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At least 595 records · Page 33Linked to original sources

USGS2013

Appraising options to reduce shallow groundwater tables and enhance flow conditions over regional scales in an irrigated alluvial aquifer system

Some of the world’s key agricultural production systems face big challenges to both water quantity and quality due to shallow groundwater that results from long-term intensive irrigation, namely waterlogging and salinity, water losses, and environmental problems. This paper focuses on water quantity issues, presenting finite-difference groundwater models developed to describe shallow water table levels, non-beneficial groundwater consumptive use, and return flows to streams across two regions within an irrigated alluvial river valley in southeastern Colorado, USA. The models are calibrated and applied to simulate current baseline conditions in the alluvial aquifer system and to examine actions for potentially improving these conditions. The models provide a detailed description of regional-scale subsurface unsaturated and saturated flow processes, thereby enabling detailed spatiotemporal description of groundwater levels, recharge to infiltration ratios, partitioning of ET originating from the unsaturated and saturated zones, and groundwater flows, among other variables. Hybrid automated and manual calibration of the models is achieved using extensive observations of groundwater hydraulic head, groundwater return flow to streams, aquifer stratigraphy, canal seepage, total evapotranspiration, the portion of evapotranspiration supplied by upflux from the shallow water table, and irrigation flows. Baseline results from the two regional-scale models are compared to model predictions under variations of four alternative management schemes: (1) reduced seepage from earthen canals, (2) reduced irrigation applications, (3) rotational lease fallowing (irrigation water leased to municipalities, resulting in temporary dry-up of fields), and (4) combinations of these. The potential for increasing the average water table depth by up to 1.1 and 0.7 m in the two respective modeled regions, thereby reducing the threat of waterlogging and lowering non-beneficial consumptive use from adjacent fallow and naturally-vegetated lands, is demonstrated for the alternative management intervention scenarios considered. Net annual average savings of up to about 9.9 million m 3 (8000 ac ft) and 2.3 million m 3 (1900 ac ft) of non-beneficial groundwater consumptive use is demonstrated for the study periods in each of the two respective study regions. Alternative water management interventions achieve varying degrees of benefits in each of the two regions, suggesting a need to adopt region-specific interventions and avoid a ‘one-size-fits-all’ approach. Impacts of the considered interventions on return flows to the river were predicted to be significant, highlighting the need for flow augmentation to comply with an interstate river compact and portending beneficial impacts on solute loading.

Colorado↗

USGS2018

Satellite remote sensing estimation of river discharge: Application to the Yukon River Alaska

A methodology based on general hydraulic relations for rivers has been developed to estimate the discharge (flow rate) of rivers using satellite remote sensing observations. The estimates of discharge, flow depth, and flow velocity are derived from remotely observed water surface area, water surface slope, and water surface height, and demonstrated for two reaches of the Yukon River in Alaska, at Eagle (reach length 34.7 km) and near Stevens Village (reach length 38.3 km). The method is based on fundamental equations of hydraulic flow resistance in rivers, including the Manning equation and the Prandtl-von Karman universal velocity distribution equation. The method employs some new hydraulic relations to help define flow resistance and height of the zero flow boundary in the channel. Estimates are made both with and without calibration. The water surface area of the river reach is measured by using a provisional version of the U.S. Geological Survey (USGS) Landsat based product named Dynamic Surface Water Extent (DSWE). The water surface height and slope measurements require a self-consistent datum, and are derived from observations from the Jason-2 satellite altimeter mission. At both reach locations, the Jason-2 radar altimeter non-winter heights consistently tracked the stage recorded at USGS streamgages with a standard deviation of differences (error) during the non-winter periods of less than 7%. Part of the error may be due to differences in the gage and altimeter crossing locations with respect to the range of stage change and the response to changes in discharge at the upstream and downstream locations. For the non-winter periods, the radar derived slope estimates (mean = 0.0003) were constant over the mission lifetime, and in agreement with previously measured USGS water surface slopes and slopes determined from USGS topographic maps. The accuracy of the mean of the uncalibrated daily estimates of discharge varied between reaches, ranging from 13% near Stevens Village (N = 90) to −21% at Eagle (N = 246) based on the absolute error, and 5% to −6% based on the error of the log of the estimates. Calibrating to the mean of USGS daily discharge estimates from the streamflow rating for the same period of record at each streamgage resulted in mean absolute errors ranging from 1% to 2%, and log errors ranging from 1% or less. The error pattern of the estimates shows that without calibration, even though the mean is well simulated, the high and low end values over the range of estimates may have significant bias.

