Mark H. Scheihing, Hermann W. Pfefferkorn
Carbonized plant remains preserved in fine-grained clastic rocks are a major source of information about the nature of ancient floras and the sedimentary facies in which their remains are found. To reconstruct fossil floras accurately and to use plant fossils as an indicator of depositional environments, processes governing incorporation of plant parts in clastic sediments must be well understood. A direct approach to understanding these processes is their study in modern analogs. The Orinoco delta in eastern Venezuela is a well-suited modern analog to Pennsylvanian coal-bearing depositional environments with regard to climate, physiography, sedimentary facies, and vegetational types.
Processes that incorporate plant parts in clastic sediment were studied in major subenvironments of the delta (e.g., levee, point bar, distributary channel, swamp). Cored clastic facies contained plant matter described in terms of distribution in the sediments, preservational state, and relationship to surrounding growing vegetation. Experiments were conducted in plant-part transport by tidal and fluvial processes.
Results of this investigation indicate that (1) aerial parts of plants are often preserved close to their site of growth, but rarely in the soils in which they grew; (2) the geometry and lateral extent of clastic facies that preserve plant parts are controlled by subtle differences in sedimentation rate; (3) tidal flooding in the lower delta plain exerts a profound influence on plant-part transport and burial; and (4) coastal environments are sites of hydraulically sorted and transported plant parts.
AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.