Facies analysis of Pleistocene limestones from Neil West Coast Formation,Neil Island,Ritchie’s archipelago of South Andaman,India     

Arindam Chakraborty  Amit K. Ghosh  Abhijit Mazumder 《Journal of the Geological Society of India》2017,90(4):428-436

Petrographic thin section analysis of the samples collected from the type section of Neil West Coast Formation, situated in the west coast of Neil Island yielded moderately preserved coralline red algae, benthic and planktic foraminifers, coral fragments, echinoid spines and gastropod shells. The coralline red algae are represented by both non-geniculate and geniculate forms. The non-geniculate forms belong to melobesids, lithophylloids and mastophoroides. The geniculate forms are represented by species of Amphiroa, Corallina, and Jania. However, the diversity and abundance of coralline algal forms are less in comparison to the benthic foraminifers those are represented by Amphistegina, Neorotalia, Ammonia, Elphidium, Operculina, Assilina, Amphisorus and texularids. Planktic foraminifers like Globigerinoides and other biogenic components viz., gastropod shells, echinoid spines and coral fragments are also common. A foraminiferal-algal grainstone facies has been recognized as observed in the field as well as in thin section analysis. The overall assemblage of the biogenic components and facies analysis indicate intertidal to near shore environment of deposition with high energy condition and increased hydrodynamic activity.  相似文献   

Magnetic Data Interpretation for the Source-Edge Locations in Parts of the Tectonically Active Transition Zone of the Narmada-Son Lineament in Central India     

G. K. Ghosh 《Pure and Applied Geophysics》2016,173(2):555-571

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The changes in La Niña induced summertime interannual variability of sea level anomaly along the western boundary of the Bay of Bengal     

Mukherjee  Arnab  Ghosh  Supriyo 《Ocean Dynamics》2023,73(6):373-386

Ocean Dynamics - In this study, interannual variability and associated dynamics of sea level anomaly (SLA) along the western boundary of the Bay of Bengal (WBoB) during the summer...  相似文献   

Effect of autocorrelation on temporal trends in rainfall in a valley region at the foothills of Indian Himalayas     

Atul?Kant?PiyooshEmail author  Sanjay?Kumar?Ghosh 《Stochastic Environmental Research and Risk Assessment (SERRA)》2017,31(8):2075-2096

This study examines the effect of autocorrelation on step and monotonic trends in seasonal and annual rainfall. Initially, for step change, modified-Pettitt test is applied in two ways. First, using the corrected and unbiased trend-free-pre-whitening (TFPWcu) approach. Second, using a new approach in which time series is modelled by intervention analysis for modified Pettitt test. Subsequently, for monotonic trends, Mann–Kendall (MK) and six approaches of modified Mann–Kendall (MMK) test are applied to NCDC data for period 1901–2012 and its sub-periods. Approaches of MMK include pre-whitening (PW), trend-free-pre-whitening (TFPW), TFPWcu, two Variance Correction Approaches (VCAs) based on empirical formula (VCA:CF1) and Monte-Carlo-Simulations (VCA:CF2) and long term persistence (MK-LTP). A single change point is identified in 1970 for annual and monsoon rainfall from original and modified-Pettitt’s test using TFPWcu, while time series modelling approach has not exhibited any change point. Process shift in rainfall series is also studied using CUSUM and multiple change points are identified using Segment-Neighbourhood method. Outcomes of MMK show that TFPWcu is able to efficiently limit the effect of autocorrelation and may be preferred over PW and TFPW. The VCA:CF2 is not dependent on whole autocorrelation structure and corrects variance of all data series using lag-1 autocorrelation and may be preferred over VCA:CF1. MK-LTP considers long term persistence and it has exhibited presence of weaker trends than exhibited by other approaches. VCA:CF2 and MK-LTP are used to study trends of rainfall in Dehradun.  相似文献   

Monitoring field scale CO<Subscript>2</Subscript> injection from time-lapse seismic and well log,integrating with advanced rock physics model at Cranfield EOR site     

Ranjana Ghosh 《Acta Geophysica》2017,65(6):1207-1218

Causes and effects of global warming have been highly debated in recent years. Nonetheless, injection and storage of CO₂ (CO₂ sequestration) in the subsurface is becoming increasingly accepted as a viable tool to reduce the amount of CO₂ from the atmosphere, which is a primary contributor to global warming. Monitoring of CO₂ movement with time is essential to ascertain that sequestration is not hazardous. A method is proposed here to appraise CO₂ saturation from seismic attributes using differential effective medium theory modified for pressure (PDEM). The PDEM theory accounts pressure-induced fluid flow between cavities, which is a very important investigation in the CO₂-sequestered regime of heterogeneous microstructure. The study area is the lower Tuscaloosa formation at Cranfield in Mississippi, USA, which is one of the active enhanced oil recovery (EOR), and CO₂ capture and storage (CCS) fields. Injection well (F1) and two observation wells (F2 and F3) are present close (within 112 m) to the detailed area of study for this region. Since the three wells are closely situated, two wells, namely injection well F1 and the furthest observation well F3, have been focused on to monitor CO₂ movement. Time-lapse (pre- and post-injection) log, core and surface seismic data are used in the quantitative assessment of CO₂ saturation from the PDEM theory. It has been found that after approximately 9 months of injection, average CO₂ saturations in F1 and F3 are estimated as 50% in a zone of thickness ~ 25 m at a depth of ~ 3 km.  相似文献   

A non-stationary geostatistical approach to multigaussian kriging for local reserve estimation     

Mainak?ThakurEmail authorView author&#;s OrcID profile  Biswajit?Samanta  Debashish?Chakravarty 《Stochastic Environmental Research and Risk Assessment (SERRA)》2018,32(8):2381-2404

Multigaussian kriging technique has many applications in mining, soil science, environmental science and other fields. Particularly, in the local reserve estimation of a mineral deposit, multigaussian kriging is employed to derive panel-wise tonnages by predicting conditional probability of block grades. Additionally, integration of a suitable change of support model is also required to estimate the functions of the variables with larger support than that of the samples. However, under the assumption of strict stationarity, the grade distributions and important recovery functions are estimated by multigaussian kriging using samples within a supposedly spatial homogeneous domain. Conventionally, the underlying random function model is required to be stationary in order to carry out the inference on ore grade distribution and relevant statistics. In reality, conventional stationary model often fails to represent complicated geological structure. Traditionally, the simple stationary model neither considers the obvious changes in local means and variances, nor is it able to replicate spatial continuity of the deposit and hence produces unreliable outcomes. This study deals with the theoretical design of a non-stationary multigaussian kriging model allowing change of support and its application in the mineral reserve estimation scenario. Local multivariate distributions are assumed here to be strictly stationary in the neighborhood of the panels. The local cumulative distribution function and related statistics with respect to the panels are estimated using a distance kernel approach. A rigorous investigation through simulation experiments is performed to analyze the relevance of the developed model followed by a case study on a copper deposit.  相似文献