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| 1 | Siliciclastic-carbonate mixing modes in the river-mouth bar palaeogeography of the Upper Cretaceous Garudamangalam Sandstone(Ariyalur, India)显示文摘Mixed siliciclastic-carbonate rocks constitute the Upper Cretaceous Garudamangalam Sandstone Formation, Ariyalur(India), and offer an opportunity to look into the broad spectrum of mixing of compositionally and genetically different components. The palaeogeographic reconstruction indicates that deposition in the nearshore zone differed strongly in energy and active processes operatives due to the presence of a shore-parallel river-mouth bar. The western wing of the Mississippi bird-foot delta is considered to be a present-day analogon. Facies analysis in combination with petrography clearly shows the variability in palaeoenvironmental characteristics, both biogenic and non-biogenic. It also indicates diagenetic uptake of carbonate that filled empty spaces and actively replaced original components. Chemical staining followed by limited application of cathodoluminescence and energy dispersive X-ray analysis(EDAX) hint at intricacies in mixing arising from the compositional variations in the carbonate components. A model of siliciclastic-carbonate sediment mixing, including both the depositional and diagenetic developments, is presented; it is aimed at generating a better overview of, and a deeper insight into, the physical and chemical mechanisms involved. | Subir Sarkar Nivedita Chakraborty Anudeb Mandal Santanu Banerjee Pradip K.Bose | 2014 | Journal of Palaeogeography2014，3，3： | 4 |
| 2 | Microbial mat-related structures shared by both siliciclastic and carbonate formations显示文摘Microbiota has always been the dominant life form,records of which are preserved in delicate forms within siliciclastic rocks.More pronounced record in the form of stromatolites possibly obscured the fact that many of the same delicate structures may be recognizable within carbonate rocks too.The Neoproterozoic Bhander Limestone in central India bears many such structures that are quintessentially similar to microbial mat-related structures reported from the Paleoproterozoic Chorhat Sandstone preserved within the same,Vindhyan Basin.Extensive microscopic,ultramicroscopic,and geochemical studies address the apprehension that such bedding plane structures in carbonate rocks could be merely weathering products.Trapping,binding and stabilitization of sediment by microbial mats are all evident.Preferred pyritization along the inferred,predefined microbial mats confirmed on the basis of EPMA(Electron Probe Microanalysis) results,and the enhanced carbon content along these mats layers and within suspected mat chips associated with them,are revealing.Raman spectroscopy,indeed,evinces enhanced kerogen content within both mats and mat chips.Interestingly,these microbial mat layers are recognized selectively within the lower of the two tiers of the Bhander Limestone.The lagoonal carbonate of the lower tier of the Bhander Limestone is muddy and contains a substantial proportion of silt-sized quartz grains that possibly impeded stromatolite growth.Stromatolites abound in the wave agitated upper tier of the Bhander Limestone which is dominated by oosparite.This paper provides evidence that the delicate microbial mat-related structures reported so far only from siliciclastic rocks can also be recognized within carbonate formations,and hopes to stimulate the search for additional such features,more preferably within carbonates originated in shallow and quiet water. | Subir Sarkar Adrita Choudhuri Sunipa Mandal Patrick G. Eriksson | 2016 | Journal of Palaeogeography2016，5，3： | 3 |
| 3 | Performance evaluation and comparison of AODV and AOMDV显示文摘 | Biradar S R Koushik Majumder Subir Kumar Sarkar | 2010 | International Journal on Computer Science and Engineering2010，2，2： | 1 |
| 4 | Microbial mat mediated structures in the Ediacaran Sonia Sandstone, Rajasthan, India, and their implications for proterozoic sedimentation 显示文摘 | Subir Sarkar Pradip K Bose Pradip Samanta | 2007 | Geobiology2007，47，1： | 1 |
| 5 | Intermittency in the Slow Particle Emission During Hadron–Nucleus Interactions显示文摘 | Subir Sarkar T.D. Goswami Dipak Ghosh Argha Deb | 2003 | Czechoslovak Journal of Physics2003，，2： | 1 |
| 6 | Microbial mat-induced sedimentary structures in siliciclastic sediments: Examples from the 1.6 Ga Chorhat Sandstone, Vindhyan Supergroup, M.P., India显示文摘 | Subir Sarkar Santanu Banerjee Pradip Samanta Silambuchelvan Jeevankumar | 2006 | Journal of Earth System Science2006，，1： | 1 |
