Partha Chakraborty - Academia.edu (original) (raw)

Papers by Partha Chakraborty

The Indian Journal of Pediatrics, 2007

... Partha Pratim Chakraborty, Asish Kumar Basu, Sanjay Kumar Mandal and Dipanjan Bandyopadhyay D... more ... Partha Pratim Chakraborty, Asish Kumar Basu, Sanjay Kumar Mandal and Dipanjan Bandyopadhyay Department of Medicine, Medical College, Kolkata, 88, College Street, Kolkata ... 3. Schaefer GB, Rosenbloom AL, Guevara-Aguirre J, Campbell, EA, Ullrich F, Patil K, Frias JL. ...

Precambrian Research, 2008

Outcrop-based sequence analysis across the transition from the Chaporadih to the Kansapathar Form... more Outcrop-based sequence analysis across the transition from the Chaporadih to the Kansapathar Formation of Chandarpur Group, Chattisgarh Supergroup, central India, resolved a long-standing uncertainty on occurrence of depositional discontinuity through undoubted identification of a forced regressive wedge and associated intraformational unconformity. Process-based facies analysis identified eleven different facies types that are grouped into five different facies associations. Paleoenvironments range from shelf, shoreface, foreshore and beach, tide-influenced estuary and delta. Bounded between the 'Surface of marine erosion' at its base and subaerial unconformity (marked by paleosol development) at its top, the coarse grained wedges of shoreface sandstone is interpreted as forced regressive in origin. The basinward downstepping of two such regressive wedges bears evidence for lowering of wavebase in connection with relative fall in sea level.

Gondwana Research, 2003

Bed thickness data of two turbidite sections viz., Corbyns Cove section, South Andaman and Kalipu... more Bed thickness data of two turbidite sections viz., Corbyns Cove section, South Andaman and Kalipur section, North Andaman those belong to Oligocene Andaman Flysch Group, a forearc submarine fan system, were assessed for facies clustering employing Hurst statistics. Both the sections show Hurst phenomenon and reveal clustering in terms of thick and thin beds. Forcing behind event (bed) depositions in either of the studied sections was assessed statistically and inferred to be non-random and with cyclicities of irregular physical length. The inferred paleogeography through Hurst criteria though worked well for distal fan setting i.e., basin floor sheet sandstones of Corbyns Cove section, its unequivocal application in proximal fan deposits remains to be tested. The mismatch in paleogeographic interpretation between Hurst test result (lobe-interlobe) and field observation (channel-levee) for the inner fan deposit is explained through differential facies stacking between fans grow in sea-level lowstand and highstand. Lower bed amalgamation, poor sand to mud ratio and subordinately present thick event deposits may be the result of active growth of Andaman Flysch fan in sea level highstand and expressed in lower Hurst K value for inner fan channel-levee association (Kalipur section) compared to many of the channel-levee deposits of lowstand fan systems observed world over.

Journal of Asian Earth Sciences, 2002

The bed thickness distribution of two turbidite successions in the Oligocene Andaman Flysch Group... more The bed thickness distribution of two turbidite successions in the Oligocene Andaman Flysch Group, India, which differ in terms of their paleogeography and sediment supply, has been assessed statistically. The purpose was to evaluate depositional cyclicity using the nonparametric Waldron test, and also to assess possible environmental control on the bed thickness -magnitude distribution. Both sections reveal a positively skewed distribution in bed thickness patterns. The Z value obtained through Waldron's test failed to reject the null hypothesis of randomness and thus discards a cyclic pattern. Juxtaposition of sediments of different proximalities in an elongated forearc fan complex is the possible cause for this absence of cyclicity.

Carbonates and Evaporites, 1998

The late Proterozoic Bhander Limestone in Son valley, India developed in a very shallow epeiric r... more The late Proterozoic Bhander Limestone in Son valley, India developed in a very shallow epeiric ramp setting that partially emerged time and again above the sea surface. Landward extensive karstified sediments attest to three events of considerable regressions.The resultant intraformational unconformities are characterized by C12-enrichment in the scale of their Phanerozoic equivalents. Early diagenetic void-fill cements in these karsts are even more enriched. These sediments and cements in relatively seaward part show relatively lesser degree of enrichment, possibly because of shorter duration of exposure. The late Proterozoic meteoric water seems to have turned rich in C12 with contribution from land plants similar to Phanerozoic meteoric water.

Gondwana Research, 2001

Detailed facies analysis in the upper Eocene—Oligocene Andaman Flysch Group reveals fourteen diff... more Detailed facies analysis in the upper Eocene—Oligocene Andaman Flysch Group reveals fourteen different facies, grouped into three different associations. These facies associations represent two anatomical divisions of a submarine fan, viz. inner fan and depositional lobe in middle fan. Paleocurrent pattern, high percentage of quartz in the sandstones and outer arc derived clasts in the inner fan channel conglomerates suggest dual sediment supply in this fan. A longitudinal geometry of the basin has been inferred where juxtaposition of sediments of different proximality deterred development of any definite sequence pattern. A tectonically induced active sediment supply in a rising sea level stand is thought to be responsible for development of the fan.

