Biomarker signatures from Neoproterozoic–Early Cambrian oil,western India

The Neoproterozoic–Early Cambrian time is the cradle of multicellular, eukaryotic life and thereafter metazoan life started populating the planet. Biomarkers, which record the chronicles of biotic events on Earth, have been investigated using gas chromatography–mass spectrometry from a suite of nine oil samples extracted from oil stained sediments and a crude oil of Neoproterozoic–Early Cambrian age from Bikaner-Nagaur Basin, western India. The biomarker distribution is characterized by high concentration of both tricyclic terpanes and pentacyclic hopanes. The predominance of C₂₉ regular sterane over C₂₇ and C₂₈ steranes indicates green algal contribution and may imply the prominence and diversification of the same algal group. The low pristane/phytane ratio and occurrence of substantial quantity of gammacerane, monomethyl 2-methyl-2-(2,4,8-trimethyltridecyl) chroman and 1,1,7,8-tetramethyl-1,2,3,4 tetrahydrophenanthrene are indicative of stratified water column as well as anoxic and enhanced salinity condition of the environment of deposition. This paper reports for the first time the presence of methyltrimethyltridecyl chromans (MTTCs) from Neoproterozoic–Early Cambrian time. Putative C₁₉ norsteranes, probably indicative of sponge input, are recorded in the studied samples and also reported from other infracambrian oils and sediments. Normal alkanes (n-C₁₇ and n-C₁₈) and isoprenoids (pristane and phytane) are highly depleted in δ¹³C. The overall biomarker distribution and carbon isotope data of oils from Bikaner-Nagaur Basin show similarities with those of other infracambrian oils like Huqf oils from Oman and Baykit High oils from eastern Siberia.     

Near N–S paleo-extension in the western Deccan region,India: Does it link strike-slip tectonics with India–Seychelles rifting?

This is the first detailed report and analyses of deformation from the W part of the Deccan large igneous province (DLIP), Maharashtra, India. This deformation, related to the India–Seychelles rifting during Late Cretaceous–Early Paleocene, was studied, and the paleostress tensors were deduced. Near N–S trending shear zones, lineaments, and faults were already reported without significant detail. An E–W extension was envisaged by the previous workers to explain the India–Seychelles rift at ~64 Ma. The direction of extension, however, does not match with their N–S brittle shear zones and also those faults (sub-vertical, ~NE–SW/~NW–SE, and few ~N–S) we report and emphasize in this work. Slickenside-bearing fault planes, brittle shear zones, and extension fractures in meso-scale enabled us to estimate the paleostress tensors (directions and relative magnitudes). The field study was complemented by remote sensing lineament analyses to map dykes and shear zones. Dykes emplaced along pre-existing ~N–S to ~NE–SW/~NW–SE shears/fractures. This information was used to derive regional paleostress trends. A ~NW–SE/NE–SW minimum compressive stress in the oldest Kalsubai Subgroup and a ~N–S direction for the younger Lonavala, Wai, and Salsette Subgroups were deciphered. Thus, a ~NW/NE to ~N–S extension is put forward that refutes the popular view of E–W India–Seychelles extension. Paleostress analyses indicate that this is an oblique rifted margin. Field criteria suggest only ~NE–SW and ~NW–SE, with some ~N–S strike-slip faults/brittle shear zones. We refer this deformation zone as the "Western Deccan Strike-slip Zone" (WDSZ). The observed deformation was matched with offshore tectonics deciphered mainly from faults interpreted on seismic profiles and from magnetic seafloor spreading anomalies. These geophysical findings too indicate oblique rifting in this part of the W Indian passive margin. We argue that the Seychelles microcontinent separated from India only after much of the DLIP erupted. Further studies of magma-rich passive margins with respect to timing and architecture of deformation and emplacement of volcanics are required.     

