CARROLL, RICHARD E., Geological Survey of Alabama, Tuscaloosa, AL
ABSTRACT: Palynofacies of Lignites and Associated Sediments in the Upper Paleocene Tuscahoma Sand of Southwestern Alabama and Eastern Mississippi
The Tuscahoma Sand of the Wilcox Group is composed of fine-grained sand, laminated sandy clay, marl, and lignite. The Tuscahoma forms a poorly exposed belt from southeastern Alabama and extends northwestward into western Alabama and eastern Mississippi. The sand is assigned to the late Paleocene planktonic foraminiferal Morozovella velascoensis interval zone.
Lignites in the Tuscahoma Sand occur as parasequence deposits in the highstand systems tract of a type 2 depositional sequence near the top of the formation. Organic debris associated with these highstand-systems-tract deposits is dominated by land-derived plant tissues, such as angiosperm and gymnosperm pollen; spores of ferns, lycopods, and fungi, plant cuticle, and wood in various states of degradation; charcoal or inertinite; cysts of freshwater algae; and resins. Marine influence in some samples is evidenced by the rare occurrence of dinoflagellate cysts, microforaminiferal test linings, and the presence of gray, amorphous organic matter.
Three palynofacies are recognized within highstand-systems-tract deposits in the upper Tuscahoma Sand based on the occurrence of organic debris. These palynofacies represent freshwater swamp, brackish marsh, and marginal- to shallow-water marine depositional environments. Lignites in the Tuscahoma Sand are dominated by an angiosperm pollen assemblage. Pollen similar to that produced by the Betulaceae and Myricaceae, modem arborescent angiosperms, is common in these assemblages, as are fern spores, spores of Sphagnum, woody tissue, and charcoal. Gymnosperm pollen is rare, and marine forms are absent. This assemblage reflects deposition under fresh-water swamp conditions. Carbonaceous clay samples vary in the composition of organic debris. However, many are characterized by the occurren e of herbaceous angiosperm pollen such as Carex, Arecipites, Calamuspollenites, and Liliacidites. Arborescent angiosperm pollen also is common, as are fern spores. Bisaccate conifer pollen is common, and dinoflagellate cysts are rare. Fungal elements are abundant, and woody tissue commonly is more degraded than in lignite samples. This assemblage represents deposition in coastal, brackish marsh environments. Organic debris in laminated clays, silts, and sands typically have angiosperm and gymnosperm pollen, dinoflagellate cysts, degraded terrestrial plant material, and amorphous organic matter, and represent shallow-marine and marginal-marine deposits.
AAPG Search and Discovery Article #90989©1993 GCAGS and Gulf Coast SEPM 43rd Annual Meeting, Shreveport, Louisiana, October 20-22, 1993.