-dose (SAR) optically stimulated luminescence (OSL) techniques. The resulting geochronology was incorporated into a high-resolution stratigraphic framework defined by ground penetrating radar calibrated with deep sediment cores, many of which contain a complete sequence of highstand deposition. Three emergent barrier complexes were identified within the Lower Talbot, Pamlico, and Princess Anne terraces, and assigned to sea-level highstands during interglacial periods between 240 to 80 ka, which correspond to marine isotope stages (MIS) 7, 5e, and 5a. The stratigraphic architecture of each shoreline complex consists of a distinct succession of lithofacies deposited in lagoonal, shoreface, and eolian environments typical in a siliciclastic shoreline setting. Relict shoreface facies contain swash zone strata that precisely document the peak elevations attained by specific relative sea-level highstands. First, a transgression during MIS 7 (230 ka) emplaced swash zone strata at 12 ±1 meters above present day sea-level (mASL). This was followed by two separate transgressions during MIS 5e (140 to 125 ka) that attained elevations of 9 and 6 ±1 mASL, respectively. Finally, a MIS 5a (80 ka) highstand peaked at 5 ±1 mASL. The present day elevations of the MIS 7 and MIS 5e highstand deposits can be explained with a consistent uplift rate of ~5 cm/kyrs. However, the elevation of MIS 5a deposits conflicts with most global estimates of this highstand. This implies the MIS 5a highstand was actually closer to present day sea-level, in a global sense, or that complex glacio-hydro-isostatic effects have played a major role through multiple glacial-interglacial cycles in this region.