Abstract
The history of Holocene glaciation serves as an important record of glacier mass balance and, therefore, of climatic change. The moraine record of Holocene glaciation in the tropical Andes, however, is fragmentary and poorly dated. In contrast, increases in the rate of accumulation of inorganic sediment in glacier‐fed lakes have been linked to periods of Neoglaciation in many mountain regions. The interpretation of such a record of Neoglaciation from sediment cores in glacier‐fed lakes in the tropical Andes can provide the continuity and chronologic control that is lacking in the existing moraine record. Unusual exposures of glacial lacustrine sediment in the Cordillera Blanca, Peru, provide a rare opportunity to assess the link between climatic change, glaciation, and lacustrine sedimentation. Intentional lowering of water levels in Laguna Parón (9°S, 77°44′ W, 4200 m a.s.l.) in 1985 resulted in the incision and exposure of at least 20 m of deltaic deposits at the eastern end of the lake. Three deltaic units can be identified: horizontal topset beds, steeply dipping and deformed foreset beds, and horizontally laminated fine‐grained sediment. Six radiocarbon ages ranging from 1800 ± 210 to 465 ± 95 14 C yr BP on wood indicate that the average rate of delta progradation in the late Holocene has been approximately 290 m per 1000 yr. The lake formed during deglaciation at least 10 000 yr ago and if such a rate of progradation of the delta had prevailed over the entire Holocene, then the delta would be at least three times as extensive as it is today. Thus the rate of delta progradation has varied significantly over the Holocene. We suggest that the rate of delta progradation was at least three times greater when glaciers were in advanced positions. These positions are clearly delimited by Neoglacial moraines, which are within 1–2 km of the exposures studied and within 1 km of modern ice limits. The most recent increase in the rate of delta progradation is evidenced by an increase in sedimentation rate ca. 575 ± 90 14 C yr BP, coincident with the onset of the Little Ice Age. Copyright © 2005 John Wiley & Sons, Ltd.