TY - JOUR
T1 - Revised chronostratigraphy and biostratigraphy of the early-middle Miocene Railroad Canyon section of central-eastern Idaho, USA
AU - Harris, Elisha B.
AU - Strömberg, Caroline A.E.
AU - Sheldon, Nathan D.
AU - Smith, Selena Y.
AU - Ibañez-Mejia, Mauricio
N1 - Funding Information:
We would like to thank C. Trinh-Le, A. Padgett, C. Bitting, E. Fredrickson, K. Smith, A. Jijina, T.-Y. Le, J. Benca, M. Dennis, and E. Hyland for field assistance during this project. Additionally, we thank R.E. Dunn for laboratory support and assistance with paleomagnetic correlation, A.D. Barnosky for assistance acquiring field notes and general discussion about the Railroad Canyon section, and the Arizona LaserChron and MIT-IG laboratories for making their analytical facilities available to Ibañez-Mejia for zircon U-Pb analysis. Finally, we would like to thank Brad Singer, A.E. Troy Rasbury, and two anonymous reviewers for their comprehensive and thorough reviews of the manuscript. Funding for this project was provided by National Science Foundation grants EAR-1024681 to C.A.E. Strömberg, and EAR-1024535 to N.D. Shel-don and S.Y. Smith, an Evolving Earth Foundation grant to Harris, and a University of Washington Biology Iuvo Award to Harris, as well as funding from the Burke Museum of Natural History and Culture.
Publisher Copyright:
© 2017 Geological Society of America.
PY - 2017/9/1
Y1 - 2017/9/1
N2 - 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 highprecision U-Pb dating of single zircon crystals from four ash horizons throughout the section. The resulting dates span from 22.65 ± 0.37 Ma to 15.76 ± 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, ~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.
AB - 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 highprecision U-Pb dating of single zircon crystals from four ash horizons throughout the section. The resulting dates span from 22.65 ± 0.37 Ma to 15.76 ± 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, ~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.
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U2 - 10.1130/B31655.1
DO - 10.1130/B31655.1
M3 - Article
AN - SCOPUS:85028848330
SN - 0016-7606
VL - 129
SP - 1241
EP - 1251
JO - Bulletin of the Geological Society of America
JF - Bulletin of the Geological Society of America
IS - 9-10
ER -