Climate signal in varve thickness: Lake La Cruz (Spain), a case study

Lake La Cruz is a meromictic, karstic lake with annually laminated sediment formed by summer pulses of calcite deposition. The aim of this study was to explore the potential use of the laminated sediment from Lake La Cruz as a quantitative climate proxy, by calibrating lamina thickness against instrumental climate data. Statistical analysis of the relation between lamina thickness and the meteorological dataset indicated a high correlation between calcium carbonate lamina thickness and rainfall from December to March (r  = 0.725, P < 0.01, n = 35). Winter rainfall anomalies in the area are, in turn, highly negatively correlated with the North Atlantic Oscillation index (NAO, r = −0.832; P < 0.01; n = 53). We propose a regression model to infer past winter rainfall from calcium carbonate laminae thickness. These results highlight new possibilities for paleoenvironmental research using calcite laminated sediment records as climate proxies, especially to study past rainfall variability.     

Insights in the exhumation history of the NW Zagros from bedrock and detrital apatite fission‐track analysis: evidence for a long‐lived orogeny

We present the first fission‐track (FT) thermochronology results for the NW Zagros Belt (SW Iran) in order to identify denudation episodes that occurred during the protracted Zagros orogeny. Samples were collected from the two main detrital successions of the NW Zagros foreland basin: the Palaeocene–early Eocene Amiran–Kashkan succession and the Miocene Agha Jari and Bakhtyari Formations. In situ bedrock samples were furthermore collected in the Sanandaj‐Sirjan Zone. Only apatite fission‐track (AFT) data have been successfully obtained, including 26 ages and 11 track‐length distributions. Five families of AFT ages have been documented from analyses of in situ bedrock and detrital samples: pre‐middle Jurassic at ～171 and ～225 Ma, early–late Cretaceous at ～91 Ma, Maastrichtian at ～66 Ma, middle–late Eocene at ～38 Ma and Oligocene–early Miocene at ～22 Ma. The most widespread middle–late Eocene cooling phase, around ～38 Ma, is documented by a predominant grain‐age population in Agha Jari sediments and by cooling ages of a granitic boulder sample. AFT ages document at least three cooling/denudation periods linked to major geodynamic events related to the Zagros orogeny, during the late Cretaceous oceanic obduction event, during the middle and late Eocene and during the early Miocene. Both late Cretaceous and early Miocene orogenic processes produced bending of the Arabian plate and concomitant foreland deposition. Between the two major flexural foreland episodes, the middle–late Eocene phase mostly produced a long‐lasting slow‐ or nondepositional episode in the inner part of the foreland basin, whereas deposition and tectonics migrated to the NE along the Sanandaj‐Sirjan domain and its Gaveh Rud fore‐arc basin. As evidenced in this study, the Zagros orogeny was long‐lived and multi‐episodic, implying that the timing of accretion of the different tectonic domains that form the Zagros Mountains requires cautious interpretation.     

Leucogranite intruding the South Tibetan Detachment in western Nepal: implications for exhumation models in the Himalayas

The most popular models regarding the exhumation of the Greater Himalayan Sequence (GHS), such as extrusion, channel flow, critical taper and wedge extrusion, require prolonged activity of the two bounding shear zones and faults, the Main Central Thrust (MCT) and the South Tibetan Detachment (STD). We present the crystallization age of an undeformed leucogranite that intrudes both the GHS and the Tethyan Himalaya Sequence (THS). Zircon and monazite U‐Pb ages in the leucogranite give ages between 23 and 25 Ma constraining, at that time, the end of shearing along the STD. Our results limit the contemporaneous activity of the MCT and STD to a short period of time (~1–2 Ma) and thus argue against exhumation models requiring prolonged contemporaneous activity of the MCT and STD.     

LusTRE: a framework of linked environmental thesauri for metadata management

The paper illustrates a Linked Thesaurus Framework for the Environment, named LusTRE, to facilitate data sharing across different environmental disciplines. It provides a knowledge infrastructure of multilingual thesauri and code lists, interlinking them so that they can be used as one integrated linked data source. This multilingual thesaurus is published according to the Linked Data Best Practices and supports metadata compilation and data discovery for describing and finding Environmental geodata. A human readable web interface is provided for the exploitation of LusTRE as well as a set of web services for programmatic access to the knowledge infrastructure. LusTRE has been exploited within the European directive INSPIRE and SEIS piloting testbeds implemented within the EU project eENVplus in order to support cross-border and cross-domain data sharing. It is aimed at supporting multilingual data search and query refinement. In order to show how interlinked content can help users to more easily express metadata within Spatial Data Infrastructures (SDI), LusTRE web services have been integrated within existing metadata editors and geoportals.     

