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The Garzn Complex of the Garzn Massif in SW Colombia is composed of the Vergel Granulite Unit (VG) and the Las Margaritas Migmatite Unit (LMM). Previous studies reveal peak temperature conditions for the VG of about 740 A degrees C. The present study considers the remarkable exsolution phenomena in feldspars and pyroxenes and titanium-in-quartz thermometry. Recalculated ternary feldspar compositions indicate temperatures around 900-1,000 A degrees C just at or above the ultra-high temperature-metamorphism (UHTM) boundary of granulites. The calculated temperatures range of exsolved ortho- and clinopyroxenes also supports the existence of an UHTM event. In addition, titanium-in-quartz thermometry points towards ultra-high temperatures. It is the first known UHTM crustal segment in the northern part of South America. Although a mean geothermal gradient of ca 38 A degrees C km(-1) could imply additional heat supply in the lower crust controlling this extreme of peak metamorphism, an alternative model is suggested. The formation of the Vergel Granulite Unit is supposed to be formed in a continental back-arc environment with a thinned and weakened crust behind a magmatic arc (Guapotn-Mancagua Gneiss) followed by collision. In contrast, rocks of the adjacent Las Margaritas Migmatite Unit display "normal" granulite facies temperatures and are formed in a colder lower crust outside the arc, preserved by the Guapotn-Mancagu Gneiss. Back-arc formation was followed by inversion and thickening of the basin. The three units that form the modern-day Garzn Massif, were juxtaposed upon each other during collision (at ca. 1,000 Ma) and exhumation. The collision leading to the deformation of the studied area is part of the Grenville orogeny leading to the amalgamation of Rodinia.
The actual evapotranspiration is an important, but difficult to determine, element in the water balance of lakes and their catchment areas. Reliable data on evapotranspiration are not available for most lake basins for which paleoclimate reconstructions and modeling have been performed, particularly those in remote parts of Africa. We have used thermal infrared multispectral data for 14 ASTER scenes from the TERRA satellite to estimate the actual evapotranspiration in the 12,800 km(2) catchment of the Suguta Valley, northern Kenya Rift Evidence from sediments and paleo-shorelines indicates that, during the African Humid Period (AHP, 14.8 to 5.5 kyrs BP), this valley contained a large lake, 280 m deep and covering similar to 2200 km(2), which has now virtually disappeared. Evapotranspiration estimates for the Suguta Basin were generated using the Surface Energy Balance Algorithm for Land (SEBAL). Climate data required for the model were extracted from a high-resolution gridded dataset obtained from the Climatic Research Unit (East Anglia, UK). Results suggest significant spatial variations in evapotranspiration within the catchment area (ranging from 450 mm/yr in the basin to the north to 2000 mm/yr in more elevated areas) and precipitation that was similar to 20% higher during the AHP than in recent times. These results are in agreement with other estimates of paleo-precipitation in East Africa. The extreme response of the lake system (similar to 280 m greater water depth than today, and a lake surface area of 2200 km(2)) to only moderately higher precipitation illustrates the possible sensitivity of this area to future climate change.
A temporary seismic network composed of 11 stations was installed in the city of Potenza (Southern Italy) to record local and regional seismicity within the context of a national project funded by the Italian Department of Civil Protection (DPC). Some stations were moved after a certain time in order to increase the number of measurement points, leading to a total of 14 sites within the city by the end of the experiment. Recordings from 26 local earthquakes (M-l 2.2-3.8 ) were analyzed to compute the site responses at the 14 sites by applying both reference and non-reference site techniques. Furthermore, the Spectral Intensity (SI) for each local earthquake, as well as their ratios with respect to the values obtained at a reference site, were also calculated. In addition, a field survey of 233 single station noise measurements within the city was carried out to increase the information available at localities different from the 14 monitoring sites. By using the results of the correlation analysis between the horizontal-to-vertical spectral ratios computed from noise recordings (NHV) at the 14 selected sites and those derived by the single station noise measurements within the town as a proxy, the spectral intensity correction factors for site amplification obtained from earthquake analysis were extended to the entire city area. This procedure allowed us to provide a microzonation map of the urban area that can be directly used when calculating risk scenarios for civil defence purposes. The amplification factors estimated following this approach show values increasing along the main valley toward east where the detrital and alluvial complexes reach their maximum thickness.
Ostracods from water bodies in hyperarid Israel and Jordan as habitat and water chemistry indicators
(2012)
The hyperarid region of Israel and Jordan covers a large area where numerous sites of Pleistocene lake sediments suggest that climate conditions were significantly wetter during the Pleistocene. This region experienced a significant increase in aridity in recent decades and the number of existing surface waters is diminishing rapidly. We studied ostracod shells from 49 pond and stream sites to determine the species distribution and to infer ecological preferences especially with respect to general differences in water movement, conductivity and ion composition. Twenty-two ostracod species were identified in total of which 12 taxa occur at three or more sites. Among the rarer species. Cyprinotus scholiosus was identified for the first time after two records from Plio- and Pleistocene sites in Yemen and Saudi Arabia. Further, Paracypretta amati was recorded and its ecological preferences discussed for the first time following the description of the species from its type locality in Sudan. Cypridopsis elongata is the only typical inhabitant of lotic habitats, strictly preferring freshwater conditions and waters with an alkalinity/Ca ratio around 1 and cations dominated by Ca(2+) and anions by HCO(3)(-). In contrast, Cyprideis torosa, Limnocythere inopinata and Heterocypris incongruens apparently prefer waters dominated by Na(+) associated with cations and Cl(-) associated with anions. Heterocypris salina and C. torosa occur over a wide conductivity (or salinity) range and in waters with alkalinity/Ca ratios around 1 and with significant alkalinity depletion. Humphcypris subterranea, Ilyocypris spp. and H. sauna are the only taxa which do not show any preference with respect to both the cation and anion dominance of the waters. The ecological preferences of the ostracod species from water bodies in the study area are discussed in detail and can be used for a qualitative assessment of the hydrodynamical and hydrochemical conditions of former water bodies in the presently hyperarid environment based on ostracod species composition analysis of Pleistocene aquatic sediments.
Ostracodes (Ostracoda, Crustacea) are aquatic micro-crustaceans with a significant representation in the fossil record. If the environmental influence on the species composition of their communities is robustly quantified, past changes in ostracode communities reflected in fossil assemblages can be used for paleo-environmental reconstruction. We analyzed ostracode assemblages in recently deposited surface sediments from 56 lakes in western and central Mongolia, and simultaneously recorded local water chemistry and solute concentration in order to elucidate the distribution of individual ostracode species in relation to these broad environmental gradients. Multivariate analysis indicated that the species variation in ostracode assemblages could be mainly attributed to variations in percent calcium (%Ca) relative to total cation content, mean annual precipitation, calcium concentration, alkalinity, percent bicarbonate relative to total anion content, and mean July temperature. This matches well with the results of a similar analysis on presence/absence data of living ostracodes in nearshore samples, even though some differences exist between the faunal composition of both datasets. The documented response of ostracode species to environmental variation tracks the typical solute evolutionary pathway for surface waters in this region, characterized by calcite precipitation and consequent depletion in dissolved calcium. Hence, the best quantitative inference model (WA-PLS model with R-jack(2) = 0.70, RMSEP = 0.40) for paleolimnological application was obtained for %Ca. Comparison between this model and a specific conductance (SC) inference model based on the same dataset, and based on ostracode datasets from different regions, indicated that the %Ca inference model suffers less than the SC inference model from a step-change in reconstructed values. The statistical power of different inference models based on Mongolian ostracodes are variously affected by the common dominance of a single euryhaline species (Limnocythere inopinata), limited faunal turnover in the freshwater portion of the salinity gradient, and the bimodal frequency distribution of SC among regional lakes. The latter probably represents true scarcity of lakes with intermediate salinity rather than a biased representation in our dataset. In a broader context of ostracode ecology, and with respect to regional paleolimnological applications, we highlight the potential of fossil Mongolian ostracode assemblages to trace past hydrological shifts associated with changes in groundwater inflow.
We investigate the crust, upper mantle and mantle transition zone of the Cape Verde hotspot by using seismic P and S receiver functions from several tens of local seismograph stations. We find a strong discontinuity at a depth of similar to 10 km underlain by a similar to 15-km thick layer with a high (similar to 1.9) Vp/Vs velocity ratio. We interpret this discontinuity and the underlying layer as the fossil Moho, inherited from the pre-hotspot era, and the plume-related magmatic underplate. Our uppermost-mantle models are very different from those previously obtained for this region: our S velocity is much lower and there are no indications of low densities. Contrary to previously published arguments for the standard transition zone thickness our data indicate that this thickness under the Cape Verde islands is up to similar to 30 km less than in the ambient mantle. This reduction is a combined effect of a depression of the 410-km discontinuity and an uplift of the 660-km discontinuity. The uplift is in contrast to laboratory data and some seismic data on a negligible dependence of depth of the 660-km discontinuity on temperature in hotspots. A large negative pressure-temperature slope which is suggested by our data implies that the 660-km discontinuity may resist passage of the plume.
