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This poster presents evidence of progressive soft-sediment deformation from stratified Middle Pleistocene -age tills and glaciolacustrine deposits from north Norfolk, Eastern England. The sediment sequence was deposited during an ice advance from the north however, these sediments have been subsequently been tectonised by subglacial shearing during a later ice advance from the southwest.
Three phases of deformation have been recognised: a first phase of ductile folding and sediment remobilisation (D1); a second phase characterised by brittle failure and faulting along Reidel shears (D2); a final third phase associated with hydrofracturing and sediment remobilisation (D3). The dominant control of deformation and the transition through D1-D3 appears to relate the rate of till accretion, and the pore-water content / pressure with different parts of the deforming layer, and these properties vary in both time and space. A hybrid 'mosaic' - 'pervasive' deformation model is presented to explain the evolution of this subglacial shear zone.
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