Contribution to the paleolimnology of lake Valencia, Venezuela: Seismic stratigraphy

Lake Valencia is situated in a graben at 402 m a.s.l. in northern South America. The lake is slightly larger than 300 km² and the basin area is approximately 2750 km². Observations during the last two centuries suggest that the lake level has oscillated significantly. It is thought that the lake originated during the Quaternary, but its age may be as old as the Late Tertiary. Acoustic reflection profiles (UNIBOOM) indicate that, to the depth reached, the subsurface seismic stratigraphy consists of three units (Units I, II and III) separated by prominent reflectors. A 7.43 m core was obtained in the central part of the lake which reached approximately the base of Unit I. Sedimentological, palynological, and radiocarbon analyses indicate that Unit I is a Holocene lacustrine deposit, and that in the Late Pleistocene the lake either did not exist or was greatly reduced. Units II and III probably represent similar older lacustrine units. The stratigraphy is interrupted by Late Pleistocene-Holocene faulting. Clastic lenses were found near the base of Unit I, above the reflector which separates it from Unit II, in the eastern seismic profiles. These are interpreted as Early Holocene fluvio-lacustrine sediments which were deposited subaerially or as deltas.