Chandan Chakraborty

• Ĺkl
• Indian Statistical Institute

This paper presents the spatio-temporal variations in bed elevations and the near-bed turbulence statistics over the deformed bed generated around the submerged cylindrical piers embedded vertically on loose sediment bed at a constant flow discharge. Experiments were carried out in a laboratory flume for three blockage ratios in the range of 0.04–0...

This work presents a study of spatiotemporal changes of scour-holes around sand embedded submerged circular and non-circular cylinders with associated turbulence properties and aims at analyzing the contribution of each quadrant event to the Reynolds shear stress. Experiments were carried out using submerged circular, elliptical, square and triangu...

This paper studies the spatial and temporal bed changes due to submerged cylindrical piers at a constant flow discharge. Experiments were carried out with three cylinder diameters of 4, 5 and 6 cm placed vertically at the centerline of the flume separately, possessing a common submergence ratio of 0.6. Instantaneous sand bed elevations at selected...

The Matiali fan is a coarse-grained, small alluvial fan in the eastern Himalayan foothills. It co-exists side by side with the large Tista megafan and other Quaternary fluvial deposits, and has been affected by a number of young thrust faults. It is generally believed that tectonics is the main control in the deposition of these proximal fan–terrac...

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Flume experiments were carried out to study the turbulence and its impact on suspension and segregation of grain-sizes under unidirectional flow conditions over the sand-gravel mixture bed. The components of fluid velocity with fluctuations were measured vertically using 3-D Micro-acoustic Doppler velocimeter (ADV). The theoretical models for veloc...

The Late Palaeozoic, glaciomarine Talchir Formation in the Satpura Gondwana basin, central India hosts sparse to profuse trace fossils of various kinds, although sporadically. Among the three principal depositional systems that gave rise to the Talchir succession, deposits of the ice-contact fan delta system and the glacial outwash braidplain delta...

Non-cylindrical sheath folds often develop by the accentuation of inherent geometrical irregularities along the hinge line during progressive deformation. This paper presents an analysis of the growth of such non-cylindrical folds in pure shear as a function of a non-dimensional initial irregularity factor zo (zo¼�log10 [Ao/Wo], where Ao and Wo are...

We performed simple shear experiments to investigate the development of low- (R1) and high- (R2) angle Riedel shear localization in wet sand–talc mixtures with varying volume proportions. With increasing talc content, the granular medium underwent rheological changes, showing larger homogeneous ductile strains prior to brittle failure. Talc-rich mo...

Using analogue experiments on polymethylmethaacrylate (PMMA) models, we investigated the process of deformation localization at the tips of preexisting planar shear cracks. Experiments show that this can take place in any of the following four principal mechanisms. Mechanism A: Brittle deformation is the dominant process and forms a pair of long te...

The Talchir Formation of Permian age is the lowermost lithostratigraphic unit of the Indian Gondwana successions preserving a record of the Late Paleozoic glaciation that affected the whole Gondwanaland. The formation unconformably overlies the Precambrian basement in all the Gondwana basins of India, and marks initiation of sedimentation after a l...

The invasion of maternal decidua and uterine spiral arteries by a trophoblast subpopulation called extravillous trophoblast (EVT) is essential for the establishment of a normal placenta and an adequate blood flow toward the fetus. Derangements in these processes underlie pregnancy-related diseases like preeclampsia and intrauterine growth restricti...

Prostaglandin (PG) E(2) may regulate invasiveness of human placenta because we previously reported stimulation of migration of placental trophoblasts by PGE(2) acting through PGE receptor (EP)-1 and activating calpain. RhoA GTPase and its important effector Rho kinase (ROCK) have also been previously shown to regulate trophoblast migration. Using i...

Using analogue experiments we investigate how far the extensional strain estimated from an array of rigid boudins tracks the bulk extension of the host rock. The quadratic elongations of boudinaged objects (λb) were compared with the corresponding bulk quadratic elongations in physical models (λm) both for pure and simple shear. A noticeable differ...

In the Precambrian Singhbhum Craton of eastern India, newer dolerite dikes occur profusely with varying outcrop lengths. We have analysed the nature of their length-size and orientation distributions in relation to the theory of fractals. Two orientational sets of dikes (NW–SE and NE–SW) are present. Both the sets show strongly non-power-law size d...

