Document Type

Article

Journal/Book Title/Conference

Geology

Volume

49

Issue

6

Publisher

Geological Society of America

Publication Date

2-22-2021

Journal Article Version

Version of Record

First Page

1

Last Page

21

Abstract

Sanidine dating and magnetostratigraphy constrain the timing of integration of the lower Colorado River (southwestern United States and northern Mexico) with the evolving Gulf of California. The Colorado River arrived at Cottonwood valley (Nevada and Arizona) after 5.24 Ma (during or after the Thvera subchron). The river reached the proto–Gulf of California once between 4.80 and 4.63 Ma (during the C3n.2r subchron), not at 5.3 Ma and 5.0 Ma as previously proposed. Duplication of section across newly identified strands of the Earthquake Valley fault zone (California) probably explains the discrepancy. The data also imply the start of focused plate motion and basin development in the Salton Trough (California) at 6–6.5 Ma and relative tectonic stability of the southernmost part of the lower Colorado River corridor after its integration. After integration, the Colorado River quickly incised through sediment-filled basins and divides between them as it also likely excavated Grand Canyon (Arizona). The liberated sediment from throughout the system led to deposition of hundreds of meters of Bullhead Aluvium downstream of Grand Canyon after 4.6 Ma as the river adjusted to its lower base level.

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