THE DISTRIBUTION OF MAASTRICHTIAN (UPPER CRETACEOUS) DEPOSITIONAL ENVIRONMENTS IN THE COASTAL PLAIN OF GEORGIA AND SOUTH CAROLINA

The Maastrichtian Stage in the Georgia and South Carolina Coastal Plain consists of six depositional environments that can be recognized across four allostratigraphic units. These environments are dominated by a prograding deltaic complex with its axis of deposition located in the vicinity of the present-day Savannah River. The specific depositional environments recognized are: upper delta plain; lower delta plain; delta front; prodelta/shelfal; shoreface/beach; and restricted marine. These depositional environments occur within five lithostratigraphic units: the Sawdust Landing Member of the Rhems Formation, the Peedee Formation, the Steel Creek Formation, the Providence Sand, and the uppermost part of the Ripley Formation.

The depositional environments and their stratigraphic relationships were established in more than 60 outcrop and subsurface sections, and were interpreted on the basis of lithology, sedimentary structures, paleontologic characteristics, and wireline log signature. The criteria used to recognize the unconformities that bound the allostratigraphic units include lithologic, wireline log, and biostratigraphic data. Two regional cross sections and four maps were constructed that illustrate the distribution of the depositional environments throughout Georgia and South Carolina during the Maastrichtian.

Use of allostratigraphic units as the basis for subdividing the Maastrichtian resulted in consistent regional correlations, and helped clarify the complex relationships and stacking patterns among the various deltaic and nearshore environments. In addition, post-depositional tectonic and structural deformation is expressed on cross sections adjusted to present-day sea-level, and are suggested by anomalies in thickness, regional trends, and elevation of the Maastrichtian allostratigraphic units.