Two questions are raised with regard to interpretation of tidal bundles. 1. Does the thick-thin alternation of foreset laminae generally represent semi-diurnal tide? 2. Is it a valid inference that the packages of mud-draped foresets, which occur in alternation with packages of foresets devoid of mud-drapes in a cross-set, denote neap periods? Unde...

The features of the Vindhyan succession clearly indicate a vast intracratonic basin that remained within tens of meters of sea level throughout its lifetime. Apparently, shallow water condition was maintained over a large area for a long period of time suggesting that the sub-Vindhyan lithosphere suffered subsidence over a larger area producing a w...

The Gondwana basins of peninsular India are traditionally considered as extensional-rift basins due to the overwhelming evidence of fault-controlled synsedimentary subsidence. These basins indeed originated under a bulk extensional tectonic regime, due to failure of the attenuated crust along pre-existing zones of weakness inherited from Precambria...

Many rocks are representative of inclusion–matrix systems where rigid inclusions float on a ductile matrix. The geological analogues of such inclusion–matrix systems are theoretically modelled with the help of Jeffery's (1922) theory. In recent years, there have been a number of reinvestigations on the rotational motion of rigid inclusions to accou...

Nine different types of cross-stratified packages from the coal-bearing, deltaic succession of the Barakar Formation (Permian) of the Satpura Gondwana Basin, central India, are described. The deposits are characterized by periodic mudstone drapes, reactivation surfaces including all other features suggestive of deposition from periodically unsteady...

This paper deals with a theoretical analysis of extensional fissures around spherical rigid inclusions hosted in a ductile matrix undergoing bulk shear. The analysis shows that the mechanical interaction of inclusions is a function of the inclusion concentration a/b (2a and 2b are the inclusion diameter and mean inter-inclusion distance, respective...

The paper describes micro-scale folds within a narrow ductile shear zone of the Peninsular Gneissic Complex, South India. The characteristics of the folds indicate that they have formed by buckling on the mylonitic foliation parallel to the C fabric. This raises the question of how a buckling instability could develop on the mylonitic foliation, as...

The coal-bearing Barakar succession of the Satpura basin is typical of the Gondwanan coal basins of peninsular India, in that it has previously been interpreted as continental in origin. The succession comprises three main facies associations, which are documented within this paper. Medium- to fine-grained muddy sandstone deposits of 5-75 m thickne...

The Gondwana successions (1–4 km thick) of peninsular India accumulated in a number of discrete basins during Permo-Triassic period. The basins are typically bounded by faults that developed along Precambrian lineaments during deposition, as well as affected by intrabasinal faults indicating fault-controlled synsedimentary subsidence. The patterns...

Aberrant upregulation of COX-2 enzyme resulting in accumulation of PGE2 in a cancer cell environment is a marker for progression of many cancers, including breast cancer. Four subtypes of cell surface receptors (EP1, EP2, EP3, and EP4), which are coupled with different G-proteins, mediate PGE2 actions. Since migration is an essential step in invasi...

The Permian Barakar Formation in the Mohpani coalfield, Satpura Gondwana basin, is composed of three broad lithologies that occur repetitively and are iterdigitated: (1) several metres thick coarse- to medium-grained sandstone bodies with scoured bases, (2) 5-20 m thick medium- to fine-grained sandstone bodies and (3) 5-20 m thick mudstone-dominate...

Impaired trophoblast invasiveness and spiral arterial remodelling, which results in poor placental perfusion during early pregnancy, is believed to cause fetal injury and growth retardation, and also endothelial cell activation/dysfunction in a susceptible mother, leading to clinical manifestations of pre-eclampsia. This article briefly reviews the...

Impaired trophoblast invasiveness and spiral arterial remodelling, which results in poor placental perfusion during early pregnancy, is believed to cause fetal injury and growth retardation, and also endothelial cell activation/dysfunction in a susceptible mother, leading to clinical manifestations of pre-eclampsia. This article briefly reviews the...

