Probable Late Wisconsinan ice margin on the upper continental slope off St. Pierre Bank, eastern Canada

Abstract

Seismic reflection profiles from the continental slope off St. Pierre Bank show a distinctive acoustic facies characterized by incoherent reflections (unit E) overlain by 5–20 m of stratified sediments (units D–A). Cores from unit E include poorly sorted silty diamict, locally overconsolidated and including in places some foraminifera. Stratified sediments also occur in places in this facies.The overlying sediments of units D–A, except for the topmost metre of unit A, have a foraminiferal fauna dominated by Elphidium excavatum forma clavata and Cassidulina reniforme, which has been interpreted elsewhere as indicating ice-margin sedimentation. The sediments contain turbidites and rare ice-rafted detritus, and are bioturbated. Accelerometer mass spectrometer radiocarbon dating of shells from the stratified sediments yielded dates between 3.3 and 11.8 ka. Facies E, the top of which has an extrapolated age of 11.5–12.0 ka, is interpreted as slumped morainal diamict and proglacial sediment resulting from a late Wisconsinan ice surge through Halibut Channel. Low basal shear stresses in this thin ice surge left little record in the mud-accumulating basins of the continental shelf.