Geology topics

James K. Crowley

Publications and source records attributed to James K. Crowley.

6 recordsLinked to original sources

USGS2024

Near-infrared reflectance spectra of mixtures of kaolin-group minerals: Use in clay mineral studies

Near-infrared (NIR) reflectance spectra for mixtures of ordered kaolinite and ordered dickite have been found to simulate the spectral response of disordered kaolinite. The amount of octahedral vacancy disorder in nine disordered kaolinite samples was estimated by comparing the sample spectra to the spectra of reference mixtures. The resulting estimates are consistent with previously published estimates of vacancy disorder for similar kaolin minerals that were modeled from calculated X-ray diffraction patterns. The ordered kaolinite and dickite samples used in the reference mixtures were carefully selected to avoid undesirable particle size effects that could bias the spectral results. NIR spectra were also recorded for laboratory mixtures of ordered kaolinite and halloysite to assess whether the spectra could be potentially useful for determining mineral proportions in natural physical mixtures of these two clays. Although the kaolinite-halloysite proportions could only be roughly estimated from the mixture spectra, the halloysite component was evident even when halloysite was present in only minor amounts. A similar approach using NIR spectra for laboratory mixtures may have applications in other studies of natural clay mixtures.

Clays and Clay Minerals↗

USGS2012

Visible and near-infrared (0.4-2.5 μm) reflectance spectra of playa evaporite minerals

Visible and near-infrared (VNIR; 0.4–2.4 μm) reflectance spectra were recorded for 35 saline minerals that represent the wide range of mineral and brine chemical compositions found in playa evaporite settings. The spectra show that many of the saline minerals exhibit diagnostic near-infrared absorption bands, chiefly attributable to vibrations of hydrogen-bonded structural water molecules. VNIR reflectance spectra can be used to detect minor hydrate phases present in mixtures dominated by anhydrous halite or thenardite, and therefore will be useful in combination with X ray diffraction data for characterizing natural saline mineral assemblages. In addition, VNIR reflectance spectra are sensitive to differences in sample hydration state and should facilitate in situ studies of minerals that occur as fragile, transitory dehydration products in natural salt crusts. The use of spectral reflectance measurements in playa studies should aid in mapping evaporite mineral distributions and may provide insight into the geochemical and hydrological controls on playa mineral and brine development.

Journal of Geophysical Research↗

USGS2012

Morphological and chemical evidence of stromatolitic deposits in the 2.75 Ga Carajás banded iron formation, Brazil

We describe evidence of biogenicity in the morphology and carbon content of well-preserved, Neoarchean samples of banded iron formation (BIF) from Carajás, Brazil. Silica-rich BIF layers contain translucent ellipsoidal or trapezoidal structures (∼5–10 μm diameter) composed of silica, hematite, and kerogen, which are arranged in larger ring-like forms (rosettes). Stable carbon isotope analysis yields a δ 13 C value of −24.5‰ indicating that the contained carbon is likely biogenic. Raman and SEM analyses, as well as wavelength-dispersive X-ray elemental maps, show kerogen inside the rosette forms. Within the iron-rich BIF layers, tubular structures (0.5–5 μm) were observed between hematite granules and blades. Kerogen and kaolinite are present in these structures. Both the rosettes and the tubular structures resemble morphologies that are characteristic of some bacterial species. We hypothesize that the Carajás BIFs originated as biomats formed by one or more species that over time produced large stromatolitic structures. The rosettes and the tubular structures, associated with chert-rich and iron-rich BIF layers, respectively, may represent two different species, or perhaps, two phases of a bacterium life cycle. For example, some modern myxobacteria exhibit similar morphologies in their resting and vegetative stages. Fe(III) precipitation may have occurred by contact of Fe(II) with bacterial slime, leading to oxidation by chemical reactions with exposed polysaccharide hydroxyl and carboxyl groups. The Fe(III) would then have been available for use as a source of energy in a dissimilatory iron reduction type of metabolism. Organic carbon input presumably came from primary producers (not necessarily aerobic) within the local water column, perhaps in shallow-water communities. Alternatively, the carbon may have originated by Fischer–Tropsch synthesis at ocean hydrothermal vents. The observed lateral continuity of BIF layers may perhaps be explained by chemical signaling by the bacteria of favorable or unfavorable environmental conditions, leading to nearly synchronous cell morphogenesis from a vegetative to resting phase and vice versa.