Arsenic mobilization in alluvial soils of Punjab, North–West India under flood irrigation practices

A laboratory investigation was carried out to examine the mechanism of arsenic (As) mobilization under flooded conditions (24 and 240 h) in 18 alluvial soils of Punjab, North–West India. Total dissolved As increased from a range of 3–16 μg L^?1 (mean 9 μg L^?1) to a range of 33–1,761 μg L^?1 (mean 392 μg L^?1) with the increase in flooding period from 24 to 240 h. The amount of As mobilization varied depending upon redox potential (pe) created by flooding conditions. After 24 h of flooded conditions, pe of soil water suspension ranged from ?1.75 to 0.77 (mean ?0.24). Increasing the flooding period to 240 h, pe of soil water suspension decreased in the range of ?4.49 to ?2.74 (mean ?3.29). Pourbaix diagram identified arsenate (HAsO₄ ^2?) as predominant species in most of the alluvial soil–water suspensions under oxidized conditions, after 24 h of equilibration period, which ultimately transformed to arsenite (H₃AsO₃ ⁰) after 240 h of anaerobic condition due to more reduced status. The solid phase identified was orpiment (As₂S₃). Identification of iron and manganese species in alluvial soil water suspension by Pourbaix diagram indicated decline in both soluble Fe²⁺ and SO₄ ^2? concentration due to the formation of iron sulfide mineral phase after 240 h under anaerobic conditions. In these soils, decline in soluble Fe was also due to the precipitation of vivianite [Fe₃(PO₄)₂·8H₂O]. Elevated arsenic content and low pe value were measured in aquifers located in paddy growing fields comparative to aquifers of other sites. Large degree of variability in As concentrations was recorded in aquifers located at same sites. Thus, it is better to analyze each aquifer for their As content rather than to depends on the prediction on As content of neighbouring wells. The present investigation elucidates that flood irrigation practices in Punjab for growing paddy crop could induce the geochemical conditions favorable to mobilize arsenic from surface soils which could eventually elevate its content in the underlying shallow aquifers. Water abstracted from these aquifers by hand pumps or tube wells for drinking purposes could create hazards for local population due to loading with arsenic concentration above the safe limits. Thus, to avoid further contamination of shallow aquifers with arsenic, it is advisable to shift the flooded rice cultivation to other upland crops having lesser water requirement.     

Rank-size distribution and primate city characteristics in India — A temporal analysis

This paper is an analysis of the historical change in city size distribution in India from the perspectives provided by Zipf and Jefferson. Rank-size distribution at national level and primate city-size distribution at regional levels are examined. India's national urban system is gradually evolving towards Zipf's rank-size distribution. But primate cities have persisted in three of the four macro-regions in India. The paper also examines, in the Indian context, the relation between rank-size distribution and an integrated urban system, and the normative nature of the latter as a spatial organization of human society. Finally, we have made a modest attempt to locate the research on city-size distribution, especially Berry's system-theoretic interpretation of rank-size distribution, on the realm of the political economy of urbanization.     

Mapping the sub-trappean Mesozoic sediments in the western part of Narmada–Tapti region of Deccan Volcanic Province,India

Deccan Traps spread over large parts of south, west and central India, possibly hiding underneath sediments with hydrocarbon potential. Here, we present the results of seismic refraction and wide-angle reflection experiments along three profiles, and analyze them together the results from all other refraction profiles executed earlier in the western part of Narmada–Tapti region of the Deccan Volcanic Province (DVP). We employ travel time modelling to derive the granitic basement configuration, including the overlying Trap and sub-trappean sediment thickness, if any. Travel time skips and amplitude decay in the first arrival refraction data are indicative of the presence of low velocity sediments (Mesozoic), which are the low velocity zones (LVZ) underneath the Traps. Reflection data from the top of LVZ and basement along with the basement refraction data have been used to derive the Mesozoic sediment thickness.In the middle and eastern parts of the study region between Narmada and Tapti, the Mesozoic sediment thickness varies between 0.5 and 2.0 km and reaches more than 2.5 km south of Sendhwa between Narmada and Tapti Rivers. Thick Mesozoic sediments in the eastern parts are also accompanied by thick Traps. The Mesozoic sediments along the present three profiles may not be much prospective in terms of its thickness, except inside the Cambay basin, where the subtrappean sediment thickness is about 1000–1500 m. In the eastern part of the study area, the deepest section (>4 km) has thick (∼2 km) Mesozoic sediments, but with almost equally thick Deccan Trap cover. Results of the present study provide important inputs for future planning for hydrocarbon exploration in this region.     

