A Middle Wisconsin interstadial in the northern Andes

This article reports the occurrence of a Middle Wisconsin interstadial, Pedregal, in the northern Venezuelan Andes, as demonstrated by high-resolution pollen analysis of a previously dated peat layer. Paleoclimatic trends are deduced mainly from changes in the abundance of tree pollen from the uppermost Andean forests. Previous calibration of this pollen with modern analogs has enabled reconstructions of prior altitudinal displacements of montane ecological belts and temperature changes. Paleotemperatures were deduced from the current lapse rate (−0.6 °C/100 m). After a glacier advance, represented by an underlying till, average temperatures increased to 3 °C lower than modern temperatures during the Pedregal interstadial and then dropped again to approximately 7 °C lower than modern. It is the oldest Quaternary paleoclimatic event reported thus far in the area.