Our data reveal beneath the islands a reduction of S velocity of a few percent between 470-km and 510-km depths. The low velocity layer in the upper transition zone under the Cape Verde archipelago is very similar to that previously found under the Azores and a few other hotspots. In the literature there are reports on a regional 520-km discontinuity, the impedance of which is too large to be explained by the known phase transitions. Our observations suggest that the 520-km discontinuity may present the base of the low-velocity layer in the transition zone.
Hydrogen isotope values (delta D) of sedimentary aquatic and terrestrial lipid biomarkers, originating from algae, bacteria, and leaf wax, have been used to record isotopic properties of ancient source water (i.e., precipitation and/or lake water) in several mid-and high-latitude lacustrine environments. In the tropics, however, where both processes associated with isotope fractionation in the hydrologic system and vegetation strongly differ from those at higher latitudes, calibration studies for this proxy are not yet available. To close this gap of knowledge, we sampled surface sediments from 11 lakes in Cameroon to identify those hydro-climatological processes and physiological factors that determine the hydrogen isotopic composition of aquatic and terrestrial lipid biomarkers. Here we present a robust framework for the application of compound-specific hydrogen isotopes in tropical Africa. Our results show that the delta D values of the aquatic lipid biomarker n-C(17) alkane were not correlated with the delta D values of lake water. Carbon isotope measurements indicate that the n-C(17) alkane was derived from multiple source organisms that used different hydrogen pools for biosynthesis. We demonstrate that the delta D values of the n-C(29) alkane were correlated with the delta D values of surface water (i.e., river water and groundwater), which, on large spatial scales, reflect the isotopic composition of mean annual precipitation. Such a relationship has been observed at higher latitudes, supporting the robustness of the leaf-wax lipid delta D proxy on a hemispheric spatial scale. In contrast, the delta D values of the n-C(31) alkane did not show such a relationship but instead were correlated with the evaporative lake water delta D values. This result suggests distinct water sources for both leaf-wax lipids, most likely originating from two different groups of plants. These new findings have important implications for the interpretation of long-chain n-alkane delta D records from ancient lake sediments. In particular, a robust interpretation of palaeohydrological data requires knowledge of the vegetation in the catchment area as different plants may utilise different water sources. Our results also suggest that the combination of carbon and hydrogen isotopes does help to differentiate between the metabolic pathway and/or growth form of organisms and therefore, the source of hydrogen used during lipid biosynthesis.
In Central and NW Europe, the transition from the Permian to the Triassic (i.e., the Zechstein-Buntsandstein boundary interval) is developed mainly in red bed facies. This continental sedimentary succession is marked by relatively high sedimentation rates providing a high temporal resolution favorable for magnetic polarity stratigraphy. Here, we present a Zechstein to Lower Buntsandstein magnetostratigraphy obtained from the c. 100 m thick Everdingen-1 core from the Netherlands. Seven magnetozones (EV1n to EV4n) and five submagnetozones (EV1n.1r to EV3r.1n) have been delineated. The Everdingen-1 magnetostratigraphy has been integrated into the well-established high-resolution Zechstein-Buntsandstein stratigraphic framework, and verifies the geomagnetic polarity record from Central Germany. This confirms the hypothesis of nearly synchronous base-level cycles within the interior of the Central European Basin. These cycles are related to solar-induced similar to 100 ka eccentricity cycles. The most distinctive feature of the Everdingen-1 magnetostratigraphy is a transition from a thin reverse to a thick dominantly normal magnetic polarity interval. This reversal predates both the terrestrial mass extinction, which is indicated by a palynofloral turnover and a major sediment provenance change at the base of the Buntsandstein, and the marine Permian-Triassic Boundary (PTB). The PTB is located within the lowermost Buntsandstein and is approximated by the last occurrence of the conchostracan Falsisca postera and a negative excursion in the carbon isotope record. According to the Buntsandstein cyclostratigraphy, the R/N reversal predates the marine end-Permian extinction event by about 0.1 Ma and the marine biostratigraphic PTB by about 0.2 Ma. The thick normal magnetozone is estimated to have lasted c. 700 ka, and roughly coincides with the main phase of Siberian Trap volcanism.
Disproportionate single-species contribution to canopy-soil nutrient flux in an Amazonian rainforest
(2012)
Rainfall, throughfall and stemflow were monitored on an event basis in an undisturbed open tropical rainforest with a large number of palm trees located in the southwestern Amazon basin of Brazil. Stemflow samples were collected from 24 trees with a diameter at breast height (DBH) > 5 cm, as well as eight young and four full-grown babassu palms (Attalea speciosa Mart.) for 5 weeks during the peak of the wet season. We calculated rainfall, throughfall and stemflow concentrations and fluxes of Na+, K+, Ca2+, Mg2+,, Cl-, SO42-, NO3- and H+ and stemflow volume-weighted mean concentrations and fluxes for three size classes of broadleaf trees and three size classes of palms. The concentrations of most solutes were higher in stemflow than in rainfall and increased with increasing tree and palm size. Concentration enrichments from rainfall to stemflow and throughfall were particularly high (81-fold) for NO3-. Stemflow fluxes of NO3- and H+ exceeded throughfall fluxes but stemflow fluxes of other solutes were less than throughfall fluxes. Stemflow solute fluxes to the forest soil were dominated by fluxes on babassu palms, which represented only 4% of total stem number and 10% of total basal area. For NO3-, stemflow contributed 51% of the total mass of nitrogen delivered to the forest floor (stemflow + throughfall) and represented more than a 2000-fold increase in NO3- flux compared what would have been delivered by rainfall alone on the equivalent area. Because these highly localized fluxes of both water and NO3- persist in time and space, they have the potential to affect patterns of soil moisture, microbial populations and other features of soil biogeochemistry conducive to the creation of hotspots for nitrogen leaching and denitrification, which could amount to an important fraction of total ecosystem fluxes. Because these hotspots occur over very small areas, they have likely gone undetected in previous studies and need to be considered as an important feature of the biogeochemistry of palm-rich tropical forest.
Evaluation of organic matter stability in wood compost by chemical and thermogravimetric analysis
(2012)
This study investigated maturation and stability levels during composting of Quercus robur (QR) woodchips mixed with different nitrogen sources (horse manure, HM and lake mud, LM) for potential agronomic utilisation. The woodchips were mixed with HM and LM, respectively, at mixing ratios of 1QR:2HM or QR:2LM. The experiment was conducted in a greenhouse over 100 days. During composting, organic carbon and its fractioning and humification constituents were quantified. In the final compost product, pH, organic matter (OM), cation exchange capacity (CEC) and selected available nutrients were measured. Thermostability of compost, compared with that of soil and compost mixed with charcoal were also quantified. Results showed OM evolution during the composting process with total organic and extractable carbons and humification indices decreasing, while the degree of humification increased. Compost produced from the 1QR:2HM mix resulted in the highest available nutrients, CEC and OM content values in the final product. Thermogravimetric profiles indicated that compost OM thermostability was higher than that in soil and higher for the 1QR:2HM than the 1QR:2LM mix. Application of charcoal revealed no additional stabilising effect of OM in wood compost.
Decomposition of geophysical signals (e.g., seismic and ground-penetrating radar data) into the time-frequency domain can provide valuable information for advanced interpretation (e.g., tuning effects) and processing (e.g., inverse Q-filtering). The quality of these subsequent processing steps is strongly related to the resolution of the selected time-frequency representation (TFR). In this study, we introduce a high-resolution spectral decomposition approach representing an extension of the recently proposed Tree-Based Pursuit (TBP) method. TBP significantly reduces the computational cost compared to the well known Matching Pursuit (MP) technique by introducing a tree structure prior to the actual matching procedure. Following the original implementation of TBP, we additionally incorporate waveforms commonly used in geophysical data processing and present an alternative approach to take phase shifts into account. Application of the proposed method to synthetic data and comparison of the results with other typically used decomposition approaches, illustrate the ability of our approach to provide decomposition results highly localized in both time and frequency. Applying our procedure to field GPR data illustrates its applicability to real data and provides examples for potential applications such as analyzing thin-bed responses and modulating the data frequency content.
