27 Bentonites in the Geologic Record

Wednesday, 16 March 2005
8:00 AM - 10:00 AM

COMPARISON OF TWO DEVONIAN ASHES: KASHONG-WINDOM BOUNDARY AND LOWER RHINESTREET SHALE, WESTERN NEW YORK STATE

Paper number: 27-2
Program: THEME SESSIONS
Time: 8:20 AM – 8:40 AM

Authors

  • Matthew John Wilcott Presenting Author
    State Univ of New York at Geneseo, Cheektowaga, NY
  • D. Over
    SUNY - College at Geneseo Dept Geological Sciences, Geneseo, NY

Abstract

Two suspected Devonian ashes, a gummy weathering bed from the Kashong Shale-Windom Shale contact and another from the lower Rhinestreet Shale, were collected from exposures in western New York. The Kashong-Windom gummy bed contained many apatite, biotite, pyrite, zircon crystals, and conodonts. The conodonts Icriodus latericrescans latericrescans and Polygnathus varcus indicate the upper Middle Devonian Middle varcus Zone. Recovered zircons are worn euhedral crystals, an indication of transport, either a result of reworking on the unconformable surface or, as suggested by recent freshwater ostracods, that the sample was contaminated by modern material. X-Ray defraction of the clay bed lacks mixed-layer minerals indicative of an ash origin for the clays.

The suspected ash bed from the lower Rhinestreet Shale (Frasnian) at Eighteenmile Creek contains apatite, biotite, pyrite, and abundant small zircons. The apatites and zircons are worn, but there is no indication of contamination. This suggests reworking of the phenocrysts at the time of deposition. This suspected ash bed was previously correlated to the Belpre Ash, recognized in Ohio, Virginia, and Tennessee where it occurs at the base of the Dowelltown Member of the Chattanooga Formation.