Paper No. 5
Presentation Time: 9:25 AM
PROVENANCE DETERMINATION AND SPECIES IDENTITY OF SILICIFIED WOOD AND INVERTEBRATE FOSSILS FROM A TERRACE OF THE SAVANNAH RIVER, HARDEEVILLE, SOUTH CAROLINA
North of Millstone Landing near Hardeeville, Jasper County, South Carolina, the Savannah River has exposed an approximately 70 to 80 meter long cut bank, resulting in a 5 to 6 meter vertical bluff of complex undifferentiated fluvial terrace deposits. The site is within the Southeast Georgia Embayment, where relief is <30 meters. The cut bank reveals an atypical stratum of poorly sorted, well-rounded, and low sphericity (prolate/oblate) clastic and bioclastic materials ranging from very fine sand (.0625mm) to boulders (>256mm), with one bioclast having a length and width of 76cm and 28cm, respectively, and weighing 15kg. The stratum varies in thickness from 4cm to 4.6meters and dominant rock types include polycyclic quartz clasts, many showing signs of prior metamorphism, interspersed with highly weathered friable microcline. There is also an abundance of silicified fossiliferous cobbles and boulders. The clasts are located at the base of the subject stratum with their long axes generally oriented at right angles to the bluff's north-south trend, indicating probable paleocurrent directions. Silicified wood bioclasts represent angiosperms and gymnosperms; thin section analysis reveals Betula and Palmoxylon (Division Magnoliophyta), as well as Metasequoia (Division Pinophyta). Silicified cobbles of homogeneous masses of Turritella contain whole and fragmented shells, and silicified cobbles with Bryozoan colonies were also recovered. The most difficult part of this project has been determining how this unique material arrived at its current location. Considering the mass and size of the material, a significant fluvial event or events must have occurred to provide the critical velocity necessary for entrainment and rounding. Times of glaciation, with increased gradients of the Savannah River caused by significantly lowered sea level could have lead to such high flow velocity events. More research is necessary to determine if this site is unique within the coastal plain environment.