The Maule earthquake of 27th February 2010 (M-w = 8.8) affected similar to 500 km of the Nazca-South America plate boundary in south-central Chile producing spectacular crustal deformation. Here, we present a detailed estimate of static coseismic surface offsets as measured by survey and continuous GPS, both in near- and far-field regions. Earthquake slip along the megathrust has been inferred from a Joint inversion of our new data together with published GPS, InSAR, and land-level changes data using Green's functions generated by a spherical finite-element model with realistic subduction zone geometry. The combination of the data sets provided a good resolution, indicating that most of the slip was well resolved. Coseismic slip was concentrated north of the epicenter with up to 16 m of slip, whereas to the south it reached over 10 m within two minor patches. A comparison of coseismic slip with the slip deficit accumulated since the last great earthquake in 1835 suggests that the 2010 event closed a mature seismic gap. Slip deficit distribution shows an apparent local overshoot that highlight cycle-to-cycle variability, which has to be taken into account when anticipating future events from interseismic observations. Rupture propagation was obviously not affected by bathymetric features of the incoming plate. Instead, splay faults in the upper plate seem to have limited rupture propagation in the updip and along-strike directions. Additionally, we found that along-strike gradients in slip are spatially correlated with geometrical inflections of the megathrust. Our study suggests that persistent tectonic features may control strain accumulation and release along subduction megathrusts.
While the Dead Sea basin has been studied for a long time, the available knowledge about the detailed seismicity distribution in the area, as well as the deeper structure of the basin, is limited. Therefore, within the framework of the international project DESIRE (DEad Sea Integrated REsearch project), a dense temporary local seismological network was operated in the southern Dead Sea area. We use 530 local earthquakes, having all together 26 730 P- and S-arrival times for a simultaneous inversion of 1-D velocity models, station corrections and precise earthquake locations. Jackknife tests suggest an accuracy of the derived hypocentre locations of about 1 km. Thus, the result is the first clear image of the absolute distribution of the microseismicity of the area, especially in depth. The seismicity is concentrated in the upper crust down to 20 km depth while the lower limit of the seismicity is reached at 31 km depth. The seismic events at the eastern boundary fault (EBF) in the southern part of the study area represent the northward transform motion of the Arabian Plate along the Dead Sea Transform. North of the Boqeq fault the seismic activity represents the transfer of the motion in the pull-apart basin from the eastern to the western boundary. We find that from the surface downward the seismic events are tracing the boundary faults of the basin. The western boundary is mapped down to 12 km depth while the EBF reaches about 17 km depth, forming an asymmetric basin. One fifth of the data set is related to a specific cluster in time and space, which occurred in 2007 February at the western border fault. This cluster is aligned vertically, that is, it is perpendicular to the direction of the dominating left-lateral strike-slip movement at the main transform fault.
Splay faults are thrusts that emerge from the plate boundaries of subduction zones. Such structures have been mapped at several convergent margins and their activity commonly ascribed to large megathrust earthquakes. However, the behavior of splay faults during the earthquake cycle is poorly constrained because typically these structures are located offshore and are difficult to access. Here we use geologic mapping combined with space and land geodesy, as well as offshore sonar data, to document surface-fault ruptures and coastal uplift at Isla Santa Maria in south-central Chile (37 degrees S) caused by the 27 February 2010 Maule earthquake (M-w 8.8). During the earthquake, the island was tilted parallel to the margin, and normal faults ruptured the surface and adjacent ocean bottom. We associate tilt and crestal normal faulting with growth of an anticline above a blind reverse fault rooted in the Nazca-South America plate boundary, which slipped during the Maule earthquake. The splay fault system has formed in an area of reduced coseismic plate-boundary slip, suggesting that anelastic deformation in the upper plate may have restrained the 2010 megathrust rupture. Surface fault breaks were accompanied by prominent discharge of fluids. Our field observations support the notion that splay faulting may frequently complement and influence the rupture of subduction-zone earthquakes.
Polarization of the electromagnetic wavefield has significant implications for the acquisition and interpretation of ground-penetrating radar (GPR) data. Based on the geometrical and physical properties of the subsurface scatterer and the physical properties of its surrounding material, strong polarization phenomena might occur. Here, we develop an attribute-based analysis approach to extract and characterize buried utility pipes using two broadside antenna configurations. First, we enhance and extract the utilities by making use of their distinct symmetric nature through the application of a symmetry-enhancing image-processing algorithm known as phase symmetry. Second, we assess the polarization characteristics by calculating two attributes (polarization angle and linearity) using principal component analysis. Combination of attributes derived from these steps into a novel depolarization attribute allows one to efficiently detect and distinguish different utilities present within 3-D GPR data. The performance of our analysis approach is illustrated using synthetic examples and evaluated using field examples (including a dual-configuration 3-D data set) collected across a field site, where detailed ground-truth information is available. Our results demonstrate that the proposed approach allows for a more detailed extraction and combination of utility relevant information compared to approaches relying on single-component data and, thus, eases the interpretation of multicomponent GPR data sets.
Deposits of submarine debris flows can build up substantial topography on the sea floor. The resulting sea floor morphology can strongly influence the pathways of and deposition from subsequent turbidity currents. Map views of sea floor morphology are available for parts of the modern sea floor and from high-resolution seismic-reflection data. However, these data sets usually lack lithological information. In contrast, outcrops provide cross-sectional and lateral stratigraphic details of deep-water strata with superb lithological control but provide little information on sea floor morphology. Here, a methodology is presented that extracts fundamental lithological information from sediment core and well logs with a novel calibration between core, well-logs and seismic attributes within a large submarine axial channel belt in the Tertiary Molasse foreland basin, Austria. This channel belt was the course of multiple debris-flow and turbidity current events, and the fill consists of interbedded layers deposited by both of these processes. Using the core-well-seismic calibration, three-dimensional lithofacies proportion volumes were created. These volumes enable the interpretation of the three-dimensional distribution of the important lithofacies and thus the investigation of sea floor morphology produced by debris-flow events and its impact on succeeding turbidite deposition. These results show that the distribution of debris-flow deposits follows a relatively regular pattern of levees and lobes. When subsequent high-density turbidity currents encountered this mounded debris-flow topography, they slowed and deposited a portion of their sandy high-density loads just upstream of morphological highs. Understanding the depositional patterns of debris flows is key to understanding and predicting the location and character of associated sandstone accumulations. This detailed model of the filling style and the resulting stratigraphic architecture of a debris-flow dominated deep-marine depositional system can be used as an analogue for similar modern and ancient systems.
A multi-proxy study including analyses of delta C-13(org) for the lake sediment core GN-02 and grain size, TOC. CaCO3 content, delta C-13(carb) and delta O-18(carb) of bulk carbonate, and the mineralogy of the parallel core GN-04 from Gun Nuur was performed to reconstruct the Holocene hydrology and climate on the northern Mongolian Plateau. The chronology was established using 40 C-14 dates of bulk organic matter in addition to nine previously published radiocarbon dates for core GN-02, and further five C-14 dates for the new core GN-04. A lake reservoir effect of 1060 C-14 years was determined as the intercept of the high-resolution GN-02 age-depth model at the modern sediment surface. The size of the reservoir effect is supported by the age of the core-top sample (1200 +/- 40 C-14 years) and the determined difference between a wood-derived radiocarbon age from the GN-02 core base and the age-model inferred age for bulk organic matter at the same stratigraphic level (1000 C-14 years). Low lake level and prevailing aeolian sediment deposition at Gun Nuur under dry conditions were recorded during the earliest Holocene (> 10,800-10,300 cal a BP). Gun Nuur expanded under significantly wetter conditions between 10,300 and 7000 cal a BP. Unstable climate conditions existed in the mid Holocene (7000-2500 cal a BP) and three periods of low lake-levels and significantly drier conditions were recorded between 7000-5700, 4100-3600 and 3000-2500 cal a BP. Intermediate lake levels were inferred for the intervening periods. Around 2500 cal a BP, the climate change and wetter conditions were established again. As a consequence, the lake level of Gun Nuur rose again due to higher effective moisture and the relatively wet present conditions were achieved ca. 1600 cal a BP. Our results suggest that the initial Holocene climate change on the northern Mongolian Plateau was not accompanied by a rapid increase in precipitation as on the Tibetan Plateau. The establishment of wetter conditions in northern Mongolia lagged behind the early Holocene moisture increase on the Tibetan Plateau by ca. 1000 years. Subsiding dry air in the north of the Tibetan Plateau resulted from the strengthened summer monsoon on the Tibetan Plateau during the period of maximum summer insolation and probably inhibited a significant precipitation increase in Mongolia. The significant moisture increase in the Gun Nuur region at ca. 10.3 cal ka BP is probably not related to the northward shift of the present summer monsoon boundary or the moisture delivery from the northern Atlantic through the westerlies. Instead, water from melting snow, ice and frozen ground and the generation of precipitation from the local recycling of moisture are discussed as possible moisture source for the early onset of wetter conditions on the Mongolian Plateau.
