Provenance analyses of the heavy-mineral beach sands of the Annaba coast,northeast Algeria,and their consequences for the evaluation of fossil placer deposit

The paper presents the first study of heavy-mineral sand beaches from the Mediterranean coast of Annaba/Algeria. The studied beaches run along the basement outcrops of the Edough massif, which are mainly composed by micaschists, tourmaline-rich quartzo-feldspathic veins, gneisses, skarns and marbles. Sand samples were taken from three localities (Ain Achir, Plage-Militaire and El Nasr). The heavy-mineral fraction comprises between 74 and 91 vol%. The garnets of the beaches are almandine rich and tourmalines vary with respect to their location from schorl to dravite. Tourmaline at Ain Achir and the Plage-Militaire is schorlits, while at El Nasr beach dravite is ubiquitous. The World Shale Average normalised REE of the sands and the basement outcrops reveal: (i) Ain Achir beach: REE pattern of sand and the coastal rocks from the studied beaches reflects a multiple sources; (ii) Plage-Militaire: the sand and the coastal outcrops show similar LREE and a strong enrichment in HREE, suggesting the presence HREE-rich phases found as inclusions in staurolite; (iii) El Nasr: two types of sand patterns are found: one with flat REE pattern similar to the proximal rocks and other one enriched in HREE suggesting a mixed source.     

Local climate change induced by groundwater overexploitation in a high Andean arid watershed,Laguna Lagunillas basin,northern Chile

The Laguna Lagunillas basin in the arid Andes of northern Chile exhibits a shallow aquifer and is exposed to extreme air temperature variations from 20 to ?25 °C. Between 1991 and 2012, groundwater levels in the Pampa Lagunillas aquifer fell from near-surface to ~15 m below ground level (bgl) due to severe overexploitation. In the same period, local mean monthly minimum temperatures started a declining trend, dropping by 3–8 °C relative to a nearby reference station. Meanwhile, mean monthly maximum summer temperatures shifted abruptly upwards by 2.7 °C on average in around 1996. The observed air temperature downturns and upturns are in accordance with detected anomalies in land-surface temperature imagery. Two major factors may be causing the local climate change. One is related to a water-table decline below the evaporative energy potential extinction depth of ~2 m bgl, which causes an up-heating of the bare soil surface and, in turn, influences the lower atmosphere. At the same time, the removal of near-surface groundwater reduces the thermal conductivity of the upper sedimentary layer, which consequently diminishes the heat exchange between the aquifer (constant heat source of ~10 °C) and the lower atmosphere during nights, leading to a severe dropping of minimum air temperatures. The observed critical water-level drawdown was 2–3 m bgl. Future and existing water-production projects in arid high Andean basins with shallow groundwater should avoid a decline of near-surface groundwater below 2 m bgl and take groundwater-climate interactions into account when identifying and monitoring potential environmental impacts.     

Impact of the 2010 tsunami on an endangered insular soil–plant system

Natural catastrophes could damage island biodiversity and ecosystems, and their effects could become devastating if combined with human disturbances. In this study, we determined the effects of the tsunami occurred in Robinson Crusoe Island (Chile) on 27 February 2010 on an endangered soil–plant system. Using data of endemic Cabbage Trees (Dendroseris litoralis Skottsb.) and soil attributes taken before and after the 2010 event, we developed thematic maps to assess the changes in population size and soil substrate of Cabbage Trees caused by the tsunami. We determined that from 153 pre-tsunami (2009) standing Cabbage Trees, only 66 (43 %) survived in 2011, mostly in elevations above 25 m a.s.l. Before the tsunami, 86 (56 %) of Cabbage Trees were established in humus-rich soil sites whereas after the tsunami, this number declined to 53 (35 %). These results represent the first report of a severe population decline after a tsunami and indicate that tsunamis are an important source of species extinction in small oceanic islands not only by reducing the population size but also by reducing the quality of sites for plant growth.     

The Sabzevar blueschists of the North-Central Iranian micro-continent as remnants of the Neotethys-related oceanic crust subduction

