March, 2025 || Volume 29 No.02
Volume 29(2) (2025)2-6
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1
Geochemical constraints on the origin of ophiolitic chert from Naga Hills Ophiolite, Northeast India
Anisha Verencar1,2, Abhishek Saha1*, M. Ram Mohan3
1CSIR-National Institute of Oceanography, Dona Paula, Goa-403 004, India
2School of Earth, Ocean and Atmospheric Sciences, Goa University, Taleiga?o Plateau, Goa-403 206, India
3CSIR-National Geophysical Research Institute, Uppal Road, Hyderabad-500 007, India
https://doi.org/10.71122/JIGU.29(2)2025.008
ABSTRACT
The uppermost part of the Naga Hills ophiolite (NHO) sequence representing vestiges of the Neo-Tethyan ocean in the Indo-Myanmar ranges, consists of Late Jurassic to Late Cretaceous cherts that carapace the ophiolitic volcanics. This contribution presents petrographic and whole rock geochemical studies to comprehend their origin and paleo-depositional environment. The occurrences of abundant radiolarian microfossils in the studied cherts are observed. Geochemical signatures of these cherts indicate that they are generated at rifted arc basin by pronounced hydrothermal activity along with terrigenous material influx from active continental margin. Redox sensitive trace element proxies U/Th (0.12-0.74), Ni/Co (0.10-0.67) and V/(V+Ni) (0.22-0.47) record oxic paleo-redox conditions of formation. The cherts of NHO are envisaged to have formed in a transitional tectonic environment associated with magmatism and subsequent sedimentation in a rifted arc basin proximal to an active continental margin.
2
Examining the salinity changes at different depths in the Indian Ocean prior to summer monsoon season and its connection to monsoon arrival in India: A case study
Dinesh K Yadav1, Archana Maurya1, R. Bhatla1,2 and B. Mandal*1
1Department of Geophysics, Institute of Science, Banaras Hindu University, Varanasi-221005, India.
2DST-Mahamana Centre of Excellence in Climate Change Research, Institute of Environment and Sustainable Development, Banaras Hindu University,
ttps://doi.org/10.71122/JIGU.29(2)2025.009
ABSTRACT
The Indian Ocean interacts intricately with the atmosphere, and its features, such as sea surface temperature and salinity. The Indian Ocean can influence the monsoon's onset, intensity, and duration. This study examines the fluctuation of the salinity in the Indian Ocean throughout the onset phase over the Indian Peninsula, with a focus on the Kerala coast. The study makes use of daily averaged reanalysis data from 1992 to 2017 from the Ocean Reanalysis System 5 (ORAS) of the European Centre for Medium-Range Weather Forecasts (ECMWF). Considerable variations in salinity have been seen in the Indian Ocean prior to the onset of the monsoon. Higher salinity levels are found in the top subsurface layers of the western Indian Ocean, namely the Arabian Sea, whereas lower salinity concentrations are found in the equivalent layers of the eastern Indian Ocean, which include the Bay of Bengal. The salinity gradient between the Arabian Sea and Bay of Bengal decreases with depth due to the inflow of freshwater into Bay of Bengal through river discharge. The peak salinity is localized in a specific region, adjacent to the Somalia and Kenya coastlines, within depths ranging from 20 to 80 meters from March to the first week of May. Subsequently, this region of heightened salinity, extends to depths ranging from 50 to 90 meters. During the pre-monsoon months of the early onset year, intense evaporation leads to immense moisture in the atmosphere. Conversely, moisture is low during normal onset and late onset years, with wind-driven moisture transport towards the Kerala coast.
3
An earthquake precursor- Outgoing Longwave Radiation (OLR) observed over the Indian and Indonesian regions during high-magnitude earthquakes (M? 6.0)
Pooja Sharma1, Ananna Bardhan1*, Raj kumari2, and D. K. Sharma1
1 Department of Sciences, Manav Rachna University, Faridabad-121004, Haryana, India
2 Department of Physics, DAV Centenary College, Faridabad-121001, Haryana, India
https://doi.org/10.71122/JIGU.29(2)2025.0010
ABSTRACT
The Earth prepares itself before an earthquake and during this time, several precursory signs have been seen across the ocean, land, and atmosphere. Earthquakes inflict significant harm to both human lives and property. Therefore, monitoring and understanding the strange behaviour of various geophysical parameters as precursors, have become extremely important. The Outgoing Longwave Radiations (OLR), emitted by the surface during the recent ten highmagnitude (M ?6.0) earthquake (EQs) events, have been examined in the present work using the Data on OLR from the NCEP website. To analyse the OLR as precursory signatures of earthquakes, the climatological analysis for the seismic precursor identification (CAPRI) methodology was carried out. An apparent change in the OLR during 2 months before the earthquake events was observed. The maximum and minimum anomalies in OLR before all ten events were analysed. The maximum and minimum anomalous increase in OLR varied from 1.16 to 1.25 and 0.71 to 1.11 times greater during the earthquake years compared to historical time series respectively, during all the ten EQ events. The study indicates a strange shift in Outgoing Longwave Radiation during periods, influenced by the seismic activity. The extent of anomalies in OLR during earthquake events is maximum over the ocean than on the land. This is because the accumulation of water vapour traps the outgoing radiation, causing an elevation in temperature over the epicentre and Earthquake Preparation Zone (EPZ)
4
Imaging challenges and mitigations in the Tripura Fold Belt areas for reservoir characterization and hydrocarbon prospecting
Manoj Kumar Bhartee1*, Uma Shankar2, Yadunath Jha1 and Nani Madhab Dutta3
1Oil and Natural Gas Corporation Limited, Dehradun-248001, India 2Banaras Hindu University, Varanasi-221005, India
3Oil and Natural Gas Corporation Limited (Retd.), Jorhat-785001, India
https://doi.org/10.71122/JIGU.29(2)2025.0011
ABSTRACT
Even though there have been substantial advancements in seismic data acquisition and processing, imaging in structurally complex regions like fold belts has seen only marginal improvement. In such geologically intricate areas, the conventional imaging approach may not yield satisfactory results. While 3D surface seismic surveys are preferred, acquiring 3D seismic data can be challenging due to logistical constraints. Moreover, the rugged terrain and difficult accessibility in these areas make 3D land seismic data acquisition prohibitively expensive. Conventional 2D land seismic data also has limitations, particularly in accurately imaging anticlinal features. An alternative to traditional 2D surveys in such contexts is the swath-line recording geometry. Swathline recording offers significantly higher fold (720-fold in the present case), compared to typical 2D land surveys, resulting in data with an improved signalto-noise ratio. However, several issues adversely impact imaging quality in thrust fold belts. Key factors affecting the quality of processed outputs include geometry, statics, and poor signal-to-noise ratio. Survey objectives may remain unmet unless these factors are addressed or minimized. We utilized a hybrid approach, combining multiple techniques including geometry corrections, nonlinear tomography-based statics solutions, velocity estimation using the CVS method, and leveraging different software suites and algorithms to address these inherent challenges.