Alaska↗

USGS2024

Two-million-year eruptive history of Laguna del Maule volcanic field

The Laguna del Maule (LdM) volcanic field, which surrounds the 54-km 2 lake of that name, covers ∼500 km 2 of mountainous glaciated terrain with Quaternary lavas and tuffs that extend 40 km westward from the Argentine frontier and 30 km north-south from the Río Campanario to Laguna Fea. Complementing recent investigations of postglacial volcanism and the ongoing geophysical unrest around the lake, we here review the longer eruptive history that spanned the entire Quaternary.

Journal of South American Earth Sciences↗

USGS2005

Ongoing hydrothermal heat loss from the 1912 ash-flow sheet, Valley of Ten Thousand Smokes, Alaska

The June 1912 eruption of Novarupta filled nearby glacial valleys on the Alaska Peninsula with ash-flow tuff (ignimbrite), and post-eruption observations of thousands of steaming fumaroles led to the name ‘Valley of Ten Thousand Smokes’ (VTTS). By the late 1980s most fumarolic activity had ceased, but the discovery of thermal springs in mid-valley in 1987 suggested continued cooling of the ash-flow sheet. Data collected at the mid-valley springs between 1987 and 2001 show a statistically significant correlation between maximum observed chloride (Cl) concentration and temperature. These data also show a statistically significant decline in the maximum Cl concentration. The observed variation in stream chemistry across the sheet strongly implies that most solutes, including Cl, originate within the area of the VTTS occupied by the 1912 deposits. Numerous measurements of Cl flux in the Ukak River just below the ash-flow sheet suggest an ongoing heat loss of ∼250 MW. This represents one of the largest hydrothermal heat discharges in North America. Other hydrothermal discharges of comparable magnitude are related to heat obtained from silicic magma bodies at depth, and are quasi-steady on a multidecadal time scale. However, the VTTS hydrothermal flux is not obviously related to a magma body and is clearly declining. Available data provide reasonable boundary and initial conditions for simple transient modeling. Both an analytical, conduction-only model and a numerical model predict large rates of heat loss from the sheet 90 years after deposition.

Alaska↗

USGS2006

Growth and collapse of Hawaiian volcanoes

This special issue is an outgrowth of a session of the same name held at the 2003 Fall Meeting of the American Geophysical Union (AGU) in San Francisco. The session served dual purposes: to highlight recent advances in our understanding of the development and internal structure of Hawaiian volcanoes, and to recognize the important contributions of James Moore to this field of study.

Hawai'i↗

USGS2006

Submarine geology of Hana Ridge and Haleakala Volcano's northeast flank, Maui

We present a morphostructural analysis of the submarine portions of Haleakala Volcano and environs, based upon a 4-year program of geophysical surveys and submersible explorations of the underwater flanks of Hawaiian volcanoes that was conducted by numerous academic and governmental research organizations in Japan and the U.S. and funded primarily by the Japan Agency for Marine–Earth Science and Technology. A resulting reconnaissance geologic map features the 135-km-long Hana Ridge, the 3000 km 2 Hana slump on the volcano's northeast flank, and island-surrounding terraces that are the submerged parts of volcanic shields. Hana Ridge below 2000 m water depth exhibits the lobate morphology typical of the subaqueously erupted parts of Hawaiian rift zones, with some important distinctions: namely, subparallel crestlines, which we propose result from the down-rift migration of offsets in the dike intrusion zone, and an amphitheater at its distal toe, where a submarine landslide has embayed the ridge tip. Deformation of Haleakala's northeast flank is limited to that part identified as the Hana slump, which lies downslope from the volcano's submerged shield, indicating that flank mobility is also limited in plan, inconsistent with hypothesized volcanic spreading driven by rift-zone dilation. The leading edge of the slump has transverse basins and ridges that resemble the thrust ramps of accretionary prisms, and we present a model to describe the slump's development that emphasizes the role of coastally generated fragmental basalt on gravitational instability of Haleakala's northeast flank and that may be broadly applicable to other ocean-island slumps.

