• Volume 122, Issue 6

December 2013,   pages  1435-1637

• The South India Precambrian crust and shallow lithospheric mantle: Initial results from the India Deep Earth Imaging Experiment (INDEX)

We present here the most comprehensive study of the thickness and composition ($Vp/Vs$ ratio) of the South India Precambrian crust and the nature of shallower mantle inferred from analysis of teleseismic receiver functions from 70 broad-band seismic stations operated as a part of the India Deep Earth Imaging Experiment (INDEX). South India could be broadly divided into regions with thin crust (32–38 km) and thick crust (38–54 km). Thin crust domains include the East Dharwar Craton (EDC), Cuddapah basin and Madurai/Kerala Khondalite Block. The thicker crust domain includes the Western Dharwar Craton (WDC) and northern part of Southern Granulite Terrain. The WDC shows progressive increase in thickness from 38 km in north to 46–54 km in south, compared to an almost flat Moho beneath the EDC. Compositionally, most of the crustal domains are felsic to intermediate ($Vp/Vs$ ∼ 1.69–1.75) except the mid Archean block in the southern WDC where it is mafic ($Vp/Vs$ &lt; 1.81). Considering erosion depth in the WDC, we argue for Himalaya like ∼70 km thick crust beneath it during the Archean. Variation in crustal thickness does not have a first-order influence on regional topography in South India and suggests significant role for the crustal composition. We also present evidence of mid-lithospheric low velocity at ∼85–100 km beneath South India.

• The Sidi Mohamed peridotites (Edough Massif, NE Algeria): Evidence for an uppe mantle origin

The Hercynian Edough massif is the easternmost crystalline massif of the Algerian coast. It consists of two tectonically superposed units composed of micaschists, gneisses, and peridotite. This study concentrates on the small and isolated Sidi Mohamed peridotite outcrop area (0.03 km2). The Sidi Mohamed peridotite is composed mainly of harzburgites (Mg-rich olivine and orthopyroxene as major minerals). The Ni (2051–2920 ppm), Cr (2368–5514 ppm) and MgO (∼28–35 wt.%) whole-rock composition and the relative depletion in Nb make these harzburgites comparable to depleted peridotites related to a subduction zone. We suggest that the Sidi Mohamed ultramafic body was derived directly from the upper mantle and tectonically incorporated into the gneiss units of the Edough metamorphic core complex in a subduction environment.

• Ichnology of the Early Cambrian Tal Group, Mussoorie Syncline, Lesser Himalaya, India

The Lesser Himalayan sequence is considered as one of the best developed sections of Cambrian successions, exposed in five different synclines. Mussoorie Syncline, being one of the five synclines, exposes the Cambrian Tal Group. This paper describes nine ichnotaxa, viz., Dimorphichnus isp., ?Diplichnites isp., Monomorphichnus isp., Nereites isp., Palaeopasichnus isp., Palaeophycus isp., Planolites montanus, Planolites isp., Skolithos isp., Treptichnus isp. from the Dhaulagiri Formation of the Tal Group. A detailed analysis of the ichnofossils indicates that the entire succession of Tal Group reflects shallow marine conditions in general and Mussoorie Syncline in particular. The above ichnofossil assemblage along with earlier ichnofossils and other faunal occurrences substantiates the assignment of Early Cambrian age to the Dhaulagiri Formation.