Possible evidence of remotely triggered and delayed seismicity due to the 2001 Bhuj earthquake (Mw?=?7.6) in western India

Remote triggering by large earthquakes at regional distances is a globally observed phenomenon. However, there are no reports of observations of dynamic triggering at regional distances of several source lengths associated with the large Mw?=?7.6 Bhuj earthquake of January 26, 2001, in western India. In the present study, a swarm of over 140 microearthquakes that occurred about 500?km southeast of Bhuj, in the geothermal province of the Western Ghats in the Deccan volcanic province (DVP) of India, immediately after the occurrence of the Bhuj earthquake in 2001 is investigated. The post-Bhuj seismicity (M?<?2.0) occurred in three bursts spread over 2?months with each burst of intense activity lasting for 2?C3?days. All the three bursts of seismicity occurred in the same volume along a 5-km-long NW?CSE trending fault. The temporal coincidence and the sudden rise in seismicity that interrupts the characteristically low background seismicity strongly suggest that the Bhuj earthquake may have remotely triggered this activity. The triggered seismicity began approximately 2.5?h after the onset of the Bhuj mainshock and continued well after the passage of the surface waves, suggesting that the dynamic stresses possibly gave rise to secondary time-dependent mechanisms leading to the triggering. It is proposed that the triggered and delayed seismicity is possibly a consequence of the redistribution in pore fluid pressure due to the Bhuj earthquake. This is the first documented observation of remotely triggered seismicity at regional distances due to the Bhuj earthquake.     

Evolution of a tertiary volcanogenic trough in SW Turkey — The Alakaya basins of the Lycien belt

Field study of several stratigraphic sections from allochthonous thrust fault slices of SW Turkey reveal that a deeply subsiding volcanogenic trough, the Alakaya basin existed during Paleocene-Middle Eocene times along the Lycian belt. The Alakaya basin was located along a tectonically active zone of weakness between two relatively stable tectonic terrains, the Menderes massif to the northwest and the Beydaglari continental platform to the southeast. The basin was underlain by continental substratum. All known outcrops of the Alakaya sediments overlie platform carbonates of Cretaceous age that correlate with the Beydaglari shelf sediments. The generation of the volcanogenic Alakaya basin reflects a tensional period that culminated in Middle Eocene when basic volcanic activity took place. The tensional stage was replaced by a compressional regime in Late Eocene and large scale overthrust faulting took place. The Alakaya basin was closed when the Tefenni nappe from the north was emplaced on its sediments in Late Eocene. The Alakaya sediments overlying the Tefenni nappe and underlying the Cretaceous platform carbonates moved southeastward over a hundred kilometers onto the autochthonous sediments of the Beydaglari terrain in Miocene time. The Alakaya basin is analogous to the Maden basin of SE Turkey thrust fault belt. Both basins were located along tectonically active belts. The main stage of basin subsidence and volcanism was in Middle Eocene. Closure of both basins by large scale thrust faulting was in Late Eocene. The creation and destruction of the volcanogenic Alakaya basin may be related to the regional adjustments in plate motions in Paleocene-Eocene times.

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Zusammenfassung Geländestudien einiger stratigraphischer Profile von allochthonen Überschiebungspaketen in der SW Türkei zeigen, daß ein tief abgesunkener vulkanogener Trog, das Alakaya Becken, während des Paläozäns und Mittel Eozäns entlang der Lyzischen Zone bestand. Das Alakaya Becken lag innerhalb einer tektonisch aktiven Schwächezone zwischen zwei relativ stabilen tektonischen Terrains, dem Menderes Massiv im NW und der Beydaglari Kontinentalplattform im SE. Das Becken besaß eine kontinentale Unterlage. Alle bekannten Aufschlüsse mit Alakaya Sedimenten lagern über kretazischen Plattformkarbonaten, die sich mit den Beydaglaria Schelfsedimenten korrelieren lassen. Die Entwicklung des vulkanogenen Alakaya Bekkens spiegelt eine Spannungsperiode wieder, die im Mittel Eozän mit basischem Vulkanismus kulminierte. Diese Periode der Zugspannung wurde im späten Eozän von einer kompressiven Beanspruchung abgelöst, welche zu großmaßstäblichen Überschiebungen führte. Das Alakaya Becken wurde geschlossen, als auf Grund der späteozänen Platznahme die aus dem Norden stammende Tefenni Decke auf deren Sedimenten zu liegen kam. Die Alakaya Sedimente zusammen mit der überlagernden Tefenni Decke und den unterlagernden kretazischen Plattformkarbonaten wurden während des Miozäns über einhundert Kilometer südostwärts auf die autochthonen Sedimente des Beydaglari Terrains überschoben. Das Alakaya Becken ist ein Analogon zu dem Maden Becken der SE Türkischen Überschiebungszone. Beide Becken lagen entlang tektonisch aktiver Zonen. Während des Mittel Miozäns war das Hauptstadium der Beckensubsidenz und des Vulkanismus. Das Schließen der Becken mittels großmaßstäblicher Überschiebung fand in beiden Fällen im späten Eozän statt. Die Bildung und der Zerfall des vulkanogenen Alakaya Beckens scheint mit den regionalen Anpassungen an die Plattenbewegung während des Paläozäns und Eozäns verbunden zu sein.

