February Geosphere media highlights

Late Cenozoic paleogeographic evolution of northeastern Nevada: Evidence from the sedimentary basins
Alan R. Wallace, et al., U.S. Geological Survey, MS 176, Mackay School of Earth Sciences and Engineering, University of Nevada, Reno, Reno, Nevada 89557, USA.
Keywords: sedimentary basins, tectonics, geomorphology, Nevada, Miocene, Pliocene, gold, Humboldt River.

New geologic and dating studies along a 200-km-long transect across northeastern Nevada has led a better understanding of how the landscape has changed over the past 20 million years (m.y.). The studies focused on four sedimentary basins along the transect (Chimney, Ivanhoe, Carlin, and Elko, from west to east) because they record events, such as the formation of mountains and erosion by streams, that produced the landscape changes over time. The landscape was a subdued, eroding upland until about 16 m.y. ago, when volcanic eruptions in the western half of the transect and faulting in the eastern half dammed streams and formed the sedimentary basins. These basins gradually filled up and partially buried adjacent highlands. The dams for the western three basins failed after about 2 m.y., and the streams integrated into the beginnings of the Humboldt River drainage system. The Elko basin remained isolated until about 10 m.y., at which point it began to drain to the west into the Humboldt system. The river system flowed westward into northwestern Nevada, where active faulting was forming deepening valleys. As a result, the basin sediments in the upstream areas have been eroding and carried to the new downstream basins. This erosion has re-exposed the pre-basin highlands, so some modern ranges are fairly old rather than young as previously thought. Similarly, major mineral deposits in the upstream areas gradually have been exposed, weathered, or eroded, whereas those in downstream areas have been covered up. This concept is very important for the evaluation of and exploration for mineral deposits in the region.

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