Hawai'i↗

USGS2016

Thermal mapping of a pahoehoe lava flow, Kilauea Volcano

Pāhoehoe lava flows are a major component of Hawaiian eruptive activity, and an important part of basaltic volcanism worldwide. In recent years, pāhoehoe lava has destroyed homes and threatened parts of Hawai‘i with inundation and disruption. In this study, we use oblique helicopter-borne thermal images to create high spatial resolution (~1 m) georeferenced thermal maps of the active pāhoehoe flow on Kīlauea Volcano’s East Rift Zone. Thermal maps were created on 27 days during 2014–2016 in the course of operational monitoring, encompassing a phase of activity that threatened the town of Pāhoa. Our results illustrate and reinforce how pāhoehoe flows are multicomponent systems consisting of the vent, master tube, distributary tubes and surface breakouts. The thermal maps accurately depict the distribution and character of pāhoehoe breakouts through time, and also delineate the subsurface lava tube. Surface breakouts were distributed widely across the pāhoehoe flow, with significant portions concurrently active well upslope of the flow front, often concentrated in clusters of activity that evolved through time. Gradual changes to surface breakout distribution and migration relate to intrinsic processes in the flow, including the slow evolution of the distributary tube system. Abrupt disruptions to this system, and the creation of new breakouts (and associated hazards), were triggered by extrinsic forcing—namely fluctuations in lava supply rate at the vent which disrupted the master lava tube. Although the total area of a pāhoehoe flow has been suggested to relate to effusion rate, our results show that changes in the proportion of expansion vs. overplating can complicate this relationship. By modifying existing techniques, we estimate time-averaged discharge rates for the flow during 2014–2016 generally in the range of 1–2 m3 s-1 (mean: 1.3±0.4 m3 s-1) – less than half of Kīlauea’s typical eruption rate on the East Rift Zone and suggestive of a weak eruptive regime during 2014–2016. We caution, however, that this discharge rate approach requires further independent corroboration. The thermal maps provide the first synoptic characterization of pāhoehoe flow activity at high spatial resolution, essential both for operational hazard assessment and fundamental understanding of pāhoehoe behavior.

Hawaii↗

USGS2017

The spectrum of persistent volcanic flank instability: A review and proposed framework based on Kīlauea, Piton de la Fournaise, and Etna

Persistent motion of the south flank of Kīlauea Volcano, Hawai'i, has been known for several decades, but has only recently been identified at other large basaltic volcanoes—namely Piton de la Fournaise (La Réunion) and Etna (Sicily)—thanks to the advent of space geodetic techniques. Nevertheless, understanding of long-term flank instability is based largely on the example of Kīlauea, despite the large differences in the manifestations and mechanisms of the process when viewed through a comparative lens. For example, the rate of flank motion at Kīlauea is several times that of Etna and Piton de la Fournaise and is accommodated on a slip plane several km deeper than is probably present at the other two volcanoes. Gravitational spreading also appears to be the dominant driving force at Kīlauea, given the long-term steady motion of the volcano's south flank regardless of eruptive/intrusive activity, whereas magmatic activity plays a larger role in flank deformation at Etna and Piton de la Fournaise. Kīlauea and Etna, however, are both characterized by heavily faulted flanks, while Piton de la Fournaise shows little evidence for flank faulting. A helpful means of understanding the spectrum of persistent flank motion at large basaltic edifices may be through a framework defined on one hand by magmatic activity (which encompasses both magma supply and edifice size), and on the other hand by the structural setting of the volcano (especially the characteristics of the subvolcanic basement or subhorizontal intravolcanic weak zones). A volcano's size and magmatic activity will dictate the extent to which gravitational and magmatic forces can drive motion of an unstable flank (and possibly the level of faulting of that flank), while the volcano's structural setting governs whether or not a plane of weakness exists beneath or within the edifice and can facilitate flank slip. Considering persistent flank instability using this conceptual model is an alternative to using a single volcano as a “type example”—especially given that the example is usually Kīlauea, which defines an extreme end of the spectrum—and can provide a basis for understanding why flank motion may or may not exist on other large basaltic volcanoes worldwide.

