OUT OF THE BLUE: EVIDENCE OF A BLUE CLAY ZONE ON SKIDAWAY ISLAND: PROMISING INDICATION OF A QUATERNARY MARKER ON THE GEORGIA COAST?

Stiff blue clay was encountered underlying the high marsh at a depth of 1.30m at Skidaway Island, GA. Skidaway Island is a Pleistocene barrier island on the Georgia coast. The upper 1.30m of the core was a typical high marsh sediment sequence: 1) dense root/humic Spartina zone at the top; 2) burrowed medium to coarse grained sands (80% >63mm) grading downward into brown silty clayey sands (43% >63mm), and 3) a gradational change back to a medium clayey sand (80% >63mm). The contact with the underlying blue clay was sharp. The percent sand dropped significantly (<40% >63mm). Within the blue clay there was an interval of greater density blue clay that contained a higher mud fraction (>85%). Throughout the blue clay were brown clay mottles and oxidized mottles as well. The blue clay had a different (>63mm) mineralogy overlying high marsh sequence above. The blue clay contains less quartz (85% vs. 60%), and more heavy minerals such as zircon (<5% vs. 30%). However, there was no noticeable difference in the clay mineralogy throughout the core or the blue clay. Smectite, illite, kaolinite with a possibility of vermiculite and halloysite were present from top to bottom. The blue clay was devoid of any macrofossils and no foraminifera were present. The coarse fraction contained iron oxide. Pleistocene blue clays have been previously identified in diverse places from Massachusetts (Boston blue clay) to the Carolina Bays (Virginia to South Carolina). However, in Georgia, none have been described in any detail from a sedimentological, mineralogical and paleontological sense Palynological analysis (in progress) should shed light on the environment of deposition of this blue clay, and ¹⁴C, on the age of the overlying section.