• Volume 120, Issue 6

      December 2011,   pages  965-1188

    • Numerical study of mechanism of fold formation in a laminated rock

      P K Saini T Kumar T N Singh N Singh V K Keshr

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      A set of large deformation experiments are presented to simulate folding pattern at various energy states during formation. In order to numerically simulate this phenomenon, a rectangular layer of shale is generated and compressed at various strain rates. The results reveal the variation in distribution of stress along the length of the bed. The stress distribution during elastic behaviour of shale bed at low compression rate and the change in stress distribution leading to rupture at high compression rates is discussed. Wavelength, limb length, bulk shortening, stress distribution, displacement of particles along the length of the bed is considered for comparative study of the fold pattern generated at various compression rates. The nature and position of crack generated during the formation of fold is also explained. After rupture in shale bed, the generation of fault and stress distribution in limbs of fold sliding over one another is also described.

    • Lithostratigraphic development and neotectonic significance of the Quaternary sediments along the Kachchh Mainland Fault (KMF) zone, western India

      V Chowksey D M Maurya Parul Joshi N Khonde Archana Das L S Chamyal

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      The Kachchh Mainland Fault (KMF) is a major E–W trending seismically active fault of the Kachchh palaeorift basin whose neotectonic evolution is not known. The present study deals with the eastern part of the KMF zone where the fault is morphologically expressed as steep north facing scarps and is divisible into five morphotectonic segments. The Quaternary sediments occurring in a narrow zone between the E–W trending KMF scarps and the flat Banni plain to the north are documented. The sediments show considerable heterogeneity vertically as well as laterally along the KMF zone. (The Quaternary sediments for a northward sloping and are exposed along the north flowing streams which also show rapid decrease in the depth of incision in the same direction.) The deposits, in general, comprise coarse as well as finer gravelly deposits, sands and aeolian and fluvial miliolites. The Quaternary sediments of the KMF zone show three major aggradation phases. The oldest phase includes the colluvio-fluvial sediments occurring below the miliolites. These deposits are strikingly coarse grained and show poor sorting and large angular clasts of Mesozoic rocks. The sedimentary characteristics indicate deposition, dominantly by debris flows and sediment gravity flows, as small coalescing alluvial fans in front of the scarps. These deposits suggest pre-miliolite neotectonic activity along the KMF. The second aggradation phase comprises aeolian miliolites and fluvially reworked miliolites that have been previously dated from middle to late Pleistocene. The youngest phase is the post-miliolite phase that includes all deposits younger than miliolite. These are represented by comparatively finer sandy gravels, gravelly sands and sand. The sediment characteristics suggest deposition in shallow braided stream channels under reduced level of neotectonic activity along the KMF during post-miliolite time evidenced by vertical dips of miliolites and tilting of gravels near the scarps. The tectonically controlled incision and dissection of the Quaternary deposits is the result of neotectonic activity that continues at present day. The overall nature, sedimentary characteristics and geomorphic setting of the sediments suggest that the KMF remained neotectonically active throughout the Quaternary period.

    • Nonlinear genetic-based simulation of soil shear strength parameters

      Seyyed Mohammad Mousavi Amir Hossein Alavi Amir Hossein Gandomi Ali Mollahasani

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      New nonlinear solutions were developed to estimate the soil shear strength parameters utilizing linear genetic programming (LGP). The soil cohesion intercept (𝑐) and angle of shearing resistance (𝜙) were formulated in terms of the basic soil physical properties. The best models were selected after developing and controlling several models with different combinations of influencing parameters. Comprehensive experimental database used for developing the models was established upon a series of unconsolidated, undrained, and unsaturated triaxial tests conducted in this study. Further, sensitivity and parametric analyses were carried out. 𝑐 and 𝜙 were found to be mostly influenced by the soil unit weight and liquid limit. In order to benchmark the proposed models, a multiple least squares regression (MLSR) analysis was performed. The validity of the models was proved on portions of laboratory results that were not included in the modelling process. The developed models are able to effectively learn the complex relationship between the soil strength parameters and their contributing factors. The LGP models provide a significantly better prediction performance than the regression models.

