Orthopyroxene rim growth between olivine and quartz at low temperatures (750–950°C) and low water concentration

Orthopyroxene reaction rims were synthesized between polished plates of natural olivine or synthetic forsterite and quartz at 1.9 GPa and temperatures of 750–950°C. The experiments were performed in a piston-cylinder apparatus after drying the samples at 600°C. Each experiment comprised 4 or 7 quartz-olivine contacts that were positioned along a temperature gradient. As a monitor for water content in the samples, the water concentration in the two olivines was determined by FTIR before and after the experiments. The orthopyroxene layers show two different structural variants. Type one (normal layers) has very constant thickness at each contact and formed with equal growth rates at both interfaces. Type two (bulging layers) comprises more irregular areas with 3–5 times thicker rims where porosity provides evidence for the local presence of a fluid. In the bulging layers the growth rate at the olivine-orthopyroxene interface exceeds that at the quartz-orthopyroxene interface. The relative growth rates at the interfaces are in accordance with SiO₂-immobile growth of the normal layers and SiO₂-mobile growth of the bulging layers. The natural olivine contains about 60 wt-ppm intracrystalline water before and after experiment and took up about 20 wt-ppm water molecular adsorbed to micro- and nanocracks and -pores during the runs. The synthetic forsterite contains about 7 wt-ppm internally adsorbed molecular water before and after experiment, and during the runs took up hydrogen equivalent to 3 wt-ppm adsorbed water. The IR spectra indicate that large parts of the point defects (possibly tetrahedral) were frozen-in at the conditions of the experiments. In both olivines a new band appeared at 3,355 or 3,357 cm^?1, respectively, equivalent to about 3 wt-ppm water that at the high pressure of the experiments and opx-buffered aSiO₂ of the experiments might already mean water saturation of the olivines. Despite the effective drying before experiment and the absence of porosity, the bulk diffusivity derived from the rim growth rates is perfectly in line with data from water-bearing piston-cylinder experiments at higher temperatures. The bulk diffusivity during rim growth is 4 to 7 orders of magnitude higher than an extrapolation of really dry experiments to the temperature range of this study.     

Catalogue of ${>}\,55$ MeV Wide-longitude Solar Proton Events Observed by SOHO,ACE, and the STEREOs at ≈1${\approx}\,1$ AU During 2009 – 2016

Based on energetic particle observations made at \({\approx}\,1\) AU, we present a catalogue of 46 wide-longitude (\({>}\,45^{\circ}\)) solar energetic particle (SEP) events detected at multiple locations during 2009?–?2016. The particle kinetic energies of interest were chosen as \({>}\,55\) MeV for protons and 0.18?–?0.31 MeV for electrons. We make use of proton data from the Solar and Heliospheric Observatory/Energetic and Relativistic Nuclei and Electron Experiment (SOHO/ERNE) and the Solar Terrestrial Relations Observatory/High Energy Telescopes (STEREO/HET), together with electron data from the Advanced Composition Explorer/Electron, Proton, and Alpha Monitor (ACE/EPAM) and the STEREO/Solar Electron and Proton Telescopes (SEPT). We consider soft X-ray data from the Geostationary Operational Environmental Satellites (GOES) and coronal mass ejection (CME) observations made with the SOHO/Large Angle and Spectrometric Coronagraph (LASCO) and STEREO/Coronagraphs 1 and 2 (COR1, COR2) to establish the probable associations between SEP events and the related solar phenomena. Event onset times and peak intensities are determined; velocity dispersion analysis (VDA) and time-shifting analysis (TSA) are performed for protons; TSA is performed for electrons. In our event sample, there is a tendency for the highest peak intensities to occur when the observer is magnetically connected to solar regions west of the flare. Our estimates for the mean event width, derived as the standard deviation of a Gaussian curve modelling the SEP intensities (protons \({\approx}\,44^{\circ}\), electrons \({\approx}\,50^{\circ}\)), largely agree with previous results for lower-energy SEPs. SEP release times with respect to event flares, as well as the event rise times, show no simple dependence on the observer’s connection angle, suggesting that the source region extent and dominant particle acceleration and transport mechanisms are important in defining these characteristics of an event. There is no marked difference between the speed distributions of the CMEs related to wide events and the CMEs related to all near-Earth SEP events of similar energy range from the same time period.     

