Palynology and Paleoecology of the Lake Somerville spillway section, Late Eocene Manning Formation (Jackson Group), east-central Texas

Abstract

Analysis of lignites, freshwater and marine siliciclastic sediments from the Lake Somerville spillway section (Late Eocene, Jackson Group, Manning Formation) yielded a diverse assemblage of terrestrial palynomorphs including fungal spores (84 genera and 103 species of pollen and spores, 36 genera and 41 species of fungal spores). Common pollen taxa include: Momipites coryloides (a juglandaceous tree), Quercoidites inamoenus and Cupuliferoipollenites (both fagaceous trees) and monocots (Arecipites columellus, Monosulcities, and Liliacidites sp.) Common fern spores include Cicatricosisporites dorogensis, Verrucatosporites, Laevigatosporites, and Deltoidospora. Paleoecological analysis suggests the presence of seven palynomorph associations in this Late Eocene section. Fern-dominated associations grew on freshwater siliciclastic and peat substrates. Closed-canopy forest dominated by Momipites coryloides with Quercoidites inamoenus and either Nyssapollenites or Cupuliferoipollenites grew in lignite swamps. Open-canopy forests dominated by Momipites coryloides and low growing monocots, or Momipites coryloides and the fern Verrucatosporites also grew in lignite swamps. Nyssapollenites, an insect-pollinated tree, possibly related to modern Nyssa (Black Gum) also grew in closed-canopy swamp forests. Finally Cupuliferoipollenites, and Cyrillaceapollenites, possibly related to modern Cyrilla, form an association. This association may derive from a mangrove community, although the paleoecology of Cupuliferoipollenites remains unsolved. Significant percentages of Pinus (pine) and Picea (spruce) pollen in sandstone samples at 26.24 m provide evidence for climatic cooling in the Late Eocene. The presence of Nypa pollen in a sample at 29.00 m, above the Pinus / Picea peak, suggests tropical - subtropical conditions following episodic cooling.