Publications

The Lawlor Tuff is a widespread dacitic tephra layer produced by Plinian eruptions and ash flows derived from the Sonoma Volcanics, a volcanic area north of San Francisco Bay in the central Coast Ranges of California, USA. The younger, chemically similar Huichica tuff, the tuff of Napa, and the tuff of Monticello Road sequentially overlie the Lawlor Tuff, and were erupted from the same...

High-resolution aeromagnetic surveys are now an industry standard and they commonly detect anomalies that are attributed to faults within sedimentary basins. However, detailed studies identifying geologic sources of magnetic anomalies in sedimentary environments are rare in the literature. Opportunities to study these sources have come from well-exposed sedimentary basins of the Rio...

High-sulfidation copper–gold lode deposits such as Chinkuashih, Taiwan, Lepanto, Philippines, and Goldfield, Nevada, formed within 1500 m of the paleosurface in volcanic terranes. All underwent an early stage of extensive advanced argillic silica–alunite alteration followed by an abrupt change to spatially much more restricted stages of fracture-controlled sulfide–sulfosalt mineral...

Gneissic pegmatitic leucogranite forms a dominant component (>600 km3) of the midcrustal infrastructure of the Ruby Mountains–East Humboldt Range core complex (Nevada, USA), and was assembled and modified episodically into a batholithic volume by myriad small intrusions from ca. 92 to 29 Ma. This injection complex consists of deformed sheets and other bodies emplaced syntectonically into...

Concentrations of geogenic Cr(VI) in groundwater that exceed the World Health Organization’s maximum contaminant level for drinking water (50 μg L−1) occur in several locations globally. The major mechanism for mobilization of this Cr(VI) at these sites is the weathering of Cr(III) from ultramafic rocks and its subsequent oxidation on Mn oxides. This process may be occurring in the...

The Warner Range in northeastern California exposes a section of Tertiary rocks over 3 km thick, offering a unique opportunity to study the long-term history of Cascade arc volcanism in an area otherwise covered by younger volcanic rocks. The oldest locally sourced volcanic rocks in the Warner Range are Oligocene (28–24 Ma) and include a sequence of basalt and basaltic andesite lava...

Permafrost contains an estimated 1672 Pg carbon (C), an amount roughly equivalent to the total currently contained within land plants and the atmosphere1,2,3. This reservoir of C is vulnerable to decomposition as rising global temperatures cause the permafrost to thaw2. During thaw, trapped organic matter may become more accessible for microbial degradation and result in greenhouse gas...

We report remanent magnetization measurements from 13 sites in Cretaceous plutonic rocks in the northern Sierra Nevada (38°N–39.5°N). By increasing the number of available paleomagnetic sites, the new data tighten constraints on the displacement history of the Sierra Nevada block and its pre-extensional position relative to interior North America. We collected samples in freshly exposed...

The Amphitheater Mountains and southern central Alaska Range expose a thick sequence of Triassic Nikolai basalts that is underlain by several mafic‐ultramafic complexes, the largest and best exposed being the Fish Lake and Tangle (FL‐T) mafic‐ultramafic sills that flank the Amphitheater Mountains synform. Three‐dimensional (3‐D) modeling of gravity and magnetic data reveals details of...

The US Geological Survey recently assessed the potential for undiscovered conventional petroleum in the Arctic. Using a new map compilation of sedimentary elements, the area north of the Arctic Circle was subdivided into 70 assessment units, 48 of which were quantitatively assessed. The Circum-Arctic Resource Appraisal (CARA) was a geologically based, probabilistic study that relied...

Dissolved inorganic nitrogen, largely in reduced form (NH4(T)≈NH4(aq)++NH3(aq)o), has been documented in thermal waters throughout Yellowstone National Park, with concentrations ranging from a few micromolar along the Firehole River to millimolar concentrations at Washburn Hot Springs. Indirect evidence from rock nitrogen analyses and previous work on organic compounds associated with...

Drainage channels are among the most conspicuous surficial features of deserts, but little quantitative analysis of their influence on plant distributions is available. We analysed the effects of desert stream channels (‘washes’) on Larrea tridentata and Ambrosia dumosa density and cover on an alluvial piedmont in the Mojave Desert, based on a spatial analysis of transect data...