Seismic stratigraphy, sedimentary architecture and palaeo-glaciology of the Mackenzie Trough: evidence for two Quaternary ice advances and limited fan development on the western Canadian Beaufort Sea margin

Abstract

A comprehensive grid of high-resolution 2-D seismic reflection data from the western Canadian Beaufort Sea margin is used to reconstruct past ice-stream dynamics within the Mackenzie Trough. Eight seismic facies and five sequences, divided into two megasequences, are identified from the Mackenzie Trough stratigraphy. Evidence for two Quaternary ice advances to the shelf break is provided by two sequences of acoustically chaotic to semi-transparent facies, interpreted as subglacial till. Buried landforms interpreted as lateral moraines and a grounding-zone wedge record the positions of still-stands or re-advances in the ice margin. The continental slope beyond the trough is characterised by canyons separated by inter-canyon ridges and thin glacigenic debris flows. Correlation with the onshore record suggests that the older of the two ice advances, which excavated the Mackenzie Trough, probably occurred during the Illinoian or Early Wisconsinan glaciations. The younger ice-stream advance is interpreted to have occurred during the last, Late Wisconsinan glaciation. The onset of cross-shelf glaciation on the western Canadian Beaufort Sea margin is inferred to have been initiated significantly later than on the eastern Beaufort Sea and eastern Canadian Arctic margins, which have a longer history of ice advance and were less peripheral to the ice-sheet centre. The architecture of the slope beyond the Mackenzie Trough reflects this comparatively short history of ice advance and lacks the progradational architecture and major glacial-sedimentary depocentre or trough-mouth fan that is characteristic of slopes seaward of cross-shelf troughs on formerly-glaciated margins.