Organic matter assemblages from recent sediments of the Tacarigua coastal lagoon (northern Venezuela)

Abstract

Sediments of the Tacarigua coastal lagoon in northern Venezuela are rich in organic material. The lagoon and its sediments are therefore important as a modern-day analog for the interpretation of palynofacies assemblages in clastic sediments that formed in tropical coastal environments. Samples representative of the most important subenvironments of the lagoon were collected and prepared with standard palynological methods. The organic materials were analyzed in terms of biological origin, source area and textural characteristics. The analytical results were evaluated with standard statistical techniques. Based on Principal Components Analysis (PCA) six sample groups are differentiated. Sample groups A and B are very rich in humic gels and they represent the western part of the lagoon in which sedimentation largely reflects the influence of the River Guapo. Sample group C contains both humic gels and degraded plant material. Group C represents the central part of the lagoon where sedimentation is influenced both by the River Guapo and the lagoon mouth. Sample group F contains sub-equal percentages of degraded algal and/or bacterial material, humic gels and degraded plant material. Group F is representative of the eastern part of the lagoon where autochthonous sedimentation is important. Sample groups D and E which have a high percentage of degraded algal and/or bacterial material, are representative of sediments that were laid down in close proximity to mangrove vegetation. In view of the varied character of the organic assemblages in these modern lagoonal deposits, the interpretation in environmental terms of similar fossil assemblages is complex and requires a careful consideration of all the evidence.