Etna, Kīlauea Volcano, Piton de la Fournaise↗

USGS2006

Perspectives on basaltic magma crystallization and differentiation: Lava-lake blocks erupted at Mauna Loa volcano summit, Hawaii

Explosive eruptions at Mauna Loa summit ejected coarse-grained blocks (free of lava coatings) from Moku'aweoweo caldera. Most are gabbronorites and gabbros that have 0–26 vol.% olivine and 1–29 vol.% oikocrystic orthopyroxene. Some blocks are ferrogabbros and diorites with micrographic matrices, and diorite veins (≤2 cm) cross-cut some gabbronorites and gabbros. One block is an open-textured dunite. The MgO of the gabbronorites and gabbros ranges ∼ 7–21 wt.%. Those with MgO >10 wt.% have some incompatible-element abundances (Zr, Y, REE; positive Eu anomalies) lower than those in Mauna Loa lavas of comparable MgO; gabbros (MgO <10 wt.%) generally overlap lava compositions. Olivines range Fo 83–58 , clinopyroxenes have Mg#s ∼83–62, and orthopyroxene Mg#s are 84–63 — all evolved beyond the mineral-Mg#s of Mauna Loa lavas. Plagioclase is An 75–50 . Ferrogabbro and diorite blocks have ∼ 3–5 wt.% MgO (TiO 2 3.2–5.4%; K 2 O 0.8–1.3%; La 16–27 ppm), and a diorite vein is the most evolved (SiO 2 59%, K 2 O 1.5%, La 38 ppm). They have clinopyroxene Mg#s 67–46, and plagioclase An 57–40 . The open-textured dunite has olivine ∼ Fo 83.5 . Seven isotope ratios are 87 Sr/ 86 Sr 0.70394–0.70374 and 143 Nd/ 144 Nd 0.51293–0.51286, and identify the suite as belonging to the Mauna Loa system. Gabbronorites and gabbros originated in solidification zones of Moku'aweoweo lava lakes where they acquired orthocumulate textures and incompatible-element depletions. These features suggest deeper and slower cooling lakes than the lava lake paradigm, Kilauea Iki, which is basalt and picrite. Clinopyroxene geobarometry suggests crystallization at <1 kbar P. Highly evolved mineral Mg#s, <75, are largely explained by cumulus phases exposed to evolving intercumulus liquids causing compositional ‘shifts.’ Ferrogabbro and diorite represent segregation veins from differentiated intercumulus liquids filter pressed into rigid zones of cooling lakes. Clinopyroxene geobarometry suggests <300 bar P. Open-textured dunite represents olivine-melt mush, precursor to vertical olivine-rich bodies (as in Kilauea Iki). Its Fo 83.5 identifies the most primitive lake magma as ∼8.3 wt.% MgO. Mass balancing and MELTS show that such a magma could have yielded both ferrogabbro and diorite by ≥50% fractional crystallization, but under different fO 2 : < FMQ (250 bar) led to diorite, and FMQ (250 bar) yielded ferrogabbro. These segregation veins, documented as similar to those of Kilauea, testify to appreciable volumes of ‘rhyolitic’ liquid forming in oceanic environments. Namely, SiO 2 -rich veins are intrinsic to all shields that reached caldera stage to accommodate various-sized cooling, differentiating lava lakes.

Hawaii↗

USGS2012

Determination of sediment provenance by unmixing the mineralogy of source-area sediments: The "SedUnMix" program

Along the margins of areas such as Greenland and Baffin Bay, sediment composition reflects a complex mixture of sources associated with the transport of sediment in sea ice, icebergs, melt-water and turbidite plumes. Similar situations arise in many contexts associated with sediment transport and with the mixing of sediments from different source areas. The question is: can contributions from discrete sediment (bedrock) sources be distinguished in a mixed sediment by using mineralogy, and, if so, how accurately? To solve this problem, four end-member source sediments were mixed in various proportions to form eleven artificial mixtures. Two of the end-member sediments are felsic, and the other two have more mafic compositions. End member and mixed sediment mineralogies were measured for the < 2 mm sediment fractions by quantitative X-ray diffraction (qXRD). The proportions of source sediments in the mixtures then were calculated using an Excel macro program named SedUnMix, and the results were evaluated to determine the robustness of the algorithm. The program permits the unmixing of up to six end members, each of which can be represented by up to 5 alternative compositions, so as to better simulate variability within each source region. The results indicate that we can track the relative percentages of the four end members in the mixtures. We recommend, prior to applying the technique to down-core or to other provenance problems, that a suite of known, artificial mixtures of sediments from probable source areas be prepared, scanned, analyzed for quantitative mineralogy, and then analyzed by SedUnMix to check the sensitivity of the method for each specific unmixing problem.

