A gravel outwash/deformation till continuum, Skalafellsjokull, Iceland

A stratigraphic sequence exposed by river erosion in the foreland of Skalaf ellsjokull, southern Iceland, displays five lithofacies documenting glaciof luvial deposition Followed by glaciotectonic disturbance and subglacial def ormation, Lithofacies 1a and 1b are glaciotectonically thrust glaciofluvial outwash and subglacial deformation till respectively from an early advance of Skalafellsjokull, Lithofacies 2, massive gravels and clast-supported di amictons, documents the deposition of glaciofluvial outwash in the proto-Ri ver Skala prior to overriding by Skalafellsjokull during the Little Ice Age . During overriding, lithofacies 2 was glaciotectonically disturbed and now possesses the clast fabric and structural characteristics of G(B) (non-pen etratively deformed) and G(A) (penetratively deformed) type glaciotectonite s. A shear zone separates lithofacies 2 from overlying lithofacies 3, the l atter possessing the class fabric signature of a D-A (dilatant) type deform ation till although it was originally deposited as a discontinuous diamicto n within a glaciofluvial sequence, probably as a hyperconcentrated flow, an d appears to have been at least partially derived from underlying materials by glaciotectonic cannibalization. Lithofacies 4 is a glaciofluvial deposi t comprising two coarsening-upward sequences of gravel and diamicton. These facies have been overprinted with G(B) glaciotectonite and DA-B (dilatant to non-dilatant) deformation till structures and clast fabrics recording a vertical progression towards more pervasively deformed material. The sequen ce is capped by lithofacies 5, a two-tiered deformation till possessing the characteristics of D-A and D-B horizon subglacial tills previously reporte d from Icelandic glacier snouts. The whole sequence comprising lithofacies 2-5 represents a gravel outwash/deformation till continuum displaying varia ble strain signatures produced in response to stress induced by the overrid ing of Skalafellsjokull during the Little Ice Age. These signatures are dic tated by the sediment rheology and a vertical strain profile for the sedime nt pile during glacier overriding is reconstructed.