Provenance and palaeogeographic implications of Eocene–Oligocene sedimentary rocks in the northwestern Basin and Range

Abstract

A thick sequence of uppermost Eocene to lower Oligocene volcaniclastic and sedimentary rocks is exposed at the base of the Warner Range in northeastern California. This isolated exposure provides insight into the palaeogeographic setting of the northwestern Basin and Range during this time period. Significant thinning of the unit over 35 km of lateral exposure and predominantly volcanic clast compositions suggest that the sequence was deposited in an alluvial plain adjacent to a volcanic arc. Palaeocurrent indicators in the conglomerates define a NNE transport direction. Detrital zircon analysis on coarse sandstones and dating of individual granite cobbles show a range of ages consistent with a local, volcanic source area primarily from the SSW with some far-travelled input from northern Nevada; the far-travelled component increases in influence as the unit thins to the north. Comparison with other sedimentary sequences of Eocene age and integration with palaeofloral and geophysical data help to define drainage divides, and suggest that this sequence accumulated in a relatively isolated, intra-arc basin. This localized accumulation differs markedly from contemporaneous drainages to the south that transported material westwards from central Nevada to the palaeoshoreline, and suggests that ongoing volcanism had a strong influence on palaeogeography in this region during the Eocene and Oligocene.

Keywords:

• Warner Range
• detrital zircon geochronology
• Oligocene palaeogeography
• Basin and Range
• Steamboat Formation
• volcaniclastic sandstone

Acknowledgements

The authors thank Marty Grove and Jim Wright for running one detrital sample on the LA-ICP-MS at the University of Arizona and Kathy Surpless for dating three cobbles from the core on the SHRIMP-RG. Marty Grove, Ariel Strickland, and Joe Wooden provided invaluable help in running the remaining samples and reducing the data. Chris Henry and Joe Wooden provided timely reviews and discussions that greatly improved the manuscript.

Notes

^1. [email protected]

^2. Now at Department of Geology, University of Wyoming, Laramie, WY 82070, USA. [email protected]

Additional information

Notes on contributors

Joseph P. Colgan

1. 1. [email protected]

Carly York

2. 2. Now at Department of Geology, University of Wyoming, Laramie, WY 82070, USA. [email protected]