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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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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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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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