Cl-37 in the Dead Sea system---preliminary results

This study presents the first set of δ measurements in the Dead Sea environment. δ values for the meromictic (long term stratified) Dead Sea water column prior to its complete overturn in 1979 were −0.47‰ SMOC for the UWM (Upper Water Mass) and +0.55‰ SMOC for the LWM (Lower Water Mass). The δ values for the pre-overturn Dead Sea cannot be explained by the prevailing model on the evolution of the Dead Sea during the last few centuries and require corroboration by more measurements. The 1979 overturn wiped out almost completely the isotopic differences between the UWM and LWM. Even so, Cl isotope data could be used to decipher physical processes related to the overturn such as incomplete homogenization of the deep water mass. Inputs into the lake, comprising freshwaters (springs and the Jordan River) and saline springs gave a range of −0.37‰ to +1.0‰ with the freshwater sources being more enriched in δ . Based on the δ measurements of the End-Brine (the effluent from Dead Sea evaporation ponds) and of recent Dead Sea halite, the Cl isotopic composition of the originating brines have been estimated. They gave a narrow isotopic spread, +0.01‰ and +0.07‰ and fall within the same range with Dead Sea pore water (+0.13‰) and with the post-overturn Dead Sea (−0.03‰ and +0.16‰). Rock salt from Mount Sdom gave a value of −0.59‰ indicating its formation at the last stages of halite deposition from evaporating sea water. The hypersaline En Ashlag spring gave a depleted δ value of −0.32‰, corresponding to a residual brine formed in the very latest stages (including bishofite deposition) of seawater evaporation.     

Neoproterozoic peritidal phosphorite from the Sete Lagoas Formation (Brazil) and the Precambrian phosphorus cycle

The Neoproterozoic Sete Lagoas Formation (ca 610 Ma) of the São Francisco Basin, Brazil, is a succession of siltstone, limestone and phosphorite. Phosphorite forms part of a previously unrecognized 150 to 200 m thick, unconformity bounded depositional sequence. Lithofacies stacking patterns indicate that deposition was punctuated by higher order fluctuations in base level that produced aggradational parasequences. These shallowing‐upward cycles record the progradation of phosphate‐rich intertidal flats over shallow subtidal deposits as accommodation filled. The presence of mudcracks, authigenic chert nodules, lack of coarse terrigenous clastics and the abundance of silt with fine, abraded quartz grains suggests accumulation along an arid coastline with significant aeolian input. Delivery of phosphorus adsorbed on aeolian Fe‐(oxyhydr)oxide and clay is interpreted as having stimulated phosphogenesis in peritidal environments. Lithofacies associations indicate that windblown phosphorus promoted the establishment of cyanobacterial communities along the coast, which produced photosynthetic oxygen and the suboxic conditions necessary for the precipitation of authigenic carbonate fluorapatite. As in other Precambrian phosphatic systems, nearshore oxygen oases were a prerequisite for phosphorite accumulation because redox sensitive phosphogenic processes were pushed into the sediment to concentrate phosphorus. In more distal, anoxic environments phosphorite could not form because these biotic and abiotic processes were suspended in the water column, which cycled phosphorus in sea water rather than at the sediment–water interface. Such shallow‐water phosphorite is unlike larger, younger Neoproterozoic–Phanerozoic phosphatic deposits inferred to have formed in deeper‐upwelling related environments. The increasing size of phosphatic deposits through the latest Precambrian is interpreted as reflecting the progressive ventilation of the oceans during the Neoproterozoic Oxygenation Event, and resultant expansion of phosphogenic environments into distal settings. The widespread cycling of bioavailable phosphorus at the sea floor not only produced the first true phosphorite giants, but may have also been an important precondition for the evolution of multicellular animals.     

