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R. J. Miller

Publications and source records attributed to R. J. Miller.

At least 19 recordsLinked to original sources
USGS2009

Gravity and Magnetic Investigations of the Mojave National Preserve and Adjacent Areas, California and Nevada

Gravity and aeromagnetic data provide the underpinnings of a hydrogeologic framework for the Mojave National Preserve by estimating the thickness of Cenozoic deposits and locating inferred structural features that influence groundwater flow. An inversion of gravity data indicates that thin (<1 km) basin deposits cover much of the Preserve, except for Ivanpah Valley and the Woods Mountains volcanic center. Localized areas of Cenozoic deposits thicker than 500 m are predicted beneath parts of Lanfair Valley, Fenner Valley, near Kelso, Soda Lake, and southeast of Baker. Along the southern margin of the Mojave National Preserve, basins greater than 1 km deep are located between the Clipper and Marble Mountains, between the Marble and Bristol Mountains, and south of the Bristol Mountains near Amboy. Both density and magnetization boundaries defined by horizontal-gradient analyses coincide locally with Cenozoic faults and can be used to extend these faults beneath cover. Magnetization boundaries also highlight the structural grain within the crystalline rocks and may serve as a proxy for fracturing, an important source of permeability within the generally impermeable basement rocks, thus mapping potential groundwater pathways through and along the mountain ranges in the study area.

Open-File Report↗
USGS2007

The colonial ascidian Didemnum sp. A: current distribution, basic biology and potential threat to marine communities of the northeast and west coasts of North America

Didemnum sp. A is a colonial ascidian with rapidly expanding populations on the east and west coasts of North America. The origin of Didemum sp. A is unknown. Populations were first observed on the northeast coast of the U.S. in the late 1980s and on the west coast during the 1990s. It is currently undergoing a massive population explosion and is now a dominant member of many subtidal communities on both coasts. To determine Didemnum sp. A's current distribution, we conducted surveys from Maine to Virginia on the east coast and from British Columbia to southern California on the west coast of the U.S. between 1998 and 2005. In nearshore locations Didemnum sp. A currently ranges from Eastport, Maine to Shinnecock Bay, New York on the east coast. On the west coast it has been recorded from Humboldt Bay to Port San Luis in California, several sites in Puget Sound, Washington, including a heavily fouled mussel culture facility, and several sites in southwestern British Columbia on and adjacent to oyster and mussel farms. The species also occurs at deeper subtidal sites (up to 81 m) off New England, including Georges, Stellwagen and Tillies Banks. On Georges Bank numerous sites within a 230 km2 area are 50–90% covered by Didemnum sp. A; large colonies cement the pebble gravel into nearly solid mats that may smother infaunal organisms. These observations suggest that Didemnum sp. A has the potential to alter marine communities and affect economically important activities such as fishing and aquaculture.

British Columbia, California, Connecticut, Maine, ↗
USGS1997

New K-Ar and 40Ar/39Ar ages of plutonism, hydrothermal alteration, and mineralization in the central Wasatch Mountains, Utah

Twenty-one new K-Ar and 10 new 40 Ar/ 39 Ar ages are reported for igneous and hydrothermal minerals from intrusive rocks of the Wasatch igneous belt in the central Wasatch Mountains. Interpretation of our new data combined with previously published K-Ar ages and with new 40 Ar/ 39 Ar and U-Pb ages reported by Vogel et al. (1997) suggests that the Clayton Peak stock was emplaced at about 36 to 35 Ma, the Alta stock at about 35 to 33 Ma, and the Little Cottonwood stock at about 31 to 30 Ma. Biotite K-Ar ages progressively increase from west to east in the Little Cottonwood stock, which is consistent with more rapid cooling of the eastern part of the stock and with other evidence suggesting about 15 degrees of eastward tilting of the central Wasatch Mountains following emplacement of the Wasatch igneous belt. Most porphyry stocks in the Park City mining district were emplaced at about 41 to 40 Ma; the Ontario stock was emplaced at about 36 Ma. Vein deposits in the Park City mining district formed at about 36 to 33 Ma. The Park Premier stock was emplaced in several pulses between about 35 to 32 Ma. Alteration related to porphyry copper mineralization in the Park Premier stock formed at 33.5 Ma and advanced argillic alteration and gold mineralization formed at 31.4 Ma. Molybdenum mineralization in the eastern part of the Little Cottonwood stock formed between 26 to 23.5 Ma.

Utah↗
USGS1992

The Conterminous United States Mineral Assessment Program: Background information to accompany folio of geologic, geochemical, geophysical, and mineral resource maps of the Ajo and Lukeville 1° by 2° quadrangles, Arizona

Encompassing about 21,000 km 2 in southwestern Arizona, the Ajo and Lukeville 1° by 2° quadrangles have been the subject of mineral resource investigations utilizing field and laboratory studies in the disciplines of geology, geochemistry, geophysics, and Landsat imagery. The results of these studies are published as a folio of maps, figures, and tables, with accompanying discussions. Past mineral production has been limited to copper from the Ajo Mining District. In addition to copper, the quadrangles contain potentially significant resources of gold and silver; a few other commodities, including molybdenum and evaporites, may also exist in the area as appreciable resources. This circular provides background information on the mineral deposits and on the investigations and integrates the information presented in the folio. The bibliography cites references to the geology, geochemistry, geophysics, and mineral deposits of the two quadrangles.

Arizona↗
USGS1982

Depositional history of Louisiana-Mississippi outer continental shelf

A geological study was undertaken in 1981 in the Louisiana-Mississippi outer continental shelf for the Bureau of Land Management. The study included a high-resolution seismic reflection survey, surficial sediment sampling and surface current drifter sampling. Approximately 7100 sq km of the Louisiana-Mississippi shelf and upper slope were surveyed. The sea floor of the entire area is relatively smooth except for occasional areas of uplift produced by diapiric intrusion along the upper slope. Characteristics of the topography and subsurface shelf sediments are the result of depositional sequences due to delta outbuilding over transgressive sediments with intervening periods of erosion during low sea level stands. Little evidence of structural deformation such as faults, diapirs, and shallow gas is present on the shelf and only a few minor faults and scarps are found on the slope. Minisparker seismic records in combination with air gun (40 and 5 cu in) and 3.5-kHz subbottom profile records reveal that seven major stages of shelf development have occurred since the middle Pleistocene. The shelf development has been controlled by the rise and fall of sea level. These stages are defined by four major unconformities, several depositions of transgressive sediments, sequences of river channeling and progradational delta deposits. Surficial sediment sample and seismic records indicate tat the last major depositional event was the progradation of the St. Bernard Delta lobe. This delta lobe covered the northwestern and central regions. Surficial sediments in most of the study area are the product of the reworking of the San Bernard Delta lobe and previous progradations.

Open-File Report↗