Fluid mobilization of rare earth elements,Th, and U during the terrestrial alteration of H chondrites

The chemical effects of terrestrial alteration, with a particular focus on lithophile trace elements, were studied for a set of H chondrites displaying various degrees of weathering from fresh falls to altered finds collected from hot deserts. According to their trace element distributions, a considerable fraction of rare earth elements (REEs), Th, and U resides within cracks observed in weathered meteorite specimens. These cracks appear to accumulate unbound REEs locally accompanied by Th and U relative to the major element abundances, especially P and Si. The deposition of Ce is observed in cracks in the case of most of the weathered samples. Trace element maps visually confirm the accumulation of these elements in such cracks, as previously inferred based on chemical leaching experiments. Because the positive Ce anomalies and unbound REE depositions in cracks occur in all weathered samples studied here while none of such features are observed in less altered samples including falls (except for altered fall sample Nuevo Mercurio), these features are interpreted to have been caused by terrestrial weathering following chemical leaching. However, the overall effects on the bulk chemical composition remain limited as the data for all Antarctic meteorites studied in this work (except for heavily weathered sample A 09516, H6) are in good agreement with published data for unaltered meteorites.     

Approximations to composite GPS protection levels for aircraft precision approach and landing

Persistent pseudorange biases constitute a serious potential integrity problem for differential GPS systems used in aircraft precision approach and landing. Various approaches to solve this problem are documented in the literature, including composite protection levels (PLs) that incorporate an explicit bias term in their mathematical expressions. A statistical characterization for such a PL was previously presented in this journal. Modeling GPS error in the position domain as multivariate normal with nonzero mean resulted in the definition of vertical, horizontal, and radial composite PLs, termed VPL_c, HPL_c, and RPL_c, respectively. In the present effort, approximations to these computationally intensive PLs are presented for possible use in real time. Two of these are shown to be over-bounding approximations to exact quantities VPL_c and HPL_c. An approximation to RPL_c is also presented, as well as a method of quantitative evaluation for each of these composite PLs. Monte-Carlo simulations for a single GPS measurement epoch are then developed to illustrate the exact PLs and their approximations and demonstrate that the approximations to VPL_c and HPL_c over-bound the exact PLs. The approximation to RPL_c is shown to be far simpler computationally than the exact PL, but demonstrating that the approximation is an over-bound is left to future research. This paper makes available to the reader both the methods and the Matlab^? simulation code needed to evaluate computationally efficient PL approximations. Thus, it fosters further research into the use of GPS in safety critical applications.     

Magnetic anomalies and rock magnetism of basalts from Reykjanes (SW-Iceland)

This study presents rock magnetic properties along with magnetic field measurements of different stratigraphic and lithologic basalt units from Reykjanes, the southwestern promontory of the Reykjanes peninsula, where the submarine Reykjanes Ridge passes over into the rift zone of southwestern Iceland. The basaltic fissure eruptions and shield lava of tholeiitic composition (less than 11500 a old) show a high natural remanent magnetization (NRM, J_r) up to 33.6 A/m and high Koenigsberger ratio (Q) up to 52.2 indicating a clear dominance of the NRM compared to the induced part of the magnetization. Pillow basalts and picritic shield lava show distinctly lower J_r values below 10 A/m. Magnetic susceptibility (κ) ranges for all lithologies from 2.5 to 26×10⁻³ SI.     

Hydrogeophysical Methods for Analyzing Aquifer Storage and Recovery Systems

Hydrogeophysical methods are presented that support the siting and monitoring of aquifer storage and recovery (ASR) systems. These methods are presented as numerical simulations in the context of a proposed ASR experiment in Kuwait, although the techniques are applicable to numerous ASR projects. Bulk geophysical properties are calculated directly from ASR flow and solute transport simulations using standard petrophysical relationships and are used to simulate the dynamic geophysical response to ASR. This strategy provides a quantitative framework for determining site‐specific geophysical methods and data acquisition geometries that can provide the most useful information about the ASR implementation. An axisymmetric, coupled fluid flow and solute transport model simulates injection, storage, and withdrawal of fresh water (salinity ～500 ppm) into the Dammam aquifer, a tertiary carbonate formation with native salinity approximately 6000 ppm. Sensitivity of the flow simulations to the correlation length of aquifer heterogeneity, aquifer dispersivity, and hydraulic permeability of the confining layer are investigated. The geophysical response using electrical resistivity, time‐domain electromagnetic (TEM), and seismic methods is computed at regular intervals during the ASR simulation to investigate the sensitivity of these different techniques to changes in subsurface properties. For the electrical and electromagnetic methods, fluid electric conductivity is derived from the modeled salinity and is combined with an assumed porosity model to compute a bulk electrical resistivity structure. The seismic response is computed from the porosity model and changes in effective stress due to fluid pressure variations during injection/recovery, while changes in fluid properties are introduced through Gassmann fluid substitution.     

