Date of Award

6-25-2020

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Marine Science: Coastal and Marine Systems Science (PhD)

Department

Coastal and Marine Systems Science

College

College of Science

First Advisor

Till J.J. Hanebuth

Second Advisor

Zhixiong Shen

Third Advisor

Richard F. Viso

Additional Advisors

Andrea Hawkes (UNC-Wilmington); C. Scott Howard (SC Geological Survey); Thomas Lüdmann (University of Hamburg)

Abstract

The Quaternary stratigraphy of the continental shelf offshore of South Carolina consists of stratigraphic units deposited in coastal plain, shallow marine, and shelfal environments bound by composite erosional surfaces that developed in response to numerous glacioeustatic cycles and overprinted by regional uplift. These units are commonly distributed laterally rather than stacked vertically, a function of the long-term, low shelf gradient and the resulting lack of accommodation. This study integrates high-resolution geological and geophysical data sets acquired offshore and onshore with existing data onshore into a comprehensive conceptual model describing the Quaternary geologic evolution of the coastal plain and continental shelf within a study area of approximately 8,000 km2. We use seismic facies and core analysis to define stratigraphic units associated with transgressive, regressive, and lowstand systems offshore. Regressive systems include progradational wave- and river-dominated deltaic and shoreface deposits. Lowstand systems consist of a complex network of paleo-incisions produced by regional, Piedmont-draining fluvial systems and smaller coastal-plain rivers. Transgressive systems include paleochannel-fill successions dominated by mud-rich, tidally-influenced backbarrier deposits, cuspate and linear shelf sand ridges; and transgressive sand sheets and shoals. The low-accommodation setting of the continental shelf influences the stratigraphic record in several key ways: 1) the geometry of progradational coastal lithosomes; 2) the development of composite allogenic erosional surfaces; 3) the deposition of widespread, thin transgressive sand sheets; and 4) the restriction of thicker transgressive deposits to paleo-incisions. In this setting, the use of a hierarchical bounding surface scheme is preferable to the more common sequence stratigraphic or allostratigraphic conventions for several reasons: 1) major erosional bounding surfaces are commonly amalgamated; 2) lower-order surfaces capture internal variability which is key to the genetic interpretation of stratigraphic units; and 3) stratal stacking patterns typically used to define a sequence stratigraphic framework are rare.

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