Clays and secondary minerals as permafrost indicators: examples from the circum-Baikal region

Abstract

A proper understanding of Quaternary environments requires assessment of the possible existence of perennially frozen ground. Furthermore, the structural and mineralogical changes induced by permafrost are commonly irreversible and still affect the present soils, so that it is important to be able to recognize them. However, the regions that suffered severe, but dry periglacial conditions during cold Quaternary periods, as in southeastern Siberia, show few periglacial features. Five exposures investigated in the circum-Baikal area show permafrost features, although the same phenomena occur throughout southeastern Siberia. These exposures demonstrate that, even though evidence of permafrost may be lacking or equivocal, thorough analysis can reveal indicators of permafrost such as neoformed clays, secondary precipitates of iron, calcite, and sulphates with peculiar crystalline features, as are found in other past or presently perpetually frozen ground. In combination with sedimentary structures and the geomorphic environment, these indicators affirm the definite existence of permafrost.