Baffin Bay↗

USGS2015

Truncorotalia crassaformis from its type locality: Comparison with Caribbean plankton and Pliocene relatives

Truncorotalia crassaformis has been identified in Pliocene-Holocene assemblages globally but there has been little analysis of specimens from its type locality at Lomita Quarry, California. This has led to confusion about some diagnostic criteria, particularly the presence of a peripheral keel. To better understand variation specimens are studied from the type locality (Pleistocene, c. 400–600 ka), supplemented by material from a plankton trap in Cariaco Basin and from ODP 925, Ceara Rise (Pliocene, c. 4.3 Ma). The damaged holotype has a weak topographic ridge (keel) at the periphery of early chambers of the outer whorl. Several well-preserved specimens have a keel on all chambers of the whorl. Encrustation obscures the periphery on some and masks shell shape. Several outliers in a morphometric analysis of axial shape have distinctive discoidal outlines but ventroconical (cone-like) forms are common. Lomita Marl was deposited on a sheltered, shallow shelf in Chron 1. Foraminifera reworked from the unconformably underlying Repetto Siltstone are present. Specimens resembling the holotype are very rare and often damaged. Morphological disparity is high. It is unlikely that an autochthonous population was sampled. The weak peripheral keel present on some living specimens from Cariaco Basin is built incrementally by a thin featureless calcitic veneer deposited between the morphogenesis of each chamber. The process progressively obscures pores in the primary wall. Its earliest stages have been misidentified as a poreless zone. Ventroconical form is weak in the Ceara Rise Pliocene specimens and is distinguishable from the Cariaco sample. There is only a veneer at the periphery. Although the study does not provide a population-based diagnosis of T. crassaformis it indicates that the name should not be applied to early Pliocene forms.

Marine Micropaleontology↗

USGS2021

Multiple physical properties of gas hydrate-bearing sediments recovered from Alaska North Slope 2018 Hydrate-01 Stratigraphic Test Well

Knowledge of the petrophysical and geomechanical properties of gas hydrate-bearing sediments is essential for predicting reservoir responses to gas production from gas hydrate reservoirs. In December 2018, Stratigraphic Test Well Hydrate-01 was drilled in the western part of the Prudhoe Bay Unit, Alaska North Slope, as part of the technical planning effort for a future long-term gas hydrate production test. Side-wall pressure coring was conducted to recover gas hydrate-bearing sediments from two reservoir sections named Unit B and Unit D. A total of 34 cores were successfully recovered during five runs of a wireline deployed pressure corer, and a total of 17 cores were preserved for advanced laboratory analysis. The samples were frozen inside the pressure core autoclave by liquid nitrogen while at high pressure before being removed and stored under liquid nitrogen at atmospheric pressure. High-resolution X-ray computed tomography showed the samples were high-quality, with undisturbed lithological layers. The Unit B and D sediments were categorized as sand or sandy silt with high hydrate saturation. Gas compositions suggest the hydrates formed with thermogenic and microbial mixed gases. Permeability tests and triaxial compression tests were conducted on the hydrate-bearing sediments. Low strengthening and high permeability at hydrate saturation S h > 80% were observed. There was a small permeability reduction during the triaxial compression tests owing to porosity loss with increasing effective stress in the highly permeable sandy sediment after hydrate dissociation. The apparent minimal changes in porosity and permeability during the tests were due to the low-clay content and low compressibility of the quartz sand grains in the recovered cores. X-ray powder diffraction and thermal conductivity analysis also suggested a high quartz content for the analyzed samples.

Alaska↗

USGS2011

A probabilistic seismic risk assessment procedure for nuclear power plants: (II) Application

This paper presents the procedures and results of intensity- and time-based seismic risk assessments of a sample nuclear power plant (NPP) to demonstrate the risk-assessment methodology proposed in its companion paper. The intensity-based assessments include three sets of sensitivity studies to identify the impact of the following factors on the seismic vulnerability of the sample NPP, namely: (1) the description of fragility curves for primary and secondary components of NPPs, (2) the number of simulations of NPP response required for risk assessment, and (3) the correlation in responses between NPP components. The time-based assessment is performed as a series of intensity-based assessments. The studies illustrate the utility of the response-based fragility curves and the inclusion of the correlation in the responses of NPP components directly in the risk computation. ?? 2011 Published by Elsevier B.V.