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Résumé L'étude de terrain de plusieurs coupes stratigraphiques dans les lames charriées de l'allochtone du sud-ouest de la Turquie révèle l'existence, du Paléocène à l'Eocène moyen, d'une fosse volcanogénique fortement subsidente: le bassin d'Alakaya, situé le long de la chaîne lycienne. Ce bassin d'Alakaya s'est localisé le long d'une zone de faiblesse tectoniquement active, entre deux blocs relativement stables: le massif de Menderes au nord-ouest et la plate-forme continentale de Beydaglari au sud-est. Le bassin repose sur un substratum continental. Dans tous les affleurements connus, les sédiments d'Alakaya surmontent des carbonates de plateforme d'âge Crétacé, corrélables aux sédiments de shelf de Beydaglari. La genèse du bassin volcanogène d'Alakaya reflète une période d'extension dont le maximum se situe à l'Eocène moyen, lors de l'apparition d'une activité volcanique basique. A la phase distensive a succédé, à l'Eocène supérieur, un régime compressif marqué par des charriages de grande échelle. Le bassin d'Alakaya était fermé au moment où la nappe de Tefenni, venant du nord, s'est mise en place sur ses sédiments, à l'Eocène supérieur. Au Miocène, l'ensemble formé par la plate-forme carbonatée crétacée sous-jacente, les sédiments dAlakaya et la nappe de Tefenni surincombante a été transporté d'une centaine de km vers le sud-est sur les sédiments autochtones de Beydaglari. Le bassin d'Alakaya est analogue au bassin de Maden de la ceinture charriée du sud-est de la Turquie. Tous deux se sont localisés le long de zônes tectoniques actives. Leur phase culminante de subsidence et de volcanisme se situe à l'Eocène moyen. Dans les deux cas, les bassins ont été formés à l'Eocène supérieur par un charriage à grande échelle. La formation et la destruction du bassin d'Alakaya semblent pouvoir être rattachées aux ajustements régionaux dans les mouvements des plaques au Paléocène-Eocène.

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The igneous charnockite—high-K alkali-calcic I-type granite—incipient charnockite association in Trivandrum Block,southern India

The Pan-African (640 Ma) Chengannoor granite intrudes the NW margin of the Neoproterozoic high-grade metamorphic terrain of the Trivandrum Block (TB), southern India, and is spatially associated with the Cardamom hills igneous charnockite massif (CM). Geochemical features characterize the Chengannoor granite as high-K alkali-calcic I-type granite. Within the constraints imposed by the high temperature, anhydrous, K-rich nature of the magmas, comparison with recent experimental studies on various granitoid source compositions, and trace- and rare-earth-element modelling, the distinctive features of the Chengannoor granite reflect a source rock of igneous charnockitic nature. A petrogenetic model is proposed whereby there was a period of basaltic underplating; the partial melting of this basaltic lower crust formed the CM charnockites. The Chengannoor granite was produced by the partial melting of the charnoenderbites from the CM, with subsequent fractionation dominated by feldspars. In a regional context, the Chengannoor I-type granite is considered as a possible heat source for the near-UHT nature of metamorphism in the northern part of the TB. This is different from previous studies, which favoured CM charnockite as the major heat source. The occurrence of incipient charnockites (both large scale as well as small scale) adjacent to the granite as well as pegmatites (which contain CO₂, CO₂-H₂O, F and other volatiles), suggests that the fluids expelled from the alkaline magma upon solidification generated incipient charnockites through fluid-induced lowering of water activity. Thus the granite and associated alkaline pegmatites acted as conduits for the transfer of heat and volatiles in the Achankovil Shear Zone area, causing pervasive as well as patchy charnockite formation. The transport of CO₂ by felsic melts through the southern Indian middle crust is suggested to be part of a crustal-scale fluid system that linked mantle heat and CO₂ input with upward migration of crustally derived felsic melts and incipient charnockite formation, resulting in an igneous charnockite – I-type granite – incipient charnockite association.Editorial responsibility: T.L. Grove     