Chemical and oxygen isotopic compositions of accretionary rim and matrix olivine in CV chondrites: Constraints on the evolution of nebular dust

A correlation of petrography, mineral chemistry and in situ oxygen isotopic compositions of fine-grained olivine from the matrix and of fine- and coarse-grained olivine from accretionary rims around Ca-Al-rich inclusions (CAIs) and chondrules in CV chondrites is used here to constrain the processes that occurred in the solar nebula and on the CV parent asteroid. The accretionary rims around Leoville, Vigarano, and Allende CAIs exhibit a layered structure: the inner layer consists of coarse-grained, forsteritic and ¹⁶O-rich olivine (Fa_1-40 and Δ¹⁷O = −24‰ to −5‰; the higher values are always found in the outer part of the layer and only in the most porous meteorites), whereas the middle and the outer layers contain finer-grained olivines that are more fayalitic and ¹⁶O-depleted (Fa_15-50 and Δ¹⁷O = −18‰ to +1‰). The CV matrices and accretionary rims around chondrules have olivine grains of textures, chemical and isotopic compositions similar to those in the outer layers of accretionary rims around CAIs. There is a correlation between local sample porosity and olivine chemical and isotopic compositions: the more compact regions (the inner accretionary rim layer) have the most MgO- and ¹⁶O-rich compositions, whereas the more porous regions (outer rim layers around CAIs, accretionary rims around chondrules, and matrices) have the most MgO- and ¹⁶O-poor compositions. In addition, there is a negative correlation of olivine grain size with fayalite contents and Δ¹⁷O values. However, not all fine-grained olivines are FeO-rich and ¹⁶O-poor; some small (<1 μm in Leoville and 5-10 μm in Vigarano and Allende) ferrous (Fa_>20) olivine grains in the outer layers of the CAI accretionary rims and in the matrix show significant enrichments in ¹⁶O (Δ¹⁷O = −20‰ to −10‰). We infer that the inner layer of the accretionary rims around CAIs and, at least, some olivine grains in the finer portions of accretionary rims and CV matrices formed in an ¹⁶O-rich gaseous reservoir, probably in the CAI-forming region. Grains in the outer layers of the CAI accretionary rims and in the rims around chondrules as well as matrix may have also originated as ¹⁶O-rich olivine. However, these olivines must have exchanged O isotopes to variable extents in the presence of an ¹⁶O-poor reservoir, possibly the nebular gas in the chondrule-forming region(s) and/or fluids in the parent body. The observed trend in isotopic compositions may arise from mixtures of ¹⁶O-rich forsterites with grain overgrowths or newly formed grains of ¹⁶O-poor fayalitic olivines formed during parent body metamorphism. However, the observed correlations of chemical and isotopic compositions of olivine with grain size and local porosity of the host meteorite suggest that olivine accreted as a single population of ¹⁶O-rich forsterite and subsequently exchanged Fe-Mg and O isotopes in situ in the presence of aqueous solutions (i.e., fluid-assisted thermal metamorphism).     

Modern Vegetation and Pollen Relationships in Four Southwestern Atlantic Coastal Lagoons

Pollen studies and their relationship with modern vegetation facilitate paleoecological reconstructions while changes in pollen abundance are indicators of environmental fluctuations. We analyzed the relationships between recent pollen deposits in the sediments of four Uruguayan coastal lagoons and catchment vegetation and analyzed the temporal dynamics of submerged aquatic vegetation (SAV). We mapped terrestrial vegetation, sampled SAV biomass, and analyzed the pollen record in each lagoon. The sediment samples represented the last 49–76 years of deposition, and most vegetation types were well represented in the pollen records. Pollen of Chenopodiaceae, proposed as indicators of saltmarshes, decreased in the surface samples of all lagoons, possibly due to the salinity reduction promoted by precipitation changes in the region. Pollen of SAV was found in all lagoons but with gaps in the record, and a submerged vegetated phase was recorded. Simultaneous botanical and pollen analyses better captured the large fluctuations of SAV in coastal lagoons.     

