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Revised chronostratigraphy and biostratigraphy of the early-middle Miocene Railroad Canyon section of central-eastern Idaho, USA

Elisha B. Harris, Caroline A. E. Stroemberg, Nathan D. Sheldon, Selena Y. Smith and Mauricio Ibanez-Mejia
Revised chronostratigraphy and biostratigraphy of the early-middle Miocene Railroad Canyon section of central-eastern Idaho, USA
Geological Society of America Bulletin (June 2017) 129 (9-10): 1241-1251

Abstract

The early-middle Miocene was an important transitional period in the evolution of Earth's biota and climate that has been poorly understood in North America due to a paucity of continuous, fossil-bearing rock records in this interval for which the ages have been robustly constrained. In the northern Rocky Mountains, United States, one site in particular, known as the Railroad Canyon section, has provided biostratigraphic, magnetostratigraphic, and lithostratigraphic evidence suggesting a late early-middle Miocene age; however, radiometrically calibrated age models have been notoriously lacking. To better constrain the age of the Railroad Canyon section and the abundant fossils preserved therein, we employed moderate- and high-precision U-Pb dating of single zircon crystals from four ash horizons throughout the section. The resulting dates span from 22.65 + or - 0.37 Ma to 15.76 + or - 0.22 Ma. Using these dates, we developed a radiometrically calibrated age model for the Railroad Canyon section that constrains the age of the section to ca. 22.9-15.2 Ma, approximately 5 m.y. older than previous estimates. These results firmly establish that the Railroad Canyon section was deposited during buildup to peak warming of the mid-Miocene climatic optimum. Additionally, these dates provide definitive age estimations for the initiation and cessation of the early Miocene unconformity, a regional unconformity exposed in many intermontane basins across the northern Rocky Mountains, as ca. 21.5 and 21.4 Ma, respectively, in the Railroad Canyon section. This new chronostratigraphic analysis provides an impetus for reassessment of the biochronology of the region, in turn suggesting earlier first appearances of many biostratigraphically important taxa found in the northern Rocky Mountains, Great Plains, and American Northwest.


ISSN: 0016-7606
EISSN: 1943-2674
Coden: BUGMAF
Serial Title: Geological Society of America Bulletin
Serial Volume: 129
Serial Issue: 9-10
Title: Revised chronostratigraphy and biostratigraphy of the early-middle Miocene Railroad Canyon section of central-eastern Idaho, USA
Affiliation: University of Washington, Department of Biology, Seattle, WA, United States
Pages: 1241-1251
Published: 20170623
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
Accession Number: 2017-090178
Categories: StratigraphyGeochronology
Document Type: Serial
Bibliographic Level: Analytic
Annotation: GSA Data Repository item 2017184
Illustration Description: illus. incl. 1 table, sketch map
N44°15'00" - N45°45'00", W114°49'60" - W112°49'60"
Secondary Affiliation: University of Michigan, USA, United StatesMassachusetts Institute of Technology, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute.
Update Code: 201747
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