Alluvial Fan-lacustrine Sedimentation and its Tectonic Implications in the Cretaceous Athgarh Gondwana Basin, Orissa, India

The Athgarh Formation is the northernmost extension of the east coast Upper Gondwana sediments of Peninsular India. The formation of the present area is a clastic succession of 700 m thick and was built against an upland scarp along the north and northwestern boundary of the basin marked by an E-W-ENE-WSW boundary fault. A regular variation in the dominant facies types and association of lithofacies from the basin margin to the basin centre reveals deposition of the succession in an alluvial fan environment with the development of proximal, mid and distal fan subenvironments with the distal part of the fan merging into a lake. Several fans coalesced along the basin margin, forming a southeasterly sloping, broad and extensive alluvial plain terminating to a lake in the centre of the basin. Aggradation of fans along the subsiding margin of the basin resulted in the Athgarh succession showing remarkable lateral facies change in the down-dip direction. The proximal fan conglomerates pass into the sandstone-dominated mid-fan deposits, which, in turn, grade into the cyclic sequences of sandstone-mudstone of the distal fan origin. Further downslope, thick sequence of lacustrine shales occur. The faulted boundary condition of the basin and a thick pile of lacustrine sediments at the centre of the basin suggest that tectonism both in the source area and depositional site has played an important role throughout the deposition of the Athgarh succession of the present area. The vertical succession fines upward with the coarse proximal deposits at the base and fine distal deposits at the top, suggesting deposition of the succession during progressive reduction of the source area relief after a single rapid uplift related to a boundary fault movement.The NW-SE trending fault defining the Son-Mahanadi basin of Lower Gondwana sediments are shear zones of great antiquity and these were rejuvenated under neo-tensional stress during Lower Gondwana sedimentation. The E-W-ENE-WSW trending fault of the Athgarh basin, on the other hand, define tensional rupture of much younger date. In the Early Cretaceous period, there was a reversal of palaeoslope in the Athgarh basin (southward slope) with respect to the Son-Mahanadi basin (northward slope). During the phase drifting of the Indian continent and with the evolution of Indian Ocean in the Early Cretaceous period, the tectonic events in the plate interior was manifested by formation of new grabens like the Athgarh graben.     

Greenhouse warming over Indian sub-continent

A hierarchy of climate models have been developed and applied to the problem of doubling the CO₂ concentration in the atmosphere. Currently available general circulation models include the most complete treatment of the global wanning and are capable of providing changes in several of the meteorological parameters in time scales of half a century or even more. Much skill is gradually being achieved now for future climate simulations. In this paper, we have attempted to describe the response of the National Center for Atmospheric Research Climate Community Model (NCAR CCM), whose performance for northern hemispheric climate simulations was reported to be very satisfactory to Indian region. The seasonal (winter and summer) changes in surface temperature, rainfall and soil moisture expected over the Indian sub-continent due to doubling of CO₂ in the atmosphere as inferred from model output statistics are discussed. A probable scenario for sea level rise along the Indian coastline by the year 2030 AD as a result of ocean water’s expansion due to global warming is outlined. These projections should not be treated as predictions of what is going to happen over the Indian sub-continent. Rather, they merely illustrate to what extent we might be affected by the future climate change.     

Evaluation of potential landslide damming: Case study of Urni landslide,Kinnaur, Satluj valley,India

This work aims to understand the process of potential landslide damming using slope failure mechanism,dam dimension and dam stability evaluation. The Urni landslide, situated on the right bank of the Satluj River, Himachal Pradesh(India) is taken as the case study. The Urni landslide has evolved into a complex landslide in the last two decade(2000-2016) and has dammed the Satluj River partially since year 2013,damaging ～200 m stretch of the National Highway(NH-05). The crown of the landslide exists at an altitude of ～2180-2190 m above msl, close to the Urni village that has a human population of about 500.The high resolution imagery shows ～50 m long landslide scarp and ～100 m long transverse cracks in the detached mass that implies potential for further slope failure movement. Further analysis shows that the landslide has attained an areal increase of 103,900 ± 1142 m^2 during year 2004-2016. About 86% of this areal increase occurred since year 2013. Abrupt increase in the annual mean rainfall is also observed since the year 2013. The extreme rainfall in the June, 2013; 11 June(～100 mm) and 16 June(～115 mm),are considered to be responsible for the slope failure in the Urni landslide that has partially dammed the river. The finite element modelling(FEM) based slope stability analysis revealed the shear strain in the order of 0.0-0.16 with 0.0-0.6 m total displacement in the detachment zone. Further, kinematic analysis indicated planar and wedge failure condition in the jointed rockmass. The debris flow runout simulation of the detached mass in the landslide showed a velocity of ～25 m/s with a flow height of ～15 m while it(debris flow) reaches the valley floor. Finally, it is also estimated that further slope failure may detach as much as 0.80 ±0.32 million m^3 mass that will completely dam the river to a height of 76±30 m above the river bed.     

