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Paleomagnetics and biostratigraphy of the Pine Ridge Arikaree Group (late Oligocene--early Miocene), Nebraska
Refinement of our understanding of the geologic and paleontologic history of the Great Plains and the interrelationships of this history to events outside of the Great Plains depends on increasingly higher resolution stratigraphic and chronologic research. Three detailed correlation studies of the Pine Ridge Arikaree Group are presented in this dissertation. ^ 1. New material of Arikareean age (30–18.8 Ma) Herpetotherium (a mouse-sized opossum) is described from localities in Nebraska and Florida. The samples from the Ridgeview local fauna (UNSM Dw-121, basal Arikaree Group, Pine Ridge, Nebraska) is the largest population of Herpetotherium in the United States. Comparison of this population with Herpetotherium from different age faunas shows that early Arikareean (30–26 Ma) samples can be referred to H. fugax and are smaller, on average, than older H. fugax . Later Arikareean Herpetotherium, with a single central stylar cusp, are referable to H. youngi. H. fugax exhibits previously unappreciated variation in dental size and stylar cusp morphology. ^ 2. Mammalian fossils from the basal Arikaree Group (late Oligocene), Dawes County, Nebraska, are described for the first time constituting the Wagner Quarry local fauna. Faunal correlation is with the early early Arikareean (Ar1, 30–28 Ma). The first paleomagnetic study of the Pine Ridge basal Arikaree Group correlates the Wagner Quarry section with Chron 10n (28.9–28.25 Ma); hence older than the Wildcat Ridge Gering Fm (Chron 9r, 28.25–27.95 Ma) and younger than the White River Group “Brown Siltstone” (Chron 10r–11n, 30.08–28.9 Ma) thus filling a gap in the geologic history of Nebraska. The rodents Cedromus, n. sp (Sciuridae), Oligospermophilus (Sciuridae), and Alwoodia (Aplodontidae) are recognized for the first time in the earliest Arikareean (Ar1) of the central Great Plains. ^ 3. Magnetostratigraphy of the classic Arikaree section that incorporates the Monroe Creek Formation and Harrison Formation of J. B. Hatcher in Monroe Creek Canyon, Sioux County, Nebraska, correlates the basal Arikaree and the Monroe Creek Formation with Chron 10n–8n (28.9–26.1 Ma). Magnetic signatures are reliable in the basal Arikaree (“Gering”) sediments and in the Monroe Creek Formation, consequently a useful method of correlation outside the type area. Pedogenic and diagenetic factors in the Harrison sediments alter depositional remanent magnetization. ^
Hayes, Frederick Glynn, "Paleomagnetics and biostratigraphy of the Pine Ridge Arikaree Group (late Oligocene--early Miocene), Nebraska" (2005). ETD collection for University of Nebraska - Lincoln. AAI3151434.