| 7 | Palaeogeography, palaeohydraulics and palaeoclimate of the Mio-Pliocene Siwalik Group, eastern India显示文摘South-southwestward palaeocurrent swerved to east-southeast and then broadly to southeast over the transition from alluvial fan to axial channel and then to the flood plain in the Mio-Pliocene foreland system within which the Siwalik Group depositd in Darjeeling-Jalpaiguri Districts, eastern India. Palaeocurrent pattern is found to be multi-modal on the fans, virtually unimodal on the axial channel zone and again multi-modal, more profoundly, on the flood plain. Coarse siliciclastic mass-flows were progressively eliminated and gave way to predominant bed-load transport downfan and the axial river, and then to suspensionload dominance in fine siliciclastics on the flood plain. Distal flood plain lacustrine sediment included most of the coals and the entire bulk of the dolomitic limestone. Further resolution in palaeogeography within the frame of aforementioned foursome facies associations is elicited in twenty-six distinctive facies altogether.Critical evaluation of chemical indices(CIA, CIW, ICV, PIA, as well as Rb/Sr ratio) for weathering and depleted δ18O values indicate a high precipitation rate. The contention is further corroborated by the high discharge rate calculated from cross-set thicknesses within the main channel deposits. Reconciliation of various relevant data sets collected or calculated from all known worksites along the entire 2000 km-long exposure belt of the Siwaliks along the Himalayan foothills reveal confluence of two tributaries, one from the west and the other from the east, close to the present study area before escaping onto the Indian plains. Channel parameters, channel-belt width and discharge thus attained maxima in the present study area. The precipitation rate and temperature increased eastward overall as a prelude to the modern trend in this regard. 13C enrichment indicates that the transition from C3 to C4 vegetation had already set in. | Sunipa Mandal Subir Sarkar Nivedita Chakraborty Pradip K.Bose | 2014 | Journal of Palaeogeography2014，3，3： | 0 |
| 8 | Palaeoenvironmental and biostratigraphic implications of microbial mat-related structures:Examples from the modern Gulf of Cambay and the Precambrian Vindhyan Basin,India显示文摘A stretch of the modern hypersaline coastal plain of the Gulf of Cambay was chosen to examine the distribution of the microbial mat-related structures(MRS) on siliciclastic sediments in the intertidal and supratidal zones.The abundance of MRS increases from the lower intertidal zone to the upper supratidal zone while the type of MRS records a systematic change.While the lower intertidal zone exhibits wrinkle structures,sieve-like surfaces and patchy ripples in places,the upper intertidal zone exhibits diverse MRS related to reduced current activity on the mat layer and intermittent exposure.MRS in the upper intertidal zone include wrinkle structures,sieve-like surfaces,gas domes,reticulated surfaces,multi-directional ripples,patchy ripples,rolled-up mat fragments,setulfs and occasional petee ridges and cracked mat surfaces.The lower supratidal zone is characterized by increased occurrence of petee ridges,gas domes and cracked mat surfaces compared to the upper intertidal zone.The upper supratidal zone is distinguished by the presence of abundant cracked mat surfaces,petee ridges,gas domes and wrinkle structures.The presence of cm-scale,disc-shaped microbial colonies(DMC) with a variety of internal structures is a unique feature of the Gulf of Cambay study area.While wrinkle structures occur in all the coastal zones,setulfs occur close to the boundary between the upper intertidal and lower supratidal zones.An attempt has been made to compare the distribution of MRS in this modern environment with those in the ~1.6 Ga Chorhat Sandstone of the Vindhyan Supergroup for high-resolution palaeoenvironmental interpretation.The upper part of the intertidal segment of the Chorhat Sandstone is distinguished from its lower part by the presence of abundant cracked mat surfaces,petee ridges and gas domes in the former,while wrinkle structures,Kinneyia,rolled-up mat fragments,patchy ripples and multi-directional ripples are equally abundant in both parts.The lower part of the intertidal segment of the Chorhat Sandstone is thus analogous to the upper intertidal zone of the modern Gulf of Cambay environment,while the upper part of the Chorhat intertidal segment reflects prolonged exposure close to the high tide line.The bottom-most part of the intertidal segment of the Chorhat Sandstone with fewer MRS corresponds to the lower intertidal zone at Cambay.Inferred disc-shaped microbial fossils within Vindhyan sandstones are analogous to the DMC found in the modern environment and these features do not have any biostratigraphic implication. | Santanu Banerjee Subir Sarkar Patrick G.Eriksson | 2014 | Journal of Palaeogeography2014，3，2： | 0 |
| 9 | Syn-sedimentary tectonics and facies analysis in a rift setting: Cretaceous Dalmiapuram Formation, Cauvery Basin, SE India显示文摘The Cretaceous(Albian-Cenomanian) Dalmiapuram Formation is one of the economically significant constituents in the hydrocarbon-producing Cauvery rift basin, SE India that opened up during the Late Jurassic e Early Cretaceous Gondwanaland fragmentation. The fossil-rich Dalmiapuram Formation,exposed at Ariyalur within the Pondicherry sub-basin of Cauvery Basin, rests in most places directly on the Archean basement and locally on the Lower Cretaceous(Barremian-Aptian) Basal Siliciclastic Formation. In the Dalmiapuram Formation, a facies association of tectonically-disturbed phase is sandwiched between two drastically quieter phases. The early syn-rift facies association(FA 1), records the first carbonate marine transgression within the basin, comprising a bar-lagoon system with occasionally storms affecting along the shore and a sheet-like non-recurrent biomicritic limestone