The first 1400-year floating varve chronology for north-eastern Germany covering the late Allered to the early Holocene has been established by microscopic varve counts from the Rehwiese palaeolake sediment record. The Laacher See Tephra (LST), at the base of the studied interval, forms the tephrochronological anchor point. The fine laminations were examined using a combination of micro-facies and mu XRF analyses and are typical of calcite varves, which in this case provide mainly a warm season signal. Two varve types with different sub-layer structures have been distinguished: (I) complex varves consisting of up to four seasonal sub-layers formed during the Allered and early Holocene periods, and, (II) simple two sub-layer type varves only occurring during the Younger Dryas. The precision of the chronology has been improved by varve-to-varve comparison of two independently analyzed sediment profiles based on well-defined micro-marker layers. This has enabled both (1) the precise location of single missing varies in one of the sediment profiles, and, (2) the verification of varve interpolation in disturbed varve intervals in the parallel core. Inter-annual and decadal-scale variability in sediment deposition processes were traced by multi-proxy data series including seasonal layer thickness, high-resolution element scans and total organic and inorganic carbon data at a five-varve resolution. These data support the idea of a two-phase Younger Dryas, with the first interval (12,675-12,275 varve years BP) characterised by a still significant but gradually decreasing warm-season calcite precipitation and a second phase (12,275-11,690 varve years BP) with only weak calcite precipitation. Detailed correlation of these two phases with the Meerfelder Maar record based on the LST isochrone and independent varve counts provides clues about regional differences and seasonal aspects of YD climate change along a transect from a location proximal to the North Atlantic in the west to a more continental site in the east
In many near-surface geophysical studies it is now common practice to collect co-located disparate geophysical data sets to explore subsurface structures. Reconstruction of physical parameter distributions underlying the available geophysical data sets usually requires the use of tomographic reconstruction techniques. To improve the quality of the obtained models, the information content of all data sets should be considered during the model generation process, e.g., by employing joint or cooperative inversion approaches. Here, we extend the zonal cooperative inversion methodology based on fuzzy c-means cluster analysis and conventional single-input data set inversion algorithms for the cooperative inversion of data sets with partially co-located model areas. This is done by considering recent developments in fuzzy c-means cluster analysis. Additionally, we show how supplementary a priori information can be incorporated in an automated fashion into the zonal cooperative inversion approach to further constrain the inversion. The only requirement is that this a priori information can be expressed numerically; e.g., by physical parameters or indicator variables. We demonstrate the applicability of the modified zonal cooperative inversion approach using synthetic and field data examples. In these examples, we cooperatively invert S- and P-wave traveltime data sets with partially co-located model areas using water saturation information expressed by indicator variables as additional a priori information. The approach results in a zoned multi-parameter model, which is consistent with all available information given to the zonal cooperative inversion and outlines the major subsurface units. In our field example, we further compare the obtained zonal model to sparsely available borehole and direct-push logs. This comparison provides further confidence in our zonal cooperative inversion model because the borehole and direct-push logs indicate a similar zonation.
In the framework of the Dead Sea Integrated Research project (DESIRE), 59 seismological stations were deployed in the region of the Dead Sea Basin. Twenty of these stations recorded data of sufficiently high quality between May and September 2007 to be used for ambient seismic noise analysis. Empirical Green's functions are extracted from cross-correlations of long term recordings. These functions are dominated by Rayleigh waves, whose group velocities can be measured in the frequency range from 0.1 to 0.5 Hz. Analysis of positive and negative correlation lags of the Green's functions makes it possible to identify the direction of the source of the incoming energy. Signals with frequencies higher than 0.2 Hz originate from the Mediterranean Sea, while low frequencies arrive from the direction of the Red Sea. Travel times of the extracted Rayleigh waves were measured between station pairs for different frequencies, and tomographically inverted to provide independent velocity models. Four such 2D models were computed for a set of frequencies, all corresponding to different sampling depths, and thus together giving an indication of the velocity variations in 3D extending to a depth of 10 km. The results show low velocities in the Dead Sea Basin, consistent with previous studies suggesting up to 8 km of recent sedimentary infill in the Basin. The complex structure of the western margin of the Basin is also observed, with sedimentary infill present to depths not exceeding 5 km west of the southern part of the Dead Sea. The high velocities associated with the Lisan salt diapir are also observed down to a depth of similar to 5 km. The reliability of the results is confirmed by checkerboard recovery tests.
Site-specific soil moisture and groundwater levels are key input parameters for ecological modeling. Obtaining such information in a comprehensive manner is difficult for large regions. We studied a floodplain region in the Federal State of Brandenburg, Germany, to examine the degree to which the average depth of groundwater tables can be derived from surface temperatures obtained by the ASTER radiospectrometer (spatial resolution of 90 m per pixel). A floristic ecological indicator representing the site-specific moisture level was applied to develop a proxy between the thermal satellite data and groundwater table depth. The use of spring scenes (late April to early May) from 2 years proved to be well suited for minimizing the effects of weather and land use. Vegetation surveys along transects that were 2 m wide across the pixel diagonals allowed for the calculation of average ecological moisture values of pixel-sites by applying Ellenberg-numbers. These values were used to calibrate the satellite data locally. There was a close relationship between surface temperature and the average ecological moisture value (R2 = 0.73). Average ecological moisture values were highly indicative of the average groundwater levels during a 7-year measurement series (R2 = 0.93). Satellite-supported thermal data from spring were suitable for estimating the average groundwater levels of low-lying grasslands on a larger scale. Ecological moisture values from the transect surveys effectively allowed the incorporation of relief heterogeneity within the thermal grid and the establishment of the correlation between thermal data and average groundwater table depth. Regression functions were used to produce a map of groundwater levels at the study site.
Although a large fraction of the world's biomass resides in the subsurface, there has been no study of the effects of catastrophic disturbance on the deep biosphere and the rate of its subsequent recovery. We carried out an investigation of the microbiology of a 1.76 km drill core obtained from the similar to 35 million-year-old Chesapeake Bay impact structure, USA, with robust contamination control. Microbial enumerations displayed a logarithmic downward decline, but the different gradient, when compared to previously studied sites, and the scatter of the data are consistent with a rnicrobiota influenced by the geological disturbances caused by the impact. Microbial abundance is low in buried crater-fill, ocean-resurge, and avalanche deposits despite the presence of redox couples for growth. Coupled with the low hydraulic conductivity, the data suggest the microbial community has not yet recovered from the impact similar to 35 million years ago. Microbial enumerations, molecular analysis of microbial enrichment cultures, and geochemical analysis showed recolonization of a deep region of impact-fractured rock that was heated to above the upper temperature limit for life at the time of impact. These results show how, by fracturing subsurface rocks, impacts can extend the depth of the biosphere. This phenomenon would have provided deep refugia for life on the more heavily bombarded early Earth, and it shows that the deeply fractured regions of impact craters are promising targets to study the past and present habitability of Mars.
The most recent intense earthquake swarm in West Bohemia lasted from 6 October 2008 to January 2009. Starting 12 days after the onset, the University of Potsdam monitored the swarm by a temporary small-aperture seismic array at 10 km epicentral distance. The purpose of the installation was a complete monitoring of the swarm including micro-earthquakes (M (L) < 0). We identify earthquakes using a conventional short-term average/long-term average trigger combined with sliding-window frequency-wavenumber and polarisation analyses. The resulting earthquake catalogue consists of 14,530 earthquakes between 19 October 2008 and 18 March 2009 with magnitudes in the range of -aEuro parts per thousand 1.2 a parts per thousand currency signaEuro parts per thousand M (L) a parts per thousand currency signaEuro parts per thousand 2.7. The small-aperture seismic array substantially lowers the detection threshold to about M (c) = -aEuro parts per thousand 0.4, when compared to the regional networks operating in West Bohemia (M (c) > 0.0). In the course of this work, the main temporal features (frequency-magnitude distribution, propagation of back azimuth and horizontal slowness, occurrence rate of aftershock sequences and interevent-time distribution) of the recent 2008/2009 earthquake swarm are presented and discussed. Temporal changes of the coefficient of variation (based on interevent times) suggest that the swarm earthquake activity of the 2008/2009 swarm terminates by 12 January 2009. During the main phase in our studied swarm period after 19 October, the b value of the Gutenberg-Richter relation decreases from 1.2 to 0.8. This trend is also reflected in the power-law behavior of the seismic moment release. The corresponding total seismic moment release of 1.02x10(17) Nm is equivalent to M (L,max) = 5.4.
We have undertaken structural, geomorphological, and morphometric analyses to investigate the role of tectonism and climate in the landscape evolution in the upper Spiti valley, NW Himalayas. Geomorphometric analyses coupled with field investigations reveal active tectonic deformation in the Spiti region. The calculated geomorphic indices (steepness, concavity and Hack) demonstrate uplift/subsidence along the Kaurik-Chango fault, whereas transverse topographic index (T-index) reveals basin tilting associated with active faulting near Hansa and Lingti valley. Investigation of well-dated Mane palaeolake sediments also provides evidence of regional tectonic instability. Four episodes (ca. 7.8, 7.4, 6.5 and 6.1 cal ka) of neotectonic activity have been identified during the period of the lake's existence. We have also compiled data on the regional climate variability and compared it with the age of the Mane palaeo-landslide. Our results indicate that the landslide occurred towards the end of the early Holocene intensified monsoon phase and is located near an active fault. Our data on regional tectonic instability and the coincidences of modern and palaeo-landslides with zones of active deformation suggest that tectonism is an important factor governing landscape stability in the Spiti region.
