Glacial sequence and environmental history in the Sierra Nevada del cocuy (Colombia)

Abstract

The glacial sequence in the area of the Sierra Nevada del Cocuy (Cordillera Oriental, Colombia) was studied in the field and by means of aerial photographs in relation to the environmental history, which was studied by means of pollen analysis and radiocarbon dating. At least five (possibly six) glacial drift bodies could be recognised, and on the basis of the (groups of) bordering moraines about six main glacial stades were defined and named. Drifts 2, 3, 4 and 5 are presumably all of Fuquenian (Last Glacial) age, whereas Drift 6 is of Holocene (Neoglacial) age. In the pollen diagrams the Saravita, Susacá and Guantiva interstadials are clearly reflected as periods of a somewhat higher forest limit, a more abundant growth of Polylepis and an interesting pioneer vegetation (often with Dodonaea). The greatest extension of the glaciers took place before ca. 25,000 B.P., probably in the period between 45,000 B.P. and 25,000 B.P. The climate was relatively wet at the time and the forest limit something like 800–1000 m below the present one, and during the early period of major extension of the ice, glaciers and forest may have locally been in contact (at elevations between 2200 and 2700 m), and the páramo belt was relatively narrow and wet, with Polylepis abundant in the lower parts. Between 21,000 and 14,000 B.P., the ice extension was much less, the forest limit lower, and the climate drier, which resulted in a relatively broad and dry páramo belt. The late Glacial had a relatively wet climate again, but the annual temperature increased; there are two clear “glacial stades”. There are very clear signs of a late medieval neoglaciation; glaciers started to retire from the outermost Neoglacial bordering moraines probably after 1850 A.D., and are still decreasing.