A highly proliferative, migratory and invasive subpopulation of human placental trophoblasts, known as extravillous trophoblasts (EVT), invades the uterus and its vasculature, to establish an adequate exchange of key molecules between the maternal and fetal circulation. Our earlier studies provided evidence for a positive regulation of migration/in...

During deformation of an inclusion-matrix system, the velocity fields around individual inclusions mutually interfere with one another. Such interacting inclusions rotate at slower rates than non-interacting, single inclusions. This paper presents a theoretical model that describes the flow pattern of matrix (viscous) material around interacting ri...

Intragranular fracturing of feldspar porphyroclasts in granite mylonites of a ductile shear zone has led to development of diverse types of pull-apart and bookshelf structures. Porphyroclasts with centrally located fractures show pull-aparts with parallel walls (Type 1), whereas those with off-centered fractures display pull-aparts with both parall...

Rocks that are mechanically heterogeneous due to the presence of stiff or rigid inclusions floating in a ductile matrix, commonly show a variety of micro- to macro-scale structures developing under the influence of heterogeneous flow field in the neighbourhood of the inclusions. It is of fundamental importance to apprehend the nature of strain hete...

The human placenta is an invasive structure in which highly proliferative, migratory, and invasive extravillous trophoblast (EVT) cells migrate and invade the uterus and its vasculature. Using in vitro propagated normal first-trimester EVT cells and immortalized EVT cells, which share all of the phenotypic and functional characteristics of the norm...

Tumorigenesis results from genetic alterations that occur in a stepwise manner giving rise to cells with increasingly cancer-like characteristics. We used in vitro propagated first trimester human extravillous trophoblast (EVT) cells to identify genetic changes responsible for the transition of the EVT from a normal to premalignant stage. The model...

This paper presents a theoretical model based on strain energy and work rate calculations that evaluates the possible degrees of flattening in finite, ductile shear zones with rigid and deformable walls under constant volume conditions. The principal parameters governing the ratio of bulk flattening and shear rates (Sr=ϵ̇b/γ̇b) in shear zones with...

The Bhander Group, the uppermost stratigraphic unit of the Proterozoic Vindhyan Supergroup in Son Valley, exhibits in its upper part a 550 m thick, muddy siliciclastic succession characterized by features indicative of deposition in a wave-affected coastal, lagoon–tidal flat environment suffering repeated submergence and emergence. The basic archit...

Plane strain deformation experiments were performed on elliptical inclusions of cohesive sand embedded within a slab of pitch, with the aim of investigating the mode of fracturing of brittle inclusions within a ductile matrix. Under pure and simple shear, the inclusions failed in three different modes: tensile fracturing (Mode 1), shear fracturing...

A 40-m-thick eolian sand sheet deposit characterizes the upper part of the Proterozoic Shikaoda Formation near Hosangabad. It sharply overlies shoreface deposits and comprises wind-ripple strata (∼ 50%), adhesion strata (∼ 17%) and subaqueous strata (∼ 33%). Each stratification type defines strata packages tens of centimeters thick and few meters w...

The Denwa Formation (3̃00m thick) representing a part of the unconformity bounded Triassic (Pachmarhi-Denwa) succession of the Satpura Gondwana basin, is characterized by two different fluvial styles marked by contrasting architectural elements within the alluvial system. These fluvial styles are distinct from the underlying Pachmarhi Formation rep...

This paper presents a generalized theoretical approach towards two-dimensional numerical modeling of the mantle geometry of inequant porphyroclasts of varying shapes within a Newtonian matrix during progressive, general type of bulk deformation. The analysis takes into account the effects of synkinematic size reduction of the porphyroclast with con...

This paper presents a dynamic analysis of boudinage in multilayers of alternate brittle and ductile layers under layer-normal compression. Based on the mode of fracturing of individual brittle layers, boudinage is classified into three types: tensile fracture boudinage (Type 1), shear fracture boudinage (Type 2a) and extensional shear fracture boud...

Extravillous trophoblast (EVT) cells of the human placenta proliferate, migrate and invade the decidua and its vasculature. By utilizing in vitro propagated normal first trimester human EVT cells in functional assays, we have shown that proliferative, migratory and invasive functions of these cells are stringently regulated in situ by numerous grow...

