Research Article| December 01, 1973 Zircon Fission-Track Ages of Pearlette Family Ash Beds in Meade County, Kansas C. W. Naeser; C. W. Naeser 1U.S. Geological Survey, Denver, Colorado 80225 Search for other works by this author on: GSW Google Scholar Glen A. Izett; Glen A. Izett 1U.S. Geological Survey, Denver, Colorado 80225 Search for other works by this author on: GSW Google Scholar Ray E. Wilcox Ray E. Wilcox 1U.S. Geological Survey, Denver, Colorado 80225 Search for other works by this author on: GSW Google Scholar Author and Article Information C. W. Naeser 1U.S. Geological Survey, Denver, Colorado 80225 Glen A. Izett 1U.S. Geological Survey, Denver, Colorado 80225 Ray E. Wilcox 1U.S. Geological Survey, Denver, Colorado 80225 Publisher: Geological Society of America First Online: 01 Jun 2017 Online Issn: 1943-2682 Print Issn: 0091-7613 Geological Society of America Geology (1973) 1 (4): 187–189. https://doi.org/10.1130/0091-7613(1973)1<187:ZFAOPF>2.0.CO;2 Article history First Online: 01 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 C. W. Naeser, Glen A. Izett, Ray E. Wilcox; Zircon Fission-Track Ages of Pearlette Family Ash Beds in Meade County, Kansas. Geology 1973;; 1 (4): 187–189. doi: https://doi.org/10.1130/0091-7613(1973)1<187:ZFAOPF>2.0.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 Pearlette family volcanic ash beds at two faunally important late Cenozoic localities near Meade, Meade County, Kansas, are very similar in chemical and mineralogic composition, yet their zircon microphenocrysts have markedly different fission-track ages. Zircon microphenocrysts from type B Pearlette volcanic ash underlying sediments that contain the Borchers local fauna of Hibbard are various shades of pink and have a fission-track age of 1.9 ± 0.1 m.y. In contrast, zircon microphenocrysts from type O Pearlette volcanic ash overlying sediments that contain the Cudahy local fauna of Hibbard are colorless and have a fission-track age of 0.6 ± 0.1 m.y. These fission-track ages are in good agreement with K-Ar ages on the probable source material in Yellowstone National Park. 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.
New petrographic and chemical data indicate that the great Mount Mazama eruption at Crater Lake, Oregon, about 6600 years ago was the source of most ash which has been called "Glacier Peak" and of some ash called "Galata." Glacier Peak volcano in Washington was itself the source of an older ash deposit, perhaps very late glacial or early postglacial in age.
During the late Wisconsin glaciation, the mountainous regions of northwestern Montana were covered by glacial ice. Marias Pass, on the Continental Divide immediately south of Glacier National Park, was covered by a local ice field. This ice and that from other glaciers to the north and south flowed eastward onto the plains of Montana to form the Two Medicine Glacier, a large piedmont glacier that extended 55 km beyond the mountain front. The presence of the Glacier Peak G ash and the underlying St. Helens Jy ash in laminated lake sediments near Marias Pass indicates that in this region the Continental Divide was ice free before about 11,400 BP. Macrofossils, pollen, and spores in these same sediments indicate establishment of shrubs, herbs, and scattered conifers by that time. At Sun River Canyon, about 90 km south of Marias Pass, glaciers also flowed beyond the mountain front onto the plains to form the Sun River Glacier, another large piedmont glacier that extended beyond the mountain front for 25 km. The presence of the Glacier Peak G ash in a postglacial alluvial fan indicates
