Magnetostratigraphy and Source Characterisation Across the Early Miocene Unconformity, Northern Rocky Mountains, USA

Gerritsen, Dieke ; Gilder, Stuart A. ; Ludat, Alina L. und Wack, Michael R. (2026): Magnetostratigraphy and Source Characterisation Across the Early Miocene Unconformity, Northern Rocky Mountains, USA. In: Terra Nova, Vol. 38, No. 1: pp. 1-8

Abstract

The early Miocene unconformity (EMU) formed during a transition in the tectonic regime of western North America that coincided with faunal diversification. The Railroad Canyon section in the northern Rocky Mountains provides a complete geologic record around this event. Our new magnetostratigraphic study in combination with published U-Pb ages from intercalated ash places the end of the EMU at ~20.1 Ma with a duration of up to 1.5 Myr. The EMU is marked by an abrupt change in rock colour, an increase in magnetite concentration, and a decrease in calcite abundance. Average sedimentation rates are similar above and below the EMU, as are climate proxies; therefore, the changes in mineralogy likely reflect a reorganisation in sediment source. Drainage network reorganisation seemingly contributed to this, possibly related to a change in tectonic regime, such as the onset of Basin and Range extension and/or arrival of the Yellowstone plume.

• Item Type: Journal article
• Faculties: Geosciences > Department of Earth and Environmental Sciences > Geology
• Subjects: 500 Science > 550 Earth sciences and geology
• ISSN: 0954-4879
• Language: English
• DFG: Gefördert durch die Deutsche Forschungsgemeinschaft (DFG) - 440512084
• DFG: Gefördert durch die Deutsche Forschungsgemeinschaft (DFG) - 518204048