Radiocarbon dates from critical stratigraphic localities in southern British Columbia indicate that the growth history of the late Wisconsin Cordilleran Ice Sheet was different from that of most of the Laurentide Ice Sheet to the east. Much of southern British Columbia remained free of ice until after about 19,000 to 20,000 yr ago; only adjacent to the Coast Mountains is there a record of lowland glacier tongues in the interval 22,000 to 20,000 yr B.P. A major advance to the climax of late Wisconsin Cordilleran glacier ice in the northern States was not begun until after about 18,000 yr B.P. in the southwest of British Columbia and after about 17,500 yr B.P. in the southeast. The rate of glacier growth must have been very rapid in the two to three millennia prior to the climax, which has been dated in western Washington at shortly after 15,000 yr B.P.
Coquitlam Drift is formally defined and stratotypes established for it in the Coquitlam – Port Moody area, B.C. It is a Pleistocene formation consisting of till, glaciofluvial, ice-contact, and glaciomarine sediments deposited between 21 700 and 18 700 years BP, during the Fraser Glaciation (late Wisconsin) and prior to the main Vashon glacial maximum at about 14 500 years BP. The drift was deposited in short pulses by valley and piedmont glaciers fluctuating into the Fraser Lowland from the Coast Mountains to the north and Cascade Mountains to the east.
A knowledge of the natural environment of the Fraser Lowland, which is bounded by mountain ranges on two sides and the ocean on the third, is essential in land use planning. The geology of the area has evolved over millions of years in the case of the bedrock and hundreds of thousands of years in the case of the unconsolidated sediments. Bedrock is at or within 10 m of the surf ace in less than 5% of the Fraser Lowland, consequently the geology of most concern is that of the remaining area where unconsolidated (Quaternary) sediments between 10 and 300 m thick overlie bedrock. During the Quaternary the lowland was subjected to repeated glaciations separated by nonglacial intervals. Each major glaciation in the lowland went through three main stages: 1) an advance stage, characterized by coalescing piedmont glaciers probably terminating in the sea; 2) a maximum stage when ice attained a thickness of 1800 m or more and overrode all the Fraser Lowland and much of the adjoining mountainous areas; 3) a retreat or deglaciation stage when ice mainly occupied the valleys and arms of the sea once again. As a result of this complex Quaternary history, deposits of widely diversified origin were laid down and moulded into a succession of landscapes that were eroded and or buried, ending in our present landscape. The geological materials, climate, and physical features (including drainage) all have important roles in the engineering and agricultural development of the area. Some geological materials form very poor bases for foundations because of low bearing capacity and/or poor drainage; others are good because of their excellent bearing capacities and/or good drainage. The most troublesome materials in the Fraser Lowland on which to support foundations are 'sensitive' marine and glaciomarine silty clays, organic sediments, and loosely compacted sand and silt. The two commonest natural hazards in the Lowland are floods and landslides. Marine erosion is a problem at Point Grey. The Fraser Lowland lies in an earthquake zone and the National Building Code has incorporated the earthquake hazard potential in the regulations. Construction materials are plentiful but much of them may be lost as a result of rapid urban growth and zoning regulations. In all agricultured soil mapping the geological materials from which the 'soil' develops is a major controlling factor as to the class of topsoil. Management of the soil, including drainage and levelling, may be unsuccessful if the subsurf ace geology is not taken into account. Groundwater supplies, which are plentiful in much of the Fraser Lowland, vary according to the precipitation and the drainage of the geological materials. They may become polluted if proper disposal of sewage and wastes is not undertaken.
Two lithostratigraphic units, Quadra Sand and the Cowichan Head Formation, are overlain by Vashon till and associated glacial sediments and underlain by Dashwood and Semiahmoo drift deposits in coastal southwest British Columbia. Each unit is formally described and stratotypes are presented.Quadra Sand consists of cross-stratified, well-sorted sand, minor gravel, and silt deposited as outwash in front of glaciers advancing into the Georgia Depression at the beginning of the Fraser Glaciation. It is diachronous, deposition having commenced earlier than 29 000 years BP at the north end of the Georgia Depression but not until after 15 000 years BP at the south end of the Puget Lowland.The Cowichan Head Formation, deposited during the Olympia nonglacial interval, underlies Quadra Sand and consists of parallel-bedded silt, sand, and gravel, in part plant-bearing. The unit is divisible into a lower marine member and an upper fluvial and estuarine member.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.