SUBDUCTION AND ACCRETION TECTONICS OF HIMALAYAN AND KARAKORAM TERRANES AND THEIR PALAEOGEOLOGIC CONFIGURATION

he 2500km long Indus\|Tsangpo Suture has been recognized as one of the best examples of continent to continent collisional Suture Zone. It has come into existence as a result of subduction followed by continental collision (55～60Ma) between Indian (Sinha, 1989, 1997; Sinha et al., 1999) and Eurasian plates. While considering the recent palaeogeographic reconstruction of Pangea during late Palaeozoic it appears that a southern belt of Asian microcontinents stretching from Iran and Afghanistan through southern Tibet to western Thailand, Malaysia and Sumatra, comprise several continental blocks and numerous fragments that have coalesced since the Mid\|Palaeozoic along with the closure of Tethys. The origin, migration, assembly and timing of accretion of all these blocks to their present geotectonic position is not well known and there is no Permo—Triassic crust left in the present day Indian Ocean. The oldest ocean crust adjacent to the west African and Antarctic margin is of early or middle Cretaceous age (approximately 140～100Ma) (Searle, 1991). The Karakoram\|Hindukush microplate in the west and the Qiangtang\|Lhasa block in the central and eastern segment of South Asia margin are among those blocks already welded with Asian plates around 120～130Ma ago, before the collision of India (55～60Ma) with the collage of plates forming Peri\|Gondwanian microcontinents. But the reconstruction of palaeogeographic configuration remain incomplete due to paucity of authentic geologic information available from Karakoram, Pamir and Western Tibet. Prior to our discovery no early Permian plant remains and palynomorphs were ever reported from Karakoram terrane. Our discovery of Early Permian remains and late Asselian (about 280～275Ma) palynomorphs provides crucial clue regarding the palaeogeographic reconstruction of the Karakoram\|Himalayan block in the Permian time.     

Sub-daily variations observed in Tropical Easterly Jet (TEJ) streams

To investigate the sub-daily variation in Tropical Easterly Jet (TEJ), a few special experiments have been conducted with mesosphere–stratosphere–troposphere (MST) radar located at Gadanki(13.5°N, 79.2°E) under Study on Atmospheric Forcing and Responses (SAFAR) campaign during 2008–2009. Large sub-daily changes in the TEJ characteristics are observed within a day in addition to day-to-day changes. Based on this observational study, three possible mechanisms for the sub-daily variations are proposed i.e., (1) motion of TEJ core, (2) large updrafts and downdrafts, and (3) strong wave activity. Interestingly, TEJ peak altitude is seen above the Cold Point Tropopause altitude for about 42% of the days.     

Characteristics of the tropical tropopause over different longitudes

The characteristics of the cold point tropopause (CPT), convective tropopause (COT) and tropical tropopause layer (TTL) in the tropical region at different longitudes are studied using radiosonde data at 5 stations in the tropical belt (±15°) and high resolution GPS radiosonde data from April 2006 to December 2008 at Gadanki (13.5°N, 79.2°E) also a tropical station. The CPT over Gadanki is found to be higher than over the rest of the stations. This aspect is further confirmed using COSMIC GPS RO observations. In the Northern Hemisphere (NH) winter, the CPT is coldest over stations in the Pacific region compared to the other stations while in the NH summer, it is coldest at Gadanki, a station in the Indian monsoon region. The range of seasonal variation of the CPT temperature is found to be quite small over Gadanki compared to the other stations whereas that of the CPT altitude is nearly the same.     

A heuristic examination of cohesive sediment bed exchange in turbulent flows

Prediction of the concentration of suspended cohesive sediment in the marine environment is constrained by difficulties in interpreting experimental evidence on bed exchange, i.e. erosion and deposition of particles, which remains sparse in mechanistic details. In this paper, conditions under which bed exchange in turbulent flows collectively determines the concentration of suspended matter have been examined in the heuristic sense based on selective experimental data. It is argued that interpretation of such data can be significantly facilitated when multi-class representation of particle size, collisional interaction between suspended particles and probabilistic representations of the bed shear stress along with variables describing particle behavior (critical shear stress for deposition, bed floc shear strength) are taken into account. Aggregation—floc growth and breakup kinetics—brings about shifts in the suspended particle size distribution; bed exchange is accordingly modulated and this in turn determines concentration dynamics. Probabilistic representation of the governing variables broadens the suspended sediment size spectrum by increasing the possibilities of inter-particle interactions relative to the mean-value representation. Simple models of bed exchange, which essentially rely on single-size assumption and mean-value representation of variables, overlook the mechanistic basis underpinning particle dynamics.     

