Palynology and paleoecology of lignites from the Manning Formation (Jackson Group) outcrop in the Lake Somerville spillway of east-central Texas

Abstract

Four palynomorph assemblages, whose parent plants contributed to the formation of the lignite, occur in the lignite seams and associated sediments from the Manning Formation (Jackson Group) outcrop in the Lake Somerville spillway of Texas. The Cicatricosisporites-Laevigatosporites fern assemblage occurs in the middle and upper seam and probably derived from a freshwater herbaceous mire community. The Momipites coryloides-Arecipites columellus-Liliacidites assemblage occurs in all three seams and probably derived from a freshwater mire forest with an open canopy or shrub community. The Momipites coryloides-Nyssa-Rhoipites angustus assemblage occurs in the lower and middle seams and probably derived from a different freshwater mire forest. The Cupuliferoipollenites-Cupuliferoidaepollenites liblarensis-Siltaria cf. S. scabriextima assemblage occurs at the top of the lower and middle seams, which are overlain by marine sediments. The association between Cupuliferoipollenites dominance and the presence of marine diatoms and brackish or marine trace fossils in the lignite suggests that this assemblage may have derived from a mangrove (i.e. marine or brackish) mire forest. However, other factors may influence its distribution. Ailanthipites berryi, possibly derived from a tree or shrub related to the ‘tree of heaven’, predominates in the claystone underlying the lower lignite seam and may have colonized the coastal plain prior to the initiation of peat accumulation. We can differentiate lignite samples dominated by fern spores, Momipites pollen and Cupuliferoipollenites pollen based on gas chromatography-mass spectrometry (GC-MS) fragmentograms of triterpanes (m/z 191) and steranes (m/z 217). The lignite layers dominated by each palynomorph assemblage appear to have distinct sources and different early diagenetic (pre-coalification) histories.