Magnetostratigraphy and paleontology of Wagner Quarry, (late Oligocene, early Arikareean) basal Arikareean Group of the Pine Ridge Region, Dawes County, Nebraska

Abstract

Mammalian fossils (the Wagner Quarry local fauna) from the basal Arikaree Group (Late:Oligocene) near Chadron, Dawes County, Nebraska, are described. It is the first large mammal concentration described from the Pine Ridge Arikaree Group. Twenty-seven species of mammals are present: 1 marsupial (Herpetotherium), 2 insectivores (Proscalops, Ocajila), 9 rodents (Downsimus; Aywoodia, Cedromus savannae n. sp., Nototamias, Agnotocastor, Palaeocastor, Proheteromys, Leidymys, Geringia), 3 lagomorphs (Palaeolagus {2 sp.], Megalagus), 3 carnivores (Paradaphoenus, Canidae, Nimravus), 3 perissodaciyls (Miohippus, Diceratherium [2 sp.]), and, 6 artiodaciyls (Entelodontidae, Desmatochoerinae, Leptauchenia, Anthracotheriidae, Pseudolabis, Nanotragulus).  Faunal correlation, with the Ridgeview local fauna and the radibisotopically constrained faunas of the Wildcat Ridge indicates an early Arikareean (Arl, 30-28 Ma, Tedford et al. 2004) North American Land Mammal age for the fauna. The first paleomagnetic study of the Pine Ridge basal Arikaree Group (Wagner Quatry section) shows that polarity signals are not the same, as basal Arikaree Group sediments (Gering Formation) in the Wildcat Ridge region. Correlation of the Wagner Quarry section with Chron 10n (28.25- 28.9 Ma) places it older than the Gering Formation (Chron 9r, 27.95-28.25 Ma) and younger than the lowermost White River Group "Brown Silistone" (Chron 10r-11n, 28.9-30.08 Ma) of Nebraska. These sedimbnts could represent time not recorded in the Wildcat Ridge. Cedromus (Sciuridae), Oligospermophilus (Sciuridae), and Alwoodia (A lodontidae) are newly recognized in the earliest Arikareean (Arl) of the central Great Plains.