PRELIMINARY LITHOLOGIC CHARACTERISTICS OF GRAVEL DEPOSITS IN MISSISSIPPI

Melting of the northern hemisphere glaciers at the end of Pleistocene Epoch produced huge melt-water floods that left behind extensive sedimentary records. Two of the most famous of these are Lake Missoula flood deposits preserved in the Scabland region of the State of Washington, U.S.A., and the Altei Mountains flood deposits in southern Siberia, Russia. North American flood waters also passed through the Mississippi Valley and ended in Gulf of Mexico. These floods left numerous gravel deposits in the State of Mississippi.

This undergraduate research project includes a study of lithologic characteristics of pebble to cobble size fragments in Hammett Gravel Mine in Holmes County, Mississippi. Here, the gravel layer is 10-15 m thick and weakly lithified. It is highly unsorted but consists of rounded fragments as large as 25 cm. The gravel layer is overlain with 3-5 m of loess deposit. Gravel size particles were collected from the gravel layer as well as from gravel piles in the mine.

Particles range in size from 2 cm to 25 cm and are white, beige, gray, red, and black in color. Regardless of their size, all samples are well rounded. However, they occur in different shapes. Their length to width ratio ranges from 1 to 20. Preliminary observations indicated that gravel samples consist of plutonic igneous, metamorphic, sandstone, chert, quartz mineral, petrified wood, and completely silicified limestone that are highly fossiliferous and contain abundant brachiopod, coral, and crinoid. Surprisingly, unaltered carbonate fragments which are still composed of calcite or dolomite were not found. They must have existed at the source area. Their absence indicates that they were either dissolved or pulverized during transport. Future petrographic studies will provide additional details about rock types of these flood deposits and provinances that contributed sediments to Mississippi.