Ecological History of Lake Valencia, Venezuela: Interpretation of Animal Microfossils and Some Chemical, Physical, and Geological Features

Abstract

The developmental history of Lake Valencia, Venezuela, over the past 12 500 yr was studied by means of animal remains and some chemical and physical variables in three sediment cores. Radiocarbon dates of abandoned beach terraces also provided information for the interpretation of former lake levels. Transects of surficial sediments in the lake served as modern analogues for both animal communities in the sediments and characteristics of the sediment itself. Interpretation of cluster and multiple discriminant analyses led to the recognition of six stratigraphic zones of animal microfossils. The zones were expressions of climatically controlled fluctuations of water levels that have dominated successional processes within Lake Valencia. The animal remains were mostly carapaces of Ostracoda and Cladocera, with fewer head capsules and mouthparts of immature insects and flatworm (neorhabdocoel) egg cases. Study of the variation of animal assemblages with various environmental requirements led to the following interpretation of the zones. The basin was dry from at least 13 000 to 11 000 yr before present (BP). It filled rapidly °10 500 yr BP, and had an outflow for 2500 yr. The level then gradually declined during the time from 8000 yr BP to 2500 yr BP, but was periodically stable during which intervals several terraces were cut. The next 2000 yr included several rises, some to the outflow. As late as 1727 AD the lake was again at the outflow level, after which it began to desiccate. Cultural influences, both indigenous and European, are expressed in the sediments of the past 2000 yr. In 1979 the level was °25 m below the outlet and had been dropping at °0.1—0.2 m/yr.