PETROGRAPHIC THIN SECTION AND GEOCHEMICAL ANALYSIS OF FOSSIL PLANT MATERIAL AND ASSOCIATED SEDIMENTS FROM THE OLIGOCENE CATAHOULA FM OF EAST TEXAS

Petrographic thin-sections of the late Oligocene Catahoula Formation in Huntsville, TX show well preserved plant fragments some with clear indications of permineralization. The plant fragments show primarily a reddish-brown low grade thermal maturation. Authigenic feldspar crystals, some within the organic fragments, are clearly visible. Other cements include chert and quartz. The rock samples are either finely parallel laminated, very fine to fine grained, angular to sub-angular and moderately sorted OR wavy laminated, fine to medium grained sub-angular to sub-rounded and moderately to well sorted. The formation contains 60% pyroclastic materials, 20-30 % sandstone, 10-20% argillaceous clay and minor amounts of conglomerate (Sellards et al., 1932). Accessory minerals include feldspars- exhibiting good twinning, altered micas, zeolites and nascent stage glauconitic globules. Some specimens show cementation by opal and clays; probably related to the diagenesis of volcanic ashes into silica and smectite. The Catahoula Fm. has been described as a primarily terrigenous, fluvial, deltaic, marginal marine unit. Molluscan fossils belonging to Amblemoidea (Unios) suggest brackish water conditions. The presence of glauconite is an indication of shelf (60-550m) or shallow marine environments and/or a transgressive episode. The late Oligocene was a time of transgression after a period of lowest (-200m to –350 m relative to the present) sea level. The highly variable lithology of the samples indicates the potential of a multiple provenance rock. Some grains are clearly volcanic in origin (including clear examples of volcanic glass clasts), others are clearly detrital (principally sub-rounded quartz and chert grains), while a few others quartz grains show the characteristic undulose extinction patterns of metamorphic quartz. Geochemical analysis sheds light into the distinct provenance areas.