A COMPARISON OF LATE PALEOCENE AND LATE EOCENE LIGNITE DEPOSITIONAL SYSTEMS USING PALYNOLOGY, UPPER WILCOX AND UPPER JACKSON GROUPS, EAST-CENTRAL TEXAS

Lignites of the Wilcox and Jackson Groups in east Texas were deposited in marginal marine depositional complexes during times of cyclic sediment deposition. Thick upper Wilcox lignties occur within cycles of estuarine strata whereas thin upper Jackson lignites cap units of strandplain/shoreface deposits. Palynology of the lignites and enclosing sediments place them within two distinct climatic regimes: warm and equable during Wilcox deposition versus variable warm-cool during Jackson deposition, as indicated by increases in pine and spruce pollen and decreases in warm temperature indicator taxa in Jackson strata. Four palynologic assemblages occur in upper Wilcox strata and six palynologic assemblages occur in upper Jackson Strata. Wilcox lignites contain assemblages indicating change from closed canopy freshwater swamps populated by a community dominated by chestnut and Englehardia (a tropical Walnut) family trees, to open canopy swamps which add ferns to the community, to a community of palms and ferns which extends into the overlying marine influenced mudstones, and capped by marine siliciclastics containing an assemblage of dinoflagellates and transported cypress pollen and fern spores. The Jackson assemblages indicate a transition from a palm dominated community in the sands and silts to a fern marsh community in the silty mudstones and base of the lignites, to closed canopy freshwater communites in the lignite populated by Englehardia and swamp tupelo, to open canopy community where ferns replace the tupelo, and capped by a swamp community dominated by Cupuliferoipollenites (a chestnut-like tree) and leatherwood, especially in lignites overlain by marine sediments; marine sediments contain an assemblage of dinoflagellates, diatoms and transported Englehardia and swamp tupelo pollen. The dominant tree in Wilcox swamp communites is chestnut, while the Jackson swamps are dominated by Englehardia; ferns are common in both settings. The dominance of cypress in the estuarine-marine transition sediments of the Wilcox suggests an open water transition between peat swamp and marginal marine environments. The dominance of Cupuliferoipollenites (a chestnut-like tree) in the swamp-marine transition of the Jackson indicates a sharp boundary between peat swamp and marine environments.