Micro-mechanical analysis of soil–structure interface behavior under constant normal stiffness condition with DEM

The mechanical behavior at soil–structure interface (SSI) has a crucial influence on the safety and stability of geotechnical structures. However, the behavior of SSI under constant normal stiffness condition from micro- to macro-scale receives little attention. In this study, the frictional characteristics of SSI and the associated displacement localization under constant normal stiffness condition are investigated at both macro- and microscales by simulating a series of interface shear tests with discrete element method. The algorithm to achieve a constant normal stiffness is first developed. The macroscopic mechanical response of the interface shear tests with both loose and dense specimens at various normal stiffness is discussed in terms of shear stress, normal stress, vertical displacement, horizontal displacement and stress ratio. Then, the microscopic behaviors and properties, including shear zone formation, localized void ratio, coordination number, force chains and soil fabric, are investigated. The effect of normal stiffness is thus clarified at both macro- and microscales.

     

Long hiatus in Proterozoic sedimentation in India: Vindhyan,Cuddapah and Pakhal Basins — A plate tectonic model

Most of the Proterozoic basins in India, viz. the Vindhyan, the Cuddapah and the Pakhal Basins have experienced long hiatus between the upper and the lower group of rocks. It is proposed that the older group of rocks of Paleoproterozoic period (∼1.9–1.6 Ga) formed during the rifting phase caused by large scale magmatism in respective basins possibly due to plume tectonics. On the other hand, the younger group of rocks of Neoproterozoic (∼1.0–0.7 Ga) are formed during the final phase of convergence after mountain building that supplied sediments. These geological processes explain large scale disturbances in the older group of rocks during subsequent convergence and collision as they usually occurred along the rifted margins of the cratons. These processes also explain the undisturbed nature, devoid of magmatic rocks of the younger group of rocks and hiatus of about 0.5–0.6 Ga in each case. It is suggested that the plume that was responsible for these rifting of the Indian cratons during Paleo-Mesoproterozoic might have also been responsible for the break up of contemporary Columbian agglomeration in this section. Same model can be used to explain the formation of Proterozoic basins and related hiatus any where else where similar geological environment exist.     

Detrital zircon U–Pb ages and Hf-isotope systematics from the Gadag Greenstone Belt: Archean crustal growth in the western Dharwar Craton,India

The Western Dharwar Craton in peninsular India comprises a typical Meso- to Neo-Archean granite-greenstone terrain. Detrital zircons from two metagreywackes in a late basin from the Gadag Greenstone Belt preserve at least eight age populations ranging in age from ca 3.34 to 2.55 Ga, and grains as old as ca 3.54 Ga. The zircon provenances for the two samples appear to be the same up to ca 3.25 Ga, with relatively juvenile ε_Hf values largely between zero and depleted mantle values. After 3.25 Ga, one sample has similar ε_Hf values whereas the other has only negative values indicative of Hf-evolution in a crustal environment. After ca 3.25 Ga the source regions for the two samples were distinctly different.The detrital zircons reflect the age and evolution of the upper crust of the Western Dharwar Craton. Modeling of Hf isotopic evolution of the detrital zircons suggests two major crust-forming events at ca. 3.6 and 3.36 Ga, and some indication of juvenile addition to the crust at ca 2.6 Ga. The maximum sedimentation age of the greywackes is constrained by the youngest detrital zircon population at 2547 ± 5 Ma. Gold mineralization in the belt is dated at 2522 ± 6 Ma and constrains greywacke sedimentation, deformation and metamorphism to a ca 25 my interval.     