Large research initiatives such as the Global Earthquake Model (GEM) or the Seismic HAzard haRmonization in Europe (SHARE) projects concentrate a great collaborative effort on defining a global standard for seismic hazard estimations. In this context, there is an increasing need for identifying ground-motion prediction equations (GMPEs) that can be applied at both global and regional scale. With increasing amounts of strong-motion records that are now available worldwide, observational data can provide a valuable resource to tackle this question. Using the global dataset of Allen and Wald (2009), we evaluate the ability of 11 GMPEs to predict ground-motion in different active shallow crustal regions worldwide. Adopting the approach of Scherbaum et al. (2009), we rank these GMPEs according to their likelihood of having generated the data. In particular, we estimate how strongly data support or reject the models with respect to the state of noninformativeness defined by a uniform weighting. Such rankings derived from this particular global dataset enable us to explore the potential of GMPEs to predict ground motions in their host region and also in other regions depending on the magnitude and distance considered. In the ranking process, we particularly focus on the influence of the distribution of the testing dataset compared with the GMPE's native dataset. One of the results of this study is that some nonindigenous models present a high degree of consistency with the data from a target region. Two models in particular demonstrated a strong power of geographically wide applicability in different geographic regions with respect to the testing dataset: the models of Akkar and Bommer (2010) and Chiou et al. (2010).
We present a new tomographic model of the mantle in the area of the 2010 M8.8 Maule earthquake and surrounding regions. Increased ray coverage provided by the aftershock data allows us to image the detailed subducting slab structure in the mantle, from the region of flat slab subduction north of the Maule rupture to the area of overlapping rupture between the 1960 M9.5 and the 2010 M8.8 events to the south. We have combined teleseismic primary and depth phase arrivals with available local arrivals to better constrain the teleseismic earthquake locations in the region, which we use to conduct nested regionalglobal tomography. The new model reveals the detailed structure of the flat slab and its transition to a more moderately dipping slab in the Maule region. South of the Maule region, a steeply dipping relic slab is imaged from similar to 200 to 1000 km depth that is distinct from the moderately dipping slab above it and from the more northerly slab at similar depths. We interpret the images as revealing both horizontal and vertical tearing of the slab at similar to 38 degrees S to explain the imaged pattern of slab anomalies in the southern portion of the model. In contrast, the transition from a horizontal to moderately subducting slab in the northern portion of the model is imaged as a continuous slab bend. We speculate that the tearing was most likely facilitated by a fracture zone in the downgoing plate or alternatively by a continental scale terrane boundary in the overriding plate.
The Menderes Massif, exposed in western Anatolia, is a metamorphic complex cropping out in the Alpine orogenic belt. The metamorphic rock succession of the Massif is made up of a Precambrian basement and overlying Paleozoic-early Tertiary cover series. The Pan-African basement is composed of late Proterozoic metasedimentary rocks consisting of partially migmatized paragneisses and conformably overlying medium- to high-grade mica schists, intruded by orthogneisses and metagabbros. Along the southern flank of the southern submassif, we recognized well-preserved primary contact relationship between biotite and leucocratic tourmaline orthogneisses and country rocks as the orthogneisses represent numerous large plutons, stocks and vein rocks intruded into a basement of garnet mica schists. Based on the radiometric data, the primary deposition age of the precursors of the country rocks, garnet mica schist, can be constrained between 600 and 550 Ma (latest Neoproterozoic). The North Africa-Arabian-Nubian Shield in the Mozambique Belt can be suggested as the possible provenance of these metaclastics. The intrusion ages of the leucocratic tourmaline orthogneisses and biotite orthogneisses were dated at 550-540 Ma (latest Neoproterozoic-earliest Cambrian) by zircon U/Pb and Pb/Pb geochronology. These granitoids represent the products of the widespread Pan-African acidic magmatic activity, which can be attributed to the closure of the Mozambique Ocean during the final collision of East and West Gondwana. Detrital zircon ages at about 550 Ma in the Paleozoic muscovite-quartz schists show that these Pan-African granitoids in the basement form the source rocks of the cover series of the Menderes Massif.
Important aspects of the Andean foreland basin in Argentina remain poorly constrained, such as the effect of deformation on deposition, in which foreland basin depozones Cenozoic sedimentary units were deposited, how sediment sources and drainages evolved in response to tectonics, and the thickness of sediment accumulation. Zircon U-Pb geochronological data from EocenePliocene sedimentary strata in the Eastern Cordillera of northwestern Argentina (PucaraAngastaco and La Vina areas) provide an Eocene (ca.similar to 38 similar to Ma) maximum depositional age for the Quebrada de los Colorados Formation. Sedimentological and provenance data reveal a basin history that is best explained within the context of an evolving foreland basin system affected by inherited palaeotopography. The Quebrada de los Colorados Formation represents deposition in the distal to proximal foredeep depozone. Development of an angular unconformity at ca.similar to 14 similar to Ma and the coarse-grained, proximal character of the overlying Angastaco Formation (lower to upper Miocene) suggest deposition in a wedge-top depozone. Axial drainage during deposition of the Palo Pintado Formation (upper Miocene) suggests a fluvial-lacustrine intramontane setting. By ca.similar to 4 similar to Ma, during deposition of the San Felipe Formation, the Angastaco area had become structurally isolated by the uplift of the Sierra de los Colorados Range to the east. Overall, the Eastern Cordillera sedimentary record is consistent with a continuous foreland basin system that migrated through the region from late Eocene through middle Miocene time. By middle Miocene time, the region lay within the topographically complex wedge-top depozone, influenced by thick-skinned deformation and re-activation of Cretaceous rift structures. The association of the Eocene Quebrada del los Colorados Formation with a foredeep depozone implies that more distal foreland deposits should be represented by pre-Eocene strata (Santa Barbara Subgroup) within the region.
The details of how narrow, orogen-parallel ocean basins are filled with sediment by large axial submarine channels is important to understand because these depositional systems commonly form in through-like basins in various tectonic settings. The Magallanes foreland basin is an excellent location to study an orogen-parallel deep-marine system. Conglomerate lenses of the Upper Cretaceous Cerro Toro Formation have been previously interpreted to represent the fill of a single submarine channel (48 km wide, >100 km long) that funneled coarse detritus southward along the basin axis. This interpretation was based on lithologic correlations. New U/Pb dating of zircons from volcanic ashes and sandstones, coupled with strontium isotope stratigraphy, refine the controls on depositional ages and provenance. Results demonstrate that north-south oriented conglomerate lenses are contemporaneous within error limits (ca. 8482 Ma) supporting that they represent parts of an axial channel belt. Channel deposits 20 km west of the axial location are 8782 Ma in age. These channels are partly contemporaneous with the ones within the axial channel belt, making it likely that they represent feeders to the axial channel system. The northern Cerro Toro Formation spans a Turonian to Campanian interval (ca. 9082 Ma) whereas the formation top, 70 km to the south, is as young as ca. 76 Ma. KolmogorovSmirnoff statistical analysis on detrital zircon age distributions shows that the northern uppermost Cerro Toro Formation yields a statistically different age distribution than other samples from the same formation but shows no difference relative to the overlying Tres Pasos Formation. These results suggest the partly coeval deposition of both formations. Integration of previously acquired geochronologic and stratigraphic data with new data show a pronounced southward younging pattern in all four marine formations in the Magallanes Basin. Highly diachronous infilling may be an important depositional pattern for narrow, orogen-parallel ocean basins.
A 352 cm long sediment core from Hersek Lagoon (Gulf of Izmit) was investigated for its ostracod species composition in order to evaluate the potential of ostracods to detect tsunami deposits in coastal environments. The Gulf of Izmit is the eastern bay of the Marmara Sea which is tectonically controlled by the North Anatolian Fault. Ostracod shells are rare in the lower third of the core, which probably represents a coastal wetland environment. According to radiocarbon dating of terrestrial plant remains, this unit was deposited between AD 500 and AD 800. Above, ostracod shells are abundant and dominantly monospecific, composed almost exclusively of the widespread brackish water ostracod Cyprideis torosa. This almost monospecific occurrence indicates the establishment and maintenance of the Hersek Lagoon after AD 800. Three distinct layers of mollusc shells and fragments contain ostracod shells of marine and to a lesser extent non-marine origin in addition to those of C. torosa. The shell layers are further characterized by significant maxima in total ostracod shell numbers. The high concentration of ostracod shells, the higher species numbers and the mixture of marine, lagoonal and non-marine ostracod shells shows that shell layers were formed as high-energy deposits resulting from tsunamis or large storms in the Marmara Sea. The partial occurrence of non-marine ostracod shells in the shell layers possibly indicates that tsunamis with extensive run-ups and significant backwash flows caused the high-energy deposits rather than large storms. The investigated sediments show that lagoonal ostracods can serve as good proxies for tsunamis or large storms through significant variations in total shell numbers, species numbers and the mixing of shells of different origin.