Conference Paper↗

USGS2007

Ore controls in the Charters Towers goldfield, NE Australia: Constraints from geological, geophysical and numerical analyses

The approach taken in this paper, namely synthesising a wealth of previous information with new data and a genetic model, in combination with integrated numerical analyses, led to new insights into the geological controls on the localisation of auriferous veins and residual prospectivity of the Charters Towers goldfield, NE Australia. The method also has implications for the assessment of other "mature" goldfields worldwide. Despite a number of different ore controls having operated within the Charters Towers goldfield, the controlling factors can be linked to a single genetic model for orogenic, granitoid-hosted lode-gold mineralisation in a brittle deformation regime (D4) of NE-SW to NNE-SSW shortening, under conditions of supralithostatic fluid pressure and low stress difference. Spatial autocorrelation results suggest district-scale alignment of the auriferous veins parallel to and overlapping with the ESE-WNW- to E-W-striking Charters Towers-Ravenswood lineament, a major crustal boundary in the basement to the Ravenswood batholith. At the camp-scale, auriferous veins have abundance and proximity relationships with NW-SE-, NNW-SSE-, NE-SW- and ENE-WSW-oriented lineaments, suggesting that structures that controlled gold deposition in one camp did not necessarily control mineralisation in other camps. Fractal dimensions obtained with the box-counting method range from 1.02 to 1.10, whereas veins in the Charters Towers City camp are characterised by a significantly higher fractal dimension of 1.28. This discrepancy may be taken to imply that most or all outcropping and near-surface deposits within the Charters Towers City camp have been found and that new discoveries are more likely to occur at greater levels of depth, or outside the boundaries of this camp. The new understanding has implications for the assessment of the residual prospectivity of the Charters Towers goldfield, where large areas of prospective rock types and structures (e.g., approximately 40% of the Charters Towers-Ravenswood lineament) are hidden under cover. This parameter space was inaccessible to the historic prospectors and has received relatively little attention from recent explorers. The following steps are suggested for the development of a targeting strategy for lode-gold exploration in areas of the goldfield under cover: (1) identify from geological and geophysical data the ENE-WSW (?? 15??) and NNW-SSE (?? 15??) striking structures and geological boundaries within a 20-km-wide corridor parallel to and centred upon the Charters Towers-Ravenswood lineament, the potential control on gold deposit distribution at the regional- to district-scale, (2) interpret from geological and geophysical data the distribution of pre-Middle Devonian granitoids within these areas that are the preferred host rocks of the payable gold deposits, (3) deduce from geophysical data the ENE-WSW (?? 15??) and NNW-SSE (?? 15??) striking structures that cut or bound the intrusions identified in step 2, (4) locate segments along the structures identified in step 3 that deviate most from the geometry of a straight line (e.g., potential bends or splays) and/or intersect other structures or geological contacts, or both, and (5) define and rank potential targets within the prospective areas identified in step 4 and systematically test the best ones. ?? 2006 Elsevier B.V. All rights reserved.

Ore Geology Reviews↗

USGS2017

Element migration of pyrites during ductile deformation of the Yuleken porphyry Cu deposit (NW-China)