Geology and geochemistry of the Degana pluton—A proterozoic rapakivi granite in Rajasthan,India

Summary The Degana pluton hosts one of the few known tungsten deposits in India It is an epizonal, moderately high silica pluton emplaced during the Proterozoic in a posttectonic setting. Though homogeneous in composition, it displays textural heterogeneity from coarse-grained hypidiomorphic to fine-grained porphyritic to hypabyssal granite porphyry. Genetically related rhyolites are also present. Coherency of geochemical and mineralogical attributes in the Degana pluton can be explained by fractional crystallisation. Complex variety of hydrothermal and pneumatolytic features is also present. At shallow depths, emanation differentiation has led to progressive enrichment of Li, Rb, and W. Both the plutonic and volcanic phases of the magma show development of rapakivi texture and other diagnostic characteristics of the rapakivi granites.The Degana granite is a specialised granite and classified as an A-type intraplate anorogenic granite of mantle plume origin. The mineralogy and chemistry of the Degana pluton compares well with the various rapakivi granites of south-eastern Fennoscandia. Chemical and textural characteristics of the Degana pluton provide a constraint on the formation of the rapakivi texture when interpreted in terms of experimentally determined phase equilibria. The mantling process is interpreted as a result of pressure fluctuations due to escape and recharging of volatiles (e.g., H2O and F) accompanying the emplacement of the magma.

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Geologie und Geochemie des Degana-Plutons—ein proterozoischer Rapakivi Granite in Rajasthan, Indien

Zusammenfassung Der Degana Pluton enhält eine der wenigen in Indien bekannten Wolfram-Lagerstätten. Es handelt sich hier um einen epizonalen Pluton mit höheren Si-Gehalten, der während des Proterozoikums in ein posttektonisches Setting intrudiert wurde. Obwohl er in seiner Zusammensetzung homogen ist, zeigt er Heterogenität auf dem texturellen Bereich, die von grobkörnig hypidiomorph bis feinkörnig porphyritisch und schließlich bis zu hypabyssischen Granitporphyren reicht. Genetisch verwandte Rhyolite kommen im Untersuchungsgebiet auch vor. Übereinstimmende geochemische und mineralogische Parameter können auf fraktionierte Kristallisation zurückgeführt werden. Eine komplexe Vielfalt von hydrothermalen und pneumotolytischen Erscheinungen ist bemerkenswert. In geringen Tiefen hat die Emanations-Differentiation zu einer progressiven Anreicherung von Li, Rb und W geführt. Sowohl die plutonischen als auch die vulkanischen Erstarrungsprodukte des Magmas zeigen die Entwicklung von Rapakivi-Texturen und anderen diagnostischen Eigenschaften der Rapakivi-Granite.Der Degana-Granit ist ein spezialisierter Granit und ist als ein anorogener Intraplattengranit des A-Typs zu klassifizieren, der auf einen mantle plume zurückgeführt wird. Die Mineralogie und Chemie des Degana-Plutons läßt sich gut mit der verschiedener Rapakivi Granite im südöstlichen Fennoskandien vergleichen. Chemische und texturelle Eigenheiten des Degana Plutons ermöglichen eine Eingrenzung der Bildung von Rapakivi Texturen, sofern sie im Sinne experimentell bestimmter Phasen-Gleichgewichte interpretiert werden. Die Entstehung von Überwachsungen einzelner Kristalle wird als Resultat von Druckschwankungen interpretiert, die auf das Entweichen und die Neuzufuhr von volatilen Phasen (i.e. H₂O und F) im Gefolge der Platz nahme des Magmas zurückzuführen sind.

