Vaibhava Srivastava

Fuzzy gamma based geomatic modelling for landslide hazard susceptibility in a part of Tons river valley, northwest Himalaya, India

Himalaya, being an active orogen, is continuously undergoing tectonic activities that pose threats of land stability on the mountains. A large number of mass movement occurrences have been observed in a part of the Tons river valley area. Remote sensing and geographical information system (GIS) based techniques have been used to derive and analyse various parameters and attributes pertinent to the landslide hazards. The GIS based analysis in the present work, incorporating the fuzzy membership values from the existing landslides, has been used for spatial modelling of the parameter maps including geology, slope amount, slope aspect, weathering, erosion, drainage influence, tectonic influence and landuse/land cover for landslide hazard zonation. The model has been used to spatially classify the study area into zones of very high, high, moderate, low and very low landslide hazard zones. Eighty-five percent of the active landslides have been observed to occur in very high and high hazard zones.

Classification of multilayered folds based on harmonic analysis: example from central India

Abstract The harmony of multilayered folds can be determined objectively by comparing the b3/b1 (ratio of third and first coefficient of harmonic components of the Fourier series) for different surfaces in an individual fold. A plot of the b3/b1 value against surface number provides a simple graphical technique for assessing fold harmony. On such a diagram, a straight line parallel to abscissa denotes a strictly harmonic fold, while other lines and curves denote variation of fold shape from surface to surface. A new scheme of multilayered fold classification based on ‘Index of Non-Harmony (INH)’, which reveals the degree of variation in shape of different surfaces of the fold, is proposed. INH is obtained from standard deviation (σn) of b3/b1 ratios of ‘n’ number of surfaces of a quarter wave sector. On the basis of values of INH ( = 1000 · σn) the multilayered folds are classified as ‘Strictly Harmonic’ (INH = 0), ‘Periharmonic’ (0 75). In a case study of polydeformed Precambrian rocks of central India, it is found that the index of nonharmony decreases in folds of later (younger) generations.

Provenance of the Late Paleocene Sandstones of the Jaisalmer Basin, Western India

Provenance of the late Paleocene sandstone of the Jaisalmer basin has been determined by petrographic and heavy minerals analysis supported by paleocurrent study. Petrography of the quartzose-arenite sandstone reveals an abundance of sub-angular to sub-rounded monocrystalline non-undulatory quartz and some amount of feldspar and rock fragments. The rock fragments are dominated by argillites (slate, phyllite) and limestone. The heavy minerals suite of these sandstones comprises of angular to sub-angular grains of magnetite, zircon, tourmaline, kyanite and staurolite. The paleocurrent analysis indicates bipolar paleocurrent pattern with the dominance of NW flow suggesting that the provenance was in the SE direction of the depositional basin. Q-F-L and Qm-F-Lt diagrams suggest for a provenance at the margin of the craton interior and transitional continental. It is envisaged that the basic igneous rocks of the Deccan basalt, low- to medium-grade metamorphic rocks of the Aravalli belt and Jurassic limestones present in the vicinity are the source rocks for the late Paleocene sandstones of the Jaisalmer basin.

Characteristics of modern biotic data and their relationship to vegetation of the Alpine zone of Chopta valley, North Sikkim, India: Implications for palaeovegetation reconstruction:

We examined the modern pollen palynomorphs (PP) distribution complemented with non-pollen palynomorphs (NPP) and stable carbon isotopic data of soil organic matter (SOM) to explore relationships of these proxies to vegetation communities in the Chopta valley, a closed valley in alpine zone of the North Sikkim, India, in an attempt to check the efficiency for reconstructing past vegetation and climate. A total of 24 surface soil samples were collected from both the windward and leeward sides of the valley and they did not show any significant difference in the palynoassemblages. The average value of δ13C is −26.6%, which clearly indicates a C3-dominated vegetation in this valley which is also corroborated by the palynological data. However, signature of upthermic wind transport was evident by the significant presence of extra-local and regional forest elements in the palynoassemblages. NPP data indicated grazing activity in the valley and is in conformity with the present-day scenario. Furthermore, cluster analysis (CA) and principal component analysis (PCA) done on the PP and NPP data broadly grouped the samples according to the location of collection to some extent and reflected the relationships among the taxa with the extant vegetation. This study provides a basis for future palaeovegetation and palaeoclimate reconstruction from the region.

