Stratigraphy of the Lewis Shale, Wyoming, USA: Applications to Understanding Shelf-edge to Base-of-slope changes in Stratigraphic Architecture of Prograding Basin Margins
Published:January 01, 2008
David R Pyles, Roger M Slatt, 2008. "Stratigraphy of the Lewis Shale, Wyoming, USA: Applications to Understanding Shelf-edge to Base-of-slope changes in Stratigraphic Architecture of Prograding Basin Margins", Atlas of Deep-Water Outcrops, Tor H. Nilsen, Roger D. Shew, Gary S. Steffens, Joseph R. J. Studlick
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The Cretaceous Lewis Shale of Southern Wyoming is an excellent outcrop example of a submarine fan deposited basinward of a coeval, prograding margin. A regional cross section constructed from outcrop and subsurface data reveal several large-scale attributes of the system. Regionally continuous, condensed sections in the Lewis Shale define southward-prograding clinoforms that are related to a shelf-slope-basin physiography during deposition. The condensed sections form the boundaries to fourth-order stratigraphic cycles/parasequences. The average height of the clinoforms is ~400 m (~1300 ft), which is interpreted to reflect the minimum water depth during deposition. Strata with 50% or more sandstone are located in fluvial-deltaic strata on the topset of the clinoforms and submarine-fan strata are located on the bottomset of the clinoforms. Slope strata on the foresets of clinoforms contain 15–20% sandstone. Although the sandiest strata are located in shelf and base-of-slope strata, the depocenter of each fourth-order cycle is consistently located in muddy slope strata.
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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