The strongly deformed Yuleken porphyry Cu deposit (YPCD) occurs in the Kalaxiangar porphyry Cu belt (KPCB), which occupies the central area of the Central Asian Orogenic Belt (CAOB) between the Sawu’er island arc and the Altay Terrane in northern Xinjiang. The YPCD is one of several typical subduction-related deposits in the KPCB, which has undergone syn-collisional and post-collisional metallogenic overprinting. The YPCD is characterized by three pyrite-forming stages, namely a hydrothermal stage A (Py I), a syn-ductile deformation stage B (Py II) characterized by Cu-Au enrichment, and a fracture-filling stage C (Py III). In this study, we conducted systematic petrographic and geochemical studies of pyrites and coexist biotite, which formed during different stages, in order to constrain the physicochemical conditions of the ore formation. Euhedral, fragmented Py I has low Pb and high Te and Se concentration and Ni contents are low with Co/Ni ratios mostly between 1 and 10 (average 9.00). Py I is further characterized by enrichments of Bi, As, Ni, Cu, Te and Se in the core relative to the rim domains. Anhedral round Py II has moderate Co and Ni contents with high Co/Ni ratios >10 (average 95.2), and average contents of 46.5 ppm Pb and 5.80 ppm Te. Py II is further characterized by decreasing Bi, Cu, Pb, Zn, Ag, Te, Mo, Sb and Au contents from the rim to the core domains. Annealed Py III has the lowest Co content of all pyrite types with Co/Ni ratios mostly <0.1 (average 1.33). Furthermore, Py III has average contents of 3.31 ppm Pb, 1.33 ppm Te and 94.6 ppm Se. In addition, Fe does not correlate with Cu and S in the Py I and Py III, while Py II displays a negative correlation between Fe and Cu as well as a positive correlation between Fe and S. Therefore, pyrites which formed during different tectonic regimes also have different chemical compositions. Biotite geothermometer and oxygen fugacity estimates display increasing temperatures and oxygen fugacities from stage A to stage B, while temperature and oxygen fugacities decrease from stage B to stage C. The Co/Ni ratio of pyrite depends discriminates between the different mineralizing stages in the Yuleken porphyry copper deposit: Py II, associated with the deformation stage B and Cu-enrichment, shows higher Co/Ni ratios and enrichments of Pb, Zn, Mo, Te and Sb than the pyrites formed during the other two stages. The Co/Ni ratio of pyrite can not only apply to discriminate the submarine exhalative, magmatic or sedimentary origins for ore deposits but also can distinguish different ore-forming stages in a single porphyry Cu deposit. Thus, Co/Ni ratio of pyrites may act as an important exploration tool to distinguish pyrites from Cu-rich versus barren area. Furthermore, the distribution of Cu, Mo, Pb, Au, Bi, Sb and Zn in the variably deformed pyrite is proportional to the extent of deformation of the pyrites, indicating in accordance with variable physicochemical conditions different element migration behavior during the different stages of deformation and, thus, mineralisation.

Ore Geology Reviews↗

USGS2008

Increasing maturity of kerogen type II reflected by alkylbenzene distribution from pyrolysis-gas chromatography-mass spectrometry

A series of Late Devonian to Early Mississippian type II kerogens with vitrinite reflectance values Ro 0.29-2.41% were analyzed using py-GC-MS. In addition, a low maturity kerogen with Ro 0.44% was separated into fractions via density gradient centrifugation, followed by py-GC-MS of the alginite and amorphinite maceral concentrates. Alkylbenzenes and n-alk-1-ene/n-alkane doublets represented the main compound classes identified in all pyrolysates. The pyrolysate from alginite featured 1,2,4-trimethylbenzene and toluene as the two most prominent alkylbenzenes. In contrast, alkylbenzenes in pyrolysates from amorphinite and low maturity bulk kerogens with Ro 0.29-0.63% were dominated by 1,2,3,4-tetramethylbenzene. With increasing thermal maturity, pyrolysates were increasingly dominated by (i) alkylbenzenes with fewer methyl groups, namely by tri- and dimethylbenzenes at medium maturity (Ro 0.69-1.19%), and (ii) by toluene at higher maturity (Ro 1.30-2.41%). With increasing maturity of kerogen type II, the decreasing abundance of highly methyl-substituted alkylbenzenes and the parallel increase in less methyl-substituted alkylbenzenes in flash pyrolysates suggest that demethylation is an important chemical process in the thermal maturation of kerogen type II. ?? 2008 Elsevier Ltd. All rights reserved.

Organic Geochemistry↗

USGS2010

Comparison of XAD with other dissolved lignin isolation techniques and a compilation of analytical improvements for the analysis of lignin in aquatic settings

