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Chinmoy Rajkonwar , R. P. Tiwari , S. J. Patel

Abstract

A well preserved and diversified trace fossil assemblage has been identified from the Middle Bhuban unit of the Bhuban Formation, Surma Group (Lower to Middle Miocene) exposed along the Bawngkawn-Durtlang road section, Aizawl, Mizoram. A 615 meter thick succession comprising sandstone, siltstone, shale, mudstone and their admixtures in various proportions is exposed along this section. Trace fossils mostly occurred in fine to medium grained sandstone. These are ethologically diverse and represent predominantly infaunal structures of both suspension and deposit feeders. A total of 30 ichnospecies belonging to 19 ichnogenera have been identified from the collection. These are Arenicolites carbonarius, A. tenuis, A. helixus isp. nov., Conichnus conicus, Didymaulichnus Iyelli, Diplocraterion helmerseni,Gordia marina, Gyrolithes isp.,Katbergia isp, Laevicyclus mongraensis, Lanicoidichna metulata. Lockeia siliquaria, Monomorphichnus bilinearis, Ophiomorpha irregulaire, O. nodosa. Palaeophycus annulatus, P. tubularis, P. heberti, P. striatus, Planolites beverleyensis, Polykladichnus irregularis, Psilonichnus Iutimuratus. P. upsilon, Skolithos linearis, S. verticalis. Teichichnus flexuosus, T. rectus. Thalassionoides horizontalis, T. paradoxicus, T. suevicus, and a large complex burrow system. Vertical burrows of Arenicolites, Gyrolithes, Psiloniclmus, Skolithos and Ophiomorpha are infaunal colonization of the suspension feeders under high energy and shifting substrate conditions. Horizontal burrows like Planolites. Palaeophycus. Teichichnus and ThaIassinoides are the infaunal deposit feeder structures, which usually live at sediment-sediment interface in low to moderate energy conditions. The behavioural nature and distribution pattern of the ichnofossils as well as sedimentological attributes suggests that Middle Bhuban succession was deposited under fluctuating energy conditions in foreshore to shorefacefoffshore zones of shallow marine environment.

Keywords

Trace Fossils, Bhuban Formation, Surma Group, Lower-Middle Miocene, Aizawl, Mizoram, India

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R. P. Tiwari

Abstract

No Abstract.

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R. P. Tiwari ¹, J. Malsawma ¹, S. J. Sangode ², B. R. Arora ²

Affiliations
1 Department of Geology, Mizoram University, Aizawl - 796009, IN
2 Wadia Institute of Himalayan Geology, 33 General Mahadev Singh Road, Dehradun - 248 001, IN

Abstract

A 560 m thick rock succession of Middle Bhuban Formation (Surma Group) exposed between Bawngkawn and Durtlang, Aizawl, Mizoram has been studied for its magnetostratigraphic attributes. A total of 7 normal and 7 reverse magneto-Zones have been delineated in this section. The GPTS correlated ages of this section lie between -21.77 Ma (at the base) to ∼15.16 Ma (at the top) with a total duration of ∼6.6 Ma. The GPTS event C6n occurring at the stratigraphic level between 146 m to 266 m may be considered for basin wide correlation as it is the longest normal event that has been recorded with greater confidence i. e. better alpha- 95. The average sediment accumulation rate (SAR) estimated for this section is 8.48 cm/Ka. Overall the SAR is higher in the lower part of the section with a spike of 26.8 cm/Ka at <21 Ma. The decrease in SAR to 2.1 cm/Ka at around 18 Ma in the upper part of the section may be investigated for possible hiatus.

Keywords

Magnetostratigraphy, Sediment Accumulation Rate (SAR), Surma Group, Middle Bhuban Formation, Aizawl, Mizoram.

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R. P. Tiwari ¹, S. J. Sangodi ², S. K. Patil ³, C. H. Sivaji ⁴

Affiliations
1 Department of Geology, Mizoram university,Aizawl - 796 012, Mizoram, IN
2 Wadia Institute of Himalayan, Geology, Dehra Dun - 245 001, Uttarachal, IN
3 Indian Institute of Geomagnatism, Magnetic Observatory, Alibagh, Raigarh, IN
4 ESS Division, Dept of Science & Technology, New Delhi, IN

Abstract

No Abstract.

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J. Malsawma ¹, P. Lalnuntluanga ¹, A. Badekar ², S. J. Sangode ², R. P. Tiwari ¹

Affiliations
1 Department of Geology, Mizoram University, Aizawl - 796 009, IN
2 Department of Geology, University of Pune, Pune - 411 007, IN

Abstract

A 1355 m thick Bhuban sequence exposed along Tuirial section in the Aizawl district, Mizoram has been studied for magnetostratigraphic and rock magnetic attributes. The study reveals mono-mineral nature of the rocks with magnetite in the range of Stable Single Domain (SSD) showing the most favourable mineralogy to produce authentic (Natural Remanent Magnetization) NRM directions. Using routine demagnetization methods we reveal a total of 7 normal magneto-zones in the studied part of the Tuirial section. Correlation of the observed polarity with GPTS gives ages ~12.5 Ma to ~8 Ma. A notable increase in the rate of sedimentation at ~9.5 Ma (~750 m level in the section) indicates facies change from turbidite like sequence to pro-delta system. Detailed sedimentologic work is under progress to relate the magnetostratigraphy to understand some of the basin evolutionary processes.

