Recently published thermochronological and paleoelevation studies in the Grand Canyon region, combined with sedimentary provenance data in both the coastal and interior portions of the North American Cordillera, place important new constraints on the paleohydrological evolution of the southwestern United States. Review and synthesis of these data lead to an interpretation where incision of a large canyon from a plain of low elevation and relief to a canyon of roughly the length and depth of modern Grand Canyon occurred primarily in Campanian time (80–70 Ma). Incision was accomplished by a main-stem, NE-flowing antecedent river with headwaters on the NE slope of the North American Cordillera in California, referred to herein after its source region as the California River. At this time, the river had cut to within a few hundred meters of its modern erosion level in western Grand Canyon, and to the level of Lower Mesozoic strata in eastern Grand Canyon. Subsequent collapse of the headwaters region into a continental borderland and coeval uplift of the Cordilleran foreland during the Laramide orogeny reversed the river's course by Paleogene time. After reversal, its terminus lay near its former source regions in what is now the Western Transverse Ranges and Salinian terrane. Its headwaters lay in the ancient Mojave/Mogollon Highlands region of Arizona and eastern California, apparently reaching as far northeast as the eastern Grand Canyon region. This system is herein referred to after its source region as the Arizona River. From Paleogene through late Miocene time, the interior of the Colorado Plateau was a closed basin separated from the Arizona River drainage by an asymmetrical divide in the Lees Ferry–Glen Canyon area, with a steep SW flank and gently sloping NE flank that drained into large interior lakes, fed primarily by Cordilleran/Rocky Mountain sources to the north and west, and by recycled California River detritus shed from Laramide uplifts on the plateau. By Oligocene time, the lakes had largely dried up and were replaced by ergs. By mid-Miocene time, a pulse of unroofing had lowered the erosion level of eastern Grand Canyon to within a few hundred meters of its present level, and the Arizona River drainage below modern Grand Canyon was deranged by extensional tectonism, cutting off the supply of interior detritus to the coast. Increasing moisture in the Rocky Mountains in late Miocene time reinvigorated fluviolacustrine aggradation NE of the asymmetrical divide, which was finally overtopped between 6 and 5 Ma, lowering base level in the interior of the plateau by 1500 m. This event reintegrated the former Arizona drainage system through a cascade of spillover events through Basin and Range valleys, for the first time connecting sediment sources in Colorado with the coast. This event, combined with the intensification of summer rainfall as the Gulf of California opened, increased the sediment yield through Grand Canyon by perhaps two orders of magnitude from its Miocene nadir, giving birth to the modern subcontinental-scale Colorado River drainage system. The Colorado River has thus played a major role in unroofing the interior of the Colorado Plateau, but was not an important factor in the excavation of Grand Canyon.

The California River and its role in carving Grand Canyon

The Cenozoic history of crustal deformation, surface uplift, and erosion of the central Colorado Plateau (southwestern USA) is distinct from and relatively poorly understood compared with surrounding regions in the North American Cordillera, including the Grand Canyon region and the southwestern Plateau margin. Here, we present new apatite thermochronologic results from Paleozoic-Mesozoic sandstones sampled in the Canyonlands region—the interior of the Colorado Plateau in southeastern Utah. The apatite (U-Th-Sm)/He (He) ages are highly dispersed, with both positive-slope and negative-slope age-effective U (eU) trends. Samples with apatite He results suitable for thermal history modeling are from the Abajo and La Sal mountains intrusive complexes and the Permian, Triassic, and Jurassic rocks sampled near the Colorado River at Lees Ferry, Arizona, and Hite, Utah. Samples with the richest thermal history information have positive-slope apatite He age-[eU] trends, with ages ca. 10 to 5 Ma at [eU] 60 ppm. Modeled thermal histories that best predict this pattern require two periods of rock cooling: one during the middle Cenozoic ca. 30 to 20 Ma and the other since the latest Miocene ca. 6 Ma. The most recent cooling documents the transition from a slowly eroding Miocene landscape to recent rapid erosion that likely postdates 6 Ma and the integration of the modern Colorado River. Middle Cenozoic rock cooling can be attributed to either ∼1 km of erosion between ca. 25 and 15 Ma, as previous workers have suggested in other parts of the Colorado Plateau region, or relaxation of a geothermal gradient transiently doubled by magmatism associated with the vigorous magmatic flare-up that swept through the region ca. 34 to 20 Ma. The ambiguity of using middle Cenozoic rock cooling as a proxy for erosion in this region means that this event should be described using a nongenetic term: the Middle Cenozoic Cooling Event.

