Toe-of-slope Channel Complexes at Buena Vista, Upper Brushy Canyon Formation, Texas, USA
C Rossen, R. T Beaubouef, 2008. "Toe-of-slope Channel Complexes at Buena Vista, Upper Brushy Canyon Formation, Texas, USA", Atlas of Deep-Water Outcrops, Tor H. Nilsen, Roger D. Shew, Gary S. Steffens, Joseph R. J. Studlick
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Upper Brushy Canyon strata at the Buena Vista locality are interpreted as channel complexes deposited in a toe-of-slope environment along a major sediment-transport fairway into the basin (Figure 1) (Zelt and Rossen, 1995; Beaubouef et al., 1999). Architectural styles are calibrated by excellent outcrop exposures, and by cores and well logs from two research boreholes. At Buena Vista (Figure 2A, B), the upper Brushy Canyon sandstones are 80 m (262 ft) thick and exposed along a northwest-trending ridge that is 1000 m (3280 ft) long. The outcrop is oriented oblique to paleoflow, which is variable but generally directed eastward. Units of laminated siltstones are relatively thin compared to Guadalupe Canyon, and the upper Brushy Canyon sandstones are broadly tabular in external geometry, although they are highly channelized internally. A sequence boundary is interpreted at the sharp, subplanar contact between upper Brushy Canyon sandstones and the underlying, laterally extensive, laminated siltstone unit (“40 Ft Siltstone,” Zelt and Rossen, 1995). The upper Brushy Canyon is composed of at least two sandstone-prone channel complexes, which are separated by a thin, laterally extensive, organic-rich siltstone (“Marker Bed,” Zelt and Rossen, 1995) that is interpreted as an abandonment interval. Axial areas of the channel complexes are characterized by high net-to-gross, amalgamated, thick-bedded sandstones. The axial areas contain numerous, inter-cutting, sandstone-filled channels (up to 15 m [50 ft] deep) that stack in a laterally offset, or compensational, pattern. Towards the off-axis and margin areas of the channel complexes, the sandstones become less amalgamated and transition into tabular sandstone ledges separated by recessive siltstones.
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Atlas of Deep-Water Outcrops
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