The taphonomy of land plants in the orinoco delta: A model for the incorporation of plant parts in clastic sediments of late carboniferous age of euramerica

Abstract

The Orinoco Delta in eastern Venezuela is an excellent modern analog for Upper Carboniferous depositional environments in terms of climate, physiography, sedimentology, and the presence of morphological analogs for Upper Carboniferous plants. Processes resulting in the incorporation of plant parts in sediment were studied to assess the effects of transport and deposition on plant parts preserved as compressions in clastic strata of Late Carboniferous age. Sub-environments of the delta (e.g. levee, point bar, clastic swamp, and distributary channel) were cored and the contained plant matter described in terms of its distribution in sediment, preservational state, and relationship to living vegetation. Several experiments were performed to assess the role of tidal and fluvial transport of plants parts. We reached the following conclusions from the study: (1) Aerial parts of plants are buried relatively close to their site of growth but rarely in the actual soils in which the plants lived. (2) Plant parts are preferentially preserved in areas with slightly higher rates of sedimentation. (3) Natural levees are dry for half a year and any aerial parts of plants buried in levee deposits during floodstage oxidize during that time. Bioturbation by roots also contributes to the destruction of plant matter. Thus, levee sediments are virtually devoid of aerial parts of plants. (4) Tidal processes are as significant as annual flooding in forming plant-bearing deposits in the lower delta plain. (5) No storm-generated deposits are known in the Orinoco Delta, indicating that non-storm deposition is important for the generation of clastic deposits which contain plant parts.