Origin, character, application and correlation of tephra partings in tertiary coal beds of the Kenai Peninsula, Alaska

• Main Author: Reinink-Smith, Linda Margareta
• Other Authors: Hopkins, David M.
• Format: Doctoral or Postdoctoral Thesis
• Language: unknown
• Published: 1989
• Subjects: Geology; Mineralogy; Geochemistry; Fairbanks; Gulf of Alaska; Aleutian Island; Beluga; Beluga*; Alaska
• Online Access: http://hdl.handle.net/11122/9348

Dissertation (Ph.D.) University of Alaska Fairbanks, 1989 Volcanic and non-volcanic partings occur in coal beds of the Neogene Beluga and Sterling Formations along the shores of the Kenai lowland, Alaska. The partings were systematically characterized to determine their potential geological applications: Two-thirds of the partings originated as air-fall tephra. Of these, partly altered, Pliocene tephra typically contain volcanic glass + feldspar $\pm$ montmorillonite $\pm$ quartz $\pm$ kaolinite $\pm$ opal-CT. Highly altered Miocene partings are characterized by feldspar $\pm$ kaolinite $\pm$ montmorillonite $\pm$ quartz $\pm$ crandallite $\pm$ altered volcanic glass, where crandallite appears to have formed by replacement of volcanic glass prior to clay formation. About one-third of the partings are of detrital origin and contain detrital chlorite + illite + smectite + quartz $\pm$ feldspar $\pm$ siderite $\pm$ kaolinite. A Pliocene pumice parting near the top of the Sterling Formation was correlated from the northwestern to the southeastern Kenai lowland on the basis of similar glass morphologies, an absence of opaque minerals, and geochemical similarities. A crystal-tuff near the middle of the section could be traced across the Kenai lowland as one or two ash-falls, based on inertinite contents of adjacent coal, mineralogy, and geochemistry. Some other prominent tephras could not be correlated. The tephra partings are time-equivalent to DSDP cores from the Gulf of Alaska and along the Aleutian Island chain. Tephras occur every 125-500 yr in the lower part of the Beluga Formation, and their deposition probably coincides with a volcanic pulse 10.5 m.y. ago. This pulse is not well recorded in nearby DSDP cores. In the upper part of the Beluga Formation, during volcanic quiescence, tephras are recorded at an average rate of one every 9,000 yr. Time equivalent DSDP cores show a near absence of tephras. A volcanic pulse occurred during the deposition of the lower Sterling Formation, about 7.5 m.y. ago, with ...