ABSTRACT

Pleistocene sediments of glacial marine origin have recently been cored within Cascadia Basin in the northeast Pacific Ocean as far south as 44°10N. A uniform distribution of sand grains and pebbles in a clayey silt matrix indicates that ice rafting was the depositional mechanism. The mineralogy of the clay and sand fractions and the petrology of the pebbles strongly suggest a source area in the Puget Lowland and the adjacent mountains of Washington and British Columbia. These areas were covered by the Cordilleran glacier complex in late Pleistocene time. Calving of the ice front produced bergs laden with debris scoured from the continent. The distribution of the glacial marine deposits indicates that Pleistocene circulation m st have been very similar to that of today. Icebergs could have easily been carried south by the portion of the West Wind Drift which intrudes into the area of Vancouver Island and then moves southward along the coast. As the ice melted, it left a trail of debris 400 km south of the previously believed boundary for these deposits.