Detailed field studies on the regional structure of the Vindhyan strata in Son valley reveal that the Vindhyan strata define a broad syncline with a gently plunging (westerly), mildly curved fold axis (average trend ENE-WSW) and a southerly inclined axial plane. The southern limb of the broad syncline shows several smaller folds which are conspicuo...

The carbon and oxygen isotopic compositions of the minerals of carbonate rocks depend on the composition of the precipitating water and the temperature of precipitation. The carbon isotopes suffer little fractionation during precipitation of carbonate minerals and their carbon isotopic composition reflects that of the precipitating water. On the ot...

The Vindhyan basin of central peninsular India contains strata ranging in age from 1400 m.y. to 550 m.y. It is thus likely that the Precambrian-Cambrian boundary interval may be present in the upper part of the Vindhyan succession. In order to locate the boundary interval in the Vindhyan basin, carbon isotopic analyses of the carbonate horizons of...

The transitional ripples, referred to as washed-out ripples, are symmetrical to slightly asymmetrical bed forms with a convex-up profile and low-angle foresets in the direction of the main flow. The changes in morphology and migration rate with increasing flow velocity from linguoid ripples to washed-out ripples result from a spatial shift of the l...

The Deoland and Arangi Formations of the Semri Group of the Vindhyan Supergroup, comprising a 200-300 m thick sequence of conglomerate, sandstone, shale, occur as continuous E-W trending band along the southern periphery of the Vindhyan basin in the Son Valley. On the basis of lithology, sedimentary structures and texture, the sequence can be sub-d...

The Dhandraul Sandstone of the Proterozoic Vindhyan Supergroup, India, is a basinwide, 30-150 m thick sandstone unit representing deposition dominantly in a vast subaerial braidplain (upper part) and braidplain delta (lower part). Sandwiched between the sandstone sheets of the subaerial braidplain there occurs a 5-10 m thick, persistent sandstone h...

The orientations of elongate gutter casts occurring in inner shelf storm deposits of the Proterozoic Bijaygarh Shale Formation, India reveal a modal population oriented roughly parallel to the average trend of the associated wave ripples. Assuming that the wave ripple trend approximately represents the orientation of the contemporary shoreline, the...

The excellently preserved metre-scale, linear bedforms in an aeolian horizon of the Proterozoic Dhandraul Quartzite, India, show oppositely dipping strata arranged in a zigzag pattern. The strata are dominantly of translatent type, deposited by along-crest migrating ripples preserved on the flanks of dunes. The bedforms thus may be interpreted in a...

In two Proterozoic sandstones of the Indian shield cross-stratification and cross-lamination are observed to grade continuously into parallel laminations often bearing parting lineations. These are interpreted as having resulted from a gradual transition from ripple/dune to upper stage plane bed structures. During the transition the inclination of...

The shallow-marine, turbidite-like storm beds of the Proterozoic Kaimur Formation exhibit intrabed rhythmic vertical variations in sedimentary structure and texture attributable to different patterns of velocity pulsations within an event of storm current deposition.The alternate repetition of parallel-laminated (Sb) and ripple cross-laminated (Sc)...

A Proterozoic sandstone sequence belonging to the Lower Quartzite Formation of Vindhyan Supergroup, India, reveals the internal structures of near-symmetrical subtidal sandwaves formed in an area of strong tidal currents, occasionally interfered by wind-induced currents of varying magnitude.Internally, the sandwaves show decimetre-scale, herring-bo...

This paper determines, using simple mathematical models, maps of strain fields and foliation trajectories in the neighbourhood of plutonic bodies intruded into a region before, during, and after a lateral compression. The analyses reveal contrasting features for the three cases, which may be useful in distinguishing pre-, syn-, and post-tectonic pl...

Slickenlines record on a fault surface the nature of relative movement of the faulted blocks. An assemblage of straight slickenlines indicates linear-translational fault motion. Curved slickenlines, on the other hand, may arise either due to rotational-translational fault motion or due to fault motions where the translation direction changes contin...

The periodic occurrence of paleosols along cross-stratifications are widely known in Pleistocene eolian dunes, particularly in coastal ones, and these are believed to have formed during pauses in the migration of the dunes over thousands of years. Protosols with the same relationship have been observed in subrecent dunes at Bakkhali beach, West Ben...