Loading...
Thumbnail Image
Publication

First U-Pb zircon ages for late Miocene Ashfall Konservat-Lagersta¨tte and Grove Lake ashes from eastern Great Plains, USA

Smith, Jon J.
Turner, Elijah
Moller, Andreas
Joeckel, R. M.
Otto, Rick E.
Citations
Altmetric:
Abstract
This paper documents the first U-Pb zircon ages for Ashfall Fossil Beds (Nebraska, USA), a terrestrial Konservat-Lagersta¨ tte mass-death assemblage that is arguably the most diverse of its type and age. The Ashfall tephra was correlated with ignimbrites from the Bruneau-Jarbidge volcanic field (12.7–10.5 Ma) in southwest Idaho based on geochemical analysis. The methods and geochemical data supporting the original age assessment of the ash bed, however, were never published, and there has been a persistent misconception that dateable heavy minerals (e.g., zircon) are absent. Notwithstanding, we recovered abundant zircons from Ashfall Fossil Beds, and from an ash bed ~6 km to the southeast at Grove Lake, Nebraska, and analyzed them through LA-ICP-MS. Our new zircon U-Pb age of 11.86 ± 0.13 Ma substantiates correlation of the Ashfall Fossil Beds deposit to tuffs originating from the Bruneau-Jarbidge caldera (~12.7–10.5 Ma). Our U-Pb zircon age of 6.42 ± 0.06 Ma for the Grove Lake ash bed coincides with supervolcanic activity in the Heise volcanic field (6.6–4.3 Ma) in eastern Idaho. These new dates improve age constraints of strata comprising the Ogallala Group and the important paleontological site. Moreover, we find that detrital and airfall zircons are unevenly distributed in the stratified ash beds we describe herein and presumably in similar deposits worldwide. Therefore, a higher-resolution sampling scheme is necessary in such cases.
Description
Date
2018-11-08
Journal Title
Journal ISSN
Volume Title
Publisher
Public Library of Science
Research Projects
Organizational Units
Journal Issue
Keywords
Citation
Smith JJ, Turner E, Mo¨ller A, Joeckel RM, Otto RE (2018) First U-Pb zircon ages for late Miocene Ashfall Konservat-Lagersta¨tte and Grove Lake ashes from eastern Great Plains, USA. PLoS ONE 13(11): e0207103. https://doi.org/10.1371/ journal.pone.0207103
Embedded videos