Preliminary investigation and dynamic analysis of a multiphase ice-rock avalanche on July 5, 2021, in the upper Naltar valley,Gilgit, Pakistan

Landslides - On July 5, 2021, a catastrophic rock avalanche hit an area in the upper Naltar valley, located in northwestern Gilgit, Pakistan. The 14 Mm3 rock mass flowed down the hillslope and...     

Un « point chaud » sous le système du Rift syrien : données pétrologiques complémentaires sur les enclaves du volcanisme récent

Ultrabasic xenoliths (pyroxenites, lherzolites, harzburgites) in recent (Neogene–Quaternary) volcanoes have been studied in three localities within Syria: Jubates (North), Mhailbeh (Center), Tel Thannoun (South). P–T conditions of mineral equilibration have been estimated by pyroxene thermometry (temperature) and maximum CO₂ density in primary inclusions (minimum pressure). Pyroxenites equilibrate at significantly higher conditions (T about 1200 °C, P>15 kbar) than lherzolites and harzburgites (900<T<1100 °C, P between 10 and 15 kbar). All are within the spinel lherzolite field, whereas Cretaceous xenoliths originate within the garnet lherzolite field. To cite this article: A. Bilal, F. Sheleh, C. R. Geoscience 336 (2004).     

Neotethyan Evolution of the Ankara Mélange,Turkey: An Intraoceanic Subduction-Accretion System

<正>We report here new geochemical and geochronological data from mafic-ultramafic rock suites in the Ankara Mélange in north-central Turkey,and present a new tectonic model for its origin.Considered as one of most important relics of the Neotethyan realm in the region,the Ankara Mélange occurs between the Sakarya Continent     

Delineation of groundwater potential zones in Wadi Saida Watershed of NW-Algeria using remote sensing,geographic information system-based AHP techniques and geostatistical analysis

Sustainable management of groundwater resources has now become an obligation,especially in arid and semi-arid regions given the socio-economic importance of this resource.The optimization in zoning for groundwater exploitation helps in planning and managing groundwater supply works such as boreholes and wells in the catchment.The objective of this study is to use remote sensing and GIS-based Analytical Hierarchy Process(AHP)techniques to evaluate the groundwater potential of Wadi Saida Watershed.Spatial analysis such as geostatistics was also used to validate results and ensure more accuracy.Through the GIS tools and remote sensing technique,earth observation data were converted into thematic layers such as lineament density,geology,drainage density,slope,land use and rainfall,which were combined to delineate groundwater potential zones.Based on their respective impact on groundwater potential,the AHP approach was adopted to assign weights on multi-influencing factors.These results will enable decision-makers to optimize hydrogeological exploration in large-scale catchment areas and map areas.According to the results,the southern part of the Wadi Saida Watershed is characterized as a higher groundwater potential area,where 32%of the total surface area falls in the excellent and good class of groundwater potential.The validation process revealed a 71%agreement between the estimated and actual yield of the existing boreholes in the study area.     

Hydrothermal and thermal treatment of natural clinoptilolite zeolite from Bigadiç, Turkey: An experimental study

The clinoptilolite rich zeolite from Bigadiç which was formed from alteration of volcanic glass were treated with acidic (HCl, H₃BO₃, H₃PO₄), alkaline (KOH, NaOH) solutions. Hydrothermally treated and untreated samples were heat treated at 400, 550 and 700°C. XRD, ICP-MS and N₂ gas adsorption were used for physicochemical characterization of zeolites. Considering the Si/Al > 4 and Na+K/Ca+Mg < 1 ratios, zeolite sample is included to earth alkali clinoptilolite class (Heu II) which is also revealed by thermal treatments. Since zeolite structure contains low alkalies it was at collapsed 550°C. The removal of oxide elements efficiency of acids and alkalies were in the order of HCl > H₃PO₄ > HBO₃ > KOH > NaOH. XRD analysis indicated that the structure of zeolite was not altered with acids and alkali treatments. The structure of zeolite treated with HCl and other acids started to deform at 400 and 550°C respectively. In treatment with HCl, Si/Al ratio increases with significant a decrease in K content which resulted in a decrease in the heat stability of zeolite. No change was observed in the structure and thermal stability of clinoptilolite after alkali treatments. The fact that although significant amount of Na is removed with H₃BO₃ acid and Na is increased with NaOH but the thermal stability remains the same indicates that Na cation is not an important parameter as much as K. HCl and H₃PO₄ acid treatments increased the surface area depending on the dissolution of amorphous material and H₃PO₄ was found to be more effective. However, the total pore size decreased due to formation of new micropores.     