Anomaly map ofZ component of the Indian sub-continent from magnetic satellite data

An anomaly map of the Z component has been produced for the region of the Indian sub-continent for the first time by the Survey of India usingmagsat data. Data of thousands of kilometres of satellite tracks of varying altitude have been reduced to a common elevation of 400 km by removing the external field and linear trend. The entire data was plotted on a map of 1:6 M and mean values of 2°×2° blocks then accepted for contouring. A prominent magnetic low is reflected over the Himalayas and a prominent high over the Indian peninsula. The dividing line of positive and negative anomalies between the Himalayas and Deccan Traps falls along the Narmada lineament.     

Beryllium geochemistry in soils: evaluation of Be/Be ratios in authigenic minerals as a basis for age models

Soils contain a diverse and complex set of chemicals and minerals. Being an ‘open system’, both in the chemical and nuclear sense, soils have defied quantitative nuclear dating. However, based on the published studies of the cosmogenic atmospheric ¹⁰Be in soils, its relatively long half-life (1.5 Ma), and the fact that ¹⁰Be gets quickly incorporated in most soil minerals, this radionuclide appears to be potentially the most useful for soil dating. We therefore studied the natural variations in the specific activities of ¹⁰Be with respect to the isotope ⁹Be in mineral phases in eight profiles of diverse soils from temperate to tropical climatic regimes and evaluated the implications of the data for determining the time of formation of soil minerals, following an earlier suggestion [Lal et al., 1991. Development of cosmogenic nuclear methods for the study of soil erosion and formation rates. Current Sci. 61, 636–639.]. We find that the ¹⁰Be/⁹Be ratios in both bulk soils and in the authigenic mineral phases are confined within a narrower range than in ¹⁰Be concentrations. Also, the highest ¹⁰Be/⁹Be ratios in authigenic minerals are observed at the soil-rock interface as predicted by the model. We present model ¹⁰Be/⁹Be ages of the B-horizon and the corresponding soil formation rates for several soil profiles. The present study demonstrates that the ¹⁰Be/⁹Be ratios in the authigenic phases, e.g. clay and Fe-hydroxides, can indeed be used for obtaining useful model ages for soils younger than 10–15 Ma. However, the present work has to be pushed considerably further, to take into account more realistic age models in which, for instance, downward transport ¹⁰Be and clays, and in-situ dissolution of clay minerals at depths, altering the ¹⁰Be/⁹Be ratios of the acidic solutions, are included. We show that in the case of younger soils (< 1 Ma) studied here, their ¹⁰Be inventories and ¹⁰Be/⁹Be ratios have been significantly disturbed possibly by mixing with transported soils.     

Formation of the parent bodies of the carbonaceous chondrites

We have carried out extensive particle track studies for several C2 chondrites. On the basis of these and the available data on spallogenic stable and radioactive nuclides in several C1 and C2 chondrites, we have constructed a scenario for the precompaction irradiation of these meteorites. We discuss the rather severe constraints which these data place on the events leading to the formation of the parent bodies of the carbonaceous chondrites. Our analyses suggest that the precompaction solar flare and solar wind irradiation of the individual components most probably occurred primarily while the matter had accreted to form swarms of centimeter- to meter-sized bodies. This irradiation occured very early, within a few hundred my of the birth of the solar system; the pressure in the solar system had then dropped below 10^?9 atm. Further, the model assumes that soon after the irradiation of carbonaceous matter as swarms, the small bodies coalesced to form kilometer-sized objects, in time scales of 10^5±1 years, a constraint defined by the low cosmogenic exposure ages of these meteorites. Collisions among these objects led to the formation of much-larger-sized parent bodies of the carbonaceous chondrites. Implicit in this model is the existence of “irradiated” components at all depths in the parent bodies, which formed out of the irradiated swarm material.     

Tracing quartz through the environment

Quartz, SiO₂, a pure mineral with tight crystal structure, is widespread in rocks and soil. Cosmic rays produce¹⁰Be (t _1/2=1·5×10⁶, yr) and²⁶Al (t _1/2=7·05×10⁵ yr) in quartz exposed at or near the earth’s surface. The use of accelerator mass spectrometry permits measurement of these nuclides in samples exposed at sea level for typical periods.In situ production makes interpretation relatively straightforward. Potential applications include age determination, measurement of erosion and deposition rates, and use as a tracer for continental weathering processes.