ASPECTS OF LAND PLANT BIOSTRATONOMY IN UPPER CARBONIFEROUS DELTAS OF EURAMERICA (VENEZUELA, KENTUCKY, PENNSYLVANIAN

Accurate paleoecological statements about fossil plants of Pennsylvanian age in North America require that the plant-fossil assemblages represent the plant communities from which they were derived. Biased sampling, transport, or sorting of plant parts prior to incorporation in sediment may seriously distort the representation of plant communities by plant-fossil assemblages. Plants preserved as compressions and impressions in clastic strata are especially subject to biased representation.;Processes resulting in the incorporation of plant parts with sediment were studied in the Orinoco Delta in eastern Venezuela. The Orinoco Delta is an excellent modern analog to Pennsylvanian coal-bearing depositional environments in terms of climate, physiography, sedimentology, and morphological analogs to Pennsylvanian plants. Major subenvironments of the upper and lower delta plain were examined for contained plant matter and the plant matter characterized in terms of distribution in sediment, state of preservation, and relationship to surrounding growing vegetation. Results of this study indicate that (1) aerial parts of plants are buried close to their site of growth but seldom in the soils in which the plants grew; (2) the geometry of compression-bearing clastic deposits is controlled by small differences in depositional rate; (3) in the absence of levees in the lower delta plain, plant parts on forest floors are transported seaward by the tides; (4) coastal beaches serve as sites of hydraulically sorted and buried seed accumulations.;Using these results, a study of plant taxa distribution in deltaic sediments of Middle Pennsylvanian age in eastern Kentucky was conducted to determine whether vegetational patterns varied across the deltaic plain. Plant-part taxa were ranked according to presence versus absence in 34 assemblages in upper, transitional lower, and lower delta-plains. Results of this analysis indicate that pteridosperms and sphenopsids dominate assemblages throughout the section. Using the depositional model proposed for these rocks, there appears to be no discernible change in dominant taxa from upper to lower delta plain in the Pennsylvanian.