Planktonic foraminiferal biostratigraphy of the Coniacian-Maastrichtian sequences of the Bey Dağları Autochthon,western Taurides,Turkey: thin-section zonation

Planktonic foraminifer distributions in seventeen stratigraphic sections of Upper Cretaceous hemipelagic and pelagic sequences of northern Bey Da?lar? Autochthon (western Taurides) yield six biozones such as, Dicarinella concavata Interval Zone, Dicarinella asymetrica Range Zone, Radotruncana calcarata Range Zone, Globotruncana falsostuarti Partial Range Zone, Gansserina gansseri Interval Zone, and Abathomphalus mayaroensis Concurrent Range Zone. Two of the zones, Dicarinella concavata Zone and Dicarinella asymetrica Zone, are identified in the massive hemipelagic limestones of the Bey Da?lar? Formation, of Coniacian-Santonian age. They are characterized by scarce planktonic foraminifera and abundant calcisphaerulids. The other four biozones are determined from the cherty pelagic limestones of the Akda? Formation and indicate a late Campanian-late Maastrichtian time interval. The planktonic foraminifera observed in these four biozones are diverse, complex morphotypes (K-selection), suggesting open oceans. The assemblage of the Abathomphalus mayaroensis Zone shows that the latest Maastrichtian record is absent throughout the northern part of the autochthon. Two main sedimentary hiatuses are recognized within the Upper Cretaceous pelagic sequence. Early to middle Campanian and latest Maastrichtian-middle Paleocene planktonic foraminifera are absent in all measured stratigraphic sections. Hiatus durations differ between sections as a result of diachronism of onset of the hemipelagic and pelagic deposition and the post-Santonian and post-Maastrichtian erosional phases. Drowning event and the early-middle Campanian and latest Maastrichtian-middle Paleocene hiatuses in the pelagic sequence are attributed to regional tectonics during the Late Cretaceous.     

Anatomy of a eustatic event during the Turonian (Late Cretaceous) hot greenhouse climate

Sequence stratigraphic studies consider relative change in sea level (as regulated by eustasy, local tectonics and sediment supply) as the main builder of the stratigraphic record. Eustasy has generally been considered as a consequence of the growth and decay of continental ice sheets that would explain large, rapid changes in sea level, even during periods of relative global climatic warmth. However, such a mechanism has become increasingly difficult to envision during times of extreme global warmth such as the Turonian, when the equator-to-pole temperature gradient was very low and the presence of polar ice seems improbable. This paper investigates the timing and extent of sea level falls during the late Cenomanian through Turonian, especially the largest of those events, sequence boundary KTu4, which occurred during the middle to late Turonian peak of the Cretaceous hot greenhouse climate. We conclude that the amplitude of the widespread third-order sea level fall in the middle Turonian that is centered at ~91.8 Ma varies at different locations depending on the influence of dynamic topography on local tectonics and regional climatic conditions. Ice volume variations seem unlikely as a mechanism for controlling sea level at this time. However, this causal factor cannot be ruled out completely since Antarctic highlands (if they existed in the Late Cretaceous) could sequester enough water as ice to cause eustatic falls. To ascertain this requires detailed tomographic imaging of Antarctica, followed by geodynamic modeling, to determine whether high plateaus could have existed to accumulate ephemeral ice sheets. Other mechanisms for sea level change, such as transference between ground water (a small amplitude shorter time scale effect) and the ocean and entrainment and release of water from the mantle to the oceanic reservoir (a potentially large amplitude and longer time scale process), are intriguing and need to be explored further to prove their efficacy at third-order time scales.     

Evaluation of Ordinary Least Square (OLS) and Geographically Weighted Regression (GWR) for Water Quality Monitoring: A Case Study for the Estimation of Salinity

Landsat-5 Thematic Mapper (TM) dataset have been used to estimate salinity in the coastal area of Hong Kong. Four adjacent Landsat TM images were used in this study, which was atmospherically corrected using the Second Simulation of the Satellite Signal in the Solar Spectrum (6S) radiative transfer code. The atmospherically corrected images were further used to develop models for salinity using Ordinary Least Square (OLS) regression and Geographically Weighted Regression (GWR) based on in situ data of October 2009. Results show that the coefficient of determination (R²) of 0.42 between the OLS estimated and in situ measured salinity is much lower than that of the GWR model, which is two times higher (R² = 0.86). It indicates that the GWR model has more ability than the OLS regression model to predict salinity and show its spatial heterogeneity better. It was observed that the salinity was high in Deep Bay (north-western part of Hong Kong) which might be due to the industrial waste disposal, whereas the salinity was estimated to be constant (32 practical salinity units) towards the open sea.     

Constructing a 3D structural block diagram of the Central Basin in Marmara Sea by means of bathymetric and seismic data

In this study we made a comparative interpretation of multibeam bathymetric and seismic reflection data with different resolutions and penetration properties collected in the Central Basin of the Marmara Sea. Our main objectives were (i) to investigate and compare the active tectonic deformation observed on the sea bottom and within the uppermost sedimentary layers to that of the deep-seated deformation within the limits of resolution and penetration of the available geophysical data and (ii) to build a three-dimensional (3D) block diagram of the active tectonic and buried features by means of a sliced mapping technique. In this approach, we produced slice maps of the active and buried structural features at selected depths and then combined them to form a 3D structural block diagram. Motivation for our work was to produce a 3D structural diagram to derive a more detailed image of the structural features in the Central Basin where there is no available 3D seismic data. The observations from the bathymetry and seismic data and developed 3D diagram support the presence of a through-going strike-slip fault that forms a rotational depression zone against a right-stepping strike-slip faulting causing a pull-apart basin in the Central Depression zone.