The Indian Journal of Pediatrics, 1997

A total of 540 women (including 70 pregnant cases) of child bearing age with bad obstetrical hist... more A total of 540 women (including 70 pregnant cases) of child bearing age with bad obstetrical history were tested serologically for anti-toxoplasma antibody using microlatex agglutination test. Forty two women including 5 cases of pregnancy were found to be seropositive in a titre of 1:32 or more. Maximum prevalence (10.2%) and highest titer of anti-toxoplasma antibodies were observed in women of 35-42 years age group. The overall prevalence of toxoplasmosis in these women was 7.7%, whereas it was 7.1% in pregnant women. Further studies are needed to estimate the exact rate of prevalence of infection. Of the 70 pregnant women, 5 were seropositive and two of them acquired infection during pregnancy which was detected by IgM immunosorbent assay. Seropositive pregnant women were treated using combined regimen of sulfadiazine and pyrimethamine. Four infected women with pregnancy were followed up and one did not turn up subsequently. There was spontaneous abortion in one case and in 3 other cases full term normal babies were delivered. Incidence of toxoplasmosis in women is low because of infrequent and uncommon practices of ingesting undercooked or uncooked food stuff specially meat by a substantial number of the population surveyed.

Brazilian Journal of Infectious Diseases, 2007

Cytomegalovirus (CMV) infection is a relatively late complication of AIDS. Like other viruses con... more Cytomegalovirus (CMV) infection is a relatively late complication of AIDS. Like other viruses contributing to co-morbidity of HIV infection, cytomegalovirus has the propensity to cause multiorgan involvement. We report the case of a 34-year-old seropositive man who presented with bilateral lower limb weakness and symptomatic pallor. He was already on antiretroviral drugs for a month prior to presentation. Detailed clinical examination and laboratory investigations revealed cytomegalovirus polyradiculoneuropathy associated with bone marrow dysplasia. Dysplasia of haematopoeitic cell lines occurs in 30% to 70% of HIV infected patients, and is often indistinguishable from myelodysplastic syndrome. However, in our case, the bone marrow picture reverted back to normal with treatment of the CMV infection, pointing to a possible role of CMV as the causative agent of bone marrow dysplasia. Moreover, CMV has been incriminated as a pathogen producing the immune reconstitution inflammatory syndrome. The onset of the disease in our case one month after initiation of HAART strongly raises the possibility of this being a case of CMV related IRIS. This is the first reported case where IRIS has presented with CMV polyradiculoneuropathy and bone marrow dysplasia. We would like to highlight that in today&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s era of HIV care, clinicians should be aware of the possibility of multiorgan involvement by CMV, for appropriate management of this disease in the background of AIDS.

Geoscience Frontiers, 2012

The disastrous M w 9.3 (seismic moment 1.0 Â 10 30 dyn/cm) earthquake that struck northwest Sumat... more The disastrous M w 9.3 (seismic moment 1.0 Â 10 30 dyn/cm) earthquake that struck northwest Sumatra on 26 December 2004 and triggered w30 m high tsunami has rejuvenated the quest for identifying the forcing behind subduction related earthquakes around the world. Studies reveal that the strongest part (elastic core) of the oceanic lithosphere lie between 20 and 60 km depth beneath the upper (w7 km thick) crustal layer, and compressive stress of GPa order is required to fail the rock-layers within the core zone. Here we present evidences in favor of an intraplate origin of mega-earthquakes right within the strong core part (at the interface of semi-brittle and brittle zone), and propose an alternate model exploring the flexing zone of the descending lithosphere as the nodal area for major stress accumulation. We believe that at high confining pressure and elevated temperature, unidirectional cyclic compressive stress loading in the flexing zone results in an increase of material yield strength through strain hardening, which transforms the rheology of the layer from semi-brittle to near-brittle state. The increased compressive stress field coupled with upward migration of the neutral surface (of zero stress fields) under noncoaxial deformation triggers shear crack. The growth of the shear crack is initially confined in the Production and hosting by Elsevier available at www.sciencedirect.com China University of Geosciences (Beijing) GEOSCIENCE FRONTIERS journal homepage: www.elsevier.com/locate/gsf GEOSCIENCE FRONTIERS 3(4) (2012) 473e481

Indian Journal of Surgery, 2011

The Indian Journal of Pediatrics, 2009

Journal of Geology, 2009

Time bracketing of thousands-of-meters-thick, unmetamorphosed, fossil-free sedimentary succession... more Time bracketing of thousands-of-meters-thick, unmetamorphosed, fossil-free sedimentary successions is a long-standing challenge in Indian Proterozoic stratigraphy. Limited geochronologic ages from either the basal or the upper part of the successions prevent workers from ...