Ecological implications of extreme events footprints of the 2010earthquake along the chilean coast
(2012)
Deciphering ecological effects of major catastrophic events such as earthquakes, tsunamis, volcanic eruptions, storms and fires, requires rapid interdisciplinary efforts often hampered by a lack of pre-event data. Using results of intertidal surveys conducted shortly before and immediately after Chile's 2010 M-w 8.8 earthquake along the entire rupture zone (ca. 34-38 degrees S), we provide the first quantification of earthquake and tsunami effects on sandy beach ecosystems. Our study incorporated anthropogenic coastal development as a key design factor. Ecological responses of beach ecosystems were strongly affected by the magnitude of land-level change. Subsidence along the northern rupture segment combined with tsunami-associated disturbance and drowned beaches. In contrast, along the co-seismically uplifted southern rupture, beaches widened and flattened increasing habitat availability. Post-event changes in abundance and distribution of mobile intertidal invertebrates were not uniform, varying with land-level change, tsunami height and coastal development. On beaches where subsidence occurred, intertidal zones and their associated species disappeared. On some beaches, uplift of rocky subtidal substrate eliminated low intertidal sand beach habitat for ecologically important species. On others, unexpected interactions of uplift with man-made coastal armouring included restoration of upper and mid-intertidal habitat seaward of armouring followed by rapid colonization of mobile crustaceans typical of these zones formerly excluded by constraints imposed by the armouring structures. Responses of coastal ecosystems to major earthquakes appear to vary strongly with land-level change, the mobility of the biota and shore type. Our results show that interactions of extreme events with human-altered shorelines can produce surprising ecological outcomes, and suggest these complex responses to landscape alteration can leave lasting footprints in coastal ecosystems.
Coseismic coastal uplift has been quantified using sessile intertidal organisms after several great earthquakes following FitzRoy's pioneer measurements in 1835. A dense survey of such markers may complement space geodetic data to obtain an accurate distribution of fault slip and earthquake segmentation. However, uplift estimates based on diverse intertidal organisms tend to differ, because of few methodological and comparative studies. Here, we calibrate and estimate coastal uplift in the southern segment of the 2010 Maule, Chile earthquake (M-w = 8.8) using > 1100 post-earthquake elevation measurements of the sessile mussel Perumytilus purpuratus. This mussel is the predominant competitor for rocky shores all along the Pacific coast of South America, where it forms fringes or belts distinctively in the middle intertidal zone. These belts are centered at mean sea level and their width should equal one third of the tidal range. We measured belt widths close to this value at 40% of the sites, but overall widths are highly variable due to the unevenness in belt tops; belt bases, in turn, are rather regular. Belt top unevenness apparently results from locally-enhanced wave splash, whereas belt base evenness is controlled by predation. According to our measurements made beyond the earthquake rupture, the belt base is at the bottom of the middle intertidal zone, and thus we propose to estimate coastal uplift using the belt base mean elevation plus one sixth of the tidal range to reach mean sea level. Within errors our estimates agree with GPS displacements but differ from other methods. Comparisons of joint inversions for megathrust slip suggest combining space geodetic data with estimates from intertidal organisms may locally increase the detail of slip distributions.
Microbial communities can subsist at depth in marine sediments without fresh supply of organic matter for millions of years. At threshold sedimentation rates of 1 millimeter per 1000 years, the low rates of microbial community metabolism in the North Pacific Gyre allow sediments to remain oxygenated tens of meters below the sea floor. We found that the oxygen respiration rates dropped from 10 micromoles of O-2 liter(-1) year(-1) near the sediment-water interface to 0.001 micromoles of O-2 liter(-1) year(-1) at 30-meter depth within 86 million-year-old sediment. The cell-specific respiration rate decreased with depth but stabilized at around 10(-3) femtomoles of O-2 cell(-1) day(-1) 10 meters below the seafloor. This result indicated that the community size is controlled by the rate of carbon oxidation and thereby by the low available energy flux.
P receiver functions from 23 stations of the SASE experiment in southern Africa are inverted simultaneously with SKS waveforms for azimuthal anisotropy in the upper mantle. Our analysis resolves the long-standing issue of depth dependence and origins of anisotropy beneath southern Africa. In the uppermost mantle we observe anisotropy with a nearly E-W fast direction, parallel to the trend of the Limpopo belt. This anisotropy may be frozen since the Archean. At a depth of 160 km the fast direction of anisotropy changes to 40 degrees and becomes close to the recent plate motion direction. This transition is nearly coincident in depth with activation of dominant glide systems in olivine and with a pronounced change in other properties of the upper mantle. Another large change in the fast direction of anisotropy corresponds to the previously found low-S-velocity layer atop the 410-km discontinuity. Citation: Vinnik, L., S. Kiselev, M. Weber, S. Oreshin, and L. Makeyeva (2012), Frozen and active seismic anisotropy beneath southern Africa, Geophys. Res. Lett., 39, L08301, doi: 10.1029/2012GL051326.
Submarine permafrost degradation rates may be determined by a number of interacting processes, including rates of sea level rise and coastal erosion, sea bottom temperature and salinity regimes, geothermal heat flux and heat and mass diffusion within the sediment column. Observations of ice-bearing permafrost in shelf sediments are necessary in order to determine its spatial distribution and to quantify its degradation rate. We tested the use of direct current electrical resistivity to ice-bearing permafrost in Elson Lagoon northeast of Barrow, Alaska (Beaufort Sea). A sharp increase in electrical resistivity was observed in profiles collected perpendicular to and along the coastline and is interpreted to be the boundary between ice-free sediment and underlying ice-bearing submarine permafrost. The depth to the interpreted ice-bearing permafrost increases from <2 m below sea level to over 12 m below sea level with increasing distance from the coastline. The dependence of the saline sediment electrical resistivity on temperature and freezing was measured in the laboratory to provide validation for the field measurements. Electrical resistivity was shown to be effective for detection of shallow ice-bearing permafrost in the coastal zone. Historical coastal retreat rates were combined with the inclination of the top of the ice-bearing permafrost to calculate mean vertical permafrost degradation rates of 1 to 4 cm yr(-1).
The inversion of surface-wave dispersion curve to derive shear-wave velocity profile is a very delicate process dealing with a nonunique problem, which is strongly dependent on the model space parameterization. When independent and reliable information is not available, the selection of most representative models within the ensemble produced. by the inversion is often difficult. We implemented a strategy in the inversion of dispersion curves able to investigate the influence of the parameterization of the model space and to select a "best" class of models. We analyzed surface-wave dispersion curves measured at 14 European strong..-motion sites within the NERIES EC-Project. We focused on the inversion task exploring the model space by means of four distinct pararneterization classes composed of layers progressively added over a half-space. The classes differ in the definition of the shear-wave velocity profile; we considered models with uniform velocity as well as models with increasing velocity with depth. At each site and for each model parameterization, we performed an extensive surface-wave inversion (200,100 models for five seeds) using the conditional neighborhood algorithm. We addressed the model evaluation following the corrected Akaike's information criterion (AlCc) that combines the concept of misfit to the number of degrees of freedom of the system. The misfit was computed as least-squares estimation between theoretical and observed dispersion curve. The model complexity was accounted in a penalty term by AlCc. By applying such inversion strategy on 14 strong-motion sites, we found that the best parameterization of the model space is mostly three to four layers over a half-space: where the shear-wave velocity of the uppermost layers can follow uniform or power-law dependence with depth. The shear-wave velocity profiles derived by inversion agree with shear-wave velocity profiles provided by borehole surveys at approximately 80% of the sites.
Thermomechanical model reconciles contradictory geophysical observations at the Dead Sea Basin
(2012)
The Dead Sea Transform (DST) comprises a boundary between the African and Arabian plates. During the last 15-20 m.y. more than 100 km of left lateral transform displacement has been accumulated on the DST and about 10 km thick Dead Sea Basin (DSB) was formed in the central part of the DST. Widespread igneous activity since some 20 Ma ago and especially in the last 5 m.y., thin (60-80 km) lithosphere constrained by seismic data and absence of seismicity below the Moho, seem to be quite natural for this tectonically active plate boundary. However, surface heat flow values of less than 50-60 mW/m(2) and deep seismicity in the lower crust (deeper than 20 km) reported for this region are apparently inconsistent with the tectonic settings specific for an active continental plate boundary and with the crustal structure of the DSB. To address these inconsistencies which comprise what we call the "DST heat-flow paradox," we have developed a numerical model that assumes an erosion of initially thick and cold lithosphere just before or during the active faulting at the DST. The optimal initial conditions for the model are defined using transient thermal analysis. From the results of our numerical experiments we conclude that the entire set of observations for the DSB can be explained within the classical pull-apart model assuming that the lithosphere has been thermally eroded at about 20 Ma and the uppermost mantle in the region have relatively weak rheology consistent with experimental data for wet olivine or pyroxenite.