Earth and Planetary Science Letters↗

USGS2010

Identification of plant species by using high spatial and spectral resolution thermal infrared (8.0–13.5 μm) imagery

High spatial and spectral resolution thermal infrared imagery (8.0–13.5 μm) from the SEBASS airborne sensor was used to analyze and map tree canopy spectral features at the State Arboretum of Virginia, near Boyce, Virginia. Fifty tree species were analyzed and about half were directly identified with varying degrees of success on the basis of spectral matched filtering that utilized laboratory-measured leaf spectra as the target signatures. Spectral averages of pixels extracted from SEBASS emissivity data compared favorably with laboratory spectra of leaves collected from individual tree species. Best results were obtained from species having relatively strong spectral contrast, wide and flat leaves, closed planophile canopies, and/or large canopy areas. Tree species having small leaves or unfavorable leaf orientations showed spectral attenuation likely resulting from cavity blackbody effects. Increased spatial resolution and better image calibration and atmospheric correction might lead to further improvements in thermal infrared plant species identification.

Remote Sensing of the Environment↗

USGS2007

Spectral reflectance and emissivity features of broad leaf plants: Prospects for remote sensing in the thermal infrared (8.0-14.0 μm)

Field emissivity measurements were made of leaves collected from nine deciduous tree and agricultural plant species. The data show, for the first time, that it is possible to discriminate subtle spectral emissivity features of leaves from the natural background emission. Under conditions of controlled measurement geometry (leaves arranged to cover a flat surface), the field emissivity spectra agreed fairly well with emissivity values calculated from laboratory directional hemispherical reflectance measurements. Spectral features associated with a variety of leaf chemical constituents, including cellulose, cutin, xylan, silica, and oleanolic acid could be identified in the field emissivity data. Structural aspects of leaf surfaces also influenced spectral behavior, notably the abundance of trichomes, as well as wax thickness and texture. Field spectral measurements made at increasing distances from natural plant canopies showed progressive attenuation of the spectral emissivity features. This attenuation is ascribed to increased multiple scattering that superimposes an opposite-in-sign reflected component on the emittance, and to the increasing number of canopy voids within the instrument field of view. Errors associated with the removal of atmospheric features and with the non-isotropic thermal characteristics of canopies also contribute to the loss of spectral information at greater measurement distances. In contrast to visible and short-wave infrared data, thermal infrared spectra of broad leaf plants show considerable spectral diversity, suggesting that such data eventually could be utilized to map vegetation composition. However, remotely measuring the subtle emissivity features of leaves still presents major challenges. To be successful, sensors operating in the 8–14 μm atmospheric window must have high signal-to-noise and a small enough instantaneous field of view to allow measurements of only a few leaf surfaces. Methods for atmospheric compensation, temperature–emissivity separation, and spectral feature analysis also will need to be refined to allow the recognition, and perhaps, exploitation of leaf thermal infrared spectral properties.

Virginia↗

USGS1984

MULTISPECTRAL REMOTE SENSING OF CARBONATE ROCKS IN THE CONFUSION RANGE, UTAH.

Multispectral imagery recorded by the NASA/Bendix 24-channel aircraft scanner over the Confusion Range, Utah, proved to be extremely sensitive to lithologic variations in exposed carbonate rocks. Major carbonate units within a 16-km**2 study area were readily distinguished, and some aspects of their structure and stratigraphy could be inferred from image spectral signatures. Spectral data channels centered at 1. 6 and 2. 2 mu m accounted for much of the data sensitivity to lithologic differences. Rock texture, organic matter content, and weathering expression were important lithologic factors producing spectral variation.

Conference Paper↗