Molecular composition and chemosystematic aspects of Cretaceous amber from the Amazonas,Araripe and Recôncavo basins,Brazil

Amber occurrences in Brazil are rare. In this regard, the molecular composition of three such fossil resin samples from Brazilian Cretaceous sedimentary basins has been analyzed to determine the botanical origin of the resins. The samples were collected from the Amazonas (Alter do Chão Formation), Araripe (Santana Formation, Crato Member) and Recôncavo (Maracangalha Formation, Caruaçu Member) basins. The mono-, sesqui- and diterpenoids in the extracts were used as chemosystematic markers when compared with terpenoids in extant conifers. The compounds were mainly diterpenoids and their degradation products from the labdane, podocarpane, pimarane and isopimarane classes, in addition to paraffins, methoxyphenols and carboxylic acids. Tetracyclic diterpenoids such as phyllocladane, kaurenol and kauranol were also present. The biomarker compositions are certainly typical for conifers and, given the absence of triterpenoids and diterpenoids such as ozic acid, angiosperms can be excluded as a botanical source. The absence of phenolic diterpenoids (ferruginol, totarol) and their derivatives excludes podocarpaceous affinities for the ambers from the Amazonas and Araripe basins. The fossil records of the embedding sediments (e.g. Araucariaceae pollen and leaves) support the proposal of an Araucariacae origin for these ambers, but Cupressaceae and Cheirolepidiaceae cannot be excluded. On the other hand, the presence of phyllocladane and kaurane derivatives is evidence for Araucariaceae or Podocarpaceae origins for the amber from the Recôncavo basin, but Cupressaceae cannot be excluded.     

Oligo-Miocene shearing along the Ailao Shan–Red River shear zone: Constraints from structural analysis and zircon U/Pb geochronology of magmatic rocks in the Diancang Shan massif, SE Tibet, China

The left-lateral strike-slip shearing along the Ailao Shan–Red River (ASRR) shear zone in the Southeastern Tibet, China, has been widely advocated to be a result of the Indian–Eurasian plate collision and post-collisional processes. The Diancang Shan (DCS) massif, which occurs at the northwestern extension of the Ailao Shan massif, is a typical high-grade metamorphic complex aligned along the ASRR tectonic belt. Structural and microstructural analysis of the plutonic intrusions in the DCS revealed different types of granitic intrusions spatially confined to the shear zone and temporally related to the left-lateral shearing along the ASRR shear zone in the DCS massif. The combined structural and geochronological results of SHRIMP-II and LA-ICP-MS zircon U/Pb isotopic dating have revealed successive magmatic intrusions and crystallization related to the Oligo-Miocene shearing in the DCS massif. The pre-, early- and syn-kinematic emplacements are linked to regional high-temperature deformation (lower amphibolite facies) at relatively deep crustal levels. The zircon U/Pb geochronological results suggest that the left-lateral ductile shearing along the ASRR shear zone was initiated at ca. 31 Ma, culminated between ca. 27 and 21 Ma resulting in high-temperature metamorphic conditions and slowed down at ca. 20 Ma at relatively low-temperatures.     

Holocene environmental change in the Skallingen area,eastern North Greenland,based on a lacustrine record

A lacustrine record from a small lake, Lille Sneha Sø, in the Skallingen area indicates that the region was deglaciated in the early Holocene, prior to 8000 cal. a BP. Deglaciation was probably triggered by high temperatures, but it took more than 1000 years for the lake and the catchment to stabilize. Chironomids were amongst the first invertebrates to colonize the lake. The fossil chironomid assemblage is fairly rich and comparable to other records from further south in Greenland. The pioneer vegetation in the area consisted of mosses and herbaceous plants. The oldest remains of woody plants (Salix arctica) are dated to c. 7700 cal. a BP, and remains of Dryas integrifolia appear at around 6700 cal. a BP; these are the only woody plants recorded. Maximum concentrations of chironomids, maximum occurrence of ephippia of the water flea Daphnia pulex, highest organic matter contents and lowest minerogenic input from c. 7700 to 4400 cal. a BP probably reflect the Holocene thermal maximum (HTM). The highest temperatures during the HTM are indicated around 7000 cal. a BP, when Salix arctica, which is considered a warmth‐loving plant, had a maximum. Comparisons with Holocene records from East and North Greenland show similar immigration histories and similar trends, with the Little Ice Age as the coldest period during the Holocene, culminating about 150 years ago. Subsequent warming does not indicate environmental conditions comparable to the HTM yet at this stage. The occurrence of several warmth‐demanding species particularly in the early Holocene sediments indicates redeposition and implies that temperatures in the past, most likely during an interglacial period, were significantly higher than during the HTM.     