    • Present day relief-shaping systems acting on the southern slope of the Făgăraş Mountains (Romania)

      Alexandru Nedelea Laura Comanescu

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      The present topography of the Făgăraş Mountains is a snapshot of the long-term evolution that brought about significant alterations of the landscape, and especially of the relief, which has acquired different features depending on the intensity of the relationship between the exogenous and endogenous agents. At present, relief shaping in the study area is controlled by the orographic and climatic features. However, the climate of the high and middle-height mountains is the main cause that determines the mechanism, the intensity and the spatial distribution of the shaping processes. The considerable height of the Făgăraş Mountains, which exceeds 2500 m altitude is responsible for the vertical zonation of climate and vegetation which implicitly induce the setting of the systems of relief modelling, too.

    • Melanite garnet-bearing nepheline syenite minor intrusion in Mawpyut ultramafic–mafic complex, Jaintia Hills, Meghalaya

      Monoj Maitra J S David S Bhaduri

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      Mawpyut igneous suite in Jaintia Hills of Meghalaya plateau comprises differentiated suite of ultramafic–mafic rocks. The complex differs from other ultramafic–alkaline–carbonatite igneous emplacements of Shillong plateau and Mikir Hills like Jesra, Sung, Samchampi complexes, by the absence of alkaline–carbonatite rocks as major litho-units. Melanite garnet-bearing nepheline syenite, occurs as late phase minor intrusion in Mawpyut igneous complex, posseses alkaline character and shows inubiquitous relation with the host ultramafic–mafic rocks. On the other hand, this alkaline intrusive bodies of the Mawpyut igneous complex shows chemico-mineralogical resemblance with garnet-bearing nepheline syenite, ijolite litho-members of Jesra, Sung, Samchampi complexes of the region. It is interpreted that melanite garnet-bearing nepheline syenite intrusion in Mawpyut is contemporaneous with Jesra, Sung, Samchampi ultramafic–alkaline–carbonatite complexes and the host rocks of Mawpyut complex is an earlier magmatic activity possibly from a comparatively least enriched source.

    • Anthropogenic and impact spherules: Morphological similarity and chemical distinction – A case study from India and its implications

      Ambalika Niyogi Jayanta K Pati Suresh C Patel Dipak Panda Shiv K Patil

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      This paper provides first report of silica-rich anthropogenic spherules of varying colour, shape, size, surface texture and chemical composition found in road-deposited sediments (RDS) of Allahabad city, Uttar Pradesh, India. Morphological details and lithophile elemental composition of the silica-rich spherules are compared to microtektites and impact spherules from India to demonstrate their striking morphological similarities and chemical variability. This study suggests the need to use spherule data carefully while assigning an impact origin to spherule-finds or spherule-bearing lithological horizons.

    • A generalized solution for groundwater head fluctuation in a tidal leaky aquifer system

      Mo-Hsiung Chuang Hund-Der Yeh

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      A new analytical solution is developed for describing groundwater level fluctuations in a coupled leaky confined aquifer system which consists of an unconfined aquifer, confined aquifer, and an aquitard in between. The aquifer system has a tidal boundary at the seashore, a no flow boundary at remote inland side, and a confined aquifer extending under the sea and terminated with an outlet-capping. This new solution has shown to be a generalisation of most existing analytical solutions for a tidal aquifer system which includes single confined and leaky confined aquifers. In addition, the solution is used to explore the influences of the dimensionless leakance of the outlet-capping, the dimensionless hydraulic diffusivities, and the leakages of the inland and offshore aquitards on the head responses in the leaky confined aquifer.

    • Intermittent reservoir daily-inflow prediction using lumped and distributed data multi-linear regression models

      R B Magar V Jothiprakash

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      In this study, multi-linear regression (MLR) approach is used to construct intermittent reservoir daily inflow forecasting system. To illustrate the applicability and effect of using lumped and distributed input data in MLR approach, Koyna river watershed in Maharashtra, India is chosen as a case study. The results are also compared with autoregressive integrated moving average (ARIMA) models. MLR attempts to model the relationship between two or more independent variables over a dependent variable by fitting a linear regression equation. The main aim of the present study is to see the consequences of development and applicability of simple models, when sufficient data length is available. Out of 47 years of daily historical rainfall and reservoir inflow data, 33 years of data is used for building the model and 14 years of data is used for validating the model. Based on the observed daily rainfall and reservoir inflow, various types of time-series, cause-effect and combined models are developed using lumped and distributed input data. Model performance was evaluated using various performance criteria and it was found that as in the present case, of well correlated input data, both lumped and distributed MLR models perform equally well. For the present case study considered, both MLR and ARIMA models performed equally sound due to availability of large dataset.

