River mixing rate, residence time, and subsidence rates from isotopic indicators: Eocene sandstones of the U.S. Pacific Northwest

Research Article| December 01, 1992 River mixing rate, residence time, and subsidence rates from isotopic indicators: Eocene sandstones of the U.S. Pacific Northwest Paul L. Heller; Paul L. Heller 1Department of Geology and Geophysics, University of Wyoming, Laramie, Wyoming 82071 Search for other works by this author on: GSW Google Scholar Paul R. Renne; Paul R. Renne 2Institute of Human Origins, Geochronology Center, 2453 Ridge Road, Berkeley, California 94709 Search for other works by this author on: GSW Google Scholar James R. O'Neil James R. O'Neil 3Department of Geological Sciences, 1006 C.C. Little Building, Ann Arbor, Michigan 48109-1063 Search for other works by this author on: GSW Google Scholar Author and Article Information Paul L. Heller 1Department of Geology and Geophysics, University of Wyoming, Laramie, Wyoming 82071 Paul R. Renne 2Institute of Human Origins, Geochronology Center, 2453 Ridge Road, Berkeley, California 94709 James R. O'Neil 3Department of Geological Sciences, 1006 C.C. Little Building, Ann Arbor, Michigan 48109-1063 Publisher: Geological Society of America First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1992) 20 (12): 1095–1098. https://doi.org/10.1130/0091-7613(1992)020<1095:RMRRTA>2.3.CO;2 Article history First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Paul L. Heller, Paul R. Renne, James R. O'Neil; River mixing rate, residence time, and subsidence rates from isotopic indicators: Eocene sandstones of the U.S. Pacific Northwest. Geology 1992;; 20 (12): 1095–1098. doi: https://doi.org/10.1130/0091-7613(1992)020<1095:RMRRTA>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Isotopic analyses of Eocene sandstones from the Tyee Formation and related units in the U.S. Pacific Northwest provide evidence for short residence time but extensive mixing and, indirectly, slow subsidence rates within the major river feeder systems that drained the western flank of the North American Cordillera. Bulk isotopic analyses of coarse white mica are remarkably consistent throughout the Tyee Formation (mean K/Ar = 67.3 Ma, δ18O ≈+9.5) of the Oregon Coast Range. Other Tertiary sandstones in the region have similar values. Despite small scatter about these mean values, the 40Ar/39Ar ages of single grains of white mica from these units range from about 45 to 120 Ma, showing that long river systems thoroughly mixed and homogenized the transported sand grains. In addition, overlap of the youngest mica cooling ages and depositional age for the Tyee Formation show that homogenization of grains took place during a relatively short residence time in the river transport system (<2 m.y.). These results require that the sediments were multiply cycled within the active river system. This suggests that average subsidence rates along the alluvial system were low, and thus sediment could be recycled by temporary storage in, and reintroduction from, the river flood plain without spending significant time buried. The results show that extensive sediment mixing can occur in large rivers on relatively short time scales, and that isotopic analyses can provide indirect evidence of subsidence rates for basins no longer preserved. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.