Inorganic minerals form a major component of lacustrine sediments and have the potential to reveal detailed information on previous climatic and hydrological conditions. The ability to extract such information however, has been restricted by a limited understanding of the relationships between minerals and the environment. In an attempt to fill in this gap in our knowledge, 146 surface sediment samples have been investigated from 146 lakes on the Tibetan Plateau. The mineral compositions derived from these samples by X-Ray Diffraction (XRD) were used to examine the relationships between mineral compositions and the environmental variables determined for each site. Statistical techniques including Multivariate regression trees (MRT) and Redundancy Analysis (RDA), based on the mineral spectra and environmental variables, reveal that the electrical conductivity (EC) and Mg/Ca ratios of lake water are the most important controls on the composition of endogenic minerals. No endogenic minerals precipitate under hyper-fresh water conditions (EC lower than 0.13 mS/cm), with calcite commonly forming in water with EC values above 0.13 mS/cm. Between EC values of 0.13 and 26 mS/cm the mineral composition of lake sediments can be explained in terms of variations in the Mg/Ca ratio: calcite dominates at Mg/Ca ratios of less than 33, whereas aragonite commonly forms when the ratio is greater than 33. Where EC values are between 26 and 39 mS/cm, monohydrocalcite precipitates together with calcite and aragonite; above 39 mS/cm, gypsum and halite commonly form. Information on the local geological strata indicates that allogenic (detrital) mineral compositions are primarily influenced by the bedrock compositions within the catchment area. By applying these relationships to the late glacial and Holocene mineral record from Chaka Salt Lake, five lake stages have been identified and their associated EC conditions inferred. The lake evolved from a freshwater lake during the late glacial (before 11.4 cal. ka BP) represented by the lowest EC values (< 0.13 mS/cm), to a saline lake with EC values slightly higher than 39 mS/cm during the early and mid Holocene (ca. 11.4-5.3 cal. ka BP), and finally to a salt lake (after 5.3 cal. ka BP). These results illustrate the utility of our mineral-environmental model for the quantitative reconstruction of past environmental conditions from lake sediment records.
Away from active plate boundaries the relationships between spatiotemporal variations in density and geothermal gradient are important for understanding the evolution of topography in continental interiors. In this context the classic concept of the continental lithosphere as comprising three static layers of different densities (upper crust, lower crust, and upper mantle) is not adequate to assess long-term changes in topography and relief in regions associated with pronounced thermal anomalies in the mantle. We have therefore developed a one-dimensional model, which is based on thermodynamic equilibrium assemblage computations and deliberately excludes the effects of melting processes like intrusion or extrusions. Our model calculates the "metamorphic density" of rocks as a function of pressure, temperature, and chemical composition. It not only provides a useful tool for quantifying the influence of petrologic characteristics on density, but also allows the modeled "metamorphic" density to be adjusted to variable geothermal gradients and applied to different geodynamic environments. We have used this model to simulate a scenario in which the lithosphere-asthenosphere boundary is subjected to continuous heating over a long period of time (130 Ma), and demonstrate how an anorogenic plateau with an elevation of 1400 m can be formed solely as a result of heat transfer within the continental lithosphere. Our results show that, beside dynamic topography (of asthenospheric origin), density changes within the lithosphere have an important impact on the evolution of anorogenic plateaus.
Determination of the source rocks for the diatexites from the Edough Massif, Annaba, NE Algeria
(2012)
The crystalline Edough Massif is located in the oriental part of the Algerian coastline. It consists of two tectonically superposed units of gneisses, augen-gneisses and migmatitic gneisses in the lower unit and micaschists in the upper unit. The crystalline rocks underwent a low to moderate degree of metamorphism; the gneisses suffered partial melting. They display migmatitic features such as nebulitic structures with contorted leucosome layers and K-feldspar porphyroblasts and thus can be classified as diatexites. The mineralogical composition of these rocks is very homogenous and consists of K-feldspar, micas and quartz. The feldspar-rich, arkosic nature of the outcrop implies a granitic source rock. High K2O/Na2O ratios and high A/CNK > 1.1 indicate an S-type granite source and a peraluminous composition of the protolith respectively. Chondrite normalized REE distribution patterns of the Edough diatexites show gently inclined patterns with a minor negative Eu anomaly (Eu/Eu* = 0.36-0.49), which points to a very slightly differentiated granitic source. The REE pattern and trace element data of the diatexites are similar to those of average Proterozoic upper continental crust, which suggests that they are derived mainly from upper continental crust and were deposited in continental margins.
Declining groundwater levels in some forested regions in Northeast Germany indicate a reduction in groundwater recharge. Various interlinked aspects, such as changes in climate conditions and changes in forest structure, have been considered as the main factors affecting the regional level of groundwater recharge.
For this study, the water balance model WaSiM-ETH was used to calculate groundwater recharge in a 104 km(2) area between 1958 and 2007. Climate impact analysis was driven by observed data from neighbouring meteorological stations. Changes in forest stands were reconstructed from the current status and literature studies.
The model-based analysis showed that the average groundwater recharge under forest areas decreased from 1958 to 2007, with a trend of 2.3 mm/yr(2). The most important effect was changing climatic boundary conditions, which made up 53% of the decrease. Declining precipitation is identified as the main factor. Changes in tree age distribution caused 18% of the decrease, and the change of ground vegetation under pines (Pinus sylvestris) accounts for 29%.
In respect of the complexity and the interconnectivity of the processes of groundwater recharge, the necessity of using process-oriented distributed models such as WaSiM-ETH is discussed.
We conclude that changes in forest stands affecting groundwater recharge could play a significant role in the water balance, especially in regions with a priori low total runoff, this has up to now often remained unquantified.
The aim of this experimental study was to evaluate and compare the geochemical impact of pure and impure CO2 on rock forming minerals of possible CO2 storage reservoirs. This geochemical approach takes into account the incomplete purification of industrial captured CO2 and the related effects during injection, and provides relevant data for long-term storage simulations of this specific greenhouse gas. Batch experiments were conducted to investigate the interactions of supercritical CO2, brine and rock-forming mineral concentrates (albite, microcline, kaolinite, biotite, muscovite, calcite, dolomite and anhydrite) using a newly developed experimental setup. After up to 42 day (1000 h) experiments using pure and impure supercritical CO2 the dissolution and solution characteristics were examined by XRD, XRF, SEM and EDS for the solid, and ICP-MS and IC for the fluid reactants, respectively. Experiments with mixtures of supercritical CO2 (99.5 vol.%) and SO2 or NO2 impurities (0.5 vol.%) suggest the formation of H2SO4 and HNO3, reflected in pH values between 1 and 4 for experiments with silicates and anhydrite and between 5 and 6 for experiments with carbonates. These acids should be responsible for the general larger amount of cations dissolved from the mineral phases compared to experiments using pure CO2. For pure CO2 a pH of around 4 was obtained using silicates and anhydrite, and 7-8 for carbonates. Dissolution of carbonates was observed after both pure and impure CO2 experiments. Anhydrite was corroded by approximately 50 wt.% and gypsum precipitated during experiments with supercritical CO2 + NO2. Silicates do not exhibit visible alterations during all experiments but released an increasing amount of cations in the reaction fluid during experiments with impure CO2. Nonetheless, precipitated secondary carbonates could not be identified.
Landslides are a hazard for humans and artificial structures. From an ecological point of view, they represent an important ecosystem disturbance, especially in tropical montane forests. Here, shallow translational landslides are a frequent natural phenomenon and one local determinant of high levels of biodiversity. In this paper, we apply weighted ensembles of advanced phenomenological models from statistics and machine learning to analyze the driving factors of natural landslides in a tropical montane forest in South Ecuador. We exclusively interpret terrain attributes, derived from a digital elevation model, as proxies to several driving factors of landslides and use them as predictors in our models which are trained on a set of five historical landslide inventories. We check the model generality by transferring them in time and use three common performance criteria (i.e. AUC, explained deviance and slope of model calibration curve) to, on the one hand, compare several state-of-the-art model approaches and on the other hand, to create weighted model ensembles. Our results suggest that it is important to consider more than one single performance criterion.
Approaching our main question, we compare responses of weighted model ensembles that were trained on distinct functional units of landslides (i.e. initiation, transport and deposition zones). This way, we are able to show that it is quite possible to deduce driving factors of landslides, if the consistency between the training data and the processes is maintained. Opening the 'black box' of statistical models by interpreting univariate model response curves and relative importance of single predictors regarding their plausibility, we provide a means to verify this consistency.