    • A comparative study on isotopic composition of precipitation in wet tropic and semi-arid stations across southern India

      C Unnikrishnan Warrier M Praveen Babu

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      Isotopic composition of monthly composite precipitation samples from Kozhikode (𝑛 = 31), a wet tropic station and Hyderabad (𝑛 = 25), a semi-arid station across southern India were studied for a period of four years from 2005 to 2008. During the study period, the Kozhikode station recorded an average rainfall of 3500 mm while the Hyderabad station showed an average rainfall of 790 mm. The average stable isotope values in precipitation at the Kozhikode station were 𝛿18O= -3.52‰, d-excess = 13.72‰; 𝛿18O = -2.94‰, d-excess = 10.57‰; and 𝛿18O = -7.53‰, d-excess = 13.79‰, respectively during the pre-monsoon (March–May), monsoon (June–September) and post-monsoon (October–February) seasons. For the Hyderabad station, the average stable isotope values were 𝛿18O = $−$5.88‰, d-excess = 2.34‰; 𝛿18O = $−$4.39‰, d-excess = 9.21‰; and 𝛿18O = −8.69‰, d-excess = 14.29‰, respectively for the three seasons. The precipitation at the two stations showed distinctive isotopic signatures. The stable isotopic composition of precipitation at the Hyderabad station showed significant variations from the global trend while the Kozhikode station almost followed the global value. These differences are mainly attributed to the latitudinal differences of the two stations coupled with the differences in climatic conditions.

    • Impact of gridpoint statistical interpolation scheme over Indian region

      Surya K Dutta V S Prasad

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      An analysis system experiment was conducted for the month of June 2008 with Gridpoint Statistical Interpolation (GSI) analysis scheme using NCMRWF’s (National Centre for Medium Range Weather Forecasting) T254L64 model. Global analyses were carried out for all days of the month and respective forecast runs are made up to 120-hr. These analyses and forecasts are inter-compared with the operational T254L64 model outputs which uses Spectral Statistical Interpolation (SSI) analysis scheme. The prime objective of this study is to assess the impact of GSI analysis scheme with special emphasis on Indian summer monsoon as compared to SSI.

      GSI analysis scheme do have positive impact over India and its surrounding regions. Though not for all but for some fields it is in edge over Spectral Statistical Analysis Scheme. Patterns for the forecast mean error; anomaly correlation and $S_1$ scores with respect to the respective analyses are same for both GSI and SSI. Both have increasing $S_1$ scores, decreasing mean errors and anomaly correlation with the advance of forecast days. The vector wind RMSE of the model forecasts with respect to the analyses is lower for GSI at 850 hPa and higher at 250 hPa. But over tropics GSI is better at both levels. The temperature field of GSI has higher correlation and lower RMSE at both 850 and 250 hPa pressure levels. There are improvements in systematic errors for 850 and 200 hPa temperature field in GSI compared to that in SSI. The depression centre in GSI analysis is closer to observation but has produced more intense depression compared to that of SSI. Rainfall forecast of SSI is better at day-1 whereas GSI is closer to the observation at day-5 forecasts valid at the same day.

    • Development of regional wheat VI-LAI models using Resourcesat-1 AWiFS data

      Sasmita Chaurasia R Nigam B K Bhattacharya V N Sridhar K Mallick S P Vyas N K Patel J Mukherjee Chander Shekhar Dhiraj Kumar K R P Singh G D Bairagi N L Purohit J S Parihar