Sedimentary Geology, 1994

The Proterozoic Upper Rewa Sandstone in central India, is generally interpreted as entirely marin... more The Proterozoic Upper Rewa Sandstone in central India, is generally interpreted as entirely marine. A detailed study in Maihar, Madhya Pradesh, however, reveals upward transition from marine to fluvial through a mixed facies association also bearing eolian imprints. Facies associations differ in stratal geometry and arrangement, palaeocurrent direction and pattern as well as in grain size and sorting.

Precambrian Research, 2004

Outcrop-based study of high-resolution sequence stratigraphy (intra-and interfacies sedimentologi... more Outcrop-based study of high-resolution sequence stratigraphy (intra-and interfacies sedimentologic clues) in Neoproterozoic Lakheri Limestone, Central India, reveals definite signals for relative sea level variations and paleogeographic shifts between shallow beach-shoreface and distal-shelf. Depositional cycles in this carbonate formation are bound by unconformities or disconformities of ravinement origin. On outcrop scale the unconformities are sharp and irregular and marked by definite depletion in ␦ 13 C values of limestones. In the study area the entire Lakheri Limestone succession is divided into four depositional 'sequences' bound by type I unconformities. Different variants of system tracts (transgressive, highstand and lowstand), resulting from differences in paleogeographic locations, basin floor physiography and variable rates of relative sea level change, constitute the sequences developed on Lakheri carbonate ramp. A possible forcing of intrabasinal tectonics (both extension and compression) on meter to tens of meter thick Lakheri 'sequences' is inferred.

Journal of Earth System Science, 2006

The Rewa Group of the Vindhyan Supergroup in the Son valley begins with a thick (∼ 200 m) dominan... more The Rewa Group of the Vindhyan Supergroup in the Son valley begins with a thick (∼ 200 m) dominantly shaly, shelfal succession, occurring between the Dhandraul Formation of the Kaimur Group (fluvial sandstone) below and Drammondganj Formation of the Rewa Group (marginal marine sandstone) above. Such a stratigraphic disposition indicates a sharp rise in relative sea level at the onset of Rewa sedimentation, inducing a shelfal depth to the Vindhyan basin. However, a number of wedge-shaped, sandstone/conglomerate bodies (maximum thickness 23.5 m) occur at multiple stratigraphic levels within the aforesaid deeper water shale succession, which appear to be of much shallow water origin representing regressive deposits. Though these bodies do not define a single physically continuous unit, either vertically or laterally, they are still designated by a single term 'Asan Sandstone' in the literature. On the other hand, the encasing shelfal shales are termed as Panna and Jhiri Shales, in accordance with their occurrence below or above the so-called 'Asan Sandstone'. The present study reveals that in different sections spread over the Son valley, there are several discrete regressive wedges occurring vertically, and their depositional environment is also variable, ranging between braided fluvial, shoreface fan and braid delta. The features common to most of the regressive coarser clastic bodies are:

Journal of Earth System Science, 2013

The Sonia Sandstone of Proterozoic Jodhpur Group, Marwar Supergroup, exposed around the Sursagar ... more The Sonia Sandstone of Proterozoic Jodhpur Group, Marwar Supergroup, exposed around the Sursagar dam area of Jodhpur town, Rajasthan exposes two varieties of nodular features, often spectacular in shape and size. On the basis of mode of occurrence (intra-or interbed) and stratal involvement (single or multiple) the features are classified as Type I and II. From granulometric and microscopic (optical and scanning electron) studies carried out on sandstones from the nodules and their host sandstones, geochemical analysis (SEM-EDAX) of intragranular cement present within Type I nodules, and appreciation of control of associated fracture system within Type II nodules, it is proposed that the two types of nodules vary in their formative mechanism and stage of formation. While Type I nodules are identified as product of processes operative at the early diagenetic, pre-lithification stage, the Type II nodules are undoubtedly the result of post-lithification origin triggered by formation of fracture system. Here we propose generation of vapour pressure (not exceeding the overlying hydrostatic pressure) by decay of thin, laterally impersistent organic mat as the causal factor for intrabed nodule (Type I) formation, which forced rarefication of local grain packing vis-a-vis early diagenetic silica cementation. The study warrants necessity of more studies on nodules to understand possible roles of organic matter and bedtransgressive fracture systems in their formation, going beyond the generalised secondary mineralisation hypothesis. may guide in improved management of aquifers and

Journal of Clinical Neuroscience, 2007

Ossified ligamentum flavum (OLF) is being appreciated as an important cause of thoracic myeloradi... more Ossified ligamentum flavum (OLF) is being appreciated as an important cause of thoracic myeloradiculopathy. However, despite numerous epidemiological and basic science studies, the pathogenesis of OLF has not been conclusively established. Ossification and symptom development are significantly more frequent in the Japanese population, therefore supporting a genetic predilection for the disease process. We present an unusual case of OLF in a patient from a low-risk genetic background (Chinese), exposed in youth to a lifestyle and diet from a high-risk population (Japanese). Based on our case report, we support the view that dietary habits may constitute an independent risk factor for OLF and ossification of the posterior longitudinal ligament.