The Sabzevar ophiolites mark the Neotethys suture in east-north-central Iran. The Sabzevar metamorphic rocks, as part of the Cretaceous Sabzevar ophiolitic complex, consist of blueschist, amphibolite and greenschist. The Sabzevar blueschists contain sodic amphibole, epidote, phengite, calcite ± omphacite ± quartz. The epidote amphibolite is composed of sodic-calcic amphibole, epidote, albite, phengite, quartz ± omphacite, ilmenite and titanite. The greenschist contains chlorite, plagioclase and pyrite, as main minerals. Thermobarometry of a blueschist yields a pressure of 13–15.5 kbar at temperatures of 420–500 °C. Peak metamorphic temperature/depth ratios were low (~12 °C/km), consistent with metamorphism in a subduction zone. The presence of epidote in the blueschist shows that the rocks were metamorphosed entirely within the epidote stability field. Amphibole schist samples experienced pressures of 5–7 kbar and temperatures between 450 and 550 °C. The presence of chlorite, actinolite, biotite and titanite indicate greenschist facies metamorphism. Chlorite, albite and biotite replacing garnet or glaucophane suggests temperatures of >300 °C for greenschist facies. The formation of high-pressure metamorphic rocks is related to north-east-dipping subduction of the Neotethys oceanic crust and subsequent closure during lower Eocene between the Central Iranian Micro-continent and Eurasia (North Iran).     

Formation of pseudotachylitic breccias in the central uplifts of very large impact structures: Scaling the melt formation

Abstract– The processes leading to formation of sometimes massive occurrences of pseudotachylitic breccia (PTB) in impact structures have been strongly debated for decades. Variably an origin of these pseudotachylite (friction melt)‐like breccias by (1) shearing (friction melting); (2) so‐called shock compression melting (with or without a shear component) immediately after shock propagation through the target; (3) decompression melting related to rapid uplift of crustal material due to central uplift formation; (4) combinations of these processes; or (5) intrusion of allochthonous impact melt from a coherent melt body has been advocated. Our investigations of these enigmatic breccias involve detailed multidisciplinary analysis of millimeter‐ to meter‐sized occurrences from the type location, the Vredefort Dome. This complex Archean to early Proterozoic terrane constitutes the central uplift of the originally >250 km diameter Vredefort impact structure in South Africa. Previously, results of microstructural and microchemical investigations have indicated that formation of very small veinlets involved local melting, likely during the early shock compression phase. However, for larger veins and networks it was so far not possible to isolate a specific melt‐forming mechanism. Macroscopic to microscopic evidence for friction melting is very limited, and so far chemical results have not directly supported PTB generation by intrusion of impact melt. On the other hand, evidence for filling of dilational sites with melt is abundant. Herein, we present a new approach to the mysterium of PTB formation based on volumetric melt breccia calculations. The foundation for this is the detailed analysis of a 1.5 × 3 × 0.04 m polished granite slab from a dimension‐stone quarry in the core of the Vredefort Dome. This slab contains a 37.5 dm³ breccia zone. The pure melt volume in 0.1 m³ PTB‐bearing granitic target rock outside of the several‐decimeter‐wide breccia zone in the granite slab was estimated at 5.2 dm³. This amount can be divided into 4.6 dm³ melt (88%), for which we have evidenced a limited material transport (at maximum, ≈20 cm) and 0.6 dm³ melt (12%) with, at most, grain‐scale material transport, which we consider in situ formed shock melt. The breccia zone itself contains about 10 dm³ of matrix (melt). Assuming melt exchange over 20 cm at the slab surface, between breccia zone and surrounding melt‐bearing host rock volume, the outer melt volume is calculated to contain the same amount of melt as contained by the massive breccia zone. Meso‐ and microscopic observations indicate melt transport is more prominent from larger into smaller melt occurrences. Thus, melt of the breccia zone could have provided the melt fill for all the small‐scale PTB veins in the surrounding target rock. Extrapolating this melt capacity calculation for 1 m³ PTB‐bearing host rock shows that a host rock volume of this dimension is able to take up some 52 dm³ melt. Scaling up 1000‐fold to the outcrop scale reveals that exchange between a host rock volume of 2 m radius around a 37 m³ breccia zone could involve some 10 m³ melt. These results demonstrate that large melt volumes (i.e., large breccia zones) can be derived, in principle, from local reservoirs. However, strong decompression would have to apply in order to exchange these considerable melt volumes, which would only be realistic during the decompression phase of impact cratering upon central uplift formation, or locally where compressive regimes acted during the subsequent down‐ and outward collapse of the central uplift.     

Shock‐metamorphic microfeatures in chert from the Jebel Waqf as Suwwan impact structure,Jordan

