An early Miocene dome-skulled chalicothere from the "Arikaree" conglomerates of Darton : calibrating the ages of High Plains paleovalleys against Rocky Mountain tectonism. American Museum Novitates ; no. 3486

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dc.contributor.author Hunt, Robert M., Jr.
dc.date.accessioned 2005-12-14T19:42:42Z
dc.date.available 2005-12-14T19:42:42Z
dc.date.issued 2005
dc.identifier.uri http://hdl.handle.net/2246/5655
dc.description 45 p. : ill., maps ; 26 cm. en
dc.description Includes bibliographical references (p. 42-45). en
dc.description.abstract "Fragmentary skeletal remains discovered in 1979 in southeastern Wyoming, associated with a mammalian fauna of early Hemingfordian age (~18.2 to 18.8 Ma), represent the oldest known occurrence of dome-skulled chalicotheres in North America. The chalicothere and accompanying fauna were found in silica-cemented fluvial sandstones and conglomerate capping a series of west-to-east trending buttes in Goshen County, Wyoming, extending eastward into Sioux County, Nebraska. These butte caprocks, herein named the Carpenter Ranch Formation, are the reversed topographic remnants of a major paleovalley incised in the early Miocene and filled with coarse granitic/mafic gravels and sands derived from Precambrian-cored up[l]ifts to the west. The Carpenter Ranch Formation is identified as a coarser-grained, westward extension of the early Hemingfordian Runningwater paleovalley of Skinner, Skinner, and Gooris (1977) situated in northwest Nebraska. The age-diagnostic mammal faunas and coarse crystalline gravels of the Carpenter Ranch Formation of Wyoming and the coeval Martin Canyon beds of northern Colorado document the timing of tectonic rejuvenation of Rocky Mountain uplifts to the west in the early Hemingfordian. A second line of buttes situated 3 miles (~4.8 km) north of the Carpenter Ranch paleovalley includes the regional landmark recorded as 'Spoon Butte' in 19th century military and topographic surveys of the region. Spoon Butte, its caprock in northwest-southeast alignment with adjacent satellite buttes, represents a second and younger mid-Miocene paleovalley trend, characterized by silica-cemented sandstones and basal granitic/chert gravel with Barstovian mammals. N.H. Darton and G.I. Adams of the U.S. Geological Survey first described these caprocks as Arikaree conglomerates and mistakenly assumed they were of the same age as the caprock at Spoon Butte and its accompanying buttes to the north. However, this investigation shows that (a) mammal faunas from the two caprock trends are of markedly different ages; (b) the clast composition of the gravels is distinct; and (c) the paleovalleys align along two entirely different geographic trends. Furthermore, a loose gravel found on top of Spoon Butte, previously believed to date the caprock, is identified as a lag deposit sharing the same distinctive clast composition as high Quaternary terrace gravels in the vicinity. These terrace gravels include acid volcanics (not present in the Carpenter Ranch and Spoon Butte basal gravels) and a composite assemblage of water-worn mammal bones of Barstovian, Clarendonian, and Pleistocene ages. Thus they demonstrate that late Cenozoic deposits once occupied the extensive tableland east of the Hartville Uplift, but were later removed by erosion and reworked into Pleistocene and Holocene drainages"--P. 2. en
dc.format.extent 2201542 bytes
dc.format.mimetype application/pdf
dc.language.iso en_US en
dc.publisher New York, NY : American Museum of Natural History en
dc.relation.ispartofseries American Museum Novitates ; no. 3486 en
dc.subject.lcc QL1.A436 no.3486, 2005 en
dc.subject.lcsh Tylocephalonyx. en
dc.subject.lcsh Perissodactyla, Fossil -- Wyoming -- Goshen County. en
dc.subject.lcsh Perissodactyla, Fossil -- Nebraska -- Sioux County. en
dc.subject.lcsh Mammals, Fossil -- Wyoming -- Goshen County. en
dc.subject.lcsh Mammals, Fossil -- Nebraska -- Sioux County. en
dc.subject.lcsh Paleontology -- Miocene -- Wyoming -- Goshen County. en
dc.subject.lcsh Paleontology -- Miocene -- Nebraska -- Sioux County. en
dc.subject.lcsh Paleontology -- Wyoming -- Goshen County. en
dc.subject.lcsh Paleontology -- Nebraska -- Sioux County. en
dc.subject.lcsh Geology, Stratigraphic -- Miocene -- Wyoming -- Goshen County. en
dc.subject.lcsh Geology, Stratigraphic -- Miocene -- Nebraska -- Sioux County.. en
dc.subject.lcsh Geology -- Wyoming -- Goshen County. en
dc.subject.lcsh Geology -- Nebraska -- Sioux County. en
dc.subject.lcsh Stratigraphic correlation -- Great Plains. en
dc.subject.lcsh Stratigraphic correlation -- Rocky Mountains. en
dc.subject.lcsh Geology -- Great Plains. en
dc.subject.lcsh Geology -- Rocky Mountains. en
dc.title An early Miocene dome-skulled chalicothere from the "Arikaree" conglomerates of Darton : calibrating the ages of High Plains paleovalleys against Rocky Mountain tectonism. American Museum Novitates ; no. 3486 en

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  • American Museum Novitates
    Novitates (Latin for "new acquaintances"), published continuously and numbered consecutively since 1921, are short papers that contain descriptions of new forms and reports in zoology, paleontology, and geology. New numbers are published at irregular intervals.

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