This manuscript highlights numerous incremental improvements in dissolved lignin measurements over the nearly three decades since CuO oxidation of lignin phenols was first adapted for environmental samples. Intercomparison of the recovery efficiency of three common lignin phenol concentration and isolation techniques, namely XAD, C 18 with both CH 3 OH (C 18 M) and CH 3 CN (C 18 A) used independently for priming and elution steps, and tangential flow filtration (TFF) for a range of aquatic samples including fresh, estuarine and marine waters, was undertaken. With freshwater samples XAD8-1, C 18 M and TFF were all observed to recover ca. 80–90% of the lignin phenols and showed no fractionation effects with respect to diagnostic lignin parameters. With estuarine and marine samples more lignin phenols were recovered with C 18 M and XAD8-1 than TFF because of the increased prevalence of low molecular weight lignin phenols in marine influenced samples. For marine systems, differences were also observed between diagnostic lignin parameters isolated via TFF vs. C 18 M and XAD8-1 as a result of the high molecular weight lignin phenols being less degraded than the bulk. Therefore, it is recommended for future studies of marine systems that only one technique is utilized for ease of intercomparison within studies. It is suggested that for studies solely aimed at recovering bulk dissolved lignin in marine environments that C 18 M and XAD8-1 appear to be more suitable than TFF as they recover more lignin. Our results highlight that, for freshwater samples, all three common lignin phenol concentration and isolation techniques are comparable to whole water concentrated by rotary evaporation (i.e. not isolated) but, that for marine systems, the choice of concentration and isolation techniques needs to be taken into consideration with respect to both lignin concentration and diagnostic parameters. Finally, as the study highlights XAD8-1 to be a suitable method for the isolation of dissolved lignin phenols from aquatic systems (statistically indistinguishable from C 18 M, P < 0.1), lignin data representative of whole waters can be produced for IHSS reference materials or other XAD sample archives.

Organic Geochemistry↗

USGS2009

Pedogenesis of a catena of the Farmdale-Sangamon Geosol complex in the north central United States

The Farmdale-Sangamon Geosol pedocomplex consists of the Sangamon Geosol and the overlying Farmdale Geosol, which form the most extensive terrestrial record of the last interglacial to glacial transition in the Midwest United States. The geosol complex formed for upwards of 100??ka, extending from the end of MIS 6 through 4 for the Sangamon Geosol, then the Farmdale Geosol for during a brief episode at the end of MIS 3 following slow accumulation and pedogenic modification of eolian silt deposited on top of the Sangamon Geosol. Our study site consists of a buried paleo-hillslope transect that forms a catena, enabling evaluation of slope effects on interglacial-scale soil formation. The Sangamon Geosol is formed in calcareous and illitic glaciogenic sediment. Along the catena the Sangamon Geosol profiles display some morphological changes, namely in terms of colors that we interpret as indicators of differences in drainage. Most thickness and horizonation characteristics are similar all along the transect, with intact upper sola horizons (AE and E horizons) that overlie clay-enriched Bt horizons. The Bt horizons contain abundant clay that exists as illuvial clay coatings, matrix infills, and as mosaic-speckled domains. The clay originated both by in situ weathering and through illuviation from the clay depleted upper sola. Slope does not appear to affect Bt characteristics beyond redder hues of the matrix and clay coatings in the upper slope position. With depth, effects of carbonate leaching and infilling of clay in the matrix decrease and clay coatings are restricted to walls of voids adjacent to aggregates. Clay mineralogy shows illite depletion, but no interstratified kaolinite-expandable minerals, indicating the degree of weathering is not as great as is typical of Sangamon Geosol profiles formed in loess or in glaciogenic sediment of the central Illinois type area. Clay mineralogy is also stratified with depth, coincident with particle size, which probably indicates sorting of layers of illitic dolomite and shale. Variation of horizon and profile characteristics appears to largely be a function of particle size variability and stratification than topographic position in the catena. The influence of hillslope position on soil redistribution during formation of the Sangamon Geosol appears negligible given the uniformity of upper solum horizon thickness and sandy particle size characteristics, so we conclude that a bioturbation and rainwash origin of the upper solum and the texture contrast in these profiles is not the best process model explanation. We suggest that the base-rich nature of these soils led to ecosystem characteristics that discouraged erosion and encouraged infiltration and a lessivage-type origin of the texture contrast. No convincing evidence of MIS 6 through MIS 4 loess occurs at this site. The Farmdale Geosol formed in the Robein Silt, which is Roxana Silt (MIS 3 loess) that was redistributed downslope. The Robein Silt is thicker and finer in the topographic low and indicates the cooler and forested environmental conditions during MIS 3 were conducive to downslope movement of soil and also produced greater differences in drainage-induced soil morphological changes in the Farmdale Geosol. ?? 2009 Elsevier B.V. All rights reserved.

Palaeogeography, Palaeoclimatology, Palaeoecology↗