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Geoscience e-Journals





An International Year of Planet Earth-2008 Initiative

Current Issue Technical

Year 2017

Volume X

REE- bearing Quartz Syenite from Purimetla Alkaline Complex, Cuddapah Intrusive Province, Peninsular India
Sridhar Nalluri and Mallikarjuna Reddy Ragi*

The Purimetla alkaline pluton is one of the prominent nepheline syenite pluton among the several alkaline plutons emplaced along the contact of Eastern Dharwar and Eastern Ghat belt located at the eastern margin of the cuddapah intrusive province (CIP). The rift/suture between the Vinjamuru and Ongole domains of Krishna province, Eastern Ghats Belt (EGB) hosts this alkaline complex. In this pluton both alkaline (feldspathoidal) and sub alkaline (Non-feldspathoidal) rocks are co-spatially arranged. Detailed geochemical studies on the quartz syenite of Purimetla, indicate that these rocks are characterized by high alkali (9.35-12.05 wt%) especially K2O (7.12-8.8 Wt %) contents with metaluminous nature. Enriched in LILEs (Rb, Ba, and Sr) and depleted in HFSEs (Ta, Nb, Ti) along with pronounced Eu and TNT (Ta, Nb, Ti) negative anomalies are the distinguishing characteristics of these rocks. They also have high LREE contents and strong fractionation between LREEs (1826 ppm) and HREEs (92.7 ppm). Enriched LILE, LREE along with TNT negative anomalies reflect the partial melting, fractional crystallization followed by crustal contamination processes in the genesis of these syenites.


Keywords: Purimetla alkaline pluton, Quartz syenite, TNT negative anomaly, high LREE, fractional crystalisation, crustal contamination.

Morphotectonic Study of Tawang River Basin, Tawang District, Arunachal Pradesh, NE India
Chaitra Dhar Taye and Raghupratim Rakshit

In the present study we have considered the Tawang River Basin and its sub-basins located in the eastern Himalaya, northeastern India. The area under study is bounded on the north by the South Tibetan Detachment System (STDS), on the east by the Main Central Thrust (MCT), and on the south and west by the Bhutan Himalayas. It originates from the Tibet (China) and flows towards southwest direction through India to Bhutan analogously with the major regional structures of the area. The purpose of this investigation is to examine the influence of active structures by applying an integrated study on supportive field evidences, geomorphology, morphotectonics, Digital Elevation Model (DEM) and using topographic map. The measured indices for morphotectonic analysis, viz. Asymmetric Factor (AF=2 to 26), Transverse Topographic Symmetry Factor (T = 0.13 to 0.78), Stream Length gradient index (SL), Basin shape indices (Bs = 0.35 to 0.85) and lineament analysis indicated that the area is tectonically active. Lineament density plots indicate the NNE and NNW stress component and EW trend. From the present investigation, we can assume that the Tawang Chu River itself is flowing through a major anomalous structural or tectonic feature. Moreover, these findings can assist to recognize the potential geo-hazardous areas as the area is tectonically active and sound to regional threat.


Keywords: Tawang River Basin, Main Central Thrust (MCT), morphotectonics, lineaments, SL index.

Benthic Foraminiferal Biostratigraphy and Depositional Environment of Prang Limestone of Mawlong Village, South Shillong Plateau, Meghalaya
Anindita Bhattacharjya and Bikash Gogoi

