Overview: Outcrop Analysis of an Ancient, Passive Margin, Turbidite System: Windermere Supergroup, British Columbia, Canada
Published:January 01, 2008
R. W. C. Arnott, Gerry M. Ross, 2008. "Overview: Outcrop Analysis of an Ancient, Passive Margin, Turbidite System: Windermere Supergroup, British Columbia, Canada", Atlas of Deep-Water Outcrops, Tor H. Nilsen, Roger D. Shew, Gary S. Steffens, Joseph R. J. Studlick
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The Windermere Supergroup (WSG) is exposed extensively throughout western North America, extending from northwestern Mexico northward through the western United States, along the length of the Canadian cordillera (1), and into the Yukon-Alaska border region (15). The term Windermere Supergroup was coined by Walker (1926) for the mostly sedimentary rocks exposed in the Windermere Valley of southern British Columbia. Subsequent stratigraphic studies, however, have used a variety of terms to describe these rocks, including Miette Group in the western Rocky Mountains, Horsethief Creek Group for exposures in the Purcell Mountains, Kaza and Cariboo Groups in the Cariboo Mountains, and locally Mica Creek assemblage in high grade rocks of the Monashee Complex.
Stewart (1972) was the the first to suggest that the WSG consisted of two parts: A lower sequence comprising laterally discontinuous strata that accumulated synchronous with rifting, and an upper sequence characterized by laterally continuous units interpreted to have accumulated during postrift thermal relaxation. Subsequently, Ross (1991) suggested that the Windermere comprises the sedimentary and volcanic record following the break-up of the supercontinent Rodinia and the formation of the proto-Pacific Ocean >700 Ma. Present-day preservation and exposure of the WSG is the result of Mesozoic deformation during formation of the cordilleran orogenic belt.
In the southern Canadian cordillera, the WSG unconformably overlies Mesoproterozoic sedimentary rocks of the Belt-Purcell Supergroup (1.5–1.4 Ga; 5) or crystalline basement that ranges in age from 2.2–0.73 Ga (4).
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Tor H. Nilsen, a red-haired Scandinavian who stood more than six feet tall, died October 9, 2005, at his San Carlos, California, home. This was after a valiant five-year fight with melanoma cancer. He was 63. His ashes were scattered at his family plot in Norway in 2006.
He was born in New York City on November 29, 1941, to Mollie Abrahamson and Nils Marius Nilsen of Mandal, Norway, and was the first of their children to be born in the United States. After graduating from Brooklyn Tech, he earned his B.S. in geology from City College of New York in 1962. While there, his prowess on the basketball court impressed a scout from the New York Knicks, but Tor went on to graduate school and earned his M.S. and Ph.D. degrees in geology from the University of Wisconsin at Madison in 1964 and 1967, respectively. His M.S. thesis was a study of Precambrian metasedimentary deposits in the Lake Superior area, and his Ph.D. thesis was a study of Devonian alluvial-fan deposits of the Old Red Sandstone in western Norway.
Dr. Nilsen’s principal expertise was in depositional systems analysis, stratigraphic analysis, and the relationships among tectonics, eustasy, and sedimentation. He began his industry career in 1967 as a research geologist with the Shell Development Company in Houston, Texas, and Ventura, California, where he worked on the tectonics and sedimentation of Tertiary shelf systems of coastal California. He subsequently spent two years with the U.S. Army Corps of Engineers as the Military