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Chemistry of a 7.5‐m sediment core from Lake Valencia, Venezuela1

1981; Wiley; Volume: 26; Issue: 5 Linguagem: Inglês

10.4319/lo.1981.26.5.0907

1939-5604

William M. Lewis, Franz H. Weibezahn,

Paleontology and Stratigraphy of Fossils

A 7.5‐m core from the middle of Lake Valencia, Venezuela, was analyzed chemically and mineralogically. This information is interpreted with assistance from studies of the modern lake and other supplementary paleolimnological information. The basin appears to have been dry between 13,000 and 10,500 b . p . At about 10,000 b . p ., a very saline lake formed. Saline but less extreme conditions prevailed until about 9000 b . p ., as indicated by precipitated aragonite, high Mg:Ca ratios in the carbonates, and other indicators; salinity had been considerably reduced by 8000 b . p ., when the lake almost certainly discharged water. Indicators including allogenic loading, Mg:Ca ratios, carbonate precipitation, shallow‐water cores, and microfossils suggest two subsequent returns to higher salinity, the latest of which began about 2500 b . p ., causing the lake to become endorheic in a . d . 1727. The general sequence of events in the lake over the last 13,000 years is strikingly similar to sequences documented from the African lowland tropics. The chemical conditions of Lake Valencia have varied in a major way over the recent geologic past.