     

Tidal effects on groundwater dynamics in shallow coastal aquifers—southeast coast of Tamilnadu,India

Tides play a significant role in the coastal environment; the mangroves, back waters, creeks, and the coastal groundwater interface. Tidal range has been calculated by using TIDECAL software. This study attempts to find the relation between water table condition and tides in the shallow coastal aquifers. The study was conducted by selecting 12 open wells along the coast of the southern part of Cuddalore to the northern part of Nagapattinam district of Tamilnadu. Observations were made in situ for water table fluctuation, dissolved oxygen (DO), and electrical conductivity (EC) for 24 h during full moon (FM) and new moon (NM) of every 2 h. The present study shows the relationship between tidal variations with respect to water table fluctuations and helps to understand the behavior of DO and EC. An interpolation technique, inverse distance weighted (IDW) method was used to obtain the spatial distribution map. The temporal and the spatial relationships between water table fluctuation, EC, and DO were also used in order to understand the coastal ecosystem in the natural environment.     

Hydrogeomorphic classification and aquifer disposition in the Markanda river basin,Northwestern India — Hydrogeological approach

The regional hydrogeological aspects of the Markanda river basin in the Himalayan foothills, NW India have been attempted. The basin has been hydro-geomorphologically analyzed as ridge, piedmont zone, alluvial plain, flood plain and palaeochannel. Groundwater prospect in the alluvial plain, flood plain and palaeochannel areas were found to be promising. Water table contour maps of the basin revealed that groundwater flows from northeast to southwest. Groundwater permeability is low in the northern part and is high towards the southern part of the basin. The areas of recharge were identified in the northern part of the basin, while the areas of discharge were identified in the central and lower parts of the basin. Hydrogeologic transects across and along the basin indicate that aquifer horizons are made up of fine sand, medium sand and gravelly sand. These aquifer layers are laterally extensive but limited in thickness. They occur as multistoried sand bodies with pinch and swell behavior. The overall study gives an understanding of the present regional hydrogeological scenario of the Markanda basin. Such detailed integrated approach would help to locate productive groundwater areas before installing a new tubewell in the region. Also, it would help in planning future groundwater management of the region.     

Delineation of fresh aquifers in tannery belt for sustainable development — A case study from southern India

The tannery effluents discharged by the existing units on either side of the Palar river at Ambur town (known for tannery industry), has resulted in vertical and lateral spread of pollution. The study area of 55.3 km² is situated on a granitic terrain of Archaean age with undulating topography and hillocks. The shallow aquifers, in flood plain and valley fills of the river are highly polluted (with EC: 15340 μS/cm) by tannery effluents making groundwater unfit for any use, hence the local population (20000) face health hazards and shortage of potable water. Hydrogeological, geophysical and in-situ groundwater quality measurement were carried out to demarcate fresh groundwater zones and to delineate lateral and vertical extent of pollution. The results show, brackish aquifer was characterized by low order of resistivity (<20 Ω-m) with a thickness of 8.5 to 28 m located in the flood plains, valley fills, and partially in hard rock formations, whereas the fresh water aquifer resistivity varying from 23 to 216 Ω-m in hard rock. Further, these results were correlated with the water quality data and Ground Penetrating Radar (GPR) signals. The integrated studies revealed that pollution due to tannery effluents has spread over an area of 33.4 km² (60.4 %) on either side of the river and only a small area of 21.9 km² (39.6 %) was identified as fresh groundwater zone, which has to be conserved and exploited in sustainable manner for future generations.     

Phenomenological fractional stress–dilatancy model for granular soil and soil-structure interface under monotonic and cyclic loads

The stress–dilatancy relation is of critical importance for constitutive modelling of geomaterial. A novel fractional-order stress–dilatancy equation had been developed for granular soil, where a nonlinear stress–dilatancy response was always predicted. However, it was experimentally observed that after a certain extent of shearing, an almost linear response between the stress ratio and the dilatancy ratio, rather than the nonlinear response, usually existed. To capture such stress–dilatancy behaviour, a new fractional stress–dilatancy model is developed in this study, where an apparent linear response of the stress–dilatancy behaviour of soil after sufficient shearing is obtained via analytical solution. As the fractional order varies, the derived stress–dilatancy curve and the associated phase transformation state stress ratio keep changing. But, unlike existing researches, no other specific parameters, except the parameter related to fractional order, concerning such shift are required. Then, the developed stress–dilatancy model is applied to constitutive modelling of granular soil and soil–structure interface, for further validation. A series of test results of different granular soils and soil–structure interfaces under different loading conditions are simulated and compared, where a good model performance is observed.