Short communication: another reason to care about physician health: its role in climate change

There is an important connection between physician well-being, insufficient preventive care for patients, and global warming. Doctors?? good health is linked to patients?? preventive care, because physicians with healthy personal habits are more likely to encourage our patients to adopt such habits. If doctors eat less meat, consume fewer resources and pollute less, we could help our patients do so, too. Our actions help our patients make better choices, and to help heal and strengthen ourselves, our patients, and our planet.     

Reconstruction of a complex late Quaternary glacial landscape in the Cordillera de Cochabamba (Bolivia) based on a morphostratigraphic and multiple dating approach

Although glacial landscapes have previously been used for the reconstruction of late Quaternary glaciations in the Central Andes, only few data exist for the Eastern Cordillera in Bolivia. Here, we present results from detailed morphostratigraphic mapping and new data of surface exposure dating (SED), optically stimulated luminescence (OSL), and radiocarbon dating (¹⁴C) from the Huara Loma Valley, Cordillera de Cochabamba (Bolivia). Discrepancies between individual dating methods could be addressed within the context of a solid geomorphic framework. We identified two major glaciations. The older is not well constrained by the available data, whereas the younger glaciation is subdivided into at least four major glacial stages. Regarding the latter, a first advance dated to ~ 29-25 ka occurred roughly contemporaneous with the onset of the global last glacial maximum (LGM) and was followed by a less extensive (re-)advance around 20-18 ka. The local last glacial maximum (LLGM) in the Huara Loma Valley took place during the humid lateglacial ~ 17-16 ka, followed by several smaller readvances until ~ 10-11 ka, and complete deglaciation at the end of the Early Holocene.     

Late Quaternary lake-level changes of Lake El'gygytgyn, NE Siberia

Lake El'gygytgyn is situated in a 3.6 Ma old impact crater in northeastern Siberia. Presented here is a reconstruction of the Quaternary lake-level history as derived from sediment cores from the southern lake shelf. There, a cliff-like bench 10 m below the modern water level has been investigated. Deep-water sediments on the shelf indicate high lake levels during a warm Mid-Pleistocene period. One period with low lake level prior to Marine Oxygen Isotope Stage (MIS) 3 has been identified, followed by a period of high lake level (10 m above present). In the course of MIS 2 the lake level dropped to − 10 m. At the end of MIS 2 the bench was formed and coarse beach sedimentation occurred. Subsequently, the lake level rose rapidly to the Holocene level. Changes in water level are likely linked to climate variability. During relatively temperate periods the lake becomes free of ice in summer. Strong wave actions transport sediment parallel to the coast and towards the outlet, where the material tends to accumulate, resulting in lake level rise. During cold periods the perennial lake ice cover hampers any wave activity and pebble-transport, keeping the outlet open and causing the lake level to drop.     

Lithostratigraphy of the late Early Permian (Kungurian) Wandrawandian Siltstone,New South Wales: record of glaciation?

The late Early Permian (273 – 271 Ma) Wandrawandian Siltstone in the southern Sydney Basin of New South Wales represents a marine highstand that can be correlated over 2000 km. A mainly fine-grained terrigenous clastic succession, the Wandrawandian Siltstone contains evidence for cold, possibly glacial conditions based on the presence of outsized clasts and glendonites, mineral pseudomorphs after ikaite, a mineral that forms in cold (0 – 7°C) marine sediments. A lithostratigraphic and facies analysis of the unit was conducted, based on extensive coastal outcrops and continuous drillcores. Eight facies associations were identified: (i) siltstone; (ii) siltstone with minor interbedded sandstone; (iii) interbedded tabular sandstone and siltstone; (iv) admixed sandstone and siltstone to medium-grained sandstone; (v) discrete, discontinuous sandstone intervals; (vi) chaotic conglomerate and sandstone in large channel forms; (vii) chaotically bedded and pervasively soft-sediment-deformed intervals; and (viii) tuffaceous siltstone and claystone. Using lithology and ichnology, relative water depths were ascribed to each facies association. Based on these associations, the unit was divided into five informal members that reveal a history of significant relative sea-level fluctuations throughout the formation: member I, interbedded/admixed sandstone and siltstone; member II, siltstone; member III, slumped masses of members I and II; member IV, siltstone and erosionally based lensoid sandstone beds and channel bodies; and member V, interbedded/admixed sandstone and siltstone with abundant tuffs. Member I marks an initial marine transgression from shoreface to offshore depths. Member II records the maximum water depth of the shelf. Member III is interpreted to be a slump sheet; plausible mechanisms for its emplacement include seismicity produced by tectonism or glacio-isostatic rebound, changes in pore-water pressures due to sea-level fluctuations, or an increase in sedimentation rates. Members IV and V record minor fluctuations in depositional environments from offshore to shoreface water depths. Member IV includes regionally extensive, large channel bodies, with composite fills that are interpreted as storm-influenced mass-flow deposits. Member V includes a greater abundance of volcanic ash. Glacial controls (isostasy, eustasy) and tectonic affects may have worked in concert to produce the changes in depositional environments observed in the Wandrawandian Siltstone.