Keywords

Magnetic Polarity Stratigraphy, Magnetic Mineralogy, Sediment Accumulation Rate, Bhuban Succession, Surma Group, Tuirial Section, Mizoram.

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Victor Zochhuana Ralte ¹, R. P. Tiwari ¹, Lalchawimawii ¹, J. Malsawma ¹

Affiliations
1 Department of Geology, Mizoram University, Aizawl - 796 004, IN

Abstract

An interesting selachian fish assemblage having stratigraphic and palaeoecological significance is being described from the two intraformational calcareous conglomeratic horizons within the Upper Bhuban unit of Bhuban Formation, Surma Group (Lower to Middle Miocene). The assemblage consists of eighteen species of selachian fishes including two new ones (Carcharhinus bhubanicus and Hemipristis unidenticulata) belonging to thirteen genera and another thirteen forms have been identified up to generic level. It is dominated by the families Carcharhinidae and Lamnidae, and is one of the most diversified Miocene assemblages from the Indian subcontinent. The fish fauna and the associated mega-invertebrates suggest Lower Miocene (Aquitanian - Burdigalian) age for the Upper Bhuban unit of Bhuban Formation. These further suggest that the fish yielding horizons were deposited under a warm shallow marine set-up near to the shoreline in a high-energy environment.

Keywords

Selachian Fauna, Lower Miocene, Bhuban Formation, Surma Group, Mizoram.

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P. K. Misra ¹, A. K. Jauhri ², R. P. Tiwari ³, S. Kishore ¹, Ajay Pratap Singh ³, S. K. Singh ¹

Affiliations
1 Botany of Department, University of Lucknow, Lucknow - 226 007, IN
2 Department of Geology, University of Lucknow, Lucknow - 226 007, IN
3 Department of Geology, Mizoram University, Aizawl – 796 009, IN

Abstract

The present paper records nine species of coralline algae from the Prang Formation of middle-late Eocene age from the Jaintia Hills, Meghalaya. The algae are associated with the larger foraminifera including Nummulites, Alveolina and Discocyclina throughout the succession. The temporal distribution of algal species indicates that seven species are known from the Eocene. Of the remaining two, one ranges from the Palaeocene to Eocene and the other is Palaeocene in age. The coralline algae and larger foraminifers are differentiated into two associations, the lower one indicating inner-ramp environment of high energy and the upper one showing deposition in relatively calm waters of deeper ramp environment.

Keywords

Coralline Algae, Larger Foraminifera, Middle-Late Eocene, Jaintia Hills, Meghalaya.

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Gaurav Srivastava ¹, R. P. Tiwari ², R. C. Mehrotra ¹

Affiliations
1 Birbal Sahni Institute of Palaeosciences, 53 University Road, Lucknow 226 007, IN
2 Dr H. S. Gour Vishwavidyalaya, Sagar 470 003, IN

Abstract

The monsoon rainfall contributes about 30% of the total global rainfall. The Asian monsoon system (ASM) is one of the largest systems and is of great significance in the global climate system. It consists of two subsystems, namely Indian summer monsoon (ISM)/southwest (SW) monsoon/South Asia summer monsoon (SASM) and East Asia monsoon (EAM).

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J. Malsawma ¹, Paul Lalnuntluanga ¹, Saitluanga Sailo ², V. Vanthangliana ², R. P. Tiwari ³, V. K. Gahalaut ⁴

Affiliations
1 Department of Geology, Mizoram University, Tanhril, Aizawl 796 004, IN
2 Pachhunga University College, Mizoram University, Aizawl 796 001, IN
3 Department of Geology, Mizoram University, Tanhril, Aizawl 796 004, India; Central University of Punjab, Bathinda 151 401, IN
4 CSIR-National Geophysical Research Institute, Uppal Road, Hyderabad 500 007, IN

Abstract

Earthquakes in the Indo-Burmese arc occur due to interaction of India and Sunda plates along the IndoBurmese Wedge and Sagaing Fault. Majority of the moderate to major magnitude earthquakes in the Indo-Burmese Wedge occur within the Indian slab and very few of them occur on the plate interface. Earthquakes within the wedge are rare and the 22 June 2020 earthquake of magnitude 5.5 (Mw) on the India–Myanmar border in Mizoram, India, at shallow depth is probably one such earthquake. The earthquake caused moderate damage (maximum intensity VIII on MSK scale) in remote border villages (Vaphai and Chawngtui) with sparse population without any fatality. The earthquake did not seem to be related with the Mat Fault, which was transverse to the north–south trending wedge, as various estimates of mainshock and the region of maximum damage was ~20 km northeast of the surface trace of the Mat Fault. It appeared to be associated with almost north– south oriented Churachandpur Mao Fault (CMF) with dextral slip which mapped extensively and monitored geodetically in the neighbouring regions of Manipur and Nagaland to the north. Occurrence of this shallow depth earthquake may imply that some segment of the CMF might be seismically active, unlike in the north, where it appears to be predominantly aseismic. This implies that the seismic hazard along the CMF may vary along its length.

Keywords

Churachandpur Mao Fault, earthquakes, Indo-Burmese arc, tectonics.

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