Publications

Definition: 40Ar/39Ar geochronology of structural fabrics: The application of 40Ar/39Ar methods to date development of structural fabrics in geologic samples. Introduction: Structural fabrics develop during rock deformation at variable pressures (P), temperatures (T), fluid compositions (X), and time (t). Structural fabrics are represented in rocks by features such as foliations and...

Foraminiferal assemblages in the stratigraphically lower part of the Bouse Formation in the Blythe Basin indicate marine conditions whereas assemblages in the upper part of the Bouse Formation indicate lacustrine conditions and suggest the presence of a saline lake. Benthic foraminiferal assemblages in the lower part of the Bouse Formation are similar to lagoonal and inner neritic...

The Lisburne Group (Carboniferous-Permian) consists of a carbonate platform that extends for >1000 km across northern Alaska, and diverse margin, slope, and basin facies that contain world-class deposits of Zn and Ba, notable phosphorites, and petroleum source rocks. Lithologic, paleontologic, isotopic, geochemical, and seismic data gathered from outcrop and subsurface studies during the...

Vermiculite comprises a group of hydrated, laminar magnesium-aluminum-iron silicate minerals resembling mica. They are secondary minerals, typically altered biotite, iron-rich phlogopite or other micas or clay-like minerals that are themselves sometimes alteration products of amphibole, chlorite, olivine and pyroxene. Vermiculite deposits are associated with volcanic ultramafic rocks...

Rock falls from steep, exfoliating cliffs are common in many landscapes. Of the many mechanisms known to trigger rock falls, thermally driven deformation is among the least quantified, despite potentially being a prevalent trigger due to its occurrence at all times of year. Here we present the results of a field-based monitoring program using instrumentation, ground-based lidar, and...

This study estimates the location, quality, and quantity of undiscovered copper in stratabound deposits within the Neoproterozoic Roan Group of the Katanga Basin in the Democratic Republic of the Congo and Zambia. The study area encompasses the Central African Copperbelt, the greatest sediment-hosted copper-cobalt province in the world, containing 152 million metric tons of copper in...

Narraguinnep Reservoir in southwestern Colorado is one of several water bodies in Colorado with a mercury (Hg) advisory as Hg in fish tissue exceed the 0.3 μg/g guideline to protect human health recommended by the State of Colorado. Concentrations of Hg and methyl-Hg were measured in reservoir bottom sediment and pore water extracted from this sediment. Rates of Hg methylation and methyl...

The purpose of this report is to make available a large body of conventional K-Ar ages for granitic, volcanic, and metamorphic rocks collected in southern California. Although one interpretive map is included, the report consists primarily of a systematic listing, without discussion or interpretation, of published and unpublished ages that may be of value in future regional and other...

The eastern San Francisco Bay region (Contra Costa and Alameda Counties, California) is a geologically complex area divided by faults into a suite of tectonic blocks. Each block contains a unique stratigraphic sequence of Tertiary sediments that in most blocks unconformably overlie Mesozoic sediments. Age and environmental interpretations based on analysis of microfossil assemblages are...

Geologist Charles Frankel's Land and Wine: The French Terroir is not so much a scientific exposé as it is a beautifully described love triangle involving wine, rocks, and French history.

This report provides a descriptive model of heavy-mineral sands, which are sedimentary deposits of dense minerals that accumulate with sand, silt, and clay in coastal environments, locally forming economic concentrations of the heavy minerals. This deposit type is the main source of titanium feedstock for the titanium dioxide (TiO2) pigments industry, through recovery of the minerals...

Since 1998, the structure of the lead recycling industry has changed and trade patterns of the domestic lead recycling industry have shifted. Although the domestic demand for lead has remained relatively constant since 1998, production of lead has increasingly shifted to the domestic secondary lead industry. The last primary lead smelter in the United States closed at the end of 2013, at...