Glacial debris flow deposits on the Baffin Island shelf: seismic facies architecture of till-tongue-like deposits

Abstract

3-D seismic facies modeling of late Foxe/Wisconsin glacial deposits in the Savage Basin provides important new data concerning the morphology and origin of acoustically unstratified seismic units on high-latitude continental shelves. Savage basin contains a thick sequence (up to 110 m) of morainal bank deposits (Unit II) similar to ‘till tongue root’ deposits described from the Scotian and Norwegian shelves. In 2-D longitudinal cross-section, Unit II thins and differentiates northward into two acoustically unstratified wedges or ‘till tongue’-like deposits (Units IIAw and IIBw) which are observed to interbed with stratified glacimarine sediments (Unit I). Sediment transport was northeastward, away from a late glacial ice margin in outer Frobisher Bay. Both unstratified wedges are lobate in plan view with the thickest portion (5 m to 50 m) lying along the lobe axis. Upper surface contours are convex to the north and concentric to the lobate margin. Southward, at the transition to the morainal bank, the contours become concave to the north. This morphology is consistent with that of lobate debris flow deposits with the concave contours defining a zone of sediment failure. The data indicate sediment failure within morainal bank deposits which accumulated near the terminus of a temperate tide water ice sheet. Truncations of Unit I reflectors against the lower surface of the debris flows indicate that the flows were deposited episodically and that they remobilized or eroded some of the Unit I sediments. This unconformable relationship gives the same stratigraphic sequence that King et al. (1991) proposed to explain ‘till tongue’ formation from subglacial meltout beneath buoyant glacier ice in contact with the seabed. Coalescing debris flow lobes are observed along the entire distal slope of the morainal bank. These give the appearance of a continuous till tongue wedge in seismic cross-sections taken parallel and distal to the paleoice margin. Without 3-D geometry reconstructed at contour intervals ≤ 10 m, the complex lobate morphology could not be resolved.