Systematics, biometry of the species Opsidiscus from the Middle Cambrian succession of the Spiti basin, India

The Middle Cambrian succession of the Parahio Valley in general and Debsakhad section in particular is dominated by trilobites. Genus Opsidiscus, along with other trilobite forms dominates the lower Middle Cambrian succession. In the present study two new species of Opsidiscus, Opsidiscus wadiai and Opsidiscus srikantiai are reported from the lower Middle Cambrian succession of Debsakhad section. The species were differentiated on their morphological features and their multivariate analysis. The multivariate analysis applied here is used as a supplement method to qualitative analysis in order to differentiate between the cranidial characters of Opsidiscus. The qualitative study of each species studied individually shows more or less close affiliation as is observed by different quantitative methods. The presence of Opsidiscus has a great stratigraphic significance in this region, as they first appear from informal Stage 5 of Series 3 and goes up to the Drumian Stage of Series 3 of the Cambrian System in the Debsakhad section, which helps to correlate this section with other well known sections of the Middle Cambrian.     

Characteristics of sea-cliff erosion induced by a strong winter storm in the eastern Mediterranean

Changes in sea-cliff morphologies along the 30-km-long Sharon Escarpment segment of Israel's weakly cemented Mediterranean eolianite cliff line were analyzed to gain quantitative insights into erosion characteristics associated with a high-energy winter storm (10–20 year return interval). Ground-based repeat LiDAR measurements at five sites along the cliff line captured perturbations of cliff stability by basal wave scouring during the storm, subsequent post-storm gravity-driven slope failures in the cliff face above, and return of the system to transient stability within several months. Post-storm erosion, which amounted to 70% of the total volume of cliff erosion documented, resulted in dramatic local effects of up to 8 m of cliff-top retreat. And yet, at the larger scale of the 30-km cliff line examined, erosion during the storm and the year that followed affected less than 4% of the cliff length and does not appear to be above the average cliff-length annual erosion implied by previously published decadal-scale retreat rates along this sea cliff. Our results do not support a direct association between strong storm events and elevated erosion and retreat at the cliff-line scale.     

Luminescence chronology of the inland sand dunes from SE India

Records of past climate changes have been preserved variously on the earth's surface. Sand dunes are one such prominent imprint, and it is suggested that their presence is an indicator of periods of transition from arid to less arid phases. We report inland sand dunes from Andhra Pradesh (SE India) spread over an area of ~ 500 km², ~ 75 km inland from the east coast. The dune sands are examined to understand their provenance, transportation, timing of sand aggradation and their relationship to past climates. The dune distribution, grain morphology and the grain-size studies on sands suggest an aeolian origin. Physiography of the study area, heavy mineral assemblage, and abundance of quartz in the parent rocks indicate that the dune sands are largely derived from first-order streams emanating from hills in the region and from weathering of the Nellore schist belt. It appears that the geomorphology and wind direction pattern both facilitated and restricted the dune aggradation and preservation to a limited area. OSL dating of 47 dune samples ranged from the present to ~ 50 ka, thereby suggesting a long duration of sand-dune aggradation and/or reworking history.     

Neoproterozoic Deformation at a Boundary Zone Between the Nellore-Khammam Schist Belt and Pakhal Basin, SE India: Strain Analysis of Deformed Pebbles

In the Kinnerasani area in southeastern India, the terrain boundary between the Archean Nellore-Khammam Schist Belt and the Proterozoic Pakhal Supergroup overlying the Dharwar-Bastar cratons can be observed. We analyzed the mesoscopic and microscopic structural features of the highly deformed pebbles in the basal conglomerate bed of the Pakhal Supergroup that occurs at the terrain boundary. The results of the analysis of the pebbles suggest that: 1) deformation of pebbles resulted from ductile deformation during peak metamorphism 2) the mode of strain is plane strain to constrictive and maximum elongation located to be vertical and 3) the apparent stretch of the pebbles is up to 300%.In the Nellore-Khammam Schist Belt, quartz grains constituting the quartz layer of the feldspathized gneiss folded by the last-phase deformation also show vertical maximum stretching in constrictive strain. This observation suggests that the deformational features, at least the mode of strain, during the last-phase deformation is comparable to the deformation forming elongated pebbles of the Pakhal conglomerate. The last-phase deformation structures of the Nellore-Khammam Schist Belt are well observed near the terrain boundary. This indicates that the Pakhal deformation overprinted the rocks of the Nellore-Khammam Schist Belt near the boundary, and that their tectonic juxtaposition occurred during or before this deformation period. Because the Pakhal deformation took place during or soon after the peak metamorphism of the Pakhal Supergroup, which is known to be 1000 Ma, and the last metamorphism of the Nellore-Khammam Schist Belt in the Khammam area were reported to be 1100 Ma. The tectonic juxtaposition between the Pakhal Supergroup and Nellore-Khammam Schist Belt was around 10001100 Ma.     