Journal of Asian Earth Sciences, 2010

... 2003] and [Chakraborty and Paul, 2005]), transitional (shoreface, foreshore and beach, tidal ... more ... 2003] and [Chakraborty and Paul, 2005]), transitional (shoreface, foreshore and beach, tidal estuary and delta; [Patranabis-Deb and Chaudhuri, 2002] and [Chakraborty and Paul, 2008]); shallow marine (storm-dominated, intertidal and subtidal, occasionally lagoonal; [Datta et al ...

Journal of Asian Earth Sciences, 2007

Clues to the understanding of intra-and inter-plate variations in strength or stress state of the... more Clues to the understanding of intra-and inter-plate variations in strength or stress state of the crust can be achieved through different lines of evidence and their mutual relationships. Among these parameters Bouguer gravity anomalies and seismic b-values have been widely accepted over several decades for evaluating the crustal character and stress regime. The present study attempts a multivariate analysis for the Shillong Plateau using the Bouguer gravity anomaly and the earthquake database, and establishes a causal relationship between these parameters. Four seismic zones (Zones I-IV), with widely varying b-values, are delineated and an excellent correlation between the seismic b-value and the Bouguer gravity anomaly has been established for the plateau. Low b-values characterize the southwestern part (Zone IV) and a zone (Zone III) of intermediate b-values separates the eastern and western parts of the plateau (Zones I and II) which have high b-values. Positive Bouguer anomaly values as high as +40 mgal, a steep gradient in the Bouguer anomaly map and low b-values in the southwestern part of the plateau are interpreted as indicating a thinner crustal root, uplifted Moho and higher concentration of stress. In comparison, the negative Bouguer anomaly values, flat regional gradient in the Bouguer anomaly map and intermediate to high b-values in the northern part of the plateau are consistent with a comparatively thicker crustal root and lower concentration of stress, with intermittent dissipation of energy through earthquake shocks. Further, depth wise variation in the b-value for different seismic zones, delineated under this study, allowed an appreciation of intra-plateau variation in crustal thickness from 30kminitssouthernpartto30 km in its southern part to 30kminitssouthernpartto38 km in the northern part. The high b-values associated with the depth, coinciding with lower crust, indicate that the Shillong Plateau is supported by a strong lithosphere.

Island Arc, 2009

The Andaman-Sumatra margin displays a unique set-up of extensional subduction-accretion complexes... more The Andaman-Sumatra margin displays a unique set-up of extensional subduction-accretion complexes, which are the Java Trench, a tectonic (outer arc) prism, a sliver plate, a forearc, oceanic rises, inner-arc volcanoes, and an extensional back-arc with active spreading. Existing knowledge is reviewed in this paper, and some new data on the surface and subsurface signatures for operative geotectonics of this margin is analyzed. Subduction-related deformation along the trench has been operating either continuously or intermittently since the Cretaceous. The oblique subduction has initiated strike-slip motion in the northern Sumatra-Andaman sector, and has formed a sliver plate between the subduction zone and a complex, right-lateral fault system. The sliver fault, initiated in the Eocene, extended through the outer-arc ridge offshore from Sumatra, and continued through the Andaman Sea connecting the Sagaing Fault in the north. Dominance of regional plate dynamics over simple subduction-related accretionary processes led to the development and evolution of sedimentary basins of widely varied tectonic character along this margin. A number of north-south-trending dismembered ophiolite slices of Cretaceous age, occurring at different structural levels with Eocene trench-slope sediments, were uplifted and emplaced by a series of east-dipping thrusts to shape the outer-arc prism. North-south and east-west strike-slip faults controlled the subsidence, resulting in the development of a forearc basins and record Oligocene to Miocene-Pliocene sedimentation within mixed siliciclastic-carbonate systems. The opening of the Andaman Sea back-arc occurred in two phases: an early (~11 Ma) stretching and rifting, followed by spreading since 4-5 Ma. The history of inner-arc volcanic activity in the Andaman region extends to the early Miocene, and since the Miocene arc volcanism has been associated with an evolution from felsic to basaltic composition.