Introduction to Deep-water Deposits of the Tanqua Karoo, South Africa
Arnold H Bouma, Anne M Delery, Erik D Scott, 2008. "Introduction to Deep-water Deposits of the Tanqua Karoo, South Africa", Atlas of Deep-Water Outcrops, Tor H. Nilsen, Roger D. Shew, Gary S. Steffens, Joseph R. J. Studlick
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The southwestern part of the Karoo basin, South Africa is comprised of two mountain chains (Figures 1,2). The southern branch (Witteberg Swartberg Range) runs east-west, and the western branch (Cedarberg Range) is more or less north-south. Where the two meet is a northeast-trending syntaxis with two anticlinoria. This structural area encloses two foredeep areas, known as the Laingsburg subbasin and the Tanqua Karoo subbasin. The east-west running Laingsburg subbasin is a typical elongated foredeep. Later tectonic activities tilted this basin, with the result that the layers are close to vertical. Between the western branch and the anticlinoria is the location of the Tanqua Karoo subbasin. The outcrops of this basin now cover an area of 650 km2 (250 mi2). The basin is Permian age (Figure 3; Wickens and Bouma, 2000). Gradual sinking of the basin has resulted in a 7–8-km (4.36–5.0-mi)-thick package of younger deposits overlying the deep-water sediments. A later rebound eroded overburden, with the result that the Permian deep-water deposits became exposed. The outcropping area is about 34 km (21 mi) long and has no tectonic dip in the north-south direction. The visible width varies from 8 to 12 km (5–7.5 mi), and shows 1–3° tilt to the east. Lack of vegetation exposes large outcrops along the western and southern sides, as well as in the middle along the Gemsbok River (Figure 5). The outcrops make it possible to observe the depositional changes in the downslope direction. The subbasins formed during the Permian compressional collision
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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