T67 From the Afar Rift to Alaskan Arcs (and the Oregon Plateau in between): Honoring the Career and Contributions of William K. Hart

Monday, 11 October 2021
8:00 AM - 12:00 PM
Portland Ballroom 254 (Hybrid Room)

NEW MAPPING AND TEPHROCHRONOLOGY AT HAGERMAN FOSSIL BEDS NATIONAL MONUMENT, IDAHO, USA - A PROJECT DECADES IN THE MAKING

Paper number: T67-11
Program: Technical Sessions
Time: 10:30 AM – 10:50 AM

Authors

Abstract

Hagerman Fossil Beds National Monument (HAFO) is a rich Pliocene fossil site located in southern Idaho, USA. The monument contains three geologic formations but is dominated by the Pliocene Glenns Ferry Formation, which is comprised primarily of fluvial-lacustrine deposits with numerous interbedded silicic and basaltic tephra and two basaltic lava flow units.

New and updated tephrochronology provides additional data on the geochemical composition of the tephra units at HAFO, resulting in new and revised correlations and a high-resolution temporal framework for currently known and potential future fossil sites. Previous studies identified four silicic tephra (informally named the lower lapilli, Peters Gulch ash layer, Fossil Gulch ash layer, and Horse Quarry ash layer) and six basaltic tephra (informally named beds E, F, G, H, I, and J) within the monument. In addition, previous research either focused on broad regional mapping or on smaller, defined areas within or adjacent to HAFO. In comparison, we conducted detailed mapping and geochemical characterization of tephra deposits throughout nearly the entire eighteen-square-kilometer national monument.

Extension of the mapped areal distribution and correlation of tephra layers was achieved using standard field mapping techniques as well as new and updated major, minor, and trace element volcanic glass data obtained utilizing single-shard electron microprobe (EMP) and bulk purified glass inductively coupled plasma – mass spectrometry (ICP–MS) techniques. We have also identified and characterized four additional silicic tephra units (informally named the PPE ash layer, the rattlesnake ash layer, an unnamed silicic ash layer, and the Oregon Trail ash layer) and three additional basaltic tephra layers (informally named bed E2, bed F2, and bed F3). New Sr, Pb, and Nd isotopic data provide insight into the provenance of these tephra and revised dates provide refined age control, allowing us to better constrain the temporal context for associated stratigraphic units and fossil assemblages.

Geological Society of America Abstracts with Programs. Vol. 53, No. 6

doi: 10.1130/abs/2021AM-364824

© Copyright 2021 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.