The Paleogene California River: Evidence of Mojave-Uinta paleodrainage from U-Pb ages of detrital zircons

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. INTRODUCTIONReconstructions 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. In the North American Cordillera, Paleogene drainage patterns indicated by paleofl ow measurements and sedimentary provenance have been used to infer paleotopography and episodes of tectonic transition (e.g., Dickinson et al., 1986;Elston and Young, 1991;Goldstrand, 1994;Henry, 2008;Lawton, 1986;Surdam and Stanley, 1980;Young and McKee, 1978).Only recently have studies begun to unravel the areal extent of Laramide watersheds. Oxygen, 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 infl ows from a large northern drainage beginning ca. 50 to ca. 49 Ma, which tapped areas at least as distant as central Idaho Chetel et al., 2010;Davis et al., 2009). Thus, at times during the Paleogene, southward-fl owing rivers were integrated along >1000 km of the Cordillera from central Idaho to the Uinta Basin in Utah. In contrast, paleofl ow directions in southern Utah and Arizona were consistently to the north and northeast during the early Paleogene, and the source of rivers has been generally assumed to reside in the proximal hinterland west of the Sevier thrust belt (e.g., Elston and Young, 1991;Goldstrand, 1994;Lawton, 1986;Young and McKee, 1978). A notable exception is the deltaic Colton Formation of the southern Uinta Basin, the large volume (>10 3 km 3 ) and arkosic composition of which, along with the geometry of foreland structures, led some of us (Dickinson et al., 1986) to propose a more distal source in the exposed Precambrian basement of south-central on June 23, 2015 geolo...

Eocene-Early Miocene paleotopography of the Sierra Nevada-Great Basin-Nevadaplano based on widespread ash-flow tuffs and paleovalleys

“…Howard (1996Howard ( , 2000 interpreted a large paleodrainage system to the southwest, to the Pacifi c Ocean, that would have been across the divide from these northeast-draining systems. In contrast, Davis et al (2010) proposed that a Late Paleocene-Early Eocene system drained northeastward from southeastern California to Utah, perpendicular to the drainage of Howard (1996Howard ( , 2000 ? ?…”

“…10 and 11). Davis et al (2010) interpreted that a Late Paleocene-Early Eocene drainage system (California River) extended northeast from southeastern California to northeastern Utah. In contrast, Howard (1996Howard ( , 2000 interpreted a Late Paleocene-Middle Miocene, ancestral Colorado River that drained southward across southeastern California, perpendicular to and across the drainage of Davis et al (2010), and then west to the Pacifi c Ocean (Fig.…”

A stress-rifting origin of Grand Canyon

“…Timing of the plateau uplift is poor, but there appears at least two phases of uplift, the most recent one is the last 5 Ma [11]. Driving mechanisms of plateau uplift have received considerable attention over the past four decades, since the broad acceptance of plate tectonics are still under debate [3]. When the geologic and geophysical data for the Plateau are considered, however, it seems likely that more than one mechanism is required to explain the 2 km of uplift [11].…”

“…However, plateaus can also develop in intraplate regions, such as the Colorado Plateau in the western America, the Ordos Block in China or the southern African Plateau [4]. North plateaus underwent a series of uplift processes, the most recent estimate of elevation increase is more than 2 km, which we believe to be relative to thermal expansion associated with lithospheric thinning and magmatic-related crustal thickening [3]. Karlstrom et al [5] suggested a static framework for incision of the Grand Canyon which envisions a previously elevated Colorado Plateau that was passively incised by a deepening canyon system (and progressive watertable lowering) in response to base-level fall.…”

“…However, the Colorado River is cut by dozens of faults which are orthogonal to the river [1,2]. Gravel layers found in western Grand Canyon suggest that the ancestral Colorado River once flowed to the north, in the opposite direction of the modern river from about 80 to 30 Ma [3]. This suggests that something about the river's surroundings changed during this period, and that the river may not be the dominant geomorphological factor.…”