MULTIPLE LATE QUATERNARY HEAVY MINERAL PROVINCES IN SW LOUISIANA – DEFINITION OF FLUVIAL SOURCES, DISTRIBUTION AREAS AND COASTAL TERRACE AGES

Mississippi and Red River influences in SW Louisiana alluvial coastal terrace formation have been reported since 1933. OIS 7 intermediate terrace and OIS 4-3 (ca. 106-35 ka B.P.) Prairie-Beaumont terrace luminescence dates indicated multiple phases of alluvial aggradation during marine high – and lowstand stages (Otvos, 2001, 2002 and in preparation). Very little information is available, however, on the provenance-diagnostic heavy mineral components of various streams in this region. In evaluating sand provenance, high-resolution heavy mineral analysis and statistical methods were conducted for the first time to define the depositional areas of major rivers and lesser streams during the late Pleistocene. Modern Mississippi, Red, Sabine and Calcasieu River sands were analyzed to establish a compatible data base. Each river displays a distinctive heavy mineral spectrum: Mississippi sands are characterized by high but variable hornblende and pyroxene content, while the Red River contains nearly equal proportions of well-rounded zircon, tourmaline, epidote and garnet grains. The Sabine River is enriched in zircon, is free of apatite and contains abundant high-grade metamorphic minerals. Euhedral zircon, apatite, sphene and clinopyroxene grains with volcanic signatures in Mississippi River deposits reveal the eolian contribution of tephra from Caribbean volcanoes. Each heavy mineral province, mapped in terrace deposits, displays a close affinity to a particular river spectrum and clearly defines several depositional belts of late Pleistocene fluvial systems. Samples from intermediate locations contain polymict assemblages, reflecting interaction between river courses with contrasting mineral spectra. Heavy mineral composition in such instances is particularly helpful in defining the degree of intermixing. The transitional belt between the Mississippi and Red River deposits indicates either the diluting effect of Red River tributaries on Mississippi alluvium and/or Mississippi backflooding into the Red River tributary channel(s). A zone adjacent to the Sabine River province similarly reveals mineralogical signatures imparted by the Sabine, Calcasieu and Red Rivers.