Provenance of the Late Paleocene Matanomadh Sandstones, Kachchh, Western India

The late Paleocene clastic member of the Matanomadh Formation (MF) is an overall sandstone dominated succession wherein sub-ordinate proportion of thinly-laminated silty-mudstones is found lying between the sandstone beds. Provenance of these late Paleocene Matanomadh Sandstones (MS), Kachchh is not known till date and the same has been determined based on petrography and heavy mineral analysis supported by paleocurrent studies. These sandstones reveal an abundance of sub-angular to rounded monocrystalline non-undulatory quartz; and polycrystalline quartz, feldspar and rock fragments occur as minor constituents. These sandstones are classified as quartzose arenite. The rock fragments in these sandstones are dominated by mica-schist, slate, chert and limestones. Q-F-L and Qm-F-Lt diagrams suggest margin of the craton interior to transitional continental stable craton provenance for these sandstones. The paleocurrent measurements of the cross-bedded sandstones suggest NW-SE-directed bipolar and WNW-directed unimodal paleocurrent patterns and suggest a marine-continental transition zone as depositional site for these sandstones where sediments were contributed from both the shallow-marine and continental sources. The heavy mineral assemblages of these sandstones show sub-angular to rounded grains of magnetite, tourmaline, monazite, rutile, kyanite, staurolite and hematite where magnetite is the dominant component; and hence suggest that the heavy minerals might have been supplied from a basic igneous source, low- to medium-grade metamorphic rocks and reworked sedimentary rocks.

Geochemistry of Mesoproterozoic Deonar Pyroclastics from Vindhyan Supergroup of Central India: Evidences of felsic magmatism in the Son valley

Deonar Pyroclastics of Semri Group in the Vindhyan Supergroup originated as a result of violent and explosive intrabasinal submarine volcanism during the Mesoproterozoic period. These pyroclastics are rhyolitic to rhyodacitic in composition, comprised of banded, massive, pumiceous flow, breccia, vitric tuff, lapilli and volcanic bomb. The pyroclastic deposits represent welded and non-welded ignimbrites, exhibit typical eutaxitic texture. Mantle normalized multi-element patterns show enrichment in LILs and depletion in HFSFs. Ti, Nb and REE contents show close correlation with Zr, indicating their immobile character. HFSEs and Th/Nb, La/Nb and Zr/Nb values indicate contamination and these signatures represent mixing between mantle-derived rocks and the average continental crust. Deonar Pyroclastics reflect continental rift environment. Felsic magma plausibly generated by underplating of the mature Proterozoic crust of the Indian craton (which acted like a ‘heating lens’) resulted in extensive melting of metabasalt in the lower crustal levels. The high heat flow beneath the Indian shield accentuated heat generation which led to extensive partial melting of metabasalts. Thus, generation of rhyolitic magma occurred along the reactivated deep seated fractures and rifting of the craton, resulting in the explosive intra-basinal felsic vulcanicity in the Vindhyan basin.

Tectonic Consideration for Location of the Kishau Dam Site on Tons River in Lesser Himalaya, India

A 236 m high concrete gravity dam named Kishau dam is proposed on Tons river in Lesser Himalayan region of Uttarakhand state of India. The possible site for this upcoming dam on Tons river lies in the close proximity of Tons thrust which makes a tectonic boundary between allochthonous rocks of Krol nappe and the autochthonous Simla Group rocks. The Tons thrust lies in the close vicinity of the proposed dam site. Many geomorphic and geological evidences have been observed around the dam site which indicate that active tectonics is prevalent in the region. The present study examines the geological structures of the region in order to understand the tectonic conditions that the area has experienced and finds that the southward movement of the Krol nappe is responsible for active tectonics in the region. Due to mass transfer by the movement of Krol nappe from over the autochthonous zone, the autochthonous zone is getting uplifted at an average rate of 9.7 mm/per year. In light of these active movements, the Kishau village, which lies in the southwards moving allochthonous zone, cannot be good site of Kishau dam and the dam location should preferably be placed across the Tons thrust in the autochthonous zone.