With the exception of classification tree analysis, all techniques performed comparably well in our case study while being outperformed by weighted model ensembles. Univariate response curves of models trained on distinct functional units of landslides exposed different shapes following our expectations. Our results indicate the occurrence of landslides to be mainly controlled by factors related to the general position along a slope (i.e. ridge, open slope or valley) while landslide initiation seems to be favored by small scale convexities on otherwise plain open slopes.
Mapping hydrological parameter distributions in high resolution is essential to understand and simulate groundwater flow and contaminant transport. Of particular interest is surface-based ground-penetrating radar (GPR) reflection imaging in electrically resistive sediments because of the expected close link between the subsurface water content and the dielectric permittivity, which controls GPR wave velocity and reflectivity. Conventional tools like common midpoint (CMP) velocity analysis provide physical parameter models of limited resolution only. We present a novel reflection amplitude inversion workflow for surface-based GPR data capable of resolving the subsurface dielectric permittivity and related water content distribution with markedly improved resolution. Our scheme is an adaptation of a seismic reflection impedance inversion scheme to surface-based GPR data. Key is relative-amplitude-preserving data preconditioning including GPR deconvolution, which results in traces with the source-wavelet distortions and propagation effects largely removed. The subsequent inversion for the underlying dielectric permittivity and water content structure is constrained by in situ dielectric permittivity data obtained by direct-push logging. After demonstrating the potential of our novel scheme on a realistic synthetic data set, we apply it to two 2-D 100 MHz GPR profiles acquired over a shallow sedimentary aquifer resulting in water content images of the shallow (3-7 m depth) saturated zone having decimeter resolution.
We studied testate amoebae and possible correlated abiotic factors in soils of 31 mature forest ecosystems using an easily applicable and spatially explicit method. Simple counting on soil thin-sections with a light microscope resulted in amoeba densities comparable to previously reported values, i.e. 0.1 x 10(8) to 11.5 x 10(8) individuals m(-2) (upper 3 cm of soil). Soil moisture and soil acidity seem to be correlated with amoeba densities. At sites of moderate soil moisture regimes (SMR 2-7) we found higher densities of testate amoebae at pH < 4.5. At wetter sites (SMR >= 8) higher individual densities were recorded also at less acidic sites. The in situ description of amoebae, based on the analysis of a complete soil thin-section, showed a relatively uniform spatial micro-distribution throughout the organic and mineral soil horizons (no testate amoeba clusters). We discuss the pros and cons of the soil thin-section method and suggest it as an additional tool to improve knowledge of the spatial micro-distribution of testate amoebae.
Partitioning cluster algorithms have proven to be powerful tools for data-driven integration of large geoscientific databases. We used fuzzy Gustafson-Kessel cluster analysis to integrate Landsat imagery,. airborne radiometric, and regional geochemical data to aid in the interpretation of a multimethod database. The survey area extends over 3700 km(2) and is located in the Northern Cape Province, South Africa. We carefully selected five variables for cluster analysis to avoid the clustering results being dominated by spatially high-correlated data sets that were present in our database. Unlike other, more popular cluster algorithms, such as k-means or fuzzy c-means, the Gustafson-Kessel algorithm requires no preclustering data processing, such as scaling or adjustment of histographic data distributions. The outcome of cluster analysis was a classified map that delineates prominent near-to-surface structures. To add value to the classified map, we compared the detected structures to mapped geology and additional geophysical ground-truthing data. We were able to associate the structures detected by cluster analysis to geophysical and geological information thus obtaining a pseudolithology map. The latter outlined an area with increased mineral potential where manganese mineralization, i.e., psilomelane, had been located.
Questions remain about the exact ultrasonic energy level that is required to effectively disperse soil aggregates and to what extent this is accompanied by physical damage to individual soil particles. We found maximum aggregate dispersion at energy levels of 1500 J?cm3 and no evidence for the disintegration of particles < 20 mu m even at that energy level. Our findings suggest that sonication at energies much greater than those applied conventionally can disperse aggregates of high mechanical stability.
An interdisciplinary study was conducted to evaluate the relationship between geological and paleoenvironmental parameters and the bacterial and archaeal community structure of two contrasting subseafloor sites in the Western Mediterranean Sea (Ligurian Sea and Gulf of Lion). Both depositional environments in this area are well-documented from paleoclimatic and paleooceanographic point of views. Available data sets allowed us to calibrate the investigated cores with reference and dated cores previously collected in the same area, and notably correlated to Quaternary climate variations. DNA-based fingerprints showed that the archaeal diversity was composed by one group, Miscellaneous Crenarchaeotic Group (MCG), within the Gulf of Lion sediments and of nine different lineages (dominated by MCG, South African Gold Mine Euryarchaeotal Group (SAGMEG) and Halobacteria) within the Ligurian Sea sediments. Bacterial molecular diversity at both sites revealed mostly the presence of the classes Alphaproteobacteria, Betaproteobacteria and Gammaproteobacteria within Proteobacteria phylum, and also members of Bacteroidetes phylum. The second most abundant lineages were Actinobacteria and Firmicutes at the Gulf of Lion site and Chloroflexi at the Ligurian Sea site. Various substrates and cultivation conditions allowed us to isolate 75 strains belonging to four lineages: Alpha-, Gammaproteobacteria, Firmicutes and Actinobacteria. In molecular surveys, the Betaproteobacteria group was consistently detected in the Ligurian Sea sediments, characterized by a heterolithic facies with numerous turbidites from a deep-sea levee. Analysis of relative betaproteobacterial abundances and turbidite frequency suggested that the microbial diversity was a result of main climatic changes occurring during the last 20 ka. Statistical direct multivariate canonical correspondence analyses (CCA) showed that the availability of electron acceptors and the quality of electron donors (indicated by age) strongly influenced the community structure. In contrast, within the Gulf of Lion core, characterized by a homogeneous lithological structure of upper-slope environment, most detected groups were Bacteroidetes and, to a lesser extent, Betaproteobacteria. At both site, the detection of Betaproteobacteria coincided with increased terrestrial inputs, as confirmed by the geochemical measurements (Si, Sr, Ti and Ca). In the Gulf of Lion, geochemical parameters were also found to drive microbial community composition. Taken together, our data suggest that the palaeoenvironmental history of erosion and deposition recorded in the Western Mediterranean Sea sediments has left its imprint on the sedimentological context for microbial habitability, and then indirectly on structure and composition of the microbial communities during the late Quaternary.
Putting the plan into practice implementation of proposals for measures of local landscape plans
(2012)
The knowledge of the effectiveness of local landscape planning in Germany is in the main limited to particular cases and derives mostly from qualitative single case studies. This applies especially to the implementation of measures defined by landscape plans. To fill that gap, the paper focuses on the implementation of those measures. Furthermore, it discusses the factors and framework conditions which are crucial for this implementation. The potential factors and conditions of influence were derived from theory and compiled in 20 investigation hypotheses. In order to gain information on the execution of the measures, 28 randomly selected plans were first analysed, then interviews were carried out with administration representatives. It can be stated that landscape planning has positively influenced the development of nature and landscape in the investigated municipalities. A considerable number of measures had been implemented, although landscape planning as a supply-side instrument proposes generally a very large number of measures. Factors with a positive effect on the implementation of landscape planning measures are pointed out.
Terrestrial mud volcanoes (TMVs) represent geochemically diverse habitats with varying sulfur sources and yet sulfur cycling in these environments remains largely unexplored. Here we characterized the sulfur-metabolizing microorganisms and activity in four TMVs in Azerbaijan. A combination of geochemical analyses, biological rate measurements and molecular diversity surveys (targeting metabolic genes aprA and dsrA and SSU ribosomal RNA) supported the presence of active sulfur-oxidizing and sulfate-reducing guilds in all four TMVs across a range of physiochemical conditions, with diversity of these guilds being unique to each TMV. The TMVs varied in potential sulfate reduction rates (SRR) by up to four orders of magnitude with highest SRR observed in sediments where in situ sulfate concentrations were highest. Maximum temperatures at which SRR were measured was 60 degrees C in two TMVs. Corresponding with these trends in SRR, members of the potentially thermophilic, spore-forming, Desulfotomaculum were detected in these TMVs by targeted 16S rRNA analysis. Additional sulfate-reducing bacterial lineages included members of the Desulfobacteraceae and Desulfobulbaceae detected by aprA and dsrA analyses and likely contributing to the mesophilic SRR measured. Phylotypes affiliated with sulfide-oxidizing Gamma- and Betaproteobacteria were abundant in aprA libraries from low sulfate TMVs, while the highest sulfate TMV harboured 16S rRNA phylotypes associated with sulfur-oxidizing Epsilonproteobacteria. Altogether, the biogeochemical and microbiological data indicate these unique terrestrial habitats support diverse active sulfur-cycling microorganisms reflecting the in situ geochemical environment.