• An Ediacaran–Cambrian thermal imprint in Rajasthan, western India: Evidence from 40Ar-39Ar geochronology of the Sindreth volcanics

The Sindreth Group exposed near Sirohi in southern Rajasthan, western India, is a volcanosedimentary sequence. Zircons from Sindreth rhyolite lavas and tuffs have yielded U–Pb crystallization ages of ∼768–761 Ma, suggesting that the Sindreth Group is a part of the Malani magmatic event. Earlier 40Ar-39Ar studies of other Malani volcanic and plutonic rocks yielded disturbed argon release spectra, ascribed to a ∼550 Ma thermal event possibly related to the Pan-African orogeny. To test and confirm this possibility, we dated two whole-rock and three feldspar separate samples of the Sindreth volcanics by the 40Ar-39Ar method. All samples yield disturbed argon release spectra suggesting radiogenic argon loss and with plateau segments at 550 Ma or 490 Ma. We interpret these as events of argon loss at 550–490 Ma related to an Ediacaran–Cambrian thermal event, possibly related to the Malagasy orogeny. The combined older and new 40Ar-39Ar results are significant in showing that whereas Ediacaran–Cambrian magmatic and metamorphic events are well known from many parts of India, they left thermal imprints in much of Trans-Aravalli Rajasthan as well. The overall evidence is consistent with a model of multiphase assembly of Gondwanaland from separate continental landmasses.

• High-resolution seismic imaging of the Sohagpur Gondwana basin, central India: Evidence for syn-sedimentary subsidence and faulting

Gondwana sedimentary basins in the Indian Shield preserve a rich record of tectonic, sedimentary and volcanic processes that affected Gondwanaland. The Gondwana rocks were deposited in the linear rift basins that were formed during Permian–Cretaceous time, similar to their neighbours in Australia, Africa and Antarctica. In this study, we illustrate how Gondwana tectonics affected the Sohagpur Gondwana basin that occurs at the junction of the Mahanadi and Son–Narmada rift systems in the central India, through a high-resolution seismic reflection study along six profiles, covering the central part of the Sohagpur basin. The study reveals (1) ∼1000 m thick, gently dipping Barakar Formation, (2) thick coal seams at a depth of 350–550 m, and (3) NNW–SSE to NW–SE striking steeply dipping normal faults defining rift geometry. These results indicate that the Sohagpur basin contains a thick Lower Gondwana sedimentary succession with a high potential of coal resources and were affected by extensional tectonics. The rift structure in the study area is a syn- to post-sedimentary deformational structure that was formed arguably in response to tectonics that pervasively affected Gondwanaland.

• Radon and thoron anomalies along Mat fault in Mizoram, India

In this study, radon and thoron concentrations in soil gas has been monitored using LR-115(II) solid state nuclear track detectors since 15th July 2011 to February 2012. The study was carried out along Mat fault in Serchip district, Mizoram, India at two different sites – Mat Bridge (23°18′N, 92° 48′E) and Tuichang (23° 13′N, 92° 56′E). The results obtained have been correlated to the seismic events that occurred within 800km from the measuring sites over the mentioned period of time. Anomalous behaviour in radon concentrations have been observed prior to some earthquakes. Interestingly, some thoron anomalies were also recorded.

• Model of erosion–landslide interaction in the context of the reservoir water level variations (East Siberia, Russia): Factors, environment and mechanisms

A comprehensive investigation of landslide–erosion interactions has been carried out in the local shore geosystem of the Bykovo site located on the left shore of the Bratsk reservoir. The landslide process develops in the Mid-Quaternary grounds ($aQ^{3}_{II}$) of the erosion-accumulative terrace’s fragment that comprises sand, sand with pebbles, sandy loams and loams. This study aims to assess the environmental factors of interacting landslide and gully erosion processes, to estimate their temporal dynamics by comparative analysis of cartographic models based on the data of repeated theodolite surveys, and to find out what level regime of the reservoir stimulates the activation of the landslide process. The authors propose two-stage descriptive model of erosion–landslide interaction and development mechanisms in the context of the reservoir water level variations in the Bratsk reservoir. The activation of landslide processes in the reservoir shores follows the periods of high water level stands. Shore slope stability is disturbed by abrasion of slope foot and inundation of the slide zone. The soils subject to landslide, erosion–landslide and erosion processes differ in their microstructure and properties. Largest erosion susceptibility is typical of soils with skeleton-aggregated microstructure, fine- and coarse-silt sandy loams and loams of high porosity, whose interstructural bonds are attributed to water-soluble salts (Sws = 0.4–0.5%) and high carbonate contents (Scr = 34–66%). High dispersion and aggregation of clay fractions is typical of the loams of the slide zone. The structure of soils subject to deformation slide is represented primarily by fine-sand particles and aggregates with smaller cohesion and strength properties.

