Paper No. 6
Presentation Time: 9:00 AM-6:00 PM
THE EVOLUTION OF ‘HYPOGENE KARST' LANDSCAPES FROM SPELEOTHEMS OF LATE STAGE HYPOGENE SPELEOGENESIS: EXAMPLES FROM GRAND CANYON, ARIZONA AND GLENWOOD CANYON, COLORADO
The Basin and Range and Colorado Plateau provinces are areas ideal for origin of caves formed by hypogene speleogenesis. The limestone/dolostone terrains that host these hypogene caves are examples of ‘hypogene karst’ landscapes, which are characterized as landscapes that exhibit little evidence of typical karst on the surface, but significant evidence of karst in the subsurface. An example of this is the Guadalupe Mountains area where few sinkholes exist on the surface, even though significant cave development occurred in the subsurface such as the speleogenesis that formed Lechuguilla Cave and Carlsbad Cavern. The evolution of hypogene karst landscapes can be recorded to some degree in the speleothems that formed during the latest stages of hypogene speleogenesis. Two examples of this relate to canyon incision history from the study of water-table-type speleothems such as cave mammillaries, folia, rafts, and gypsum rinds. These speleothem types, in intimate association with each other, are evidence of a water table environment. These speleothem types are present in caves in Grand Canyon, Arizona and Glenwood Canyon, Colorado. Determining the age of any one of these speleothem types places paleo-water table positions at different locations and elevations within these canyons. The paleo-water tables track the elevation of the canyon-cutting river over time, thus providing a history of canyon incision. Four million years of Grand Canyon incision history are provided by U-Pb dating of mammillary calcite collected from 100 to 900 meters above the Colorado River, and evidence of water tables older than six million years exist in western Grand Canyon (Polyak et al. 2008). U-Th dating, rather than U-Pb, is currently being applied to speleothems from Glenwood Canyon. These speleothems were collected 65 to 400 meters above the Colorado River. In Glenwood Canyon, incision rates of the Colorado River are matching previously published results, and these newly acquired results from the U-Th dating of mammillary calcite illustrate the usefulness of using speleothems formed during late stage hypogene speleogenesis.
Polyak, V.J., Hill, C.A., and Asmerom, Y., 2008, 2008, Age and evolution of the Grand Canyon revealed by U-Pb dating of water table–type speleothems, Science, v. 319, p. 1377-1380.