Tephrochronology in the La Sal Mountains, Utah, USA

• Applicant: Professor Dr. Arno Kleber
• Subject Area: Physical Geography
• Term: from 2014 to 2017
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 261893142

A tephra layer in a roadcut in the La Sal Mountains, USA, was identified as an educt of the Guaje Tephra, which erupted some 1.65 Ma ago in the Jemez Mountains, New Mexico, USA. Previous work has provided evidence that this tephra layer might be in a second position, i.e. it might have been reworked long after its first deposition. Components - involving heavy minerals, volcanic glasses, and grain sizes - that likely have been derived from the tephra were identified much deeper in the profile than the distinct tephra layer itself. Despite of this presumed reworking, the layer has not been remarkably contaminated by surrounding materials. Such pure tephra is usually interpreted to be in first deposition. If this layer actually has been reworked, it is not suitable as a tephrochronological tool. The project intends to clearify whether this tephra layer has been reworked and deposited long after its eruption and first accumulation or whether there is just shear coincidence of different volcanic ejecta using electron microprobe, EDX, and zircon dating. Should there be support for the reworking hypothesis, tephrochronological findings must be treaded much more warily than to date.

• DFG Programme: Research Grants
• Participating Person: Professor Dr. Ulf-Gerhard Linnemann