February Geosphere media highlights

This paper uses LIDAR for mapping active surface faults in Houston, Texas. These faults result in damages to houses, pipelines, roads and other constructions. Accurate mapping of their locations therefore aids in hazard mitigation.

Ash-flow tuffs and paleovalleys in northeastern Nevada: Implications for Eocene paleogeography and extension in the Sevier hinterland, northern Great Basin
Christopher D. Henry, Nevada Bureau of Mines and Geology, University of Nevada, Reno, Nevada 89557.
Keywords: paleogeography, extension, Eocene, ash-flow tuff, Nevada

The distribution of distinctive volcanic and sedimentary rocks indicates that northeastern Nevada 40 million years ago was a high plateau, possibly 4 kilometers (13,000 feet) high, incised with deep valleys. Rivers in the valleys on opposite sites of a “paleo-continental divide” that ran approximately north-south slightly west of Elko, Nevada, drained either westward to the Pacific Ocean or eastward to large basins in Utah. The high plateau probably resulted from thickening of the crust following a long period of folding that ended about 60 million years ago. The plateau was probably similar to parts of the modern Andes Mountains of South America or Tibet.

Magmatic and tectonic evolution of the Caetano Caldera, north-central Nevada: A tilted, mid-Tertiary eruptive center and source of the Caetano Tuff
David A. John et al., U.S. Geological Survey, 345 Middlefield Road, Menlo Park, California 94025, USA.
Keywords: calderas, ash-flow tuff, magma resurgence, Basin and Range Province, extensional tectonics

The Caetano caldera in north-central Nevada formed during a supervolcano eruption of greater than 1100 cubic kilometers (greater than 270 cubic miles) of Caetano Tuff about 33.8 million years ago. The caldera formed by when the roof of the magma chamber collapsed as the Caetano Tuff erupted from the chamber. Collapse left an ovoid depression, a caldera, about 20 kilometers long by 12 to 18 kilometers wide and up to 1 kilometer deep. Due to younger faulting and tilting (see companion paper by Colgan and others in the same issue of Geosphere), the caldera was broken into several blocks that expose caldera features from the former surface to a depth of more than 5 kilometers. This extraordinary three-dimensional view allows a far more detailed analysis of caldera formation and evolution than is available for almost any other caldera in the world. Reconstruction of the Caetano caldera also constrains nearby Carlin-type gold deposits, presently the largest producing gold deposits in the United States, to have formed at depths of less than or equal to 1 kilometer.

Outcrop fracture characterization using terrestrial laser scanners: Deep-water Jackfork sandstone at Big Rock Quarry, Arkansas
Mariana I. Olariu et al.; John F. Ferguson, corresponding author, Geosciences Department, University of Texas at Dallas, P.O. Box 830688, Mail Station FO21, Richardson, Texas 75083-0688, USA.
Keywords: cluster analysis, fractures, turbidite, outcrop, lidar, laser scanner, laser.