Microfossil correlation of the Coosawhatchie Clay (Hawthorn Formation, Miocene) of South Carolina, and its equivalent in Georgia

Abstract

The diatom and silicoflagellate assemblages of the Coosawhatchie Clay member of the Hawthorn Formation at Dawsons Landing, South Carolina, are correlative with those of a clay bed exposed in low bluffs on the Georgia side of the Savannah River, near Berrys Landing. The Berrys Landing exposure contains calcareous nannoplankton and planktonic foraminifera, in addition to diatoms and silicoflagellates. Multiple floral and faunal correlations of these strata with standard zonations from deep-sea cores and the Serravallian stratotype are presented. This is the first integrated use of siliceous microfossil groups to correlate southeastern coastal plain outcrops and core samples from the U.S.A. to European and deep-sea stratigraphies. The silicoflagellate assemblage can be placed in the Distephanus stauracanthus Subzone of the C. triacantha Zone. The diatom assemblage can be placed in the upper part of the Craspedodiscus coscinodiscus Zone and tentatively within North Pacific Diatom (N.P.D.) Zone XX. Planktonic foraminifera from the Berrys Landing exposure and from the subsurface in Georgia suggest correlation with zones N11 to lower N12. Calcareous nannoplankton recovered from the Berrys Landing exposure suggest correlation with the Coccolithus miopelagicus Subzone. These microfossil assemblages are correlative with the lower to middle Serravallian stratotype, and can be further correlated with upper Unit 15 to lower Unit 18 from the Calvert and Choptank Formations of Maryland.