Dimensions of environmental justice in anti-gold mining movements in Latin America

The present article examines two Latin American gold mining conflicts, one in the city of Esquel (Patagonia in Argentina) and the other in Pascua–Lama (Chilean border with Argentina). We identify the emergence of three dimensions of environmental justice (distribution, recognition, participation) in the anti-mining movements of these two cases. The study finds that some dimensions of justice appear first (participation and recognition), while distribution emerges later, as movements jump scales engaging with national and international networks that provide a systemic perspective of the conflicts. The findings are consistent with other studies that refer to environmental justice as multi-scalar and context related. We also point to the relevance of studying decision-making procedures and jumping scales to understand how environmental justice claims are framed in resource extraction conflicts.     

Geology and impact features of Riachão structure,northern Brazil

Riachão, located at S7°42′/W46°38′ in Maranhão State, northeastern Brazil, is a complex impact structure of about 4.1 km diameter, formed in Pennsylvanian to Permian sedimentary rocks of the Parnaíba Basin sequence. Although its impact origin was already proposed in the 1970s, information on its geology and shock features is still scarce in the literature. We present here the main geomorphological and geological characteristics of the Riachão impact structure obtained by integrated geophysical and remote sensing analysis, as well as geological field work and petrographic analysis. The identified lithostratigraphic units consist of different levels of the Pedra de Fogo Formation and, possibly, the Piauí Formation. Our petrographic analysis confirms the presence of shock‐diagnostic planar microdeformation structures in quartz grains of sandstone from the central uplift as evidence for an impact origin of the Riachão structure. The absence of crater‐filling impact breccias and melt rocks, shatter cones, as well as the restricted occurrence of microscopic shock effects, suggests that intense and relatively deep erosion has occurred since crater formation.     

Spatial distribution of aftershocks and background seismicity in central California

We examine the spatial distribution of earthquake hypocenters in four central California areas: the aftershock zones of the (1) 1984 Morgan Hill (2) 1979 Coyote Lake, and (3) 1983 Coalinga earthquakes, as well as (4) the aseismically creeping area around Hollister. The basic tool we use to analyze these data are frequency distributions of interevent distances between earthquakes. These distributions are evaluated on the basis of their deviation from what would be expected if earthquakes occurred randomly in the study areas. We find that both background seismic activity and aftershocks in the study areas exhibit nonrandom spatial distribution. Two major spatial patterns, clustering at small distances and anomalies at larger distances, are observed depending on tectonic setting. While both patterns are seen in the strike-slip environments along the Calaveras fault (Morgan Hill, Coyote Lake, and Hollister), aftershocks of the Coalinga event (a thrust earthquake) seem to be characterized by clustering only. The spatial distribution of earthquakes in areas gradually decreasing in size does not seem to support the hypothesis of a self-similar distribution over the range of scales studied here, regardless of tectonic setting. Spatial distributions are independent of magnitude for the Coalinga aftershocks, but events in strike-slip environments show increasing clustering with increasing magnitude. Finally, earthquake spatial distributions vary in time showing different patterns before, during, and following the end of aftershock sequences.     

Oxidative stress in the mussel Mytella guyanensis from polluted mangroves on Santa Catarina Island,Brazil

Digestive glands of the mangrove mussel Mytella guyanensis, collected at one non-polluted site (site 1) and two polluted sites (sites 2 and 3), were analysed for different antioxidant defenses, lipid peroxidation and DNA damage. Thiobarbituric acid-reactive substance (TBARS) and 8-oxo-7,8-dihydro-2'-deoxyguanosine levels were enhanced at the polluted sites. With the exception of superoxide dismutase, the activities of catalase and glutathione peroxidase were also higher at the polluted sites. Greater increases were observed in glutathione reductase, glutathione S-transferase and etoxyresorufine-O-deethylase activities at the polluted sites. Conversely, reduced glutathione content was higher at the control site. Trace metal contents in mussels collected at polluted sites were increased compared to the control site, and there were strong positive correlations between TBARS and Cu and Pb contents. M. guyanensis is routinely exposed to an oxidative stress condition at both polluted sites, and considering xenobiotic bioaccumulation in bivalve molluscs, the mangrove mussel represents an excellent bioindicator for environmental monitoring studies.