| dc.description.abstract | The Miocene Lost Cabin beds of Cottonwood Valley, Arizona, represent a north-northeasterly fine-grained axial valley basin deposit fed by sediments from the Newberry and Black Mountains to the west and east, respectively. Cottonwood Valley formed within the Colorado River corridor during a period of volcanism and north moving E-W extension spanning the early to middle Miocene. This study uses magnetostratigraphy, rock magnetism, and 40Ar/39Ar dating from detrital sanidine to determine the timing of deposition of the Lost Cabin beds in relation to the arrival of Colorado River sediments. One hundred and seventy samples were used in this study from a total of thirty-nine sites. Magnetite and hematite are identified as predominate carriers of magnetic remanence, with minor contributions from titanomagnetite, titanomaghemite, and pyrrhotite. Rock magnetic measurements were consistent with identifying magnetizations that are held in magnetite and hematite. Normal and reverse polarities yielded a total of three geomagnetic polarity intervals within the Lost Cabin bed sediments. 40Ar/39Ar dating yielded one site with a young sanidine grain that produced an age of 5.49 ± 0.788 Ma. Magnetostratigraphy was correlated to the geomagnetic polarity timescale by using three ash beds with dates that spanned from 5.59 ± 0.05 Ma to 5.35 ± 0.07 Ma. Polarity intervals were identified as Subchrons C3r, and C3n.4n (Thvera), within the Gilbert Chron. Results from this study suggest a post 5.235 Ma arrival date of the Colorado River waters within Cottonwood Valley. | en_US |
