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标题：Ammonites from the upper part of the Pierre Shale and Fox Hills Formation of Colorado. American Museum novitates ; no. 3388
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作者：Landman, Neil H. ; Cobban, William Aubrey
期刊名称：American Museum Novitates
印刷版ISSN：0003-0082
电子版ISSN：1937-352X
出版年度：2003
卷号：2003
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出版社：American Museum of Natural History
摘要："The upper part of the Pierre Shale and Fox Hills Formation were deposited in the late Cretaceous (Maastrichtian) Western Interior Seaway. They crop out in a belt that roughly parallels the Front Range of the Rocky Mountains from Douglas to Weld County, Colorado. These rocks consist of sandy shales and sandstones and are overlain by the nonmarine Laramie Formation. A sparse assemblage of ammonites is present consisting of Coahuilites sheltoni Böse, 1928, Sphenodiscus pleurisepta (Conrad, 1857), Trachybaculites sp. cf. T. columna (Morton, 1834), Hoploscaphites birkelundae Landman and Waage, 1993, Hoploscaphites sp. cf. H. birkelundae, Jeletzkytes dorfi Landman and Waage, 1993, and Jeletzkytes sp. cf. J. dorfi. Hoploscaphites birkelundae and Jeletzkytes dorfi define the H. birkelundae Zone in the Western Interior, which represents the lower part of the Upper Maastrichtian. These rocks are thus equivalent in age to the Fox Hills Formation in Niobrara County, Wyoming, and older than the type Fox Hills Formation in north-central South Dakota. An analysis of the ratio of [superscript]87Sr/[superscript]86Sr in a belemnite from this zone in Morgan County, Colorado, yields a value of 0.707790 [+ or -] 0.000008 (2-sigma SE), nearly identical to that of a bivalve from the same zone in Niobrara County, Wyoming (McArthur et al., 1994). The western shoreline of the seaway during the time of H. birkelundae extended as far west as northwestern Colorado and southwestern Wyoming"--P. [1].