Petrographic thin sections of the late Oligocene Catahoula Formation in Huntsville, TX show well preserved plant fragments including 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 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 subrounded quartz and chert grains), while a few other quartz grains show the characteristic undulose extinction patterns of metamorphic quartz. The rock samples are either finely parallel laminated, very fine to fine grained, angular to subangular, and moderately sorted OR wavy laminated, fine to medium grained, subangular to subrounded, and moderately to well sorted. 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 unit. The presence of glauconite is an indication of shelf (60-550m depth) marine environments and/or a transgressive episode. The late Oligocene was a time of transgression after a period of lowest (-200 to -350 m relative to present) sea level. The rapid rise of sea level at the end of the Oligocene, increased erosion and sedimentation to the shelf, and catastrophic flooding events may all have contributed to the unusual circumstances in which glauconite is preserved as authigenic crystals within quartz grains and cements within the plant fragments. This contradicts previous descriptions suggesting that the fine laminations present in some members of the formation represent a terrestrial, oxbow lake, fluvial environment.

Key words: Oligocene, Paleobotany, taphonomy