Fabrication of synthetic calcite–muscovite rocks with variable texture — An analogue to cataclasite fabrics?

A series of large diameter calcite–muscovite aggregates has been prepared from calcite and muscovite powders, in order to gain a better understanding of how texture develops in impure carbonate rocks. The development of the microstructure and the crystallographic preferred orientation (CPO, texture) during the preparation process is described. The synthetic rocks have been fabricated from powders of calcite and muscovite by uniaxial cold-pressing at loads up to 400 MPa and subsequent hot isostatic pressing (HIPping) at pressures of 150 to 170 MPa and a temperature of 670 °C. The resulting textures and microstructures are homogeneous throughout the samples. The calcite CPO is generated by rigid body rotation and twinning during cold-pressing and is not significantly altered by recrystallization during HIPping. Grain growth during HIPping is observed in pure calcite samples, but is inhibited through high porosity and the presence of muscovite in the mixed aggregates. The preferred orientation of the calcite c-axes is found to increase with increasing uniaxial cold pressure, and to be independent of the muscovite content. The magnetic bulk susceptibility of the starting material has been changed by the formation of ferromagnetic impurities during fabrication. Comparison of the samples to natural calcite fabrics from fault zones show the potential of the experiments and fabric analyses presented to analyze and to better understand the deformation mechanisms of fault zones.     

Modelling blue and green water availability under climate change in the Beninese Basin of the Niger River Basin,West Africa

The aim of this study was to quantify climate change impact on future blue water (BW) and green water (GW) resources as well as the associated uncertainties for 4 subbasins of the Beninese part of the Niger River Basin. The outputs of 3 regional climate models (HIRHAM5, RCSM, and RCA4) under 2 emission scenarios (RCP4.5 and RCP8.5) were downscaled for the historical period (1976–2005) and for the future (2021–2050) using the Statistical DownScaling Model (SDSM). Comparison of climate variables between these 2 periods suggests that rainfall will increase (1.7% to 23.4%) for HIRHAM5 and RCSM under both RCPs but shows mixed trends (?8.5% to 17.3%) for RCA4. Mean temperature will also increase up to 0.48 °C for HIRHAM5 and RCSM but decrease for RCA4 up to ?0.37 °C. Driven by the downscaled climate data, future BW and GW were evaluated with hydrological models validated with streamflow and soil moisture, respectively. The results indicate that GW will increase in all the 4 investigated subbasins, whereas BW will only increase in one subbasin. The overall uncertainty associated with the evaluation of the future BW and GW was quantified through the computation of the interquartile range of the total number of model realizations (combinations of regional climate models and selected hydrological models) for each subbasin. The results show larger uncertainty for the quantification of BW than GW. To cope with the projected decrease in BW that could adversely impact the livelihoods and food security of the local population, recommendations for the development of adequate adaptation strategies are briefly discussed.     

Mollusc and brachiopod skeletal hard parts: Intricate archives of their marine environment

The biogenic carbonate hard parts of fossil bivalves, cephalopods and brachiopods are among the most widely exploited marine archives of Phanerozoic environmental and climate dynamics research. The advent of novel analytical tools has led many workers to explore non‐traditional geochemical and petrographic proxies, and work performed in neighbouring disciplines sheds light on the complex biomineralization strategies applied by these organisms. These considerations form a strong motivation to review the potential and problems related to the compilation and interpretation of proxy data from bivalve, cephalopod and brachiopod hard parts from the viewpoint of the sedimentologist and palaeoceanographer. Specific focus is on the complex biomineralization pathways of a given dissolved ion or food particle from its aquatic environment via the digestion and biomineralization apparatus in molluscs and brachiopods and its incorporation into a biomineral. Given that molluscs and brachiopods do not secrete their hard parts from seawater but rather from their mantle and periostracum, this paper evaluates differences and similarities of seawater versus that of body fluids. Cephalopods, bivalves and brachiopods exert a strong biological control on biomineralization that, to some degree, may buffer their shell geochemistry against secular changes in seawater chemistry. Disordered (amorphous) calcium carbonate precursor phases, later transformed to crystalline biominerals, may be significant in carbonate archive research due to expected geochemical offset relative to the direct precipitation of stable phases. A reasonable level of understanding of the related mechanisms is thus crucial for those who use these skeletal hard parts as archives of the palaeo‐environment. The impact of what is commonly referred to as ‘biological factors’ on the geochemistry of mollusc and brachiopod hard parts is explored for conventional isotope systems such as carbon, oxygen, strontium and traditionally used element to calcium ratios. In particular, the often used δ¹³C_carb or the Mg/Ca and Sr/Ca elemental proxies are fraught with problems. An interesting new research field represents the analysis, calibration and application of non‐traditional proxies to mollusc and brachiopod hard parts. Examples include the carbonate clumped isotope (Δ₄₇) approach and the analysis of the isotopes of Ca, Mg, N, Li, S or element to Ca ratios such as Li/Ca or B/Ca and rare earth elements. Based on considerations discussed here, a series of “do's and don'ts” in mollusc and brachiopod archive research are proposed and suggestions for future work are presented. In essence, the suggestions proposed here include experimental work (also field experiments) making use of recent archive organisms or, where possible, a reasonable recent analogue in the case of extinct groups. Moreover, the detailed understanding of the architecture of mollusc and brachiopod hard parts and their ultra‐structures must guide sampling strategies for geochemical analyses. Where feasible, a detailed understanding of the diagenetic pathways and the application of multi‐proxy and multi‐archive approaches should form the foundation of fossil carbonate archive research. The uncritical compilation of large data sets from various carbonate‐shelled organisms collected at different locations is not encouraged.     

