ABSTRACT

Long, J.H.; Hanebuth, T.J.J.; Alexander, C.R., and Wehmiller, J.F., . Depositional environments and stratigraphy of Quaternary paleochannel systems offshore of the Georgia Bight, southeastern USA.

Paleochannels are common subsurface geological features beneath inner continental shelves and coastal plains and are important archives of ancient depositional environments. This study, focusing on a 450-km portion of the inner continental shelf of the SE United States, adds to understanding of the timing of paleochannel development, the paleoenvironments in which they formed, and the mechanisms that drove their formation. Integrated analysis of 1089 km of high-resolution seismic reflection data and 12 sediment cores reveals that (1) most paleochannels documented here formed in backbarrier environments (estuarine or lagoonal) and were subsequently filled during transgression or following avulsion, preserving mud-rich, tidally influenced deposits; (2) the preservation of nonmarine deposits is rare; (3) paleochannels are either solitary or amalgamated, forming paleochannel complexes within which they are arranged in multistory (vertically stacked) or multilateral (horizontally offset) configurations, a product of local hydrodynamic conditions, antecedent geology, glacioeustatic cycles, and regional isostatic adjustments; and (4) a general southerly increase in the overall degree of channelization is observed across the Georgia Bight, a function of long-term accommodation, interaction with underlying stratigraphy, and dominant coastal processes. The composition and spatiotemporal distribution of paleochannel systems has implications for understanding the long-term evolution and preservation of complex coastal systems and informing regional Quaternary sea-level reconstructions.

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