Print this pageLago de Urao is an evaporative lake in a semi-closed basin, located near the village of Lagunillas in northwestern Venezuela. It sits in a small, fault-bounded depression in the Chama River Valley and has a warm, semi-arid climate and unusual geochemistry, being rich in sodium carbonates. An 8-m core and water samples collected in January 1999 serve as the foundation of my study of the Late Quaternary climate at Lago de Urao.
A previous 7.5-m core provided a high resolution record starting at 6,000 B.P., based on C-14 dating. The core contained abundant evaporite crystals up to 4-5 cm in length, as well as sediments extremely rich in sodium-carbonate minerals.
Stratigraphic analysis of the new core shows crystals only in drives (approximately 1m sections) five through eight. Using X-ray diffraction, crystals in upper sections of the core have thus far been identified as gaylussite and thermonatrite, and as nahcolite in the basal section. Preliminary diffraction analysis of sediment in all drives indicates abundant muscovite and the major clay as illite. Water analyses show that the Lago de Urao waters are at equilibrium, but near supersaturation with respect to sodium, magnesium and calcium minerals.
Further X-ray diffraction analysis of clay mineralogy and evaporite crystal morphology (scanning electron microscope) will be performed to observe fluctuations throughout the core of the abundance and mineralogy of the evaporites, clays, and other minerals. These data will allow reconstruction of Late Quaternary climatic fluctuations in the Lago de Urao basin.
AAPG Search and Discovery Article #90925©1999 AAPG Foundation Grants-in-Aid