FROM PALM SAVANNAHS TO HARDWOOD HAMMOCKS AND BACK: PALYNOLOGY OF THE PALEOCENE-EOCENE MANAWIANUI DRIVE SECTION, BASTROP COUNTY, TX

Wilcox and Claiborne group strata from Bastrop County, TX, have been studied for the past two years. An abundant and diverse pollen and spore flora has been recovered, including many important ecological indicator fungi and other non-pollen palynomorphs. The section consists of tidal-laminated silty mudstone from the uppermost Paleocene Sabinetown Formation, which is eroded by a channel subsequently infilled by subbituminous coal. Channel-fill coals and silty mudstones are disconformably overlain by cross-bedded marine sandstones of the Eocene Carrizo Formation. Of interest is how the non-pollen palynomorph spectrum tracks ecological changes determined through plant palynology. Deposition at the base of the section likely occurred on a shallow shelf offshore from a tidal marsh with an onshore hardwood wetland and fern savannah (Atrotorquata lineata and Lacrimasporites). Upsection, deposition occurred in a tidal lagoon or shallow shelf adjacent to a fire-prone fern-dominated savannah (Arnium-types, Desmidiospora willoughbyi, and Dwibeeja-types). The coals record mangrove swamps (Pseudodelitchia sp., Cigulatisporites sp., Nigrospora sacchari, and Ascobolus sp.) that gave way to hardwood hammocks (Arnium-types, Dwibeeja sp., Cortinarius spinosus, and basidiospores), and then transitioned to sawgrass marshes (Acrogenospora gigantica, basidiospores, and desmids). Carrizo deposition was abruptly different, and likely occurred on a shallow shelf offshore from a brackish tidal marsh bordered by a palm savannah (Nigrospora sacchari, Kamatella sp., Nigrospora sp., Lacrimasporites sp., Papilonospora sp., Virgaria sp., and Arthrinium cf. A. peteroconium). Upsection, abundant fungi (Striadiporites bistriatus, Inaptertisporites punctatus, Delitschia cf. D. varisporiia, Entoloma triangularis, and basidiospores) occur, as do rotifer loricas. Of interest are the non-abundant fungi, such as cf. Gliomastix, and Potamomyces sp., which are known primarily from Gondwanan sources today.