Reflection and transmission of attenuated waves at the boundary between two dissimilar poroelastic solids saturated with two immiscible viscous fluids

The phenomenon of reflection and transmission of plane harmonic waves at the plane interface between two dissimilar poroelastic solids saturated with two immiscible viscous fluids is investigated. Both porous media are considered dissipative due to the presence of viscosity in pore‐fluids. Four attenuated (three dilatational and one shear) waves propagate in such a dissipative porous medium. A finite non‐dimensional parameter is used to define the effective connections between the surface‐pores of two media at their common interface. Another finite parameter represents the gas‐share in the saturation of pores. An attenuated wave in a dissipative medium is described through the specification of directions of propagation and maximum attenuation. A general representation of an attenuated wave is defined through its inhomogeneous propagation, i.e., different directions for propagation and attenuation. Incidence of an inhomogeneous wave is considered at the interface between two dissipative porous solids. This results in four reflected and four transmitted inhomogeneous waves. Expressions are derived for the partition of incident energy among the reflected and transmitted waves. Numerical examples are studied to determine the effects of saturating pore fluid, frequency, surface‐pore connections and wave inhomogeneity on the strengths of reflected and transmitted waves. Interaction energy due to the interference of different (inhomogeneous) waves is calculated in both the dissipative porous media to verify the conservation of incident energy.     

Improving the calibration strategy of the physically-based model WaSiM-ETH using critical events

Abstract

The use of a physically-based hydrological model for streamflow forecasting is limited by the complexity in the model structure and the data requirements for model calibration. The calibration of such models is a difficult task, and running a complex model for a single simulation can take up to several days, depending on the simulation period and model complexity. The information contained in a time series is not uniformly distributed. Therefore, if we can find the critical events that are important for identification of model parameters, we can facilitate the calibration process. The aim of this study is to test the applicability of the Identification of Critical Events (ICE) algorithm for physically-based models and to test whether ICE algorithm-based calibration depends on any optimization algorithm. The ICE algorithm, which uses the data depth function, was used herein to identify the critical events from a time series. Low depth in multivariate data is an unusual combination and this concept was used to identify the critical events on which the model was then calibrated. The concept is demonstrated by applying the physically-based hydrological model WaSiM-ETH on the Rems catchment, Germany. The model was calibrated on the whole available data, and on critical events selected by the ICE algorithm. In both calibration cases, three different optimization algorithms, shuffled complex evolution (SCE-UA), parameter estimation (PEST) and robust parameter estimation (ROPE), were used. It was found that, for all the optimization algorithms, calibration using only critical events gave very similar performance to that using the whole time series. Hence, the ICE algorithm-based calibration is suitable for physically-based models; it does not depend much on the kind of optimization algorithm. These findings may be useful for calibrating physically-based models on much fewer data.

Editor D. Koutsoyiannis; Associate editor A. Montanari

Citation Singh, S.K., Liang, J.Y., and Bárdossy, A., 2012. Improving calibration strategy of physically-based model WaSiM-ETH using critical events. Hydrological Sciences Journal, 57 (8), 1487–1505.     