The thermochronologic record of erosion and magmatism in the canyonlands region of the Colorado plateau

Die afghanischen Flamingobrutplatze am Ab-e-Istada und in der Dasht-e-Nawar wurden wahrend der Jahre 1970–72 regelmasig besucht. In diesen Zeitraum fiel eine extreme Durre, in deren Folge beide Seen 1971 vollig austrockneten. In der Dasht-e-Nawar hatte sich der Wasserstand nach zwei Jahren noch nicht soweit normalisiert, das eine erfolgreiche Flamingobrut stattfinden konnte. Am Ab-e-Istada begannen die Flamingos 1970 und 1972 zwar das Brutgeschaft, wurden aber durch Menschen vergramt, denen niedriger Wasserstand Zutritt zur Brutinsel ermoglichte. Fur diesen See konnteCharadrius leschenaultii als Brutvogel neu nachgewiesen werden. Weiterhin werden Beobachtungen zur Unterwasserfauna und Beobachtungen von Herbstdurchzuglern mitgeteilt.

Beobachtungen an den Flamingobrutplätzen Afghanistans

From the mid-nineteenth through twentieth centuries, geologists attained a good, if imperfect, view of the development of the Colorado River and the Grand Canyon. Beginning in the late 1850s and continuing through the 1880s, fundamental concepts such as fluvialism, antecedence, and superposition were invoked to explain the development of the Colorado River. Early proposals envisioned the Colorado River as “old” relative to the surrounding landscape. Challenges to antecedence were slow to emerge, and it remained the most viable theory into the early twentieth century. At that time two distinct periods (and styles) of erosion were proposed: a plateau cycle with lateral stripping of strata and a canyon cycle of deep, vertical dissection. Beginning in the 1930s, newer ideas proposed that the Colorado River was “young, ” having been integrated by sequential basin spillover, the timing of which was constrained by interior basin deposits lying across the mouth of the Grand Canyon at the Grand Wash Cliffs (the Muddy Creek constraint). The field entered a period of uncertainty related to the conflicting evidence for an old (Paleogene) river upstream from the Grand Canyon versus a young (Neogene) river at Grand Wash Cliffs. Results from a symposium convened in 1964 offered a solution with a poly-phase history for the Colorado River. The poly-phase theory suggested that the river formed in a complex manner by the integration of two separate drainages, although some aspects became untenable. Efforts to resolve outstanding dilemmas from 1964, such as the ages of the Colorado River and the Grand Canyon, have ultimately led to a modern resurgence in research.

/pdf/a-pre-21st-century-history-of-ideas-on-the-origin-of-the-26pu2xn6xw.pdf

A pre–21st century history of ideas on the origin of the Grand Canyon

The Green River’s turn south from Browns Park to cut Canyon of Lodore and cross the eastern Uinta uplift is one of the most famous and long-debated drainage anomalies. For the river to flow towards and then cross the Laramide uplift, some combination of antecedence, superposition, or stream capture must have occurred in later Cenozoic time. This review of the history of ideas on how and when this happened, especially the extensive work of Wally Hansen, provides a new hypothetical scenario of events that combines previous ideas.

http://archives.datapages.com/data/uga/data/076/076001/pdfs/149.pdf

Revisiting the Classic Conundrum of the Green River’s Integration through the Uinta Uplift

/pdf/the-origin-of-green-river-mfwiq0lam9.pdf

S. F. Emmons

Papers

The origin of green river.

The Leadville porphyry.