A Comparative Investigation of Image Fusion in the Context of Classification

Image fusion assists in visual interpretation, mapping, change detection and many other applications. Multispectral and Panchromatic images are fused to produce images having enhanced spatial and spectral properties. These properties are generally distorted from original images. The aim of this paper is to identify the effectiveness of the several fusion techniques based on the distortions and applications. This paper employs seven image fusion techniques namely, Brovey transform, intensity hue saturation, high pass filter, principle component analysis, UNB Pansharpening, wavelet transform and multiplicative, available in various commercial image processing software. The data for this study are panchromatic image of Cartosat-1 and multispectral image of IRS - P6 LISS 4 sensor of study area, Bhopal Municipal Corporation area, M.P. State, India. The effectiveness of image fusion techniques is determined by quantitative and qualitative assessments. Quantitative assessment is divided into two parts: 1) assessment of fusion techniques by statistical parameters and 2) accuracy assessment of land use maps generated from the fused images. For part 1, three parameters namely, mean bias, correlation coefficient and Q4 quality index, have been used. Based on the results of part 1, UNB Pansharpening and wavelet transform are the best among seven fusion techniques. For part 2, Gaussian and Artificial Neural Network classifiers have been used to generate land cover maps. However, the accuracy results are inconclusive to identify a single best method. Nevertheless, image fusion by wavelet transform has provided best results in both the sector. Hence, wavelet transform is concluded as the best among selected fusion techniques.     

Initiation of sand transport over coarse beds in tidal entrances

A tidal entrance often acts as a source or a sink for sand in the littoral zone. At many entrances in biologically productive regions the bed in the vicinity of the throat section (minimum flow area) is composed of sediment containing coarse material including large shells, with sand occurring in the interstitial regions between the shell-defined roughness elements. A stochastic relationship giving the critical bed shear stress for the initiation of sand transport under these conditions is applied to hydraulic and sedimentary data obtained from two entrances in Florida. The results agree well with the critical bed shear stresses derived from data based on the observation of sand movement at the bed. The entrainment function based on observations is found to be approximately three times the value obtained from Shields' criterion. A practical implication is that the use of Shields' criterion in the computation of the rate of sand transport will in general overpredict the rate through the entrance.     

New record of Bathonian–Callovian calcareous nannofossils in the eastern Karakoram block: a possible clue to understanding the dextral offset along the Karakoram Fault

We report the first record of Bathonian–Callovian calcareous nannofossils from a marine sedimentary sequence of the eastern Karakoram block, in northern India. The calcareous mudstones and packstones, occasionally bearing red chert nodules, yielded calcareous nanofossils and Middle Jurassic Choffatia furcula ammonoids. Middle to Upper Jurassic nannofossil assemblage is dominated by representatives of the genus Watznaueria. The occurrence of Ansulasphaera helvetica whose range is Upper Bathonian–Upper Callovian, indicates a correlation with nannofossil zones NJ12–13. The occurrence of Cyclagelosphaera wiedmannii further infer an Upper Bathonian–Callovian age. These specimens show affinities with those found in a similar sedimentary formation exposed in north Karakoram. This suggests the existence of a narrow and elongated sedimentary basin, oriented in a NW–SE direction, at a latitude of c. 25°–30°N. At that time, the Karakoram block was situated near the already welded Qiangtang block of Asia. The northern and eastern Karakoram blocks were connected during Middle Jurassic. The activity and dextral offset of the Karakoram fault separated the Jurassic sedimentary formations of the northern and eastern Karakoram blocks by c. 150 km.     

OBSERVATIONS ON ESTUARINE FLUID MUD ENTRAINMENT

I. INTRODUCTIONPrediction of mud bed erosion by forcing due to tidal currents usually requires a numerical solution of the advection--dispersion equation for sediment mass transport. Key role is of course played inthis by the bottom boundary conditions defining erosion and deposition fluxes. The issue of erosion isbriefly considered here. noting that it is customary to calculate the rate of erosion as a function of thebed shear stress in excess of the erosion shear strength of the bed (Me…