Proglacial Lacustrine Sedimentation During Winter

Abstract

Many authors have presented photographs illustrating coarse-grained deposits within the otherwise fine-grained, winter components of glaciolacustrine varves. Few have realized the significance of these coarse units and in several cases they have been misinterpreted as summer deposits. Examples of such coarse units are given in a literature review. Conclusive examples of deposition of coarse-grained sediments during winter are presented from a modern environment at Lillooet Lake, British Columbia, and from Pleistocene glaciolacustrine deposits in central British Columbia, and in Sweden. Low sediment concentrations in the lake water, winter storms, failure of deltaic deposits, and possibly jökulhlaups are shown to be potential controls on the occurrence of underflows which deposit the coarse-grained, winter sediments. Misinterpretation of coarse-grained deposits leads to overestimation of the time represented by glaciolacustrine sedimentary sequences.