bed on the shallow shelf that laterally grades into pyrite e glauconite-bearing dark-colored shale in the deeper shelf. Spectacular breccias together with varied kinds of mass-flow products comprise the syn-rift facies association(FA 2). While the breccias occur at the basin margin area, the latter extend in the deeper inland sea. Clast composition of the coarse clastics includes large, even block-sized limestone fragments and small fragments of granite and sandstone from the basement.Marl beds of quieter intervals between tectonic pulses occur in alternation with them. Faulted basal contact of the formation, and small grabens filled by multiple mass-flow packages bear the clear signature of the syntectonic activity localized contortions, slump folds, and pillow beds associated with mega slump/slide planes and joints, which corroborates this contention further. This phase of tectonic intervention is followed by another relatively quieter phase and accommodates the late syn-rift facies association(FA 3). A tidal bar-interbar shelf depositional system allowed a transgressive systems tract motif to grow eventually passing upwards into the Karai Shale Formation, whose contact with the Dalmiapuram Formation is gradational. | Nivedita Chakraborty Subir Sarkar | 2018 | Journal of Palaeogeography2018，7，2： | 0 |
| 10 | Overprint of neotectonism along the course of River Chel,North Bengal,India显示文摘This paper aims to unveil neotectonic imprints in topography,drainage and sediments in the46.25 km long course of the River Chel from its source down to its alluvial fan at the base of the Himalayan Mountain Front in the Darjeeling-Jalpaiguri districts of India.A semi-circular ridge delimits its primary catchment.Within confinement of this watershed basin the drainage pattern is composite being convergent along the periphery and divergent on a butte inside.All these geomorphic neotectonic imprints are accompanied by ramp and flat structures and spectacular mylonitization of rocks.High hypsometric index and convex shape of the hypsometric curve derived from the central near-straight course of the river between the primary catchment and the Main Frontal Thrust(MFT) also reflects tectonic youthfulness of the river course.It is well manifested also in widely variable stream index and stream gradient index ratios(SL/K) often exceeding 2.In response to neotectonism,this river course as a whole shifted westward between 1962 and 2007.Maximum reduction of the stream gradient on top of the MFT is eloquent enough about recent uplift of the thrust ridge.The high average slope gradient of canyon wall about 45.68° is well consistent with this uplift.Very low channel-width/valley-height ratio along the river further corroborates the uplift.The alluvial fan system of the River Chel is comprised of five morphogenetic fans stacked one above another with a tendency to shrink and shift progressively upslope.They differ from each other in terms of tilt,axial orientation,primary depositional surface gradient and convexity in transverse section and thus present a writ of ongoing tectonism.Progressive upward increase in the share of distal crystalline rocks in clast composition within alluvial fan package is a clear proxy for southerly advancement of the MFT.Concomitant increase in maximum clast size is in good agreement with sediment source uplift.All the five fans are,however,dormant now.Present-day River Chel deeply incises through all of them and suggests further basement uplift in the context of frequent evidences of neotectonism all around,although the role of climate remains uncertain in absence of adequate data. | Sunipa Mandal Subir Sarkar | 2016 | Journal of Palaeogeography2016，5，3： | 0 |
| 11 | Lakshanhatti stromatolite, India: Biogenic or abiogenic?显示文摘The extraordinary lateral continuity of isopachous stromatolite laminae in the-87 m-thick Mesoproterozoic Lakshanhatti Dolomite(India) evinces chemical precipitation.Fan-shaped crystals grown on lamina surfaces further corroborate this contention;growth of fan-shaped crystals under the overhanging stromatolite column-margin indicates direct carbonate precipitation from ambient waters.The fan-shaped crystals are stacked up,separated only by thin dark micritic laminae.In a relatively upper stratigraphic interval of the formation,lighter laminae characterized by a clotted texture and traversed by numerous winding tubular voids change gradually upwards into dark micritic laminae.Some sporadically distributed lenticular intraclastic beds also have the similarly dark micritic coatings.Clear carbonate cement crusts also occur between laminae and between successive dark micritic coats around intraclasts.Dull cathodoluminescence(CL) characterizes this cement as well as the cement lining within early diagenetic voids.In contrast,the laminae with clotted textures show dirty orange luminescence,while the dark micritic laminae and the dark micritic grain-coats display clear bright orange luminescence.Pyrite and its pseudomorphs are preferably concentrated along the dark micritic laminae.Carbon content in these dark micritic components,whether laminae or coats,is much higher than in the lighter components,exceeding what can be accounted for their CaMg(CO_3)_2 composition.A large part of this