• Water level changes of high altitude lakes in Himalaya–Karakoram from ICESat altimetry

Himalaya–Karakoram (H–K) region hosts large number of high altitude lakes but are poorly gauged by in-situ water level monitoring method due to tough terrain conditions and poor accessibility. After the campaigns of ICESat during 2003–2009, now it is possible to achieve lake levels at decimetre accuracy. Therefore, in present study, high altitude lake levels were observed using ICESat/GLAS altimetry in H–K between 2003 and 2009 to generate baseline information. The study reveals that out of 13 lakes, 10 lakes show increasing trend of water levels at different rate (mean rate 0.173 m/y) whereas three lakes unveiled decreasing trend (mean rate −0.056 m/y). Out of five freshwater lakes, four lakes show an increasing trend of their level (mean rate 0.084 m/y) whereas comparatively six salt lakes (out of seven salt lakes) exhibited ∼3 times higher mean rate of lake level increase (0.233 m/y). These observed lake level rise can be attributed to the increased melt runoffs (i.e., seasonal snow and glacier melts) owing to the enhanced mean annual and seasonal air temperature during past decade in north-western (NW) Himalaya. Further, varied behaviours of lake level rises in inter- and intra-basins suggest that the local climatic fluctuations play prominent role along with regional and global climate in complex geographical system of NW Himalaya.

• Estimation of the soil strength parameters in Tertiary volcanic regolith (NE Turkey) using analytical hierarchy process

Costly and time consuming testing techniques and the difficulties in providing undisturbed samples for these tests have led researchers to estimate strength parameters of soils with simple index tests. However, the paper focuses on estimation of strength parameters of soils as a function of the index properties. Analytical hierarchy process and multiple regression analysis based methodology were performed on datasets obtained from soil tests on 41 samples in Tertiary volcanic regolith. While the hierarchy model focused on determining the most important index properties affecting on strength parameters, regression analysis established meaningful relationships between strength parameters and index properties. The negative polynomial correlations between the friction angle and plasticity properties, and the positive exponential relations between the cohesion and plasticity properties were determined. These relations are characterized by a regression coefficient of 0.80. However, Terzaghi bearing capacity formulas were used to test the model. It is important to see whether there is any statistically significant relation between the calculated and the observed bearing capacity values for model testing. Based on the model, the positive linear correlation characterized by the regression coefficient of 0.86 were determined between bearing capacity values obtained by direct and indirect methods.

• Core sediment biogeochemistry in specific zones of Cochin Estuarine System (CES)

Geochemical composition is a set of data for predicting the climatic condition existing in an ecosystem. Both the surficial and core sediment geochemistry are helpful in monitoring, assessing and evaluating the marine environment. The aim of the research work is to assess the relationship between the biogeochemical constituents in the Cochin Estuarine System (CES), their modifications after a long period of anoxia and also to identify the various processes which control the sediment composition in this region, through a multivariate statistical approach. Therefore the study of present core sediment geochemistry has a critical role in unraveling the benchmark of their characterization. Sediment cores from four prominent zones of CES were examined for various biogeochemical aspects. The results have served as rejuvenating records for the prediction of core sediment status prevailing in the CES.

