Abstract: Comparative Palynology of Clastics and Lignites from the Manning Formation, Jackson Group, Upper Eocene, Grimes County, TX

Judith A. Gennett

The 3500 lignite seam at the Gibbons Creek Mine in Grimes County, TX was sampled for pollen and spores at 10 cm intervals. The majority of samples are dominated (to 60%) by Momipites from the Juglandaceae (walnut family), as is typical of Jackson Group sediments. Other palynomorph taxa vary systematically, with a peak of pollen of the freshwater tree Nyssa (blackgum) and associated Rhoipites angustus (to 17%) occurring at the base. Higher in the seam, increase (to 55%) of Cupuliferoipollenites (a chestnut-like grain) and Cyrillaceaepollenites? ventosus (to 7%) percentages may indicate a higher salinity environment. A Chrysophyllum (satin leaf) peak (to 25%) near the top of the seam suggests relatively shallow freshwater conditi ns.

Core samples from an interval above the lignites represent a transgressive-regressive cycle in inner shelf clastics. These samples were taken at 40 cm or greater intervals and reveal the regional pollen flora. Although minor changes occur, palynomorph spectra are for the most part homogenous. The dominant grain is again Momipites coryloides, but in general percentages are lower (to 35%). Cupuliferoipollenites (to 17%), Chrysophyllum (to 5%), and Rhoipites angustus (to 3%) are not less important, but do not peak as they do in the lignite spectra. Palm leaf megafossils in one sample suggest a clastic wetland; in this sample palm pollen (mostly Arecipites, representing the modern saw palmetto) reaches 73%. Another sample contains high (26%) pe centages of the fern spore Lygodiumsporites adriennis. High percentages of these two taxa do not occur in the lignite samples.

AAPG Search and Discovery Article #90950©1996 AAPG GCAGS 46th Annual Meeting, San Antonio, Texas