Pollen distribution in sub-recent sedimentary environments of the Orinoco Delta (Venezuela) - an actuo-palaeobotanical study

A reinvestigation of the palynology of Recent and sub-Recent Orinoco Delta sediments complements the work by Jan Muller concerning the taxonomy and diversity of pollen grains. Surficial sediment samples and samples from shallow drill cores taken from three different deltaic environments (Cano Guaneira, mangrove forest, and palmswamp) were studied with light microscopy and SEM. The standing vegetational types of the sampling sites were reflected to different degrees (42-71%) by the palynomorph assemblages. Generally, the pollen taxa preserved in all sediment samples reflected (a) the most abundant and most pollen producing taxa of the local and the surrounding vegetation, and (b) the taxa common along the distributaries in the delta. In each palynomorph assemblage, 77-80% of taxa are allochthonous or parautochthonous and represent 36-78% of the pollen sum. In more open fluvial localities, these elements originated upstream and were transported by the river. Input of allochthonous palynomorphs into a more closed sedimentary system, such as a flood basin, is more restricted (36% of the pollen sum) and occurred mostly during floods. Floral composition also has an influence on the amount of autochthonous palynomorphs. The palynomorph assemblages from less diverse vegetational types (21-22 taxa) that are dominated by one or few taxa contain less allochthonous palynomorphs (39-36% of the pollen sum) than the assemblage of a diverse (>45 taxa) vegetation type that contains 78% of allochthonous palynomorphs. (C) 2002 Elsevier Science B.V. All rights reserved.