Permafrost as the main factor controlling the fluvial sedimentation style on glaciomarginal fans

Abstract

This study describes the sedimentary successions of two glaciomarginal fans (=end moraines) deposited during MIS 6 and MIS 2 in the eastern and north-western part of Poland. Sedimentological analyses of the successions indicate they were both deposited close to the ice sheet margin and are dominated by extensive gravelly and sandy sheet beds derived from the upper flow regime with single ice-wedge structures. Qualitative and quantitative analysis of the pancake-like gravelly and sandy sediments was performed using Markov chain analysis. The presence of these, admittedly common, sedimentary successions raises two key points: why sheetfloods are so common on glaciomarginal fans instead of in-channel flows, and whether sedimentary rhythms deposited by sheetfloods represent the full depositional records, or only partial ones due to accompanying erosion. While both points remain unclear, the answers to these questions may be connected to the presence of permafrost, which occupied the foreland of the ice sheet where the glaciomarginal fans were deposited: it can control the type of proglacial river flows on glaciomarginal fans, the depth of erosion and influence the record of sedimentary rhythms.