Microstructures within a modern debris flow deposit derived from Quaternary glacial diamicton—a comparative micromorphological study

Abstract

Examination of a modern debris flow in comparison with a Quaternary diamicton from which it has been derived reveals significant differentiating sedimentological characteristics. The two sediments were examined using micromorphological analyses. Thin sections of the debris flow show distinct primary microstructure sets that appear indicative of debris flow processes of turbate micro-deformation during flow and subsequent flow deceleration. Comparison of the micromorphological character of both sediments reveal many similarities but the differences seem indicative of flow processes within the active debris flow. Large turbate structures are common within the debris flow sediment and although many more turbate structures occur within the in situ diamicton, they are smaller in size possibly indicative that those structures within the debris flow sediment are not inherited but are neo-formed. Perhaps, the most distinctive and individual characteristic separating the debris flow sediment from the older diamicton is the presence of “tiled” structures. These structures result from downslope flow deceleration and dewatering resulting in transverse bands of clays developing in rhythmic-like patterns. Likewise, the debris flow sediment exhibits a “marbled” appearance, presumably indicative of intense deformation, a characteristic not found in the in situ Quaternary diamicton.