An Overview of the Ross Formation, Shannon Basin, Western Ireland
Trond Lien, Ole J. Martinsen, Roger Walker, 2008. "An Overview of the Ross Formation, Shannon Basin, Western Ireland", Atlas of Deep-Water Outcrops, Tor H. Nilsen, Roger D. Shew, Gary S. Steffens, Joseph R. J. Studlick
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The Upper Carboniferous deep-water sediments of the Shannon Group were deposited in the extensional Shannon basin of County Clare in western Ireland, and exposures occur along the sea cliffs of the Shannon Estuary (Figure 1). Carboniferous limestone floors the basin, and the basin-fill succession begins with the deep-water Clare Shales. These shales are overlain by various turbidite facies of the Ross Formation (460 m [1509 ft] thick). The type of turbidite system, scale of turbidite sandstone bodies, and the overall character of the stratigraphic succession, make the Ross Formation well suited as an analog for sand-rich turbidite plays in passive-margin basins around the world. The lower 170 m (558 ft) of the Ross Formation contains tabular turbidites with no channels. There is an overall tendency for the Ross to become sandier upwards, although there are no small-scale thickening- or thinning-upward successions. The upper 290 m (950 ft) consist of turbidites, commonly arranged in thickening-upward packages, and amalgamated turbidites. These form channel fills that are each up to 10 m (33 ft) thick. A few of the upper channels have an initial lateral-accretion phase with interbedded sandstone and mudstone deposits, which is followed by a vertical-aggradation phase with thick-bedded, amalgamated deposits. As the channels filled, more turbidites spilled farther overbank. Superb outcrops show that thickening-upward packages developed when channels initially spilled muds and thin-bedded sands up to 1 km (0.6 mi) overbank, followed by thick-bedded, amalgamated turbidites that spilled close to the channel margins. The paleocurrent directions associated with the amalgamated channel fills suggest a low channel sinuosity.
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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