Topo-stress based probabilistic model for shallow landslide susceptibility zonation in the Nepal Himalaya

While dealing with slope stability issues, determining the state of stress and the relation between driving force and resisting force are the fundamental deterministic steps. Gravitational stresses affect geologic processes and engineering operations in slopes. Considering this fact, a concept of topo-stress evaluation is developed in this research and used to produce a shallow landslide susceptibility map in a model area. The topo-stress introduced in this research refers to the shear stress induced by the gravitational forces on the planes parallel to the ground surface. Weight of the material on a slope and friction angle of the jointed rock mass are the two fundamental parameters that are considered to govern topo-stress in this study. Considering topo-stress as a main factor for initiating shallow landslides, a GIS-based probabilistic model is developed for shallow landslide susceptibility zonation. An ideal terrain in central Nepal is selected as the study area for this purpose. Two event-based shallow landslide inventories are used to predict accuracy of the model, which is found to be more than 78 % for the first event-landslides and more than 76 % for the second event-landslides. It is evident from these prediction rates that the probabilistic topo-stress model proposed in this work is quite acceptable when regional scale shallow landslide susceptibility mapping is practiced, such as in the Himalayan rocky slopes.     

Geochemical alterations in surface waters of Govind Ballabh Pant Sagar,Northern Coalfield,India

Major ions showed high concentrations, ionic strength and chemical activity in the surface waters of Govind Ballabh Pant Sagar reservoir. Various geochemical ratios showed the dominance of silicate over carbonate weathering and major ions such as Na⁺ + K⁺ account for about 52 % of the cation budget. The high Na⁺ and K⁺ showed sedimentation of rock/coal particles consisting of highly weathered silicate minerals contributed by the discharge of mine water, fly ash mixing during transportation, etc. Further, Ca²⁺ + Mg²⁺/Na⁺ + K⁺ ratio was <1 (0.92) indicating the occurrence of silicate weathering in the reservoir catchment. The comparative assessment showed that the proportion of Ca²⁺ + Mg²⁺/Na⁺ + K⁺ tends to be lower along the coal mining belts compared to non-coal mining regions in the world. The Ca²⁺/SO₄ ^2? ratio <1 revealed not only H₂CO₃ but H₂SO₄ also acting as a source of protons for rock weathering. The cause underlying these differences can be related directly to geological substrate and anthropogenic activities.     

Stable isotopic composition of precipitation in the River Bhagirathi Basin and identification of source vapour

River Ganges one of important rivers in the northern part of India receives water from two of its tributaries, Alaknanda and Bhagirathi. In this present study, we have tried to characterise the precipitation in the Bhagirathi River Basin. The study shows that isotopic composition of precipitation shows depleted nature during monsoon period due to moisture source from the oceanic region and from African region of Indian Ocean and enriched isotopic composition during non-monsoon period due to moisture source from westerlies and local evaporation. The study also shows that temperature and amount show expected positive and negative relationship with individual locations. A positive relationship is exhibited by amount for the entire region due to depleted isotopic composition with increase in altitude. The altitude effect shows that there is a depletion of up to ?0.24 to ?0.29 ‰ of isotopic composition with an increase in 100 m of elevation.     

Factors influencing the high fluoride concentration in groundwater of Vellore District,South India

Most of the arid and semi-arid zones of the Indian subcontinent experience serious health problems due to high concentration of fluoride in drinking water. The Vellore District of Tamil Nadu suffers from high concentration of fluoride in water. However, most of the past studies in this region focused on tannery-related pollution and not on fluoride contamination. The present study attempts to identify the factors influencing the origin and spatial distribution of fluoride in the district. From the observed hydrochemical results of 68 well samples in the context of water level, well depth and hydrochemical parameters, F^? concentration showed increasing trend in the presence of Na⁺ and HCO₃ ^?. This is due to the alkaline nature of groundwater that favors the dissolution of F^?-rich minerals. The occurrence of high fluoride in Na–HCO₃ type of water confirmed this hypothesis. However, Ca²⁺ showed an insignificant correlation with F^?. The high Na/Ca ratio (>1) in 73 % of the samples and the result of Na/Na+Cl plot suggest the occurrence of cation exchange in the study area. The major source of F^? was identified as products of the weathering and the dissolution of fluorites, amphiboles and micas present in the geological formations in the study area. The positive relationship between NO₃ ^? and F^? in few wells located in agricultural fields suggest possible source of F^? from the application of fertilizers. More than 25 % of the samples had higher values of fluoride than the permissible limit of drinking water according to Indian standards. Spatial distribution of fluoride showed a higher concentration in the southwest part of the study area, namely, Thirupathur and Vaniyambadi. This study shows that contamination was high in certain parts of Vellore District and the quality of water must be maintained by resorting to appropriate treatment and management strategies.