Abstract– The petrographic investigation of a shocked, chalcedony‐, quartzine‐, and quartz‐bearing allochthonous chert nodule (probably Upper Cretaceous) recovered from surficial wadi gravels in the inner parts of the central uplift of the approximately 6 km in diameter Jebel Waqf as Suwwan impact structure, Jordan, reveals new potential shock indicators in microfibrous–spherulitic silica, in addition to well‐established shock‐metamorphic effects in coarser crystalline quartz. The microcrystalline chert groundmass exhibits a macroscopic dendritic and suborthogonal fracture pattern commonly associated with thin “recrystallization bands” that intersect the pre‐existing diagenetic chert fabric. Fibrous aggregates of quartzine spherulites in chalcedony‐quartzine‐quartz veinlets locally have a shattered appearance and show conspicuous “curved fractures” perpendicular to the quartzine fiber direction (and parallel to [0001]) that commonly trend subparallel to planar fractures (PFs) in neighboring shocked quartz. Quartz exhibits PFs, feather features (FFs), and mainly single sets of planar deformation features (PDFs) parallel to the basal plane (0001) (Brazil twins) and, rarely, additional PDFs parallel to {101¯3}. Shock petrography indicates shock pressures of ≥10 GPa and high shock‐induced differential stresses that affected the chert nodule. The internal crosscutting relationships of primary diagenetic and impact‐related deformational features together with shockpressure estimates suggest that the curved fractures across quartzine spherulites might represent specific (low‐ to medium‐pressure) shock‐metamorphic features, possibly in structural analogy to basal plane PFs in quartz. The dendritic–suborthogonal fractures in the microcrystalline chert groundmass and recrystallization bands are likely related to impact‐induced shear deformation and recrystallization, respectively, and cannot be considered as definite shock indicators.     

The reflectivity spectrum and opposition effect of Titan's surface observed by Huygens' DISR spectrometers

We determined Titan's reflectivity spectrum near the Huygens' landing site from observations taken with the Descent Imager/Spectral Radiometer below 500 m altitude, in particular the downward-looking photometer and spectrometers. We distinguish signal coming from illumination by sunlight and the lamp onboard Huygens based on their different spectral signatures. For the sunlight data before landing, we find that spatial variations of Titan's reflectivity were only ～0.8%, aside from the phase angle dependence, indicating that the probed area within ～100 m of the landing site was very homogeneous. Only the very last spectrum taken before landing gave a 3% brighter reflectivity, which probably was caused by one bright cobble inside its footprint. The contrast of the cobble was higher at 900 nm wavelength than at 600 nm.For the data from lamp illumination, we confirm that the phase function of Titan's surface displays a strong opposition effect as found by Schröder and Keller (2009. Planetary and Space Science 57, 1963–1974). We extend the phase function to even smaller phase angles (0.02°), which are among the smallest phase angles observed in the solar system. We also confirm the reflectivity spectrum of the dark terrain near the Huygens' landing site between 900 and 1600 nm wavelength by Schröder and Keller (2008. Planetary and Space Science 56, 753–769), but extend the spectrum down to 435 nm wavelength. The reflectivity at zero phase angle peaks at 0.45±0.06 around 750 nm wavelength and drops down to roughly 0.2 at both spectral ends. Our reflectivity of 0.45 is much higher than all previously reported values because our observations probe lower phase angles than others. The spectrum is very smooth except for a known absorption feature longward of 1350 nm. We did not detect any significant variation of the spectral shape along the slit for exposures after landing, probing a 25×4 cm² area. However, the recorded spectral shape was slightly different for exposures before and after landing. This difference is similar to the spectral differences seen on scales of kilometers (Keller et al., 2008. Planetary and Space Science 56, 728–752), indicating that most observations may probe spatially variable contributions from two basic materials, such as a dark soil partially covered by bright cobbles.We used the methane absorption features to constrain the methane mixing ratio near the surface to 5.0±0.3%, in agreement with the 4.92±0.24% value measured in situ by Niemann et al. (2005. Nature 438, 779–784), but smaller than their revised value of 5.65±0.18% (Niemann et al., 2010. Journal of Geophysical Research 115, E12006). Our results were made possible by an in depth review of the calibration of the spectroscopic and photometric data.     

Investigating the redox sensitivity of para-toluenesulfonamide (p-TSA) in groundwater

The groundwater downstream of a former sewage irrigation farm in Berlin is contaminated with ammonium (NH₄ ⁺) and para-toluenesulfonamide (p-TSA), besides other anthropogenic pollutants. In the field, in situ removal of NH₄ ⁺ by gaseous oxygen (O₂) and air injection is currently being tested. A laboratory column experiment using aquifer material and groundwater from the site was performed to determine whether this remediation technology is also feasible to reduce high p-TSA concentrations in the anoxic groundwater. First, the column was operated under anoxic conditions. Later, compressed air was introduced into the system to simulate oxic conditions. Samples were collected from the column outlet before and after the addition of compressed air. The experiment revealed that whereas p-TSA was not removed under anoxic conditions, it was almost fully eliminated under oxic conditions. Results were modelled using a transient one-dimensional solute transport model. The degradation rate constants for p-TSA increased from 2.8E−06 to 7.5E−05 s^–1 as a result of microbial adaption to the change of redox conditions. Results show that O₂ injection into an anoxic aquifer is a successful strategy for p-TSA remediation.