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      The time of forcing of spatial LAI to crop models at single or multiple stages is important to simulate crop biomass and yield in varying agro-climatic conditions and scales. The high temporal resolution (5-day) by Advanced Wide Field Sensor (AWiFS) on-board Resourcesat-1 Satellite IRS-P6 with 56 m spatial resolution and large swath (740 km) has substantially increased the availability of regional clear sky optical remote sensing data. The present study aimed at developing empirical vegetation index VI-LAI models for wheat using AWiFS optical data in four bands and in-situ measurements sampled over five different agro-climatic regions (ACRs) during 2005–2006 followed by validation during 2006–2007. While nonlinear relations exist for all the three normalized indices such as normalized difference vegetation index (NDVI), normalized difference water index (NDWI) and Green NDVI, linear relation was the best fit for ratio vegetation index (RVI). Both NDVI and RVI models generally showed better correlation ranges (0.65–0.84 for NDVI and 0.37–0.76 for RVI) than other indices. The common NDVI-LAI model was found to produce lower root mean square errors (RMSE) between 0.5 and 1.1 from pooled model than those between 0.5 and 1.32 from regional models. The rate of substantial increase in errors from NDVILAI model (RMSE of modelled LAI: 0.85 to 1.28) as compared to RVI-LAI model (RMSE of modeled LAI: 1.12 to 1.17) at LAI greater than 3, than below 3 revealed the early saturation of NDVI than RVI. It is therefore recommended that LAI estimates can be used to force crop simulation model up to early vegetative stage based on NDVI and maximum vegetative to reproductive stages based on RVI.

    • Trace fossils from Bhuban Formation, Surma Group (Lower to Middle Miocene) of Mizoram India and their palaeoenvironmental significance

      Raghavendra P Tiwari Chinmoy Rajkonwar Lalchawimawii Paul Lalnuntluanga Jehova Malsawma Victor Z Ralte Satish J Patel

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      A detailed ichnological study performed on the Bhuban Formation, Surma Group (Lower to Middle Miocene) of Mizoram, India reveals the occurrence of rich and diverse trace fossils. These have been collected from the two localities in Aizawl, i.e., Bawngkawn and Ropaiabawk, where sandstone-shale sequence is well exposed. Total 20 ichnospecies of 14 ichnogenera have been identified which include Arenicolites isp., Cochlichnus anguineus, Helminthopsis abeli, Laevicyclus mongraensis, Ophiomorpha borneensis, Palaeophycus tubularis, Palaeophycus heberti, Palaeophycus sulcatus, Palaeophycus alternatus, Pholeus abomasoformis, Pholeus bifurcatus, Planolites beverleyensis, Planolites annularis, Polykladichnus irregularis, Rhizocorallium isp., Skolithos linearis, Taenidium satanassi, Teichichnus rectus, Thalassinoides horizontalis and Thalassinoides paradoxicus. Ethologically these ichnogenera display dwelling and feeding activities of the infaunal organisms. Arenicolites, Ophiomorpha, Polykladichnus and Skolithos are the members of the Skolithos ichnofacies while Palaeophycus, Planolites, Rhizocorallium and Thalassinoides are the members of the Cruziana ichnofacies. The presence of Skolithos ichnofacies indicates sandy shifting substrate and high energy conditions in foreshore zone while the Cruziana ichnofacies indicate unconsolidated, poorly sorted soft substrate and low energy condition in the shoreface/offshore zone. These ichnogenera indicate foreshore to shoreface-offshore zone of shallow marine environment for the deposition of the rocks of the Bhuban Formation of Mizoram.

    • Identification of non-indigenous phytoplankton species dominated bloom off Goa using inverted microscopy and pigment (HPLC) analysis

      P V Bhaskar Rajdeep Roy Mangesh Gauns D M Shenoy V D Rao S Mochemadkar

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      An unusual phytoplankton bloom dominated by unidentified green coloured spherical algal cells (∼5 𝜇 m diameter) and dinoflagellates (Heterocapsa, Scripsiella and Gymnodinium) was encountered along the coast of Goa, India during 27 and 29 January, 2005. Pigment analysis was carried out using both fluorometric and HPLC methods. Seawater samples collected from various depths within the intense bloom area showed high concentrations of Chl 𝑎 (up to 106 mg m−3) associated with low bacterial production (0.31 to 0.52 mg C m−3 h−1) and mesozooplankton biomass (0.03 ml m−3). Pigment analyses of the seawater samples were done using HPLC detected marker pigments corresponding to prasinophytes, dinoflagellates and diatoms. Chlorophyll 𝑏 (36–56%) followed by peridinin (15–30%), prasinoxanthin (11–17%) and fucoxanthin (7–15%) were the major diagnostic pigments while pigments of cryptophytes and cyanobacteria including alloxanthin and zeaxanthin formed > 10%. Although microscopic analysis indicated a decline in the bloom, pheaophytin concentrations in the water column measured by both techniques were very low, presumably due to fast recycling and/or settling rate. The unique composition of the bloom and its probable causes are discussed in this paper.

    • Subject Index

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    • Author Index

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    • Acknowledgements

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