Abstract
U-Pb age spectra of detrital zircons in samples from the Paleogene Colton Formation in the Uinta Basin of northeastern Utah and the Late Cretaceous McCoy Mountains Formation of southwestern Arizona (United States) are statistically indistinguishable. This fi nding refutes previous inferences that arkosic detritus of the Colton was derived from cratonic basement exposed by Laramide tectonism, and instead establishes the Cordilleran magmatic arc (which also provided sediment to the McCoy Mountains Formation) as the primary source. Given the existence of a north-south‐trending drainage divide in eastern Nevada and the north-northeast direction of Laramide paleofl ow throughout Arizona and southern Utah, we infer that a large river system headed in the arc of the Mojave region fl owed northeast ~700 km to the Uinta Basin. Named after its source area, this Paleogene California River would have been equal in scale but opposite in direction to the modern Green River‐Colorado River system, and the timing and causes of the subsequent drainage reversal are important constraints on the tectonic evolution of the Cordillera and the Colorado Plateau.
Highlights
Reconstructions of regional paleodrainage provide direct evidence of paleogeography and landscape evolution, in turn constraining tectonic models and informing isotopic analyses of past climate and altitude that are affected by the source of surface waters
(1) Paleocurrent measurements, clast compositions, and the distribution of ash-flow tuffs all indicate that a north-south–trending drainage divide existed in eastern Nevada during the Paleogene (e.g., Christensen and Yeats, 1992; Henry, 2008)
(2) Paleocurrent measurements in numerous studies have shown that Paleogene river networks in southern Utah and Arizona flowed north-northeast (Elston and Young, 1991; Goldstrand, 1994; Lawton, 1986; Young, 2008; Young and McKee, 1978)
Summary
Reconstructions of regional paleodrainage provide direct evidence of paleogeography and landscape evolution, in turn constraining tectonic models and informing isotopic analyses of past climate and altitude that are affected by the source of surface waters. Strontium, and lead isotope records from Eocene Green River lake deposits have demonstrated that the lakes (in southern Wyoming, northwest Colorado, and northeast Utah; Fig. 1) received inflows from a large northern drainage beginning ca.
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