PROVENANCE OF THE CRETACEOUS TUSCALOOSA FORMATION IN EASTERN ALABAMA AND WESTERN GEORGIA

The Cretaceous Tuscaloosa Formation belongs to Coastal Plain sediments deposited in fluvial and subaerial deltaic environments. Thickness of the formation in eastern Alabama and western Georgia ranges from eight to about eighty meters. Sands of the Tuscaloosa Formation are poorly sorted, ranging in grain size from fine to coarse sand. This study deals with modal composition and heavy mineral analysis of the Tuscaloosa sands in order to trace their source rocks.

Sands of the Tuscaloosa are lithic wacke, composed mostly of monocrystalline quartz and lithic fragments. Feldpars are very scarce in the sands. Sedimentary and metamorphic lithic fragments dominate. The modal composition of the sands in QtFL values plots in the “recycled orogenic” provenance field of Dickinson (1985). Heavy minerals were separated from the Tuscaloosa sands using liquid acetylene tetrabromoethane (specific gravity 2.9), and account for 0.19% to 0.85% of the sample weight. Heavy mineral assemblages include mostly opaques, garnets, zircon, tourmaline and rutile (ZTR) grains.

The high percentage of metamorphic lithic fragments supports a metamorphic source. The transport distance was short as evidenced from poor sorting and relative angularity of the framework grains. Relative lack of feldspars indicates that the sediments experienced extensive chemical weathering. Abundance of stable ZTR also implies that these sands were exposed to greater chemical weathering. This study suggests that the source area was geographically not very distant and was likely the metamorphic and sedimentary sequences of the Inner Piedmont of the southern Appalachians.