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Quaternary geology : Coquitlam-Port Moody area, British Columbia Hicock, Stephen Robert

Abstract

During Quaternary time the Coquitlam-Port Moody area underwent two and possibly three major glaciations separated by nonglacial intervals. Each glaciation was accompanied by eustatic and isostatic sea-level changes of up to 230 m, relative to present sea level, and probably some tectonic adjustment. Associated with each major ice advance were two or three local ice advances represented by tills separated by outwash deposits. During the last major glaciation (Fraser), two stades occurred (Vashon and Coquitlam), possibly separated by an interstade (Quadra). The Coquitlam Stade was the earliest and is represented by the Coquitlam Drift (between 25,000 and 21,600 radiocarbon yr. B.P.) which has not been recognized before on the B.C. mainland; it may correlate with the Evans Creek Stade discovered in northwestern Washington. Nine formational lithostratigraphic units are mapped and described for-the area, each probably representing a geologic-climatic unit. The units are separated by unconformities representing three-dimensional irregular buried landscapes which were reshaped and replaced by new ones. Consequently, the Quaternary stratigraphy is extremely complex and sediment units occur sporadically. Correlations based on other than a three-dimensional study are at best tentative and must be supported by radiocarbon dates. The topography of the area was developed before Semiahmoo? time (>62,000 radiocarbon yr. B.P.) and has remained basically the same since then. Large gravel reserves occur in the area, many of them buried in uplands and in the sediment fill occupying the lower Coquitlam River valley. Outwash gravels are the most extensive of the four types found in the area and Vashon outwash is the most commonly mined. Buried landscapes make pit run reserve estimation very difficult, and municipal zoning regulations are phasing out gravel operations and covering valuable reserves with urban and industrial subdivisions.

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