carbon is kerogen,plausibly biogenic.The dark components are,therefore,reasonably,though not unequivocally,assumed to be microbial mats.Degradation of the mats might have given rise to the light laminae with clotted textures.The fuzzy-margin tubes within the light laminae probably manifest the escape of gases generated during organic matter decomposition.Si-Al-rich terrigenous fines thinly draping the dark carbonaceous laminae was possibly the result of baffling and trapping of terrigenous fines by filamentous microbiota.Dark carbonaceous laminae encasing intraclasts was considered to be the result of binding and stabilization by microbiota.Spike-like growth of discrete laminae strongly suggests an occasional breakdown of colonial homeostasis of phototrophic microbiota.The microbial community thus appears to have played an active role in stromatolite-building in the Lakshanhatti Dolomite Member,even though the simultaneous existence of direct carbonate precipitates from sea water indicates a hybrid origin of these stromatolites.Resting on shelf sandstone and being capped by dark offshore shale,the Lakshanhatti Dolomite had been deposited in distal offshore,but not at the great depth,perhaps in an epeiric sea.Progressive deepening inhibited direct carbonate precipitation.δ^(13)C and δ^(18)O values suggest normal open marine salinity during deposition. | Adrita Choudhuri Subir Sarkar Wladyslaw Altermann Soumik Mukhopadhyay Pradip K.Bose | 2016 | Journal of Palaeogeography2016，5，3： | 0 |
| 12 | Ancient rip current records and their implications: an example from the Cretaceous Ukra Member, Kutch, India显示文摘Poorly-sorted conglomerate patches rich in granules or sturdy fossils or both, and reddish mud matrix within the interstices stand out amidst fine-grained siliciclastic shelf sediments of the trangressive systems tract(TST) of the Lower Cretaceous Ukra Member, Kutch Basin, India. The siliciclastic shelf sediments contrast the conglomerates with their remarkable lateral extension. The fossils belong to a low-diversity group of sedentary bivalves that can be traced into the shoreface facies assemblage. The shelf sandstones are almost always sculpted by wave structures,especially hummocky cross-stratification while textures in the conglomerates suggest that the sediment settling was generally from suspensions. Textural variations in conglomerates reflect an immediate variation in flow viscosity prior to the downloading. The current structures obtained from the conglomerates record offshoreward palaeocurrent, in contrast to the shore-parallel palaeocurrent in the TST. The hummocky cross-stratified(HCS) beds are interpreted as seasonal storm deposits, while the conglomerate patches are taken as rip current deposits induced by waves of much longer periods. The glauconite-rich shale that alternates with conglomerates is probable fair-weather products. The conglomerates could not be recognized either in the coarse-grained shoreface deposits occupying the lower part of the overall fining-upward TST or in the coarsening-upward and glauconite-depleted highstand systems tract(HST). In contrast to the TST, the HST is dominantly tide-imprinted, having shore-normal palaeocurrent direction. It appears that intensification of waves and weakening of tides during transgression favored strong rip currents generation, which had presumably caused severe damage to the sea coast and to the shell banks growing preferably at the necks of the rip current channels. Rapid lateral facies transitions in the shoreface deposits at the basal part of the TST suggest enhanced irregularity in the coastline, possibly because of the mega cusps indented upon it. Frequency and intensity of storms enhanced during periods of global warming caused the transgression of the Early Cretaceous Ukra Sea. | Subir Sarkar Amlan Koner | 2020 | Journal of Palaeogeography2020，9，2： | 0 |
| 13 | A two-dimensional analytical-model-based comparative threshold performance analysis of SOI-SON MOSFETs显示文摘A generalized threshold voltage model based on two-dimensional Poisson analysis has been developed for SOI/SON MOSFETs.Different short channel field effects,such as fringing fields,junction-induced lateral fields and substrate fields,are carefully investigated,and the related drain-induced barrier-lowering effects are incorporated in the analytical threshold voltage model.Through analytical model-based simulation,the threshold voltage roll-off and subthreshold slope for both structures are compared for different operational and structural parameter variations.Results of analytical simulation are compared with the results of the ATLAS 2D physics-based simulator for verification of the analytical model.The performance of an SON MOSFET is found to be significantly different from a conventional SOI MOSFET.The short channel effects are found to be reduced in an SON,thereby resulting in a lower threshold voltage roll-off and a smaller subthreshold slope.This type of analysis is quite useful to figure out the performance improvement of SON over SOI structures for next generation short channel MOS devices. | Sanjoy Deb Saptarsi Ghosh N Basanta Singh A K De Subir Kumar Sarkar | 2011 | Journal of Semiconductors2011，32，10： | 0 |
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