Abstract
AbstractOn Vancouver Island, the Dashwood Drift, Cowichan Head Formation, Quadra Sand, and Vashon Drift were deposited during late Pleistocene glacial and interstadial periods and show large variations in clay-mineral contents partly related to changing climatic conditions. Glacial deposits are characterized by iron-rich chlorite, illite (both well crystallized), and smectite with a morphology reflecting rapid derivation from volcanic rocks. The clay mineralogy of nonglacial deposits is more complex, and is marked by the presence of vermiculite, kaolinite, halloysite, and irregular mixed-layer minerals. Nonglacial clay minerals are poorly preserved and show a higher state of alteration due to pedogenesis. Large variations in nonglacial deposits compared to glacial deposits are also due to secondary factors such as selective sorting, soil and rock source variations, differences in sedimentary environment, and diagenesis. These secondary factors do not seem to obliterate significantly the climatic imprint on the clay minerals. These studies also permit the recognition of glacially reworked sediments, the determination of relationships between two units in the same section, and the establishment of the conditions of clay-mineral formation.
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