Constraints on the history and topography of the Northeastern Sierra Nevada from a Neogene sedimentary basin in the Reno

Neogene (Miocene-Pliocene) sedimentary rocks of the northeastern Sierra Nevada were deposited in small basins that formed in response to volcanic and tectonic activity along the eastern margin of the Sierra.

These strata record an early phase (about 10-11 million years ago) of extension and rapid sedimentation of boulder conglomerates and debrites deposited on alluvial fans, followed by fluvio-lacustrine sedimentation and nearby volcanic arc activity but tectonic quiescence, until about 2.6 million years ago.

The fossil record in these rocks documents a warmer, wetter climate featuring large mammals and lacking the Sierran orographic rain shadow that dominates climate today on the eastern edge of the Sierra.

This record is consistent with evidence that there was no significant topographic barrier between the Pacific Ocean and the interior of the continent east of the Sierra before about 2.6 million years ago.

However, these sediments do not record an integrated drainage system either to the east into the Great Basin like the modern Truckee River, or to the west across the Sierra like the ancestral Feather and Yuba rivers.

The Neogene Reno-Verdi basin was one of several, scattered endorheic (i.e., internally drained) basins occupying this part of the Cascade intra-arc and back-arc area.

More information:
James Trexler et al., Dept. of Geological Sciences and Engineering, MS 172, University of Nevada, Reno, Reno, Nevada 89557, USA. Posted online 11 April; doi: 10.1130/GS735.1

Provided by Geological Society of America