Date:12/28/2012

ckinson considers and rejects the hypothesis that incision of the Grand Canyon was initiated by spillover of water from a supposedly deep lake that formed in north-central Arizona east of the Kaibab-Coconino Plateau and was filled by inflow of water from the upper Colorado River in Utah. Consideration of the morphology and history of the Colorado River drainage system as a whole supports the alternative hypothesis that an ancestral Miocene Colorado River cut a shallow canyon through the Kaibab-Coconino Plateau but exited into the Virgin River drainage north of the mouth of the present Grand Canyon. Subsequent headward erosion upstream from the Grand Wash Cliffs was capable of carving the lower Grand Canyon to capture the ancestral Colorado River near the geographic center of the modern Grand Canyon, thereby integrating the courses of the upper and lower Colorado Rivers for the first time near the Miocene-Pliocene time boundary some five million years ago. Thereafter, river flow along its present course deepened and widened the full Grand Canyon.

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Identifying origins of and pathways for spring waters in a semiarid basin using He, Sr, and C isotopes: Cuatrocinegas Basin, Mexico
B.D. Wolaver et al., Bureau of Economic Geology, The University of Texas at Austin, 10100 Burnet Road, Austin, Texas 78758, USA. Posted online 13 Dec. 2012; http://dx.doi.org/10.1130/GES00849.1.

This study by B.D. Wolaver and colleagues presents the first dissolved noble gas and He isotopic data from northeastern Mexico. Helium, carbon, and strontium isotopes are used to infer spring sources in a water-stressed area. Spring-water origins and pathways in the Cuatrocinegas Basin are revealed by linking structure and geochemistry via regionally extensive fault networks. Basement involved faults with complex reactivation histories are important in northeastern Mexico tectonics and affect hydrogeolog
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Contact: Kea Giles kgiles@geosociety.org Geological Society of America Source:Eurekalert

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