• Oceansat–2 and RAMA buoy winds: A comparison

Sea surface vector winds from scatterometers onboard satellites play an important role to make accurate Numerical Weather Prediction (NWP) model analysis over the data sparse oceanic region. Sea surface winds from Oceansat-2 scatterometer (OSCAT) over the Indian Ocean were validated against the Research Moored Array for African–Asian–Australian Monsoon Analysis and Prediction (RAMA) buoy winds to establish the accuracy of OSCAT winds. The comparison of OSCAT winds against RAMA buoy winds for a period of one year (2011) shows that the wind speeds and directions derived from OSCAT agree with RAMA buoy winds. The monthly mean wind speeds from both OSCAT and RAMA buoy show maximum value during the monsoon period as expected. In the complete annual cycle (2011), the monthly mean root mean square differences in the wind speed and wind direction were less than ∼2.5 m$s^{−1}$ and ∼20°, respectively. The better match between the OSCAT and RAMA buoy wind is observed during Indian summer monsoon (June–September). During monsoon 2011, the root mean square differences in wind speed and wind direction were less than $1.9 ms^{−1}$ and 11°, respectively. Collocation of scatterometer winds against equatorial and off-equatorial buoys clearly brought out the monsoon circulation features. Collocation of Advanced Scatterometer (ASCAT) winds on-board European Space Agency (ESA) MeTop satellite with respect to RAMA buoy winds during monsoon 2011 also showed that the OSCAT wind statistics are comparable with that of ASCAT over the Indian Ocean, and indicates that the accuracy of both the scatterometers over the Indian Ocean are essentially the same.

• Upper tropospheric water vapour variability over tropical latitudes observed using radiosonde and satellite measurements

The present study deals with using long-term database for upper tropospheric water vapour (UTWV) variability studies over three tropical stations (Gadanki, Singapore and Truk), where different climatic conditions prevail. Over Gadanki (13.5°N, 79.2°E) strong seasonal variation in UTWV is revealed but not over Singapore (1.37°N, 103.98°E) and Truk (7.46°N, 151.85°E) except at 100 hPa. It is examined whether high resolution radiosonde measurements represent well the UTWV by comparing with different satellite based (Atmospheric Infrared Sounder (AIRS), Advanced Microwave Sounding Unit-B (AMSUB) and Microwave Limb Sounder (MLS)) water vapour measurements. Very good comparison in the nature of variations of UTWV is observed between radiosonde data and satellite data, except over Singapore particularly with AIRS and MLS data, on long-term basis. An attempt is also made to examine the source for UTWV. A close relationship is found between UTWV and deep convection over Gadanki indicating that the source for UTWV is convection particularly during the summer monsoon season.

• Estimating minimum and maximum air temperature using MODIS data over Indo-Gangetic Plain

Spatially distributed air temperature data are required for climatological, hydrological and environmental studies. However, high spatial distribution patterns of air temperature are not available from meteorological stations due to its sparse network. The objective of this study was to estimate high spatial resolution minimum air temperature (𝑇_{min}) and maximum air temperature (𝑇_{max}) over the Indo-Gangetic Plain using Moderate Resolution Imaging Spectroradiometer (MODIS) data and India Meteorological Department (IMD) ground station data. 𝑇_{min} was estimated by establishing an empirical relationship between IMD 𝑇_{min} and night-time MODIS Land Surface Temperature (𝑇_{s}). While, 𝑇_{max} was estimated using the Temperature-Vegetation Index (TVX) approach. The TVX approach is based on the linear relationship between 𝑇_{s} and Normalized Difference Vegetation Index (NDVI) data where 𝑇_{max} is estimated by extrapolating the NDVI-𝑇_{s} regression line to maximum value of NDVImax for effective full vegetation cover. The present study also proposed a methodology to estimate NDVImax using IMD measured 𝑇_{max} for the Indo-Gangetic Plain. Comparison of MODIS estimated 𝑇min with IMD measured 𝑇min showed mean absolute error (MAE) of 1.73°C and a root mean square error (RMSE) of 2.2°C. Analysis in the study for 𝑇_{max} estimation showed that calibrated NDVImax performed well, with the MAE of 1.79°C and RMSE of 2.16°C.

• Subject Index

• Author Index

• Acknowledgements

• Journal of Earth System Science

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Posted on July 25, 2019