T157 Near Surface Geophysics to Solve Geological Problems

Tuesday, 24 September 2024
8:00 AM - 12:00 PM
303A

MAGNETIC TRACING OF LOST TIME IN CENOZOIC SEDIMENTS FROM THE NORTHERN ROCKY MOUNTAINS, USA

Paper number: T157-13
Program: Technical Sessions
Time: 10:50 AM – 11:05 AM

Authors

Abstract

The early Miocene unconformity (EMU) occurred during a critical transition in the tectonic evolution of western North America, with profound impact on faunal biogeography and diversification. The Railroad Canyon section (RCS) in the northern Rocky Mountains provides the most complete geologic record of this period. There, our new magnetostratigraphic study in combination with published radiometrically-dated ash layers places the EMU at ~20.1 Ma with a duration of 0.1 – 1.0 Myr. The EMU is marked throughout SW Montana by a distinct change in color, an abrupt increase in magnetite concentration, and a sharp drop in carbonate abundance. Curiously, sedimentation rate in the RCS remains constant at 6.5 ± 0.1 cm/kyr through the unconformity, as do climate proxies. Alternative hypotheses to account for these observations consider (1) the exposure of magnetite-rich basement and/or (2) a change in drainage network. Both can be caused by a change in tectonic regime such as the onset of Basin and Range extension, the arrival of the Yellowstone plume, etc.

Geological Society of America Abstracts with Programs. Vol. 56, No. 5

doi: 10.1130/abs/2024AM-400712

© Copyright 2024 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.