Predicting the impact of linear landscape elements on surface runoff,soil erosion,and sedimentation in the Wahnbach catchment,Germany

Model predictions concerning the endangerment of on‐site and off‐site damages due to runoff, soil erosion and sedimentation under alternative design and operation policies are of particular importance in recent catchment planning and management. By using the raster‐based model approach, linear landscape elements, such as streets and roads, and their impacts on flow paths are often neglected. Therefore, the aim of this study was to analyse the effects of linear landscape elements on patterns of soil erosion, sediment transport and sedimentation. To accomplish this, roads are considered while determining flow paths. Simulations in the well‐investigated catchment of the Wahnbach River (54 km²) in a low mountain range in Germany were carried out using a combination of different models for hydrology and soil erosion. Although the study focuses on the catchment scale of the Wahnbach River, detailed investigations concerning the sub‐catchment scale (21 ha) were also conducted. The simulation results show that these spatial structures mainly affect the pattern of soil erosion and sedimentation. On the sub‐catchment scale, improved identification of active zones for sediment dynamic becomes possible. On the catchment scale, the predicted runoff is about 20% higher, and sediment outputs were four times larger than predicted when roads were considered. Soil erosion increases by 37% whereas sedimentation is reduced by 29%. The model improvement could not be evaluated on the catchment scale because of the high variability and heterogeneity of land use and soils, but road impacts could be explained by simulations on the sub‐catchment scale. It can be concluded that runoff concentration due to rerouted flow paths leads to lower non‐concentrated and higher concentric‐linear surface runoff. Thus, infiltration losses decline and surface runoff and soil erosion increase because sedimentation is reduced. Further, runoff concentration can cause soil erosion hot spots. In the model concept used in this study, buffering of runoff and sediments on the upslope side of roads and in local depressions adjacent to roads cannot be simulated. Flow paths will only be rerouted because of road impacts, but the temporal ponding of water is not simulated. Therefore, the drastic increase of predicted sediment output due to road impact does not seem to be reliable. However, results indicate that the consideration of roads when determining flow paths enabled more detailed simulations of surface runoff, soil erosion and sedimentation. Thus, progress in model‐based decision‐making support for river catchment planning and management can be achieved. Copyright © 2011 John Wiley & Sons, Ltd.     

Relative sea level changes during the Holocene in the Sisimiut area,south‐western Greenland

Holocene relative sea level (RSL) changes have been investigated by analysing and dating isolation sequences from five lakes near Sisimiut in south‐western Greenland. The transitions between marine and lacustrine sediments were determined from elemental analyses and analyses of macroscopic plant and animal remains. Radiocarbon dating was used to provide minimum ages for the transitions and to construct a RSL curve. Dating of a shell of the marine bivalve Macoma balthica indicates that deglaciation of the lowlands occurred in the early Holocene, at around 10 900 cal a BP. The RSL curve shows initial rapid regression from the marine limit at around 140 m, implying strong glacio‐isostatic rebound. We suggest that the margin of the Greenland Ice Sheet was located at the shelf break during the Last Glacial Maximum. Frequent remains of the ostracode Sarcypridopsis aculeata, which is a thermophilous brackish water species that is unknown from the extant fauna of Greenland, in one of the basins around 8500 cal a BP may mark the beginning of the Holocene thermal maximum in the region. Copyright © 2011 John Wiley & Sons, Ltd.