On the Vp/Vs–Mg# correlation in mantle peridotites: Implications for the identification of thermal and compositional anomalies in the upper mantle

We use thermodynamically self-consistent and hybrid methods to analyze the correlation of important physical parameters (e.g. bulk density, elastic moduli) with bulk Mg# and modal composition in mantle peridotites at upper mantle conditions. Temperature (anharmonic and anelastic), pressure and compositional derivatives for all these parameters are evaluated. The results show that the widely used correlations between Vp/Vs and Mg# in peridotites are strictly valid only for garnet-bearing assemblages at temperatures < 900 °C. The correlation breaks down when: i) spinel is the stable Al-rich phase in the assemblage and ii) when anelastic attenuation of seismic velocities becomes important (T ? 900 °C). This implies that the range of applicability of published Vp/Vs–Mg# correlations for the upper mantle is limited to a depth interval between the spinel–garnet phase transition and the 900 °C isotherm. We use numerical simulations to show that this depth interval is virtually nonexistent in lithospheres thinner than ～ 140 km and can comprise up to ～ 50% of the lithospheric mantle in thick (> 220 km) lithospheric domains. In addition, we show that for most of the upper mantle the expected Δ(Vp/Vs) values associated with compositional variations are smaller than the resolution limit of current seismological methods. All these considerations suggest that the Vp/Vs ratio is not a reliable measure of compositional variations and that for large parts of the upper mantle compositional anomalies cannot be separated from thermal anomalies on the basis of seismological studies only. We further confirm that the only reliable indicator of compositional anomalies in a peridotitic mantle is the ratio of density to shear wave velocities (ρ/Vs). Our results demonstrate that geophysical–petrological models (forward or inverse) that model these two fields (i.e. density and Vs) self-consistently within a robust thermodynamic framework are necessary for characterizing the small-scale thermal and compositional structure of the lithosphere and sublithospheric upper mantle.     

Technical guidelines for the assessment of earthquake induced liquefaction hazard at urban scale

Bulletin of Earthquake Engineering - Microzonation for earthquake-induced liquefaction hazard is the subdivision of a territory at a municipal or submunicipal scale in areas characterized by the...     

Tectonic inversion in a segmented foreland basin from extensional to piggy back settings: The Tucumán basin in NW Argentina

The Tucumán foreland basin is bounded by: 1) basement cored ranges with elevations over 6000 m in the west; 2) inverted extensional grabens to the north; 3) basement thrust blocks in the south and 4) basement cored small ranges in the east. This foreland basin is located between two geological provinces: the Sierras Pampeanas and the Santa Bárbara system.Cretaceous Salta rifting extended southwards covering the entire eastern part of the province of Tucumán in NW Argentina. Syn-rift and post-rift deposits can be recognized in accordance with their architectural geometries. Foreland basin sediments progressively covered the rift deposits as the Andean orogen propagated towards the east.Despite some early studies, the Tucumán basin is poorly documented. For the present study, 44 sections of 2D seismic surveys amounting to more than 730 km were used to describe the structure and the depositional evolution of the basin. The present structure is the result of a long sequence of events that includes a compressional deformation during the Paleozoic, a rifting stage during the Cretaceous and a foreland stage during the late Cenozoic. Although tectonic inversion, which has played a role during the foreland stage since the Miocene, can be observed in many sectors of the basin, it is more prominent along the margins. Reactivation of old basement discontinuities and inversion of Cretaceous normal faults produced the compartmentalization of the foreland, giving rise to the present shape of the Tucumán basin. This evolution is recorded in the Neogene deposits.     

Bacterial Community Dynamics in a Seagrass (<Emphasis Type="Italic">Posidonia oceanica</Emphasis>) Meadow Sediment

Some traits of the bacterial community dynamics associated to the rhizosphere of the Mediterranean seagrass Posidonia oceanica, growing in carbonate sediments, were analyzed during a 2-year period in an enclosed bay of the Balearic Islands. The diversity of the bacterial community was studied by the construction of 16S rDNA clone library. For testing temporal and vertical differences in the abundance of total cells and active Bacteria, we used 4′,6-diamidino-2-phenylindole (DAPI) staining and fluorescence in situ hybridization (FISH). Moreover, some relevant groups of sulfate-reducing bacteria (SRB) were occasionally assessed by FISH. Despite the observed decrease in the total DAPI-stained cells, bacterial counts, and sulfate reduction rates throughout the sampling time, we found an increase in both the pore-water sulfide concentration and the proportion of SRB. Overall, the results revealed a very high bacterial diversity and indicated shifts in bacterial dynamics that could not be related to temperature-dependent factors, suggesting a link between the documented regression of the seagrass meadow and the decline of the microbial community, likely due to large organic matter inputs to the bay.