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Comparative Palynology of Clastics and Lignites from the Manning Formation, Jackson Group, Upper Eocene, Grimes Co., TX
Judith A. Gennett
The 3500 lignite seam at the Gibbons Creek mine in Grimes Co., Texas was sampled for pollen and spores at 10 cm intervals. Most samples were dominated by Momipites (to 60%) from the Juglandaceae (walnut family) as is common for Jackson Group sediments. Other taxa varied systematically, with a peak of the freshwater tree Nyssa (blackgum) and Rhoipites angustus (to 17%) occurring at the base. Higher in the seam, increases (to 55%) of Cupuliferoipollenites (a chestnut-like grain) and Cyrillaceaceaepollenites? ventosus (to 7%) may indicate higher salinity. A Chryophyllum (to 25%) peak near the top of the seam suggests a return to freshwater conditions, but with perhaps a change in water depth.
Core samples from an interval above the lignites, representing inner shelf clastics, were taken at at least 40 cm intervals. These samples reveal a more regional pollen flora; although minor changes occur, palynomorph spectra are for the most part homogenous. The dominant grain is again Momipites coryloides, but percentages are lower (to 35%). Cupuliferoipollenites (to 17%), Chrysophyllum (to 5%), and Rhoipites angustus (to 3%) are not less important overall, but do not peak. Palm leaf megafossils in one sample suggest a clastic swamp; in this sample palm pollen (mostly Arecipities representing the modern palmetto) reaches 73%. Another sample contains high (26%) percentages of the fern spore Lygodiumsporites adreiennis. These high percentages do not occur in the lignite samples.
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