Four surficial geological units are defined geophysically for Hecate Strait on the northern British Columbia continental shelf. They consist of Tertiary bedrock (unit 1) unconformably overlain in much of the strait of glacial till (unit 2), which is in turn overlain below 200 m water depth by thick silts (unit 4) and above 200 m by Quaternary sands and gravels (unit 3), except in areas where till or Tertiary bedrock is at or near surface.Glacial ice covered most of the strait at some time in the Pleistocene, but evidence for a Late Wisconsinan advance is more prevalent in the principal troughs of the strait. Sea level was as low as the present-day 180 m isobath during the late Tertiary or early Quaternary and possibly as low as 100 m at the end of the Pleistocene, based on the presence of drainage channels, wave-cut terraces, and both shore-oblique and shore-parallel sand ridges. Sedimentary bedforms found ubiquitously above 100 m appear to be in equilibrium with the present hydrodynamic conditions, and their presence suggests that significant seabed erosion and transport occur within the strait.

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