Based on the species association of larger benthic foraminifera families Nummulitidae, Discocyclinidae, Alveolinidae, Hauerinidae biostratigraphic study are attempted in the Prang Limestone Member of Sylhet Limestone Formation exposed around Mawlong village of Cherrapunjee area of Shillong Plateau, NE India. All total four Taxon Range Zones were established in which FAD (First Appearance Datum) and LAD (Last Appearance Datum) of species Nummulite burdigalensis burdigalensis, Nummulite burdigalensis cantabricus, Nummulite lehneri and Nummulite gizehensis were used as criteria. The four Taxon Range Zones identified were Nummulite burdigalensis burdigalensis Taxon Range Zone, Nummulite burdigalensis cantabricus Taxon Range Zone, Nummulite lehneri Taxon Range Zone and Nummulite gizehensis Taxon Range Zone. Calibration of established benthic foraminiferal biozones with the Tethyan larger benthic foraminiferal biozonation scheme of benthic foraminifera suggests that the Prang Limestone Member ranges in age from SBZ 10 - SBZ 16 which is equivalent to P6b - P12 Zone of planktonic foraminifera. Dominant occurrence of much flatter, larger as well as thinner tested symbiont bearing forminiferal assemblage such as Nummulite, Discocyclina, Assilina, Alveolina etc. in the limestone suggests an outer shelf setting or outer ramp area indicating deposition in a somehow deep, low energy setting with reduced light condition during Early Eocene (Cuisian) - Middle Eocene (Lutetian). Petrographically these limestones are Packstone and Grainstone of Poorly Washed Biosparite and Packed Biomicrite types which reveal energy condition from powerful or persistent to weak, short lived one. The considerably distal deposit Prang Limestone Member grade into a clastic sequence Kopili Formation of the same group deposited under a coastal, marginal marine depositional environment with fresh water swamps and ponding conditions nearby.


Keywords: Biostratigraphy, Petrography, Depositional Environment, Prang Limestone, Shillong Plateau

An Assessment of Arsenic Contamination and Mitigation Measures in District Ballia, part of Ganga and Ghagra Basins, Uttar Pradesh, India
Amit Mehrotra1, A. Mishra1 and Naveen Shukla2

Arsenic in drinking water is a burning issue across the Globe. In India, in Northern Indo-Gangetic plain almost every state is facing problem of arsenic contamination in drinking water. After knowing its presence in the northern Indo-Gangetic Plain, various studies were carried out by UNICEF and various research and academic institutions. Mitigation strategies for short term and long term measures have been adopted. Short-term mitigation measure involved the installation of Arsenic Removal Units (ARU) and the long-term measure involved the construction of groundwater and surface water based drinking water supply schemes, after proper hydrogeological and geophysical studies, by Uttar Pradesh Jal Nigam. In Ballia district, Uttar Pradesh, in 2006-2007, UNICEF carried out rapid randomised screen testing by Field Test Kit (FTK), in almost all blocks. Later, results were confirmed by laboratory method for more than the desired concentration of arsenic.  On the basis of these tests, and severity, in densely populated habitations, different mitigation measures were adopted by U.P. Jal Nigam. These measures were able to provide arsenic-free water to the communities and helped them in reducing health hazards. Besides infrastructure based approach, behaviour change approaches were also used and proved to be very effective in engaging community actions. These approaches were implemented with the involvement of local NGOs. The paper aims to describe the status of arsenic contamination in the groundwater, its spatial extent and efficacy of adopted mitigation measures.


Keywords: Arsenic, FTK, northern Indo-Gangetic Plain, mitigation measure.

Review on Indian Summer Monsoon (ISM) Reconstruction since LGM from Northern Indian Ocean
K. R. Chandana1, Upasana S. Banerji1, 2, Ravi Bhushan1

Indian summer monsoon (ISM) is critical to understand the global hydrological and carbon cycles and acts as a major driving force of earth’s climate system. Paleoclimatic evidences however, suggests episodic weakening and intensification of ISM in the past since its initiation. The weather system and socio-economy of Indian subcontinent depends on the ISM strength; thus, it is important to comprehend the centennial and millennial scale variability of ISM on northern Indian Ocean. The paper attempts to review the response of two basins in the northern Indian Ocean (Arabian Sea and Bay of Bengal) towards changing ISM intensities since Last Glacial Maximum (LGM). Further, we also tried to reconcile the knowledge gaps that need to be addressed in the paleoclimatic reconstruction of ISM from marine records which will reinvigorate modelers and policy makers to have prospects of amended predictions with imperative and robust strategies.


Keywords: ISM, LGM, northern Indian Ocean, Sea Surface Temperature, Holocene, GEOTRACES