BazTech - Yadda

1

Remnant Neo-Tethyan ocean from the Ladakh Himalaya: constraints on their nature, age and tectonic setting

Talat Ahmad, Bhat Irfan, Chauhan Hiredya

Geotourism / Geoturystyka

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2023

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nr 1-2 (72-73)

11

EN

The Indus and Shyok Suture Zones represent the remnants of the Neo-Tethyan ocean in terms of Nidar arc volcanics and Zildat ophiolitic melange in the eastern Ladakh, Dras Arc volcanics and Shergol ophiolitic melange in the western Ladakh along the Indus Suture Zone. The Shyok-Nubra ophiolitic volcanics of the northern Shyok suture zone, north of the Ladakh batholith, represent the remnant northern portion of the Neo-Tethyan. The Nidar-Dras arc volcanics represent intra oceanic arc that developed as the Indian plate was moving northwards around 140 My ago. These units preserve arc tholeiite, representing primitive arc which passed on to calc alkaline series as the arc matured. These rocks are characterised by depleted nature in terms of incompatible trace elements including rare earth elements and Sm-Nd isotopic characteristics. The Zildat-Shergol ophiolitic melanges are represented by N-MORB and Ocean Island Basalt (OIB) characteristics. These units have also preserved exotic blocks of limestone, physically mixed with other units of the ophiolitic melange. The Shyok-Nubra volcanics are represented by enriched trace elements and isotopic characteristics, very different from those of the Indus Suture zone. They don’t preserve ophiolitic melange, as observed in the Indus suture zone. Our tectonic model indicate double subduction of the Neo-Tethyan ocean, in the north it got subducted under the Tibetan plate giving rise to Andean type continental arc along the Shyok suture zone. In the south the Neo-Tethyan ocean got subducted under the same oceanic crust giving rise the intra-oceanic Mariana type subduction. Thus, in the Ladakh Himalaya there is preservation of almost all components of the Neo-Tethyan ocean preserving the N-MORB and OIB type magmatism in the melange zone. The Andean and Mariana type arc components indicating very different tectonic settings. Neo-Tethyan ocean appear to have all the components that we observe presently in the Pacific-Atlantic ocean. These data will be presented and elaborated during my presentation.

2

Larger Benthic Foraminifera from Paleocene–Eocene carbonates, Eastern Tethys, Meghalaya NE India – their comparison with Western Tethys and palaeobiogeographical significance

Tewari Vinod Chandra

Geotourism / Geoturystyka

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2023

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nr 1-2 (72-73)

71--72

EN

India–Asia plate collision and uplift of the Himalaya took place during Paleocene–Eocene time (50 Ma). The extension of western Tethys Sea from Europe to Asian eastern Tethyan region has been correlated by assemblages of Larger Benthic Foraminifera (LBF). Global correlation and paleobiogeography of the eastern Meghalayan and western Tethyan Sea is discussed on the basis of SBZ of Paleocene– Eocene foraminifera assemblages (Fig. 1). Paleocene–Eocene Lakadong Limestone and Umlatodoh Limestone were deposited in shallow marine carbonate ramp depositional environment in Shillong Plateau, Meghalaya, NE India. The sedimentation basin is part of the Eastern Tethys and LBF and calcareous algae is the major carbonate facies. Coral reefs are not developed in these carbonates in contrast with the western Tethys limestones in Adriatic Platform and western European –Alpine region (Tewari et al., 2007).The LBF and algal assemblage in both the limestones is consistent with other parts of Eastern Tethys in Eastern India and Tibet (Hottinger, 1971; Scheibner & Speijer, 2008, Tewari et al., 2010). The latest Paleocene (Biozone SBZ4) miscellanids and ranikothalids are replaced by Early Eocene alveolinids and nummulitids, which dominates LBF assemblages in the western Tethyan realm at the P-E boundary (Scheibner & Speijer, 2008), Thanetian (SBZ4 Biozone) is equivalent to Tethyan platform stage II (Scheibner & Speijer, 2008). In standard biozones Ilerdian (SBZ5-SBZ6), a general reorganization in LBF communities is recorded with a long life and low reproductive potential (Hottinger, 1971). However, in the Meghalayan LBF assemblages of the lowest Eocene (biozones SBZ5/6) are still dominated by Ranikothalia and Miscellanea, while new LBFs that first emerged within this time interval elsewhere (e.g. Assilina, Alveolina and Discocyclina) are less important and Nummulites are absent. Later, in the Early Eocene there was a gradual diversification of Discocyclina and Assilina species (Fig. 1), while Ranikothalia disappeared and Miscellanea became less important by the end of the SBZ5/6 biozones. Similar LBF assemblages have been recorded in other parts of east Tethys in western India and Tibet (Scheibner & Speijer 2008; Tewari et al., 2010 and references therein). Such LBF assemblages in east Tethys thus differ from west Tethys. Palaeobiogeographical barriers must have existed between India and Eurasia during early collision of Indian Plate with Eurasia Plate around 50 Ma (Tewari et al., 2010 and references therein). These barriers prevented migration of certain LBF species of Nummulites and Alveolina between these two palaeogeographic regions. LBF dominated facies in the other basins of Meghalaya like Umlatodoh Limestone are well developed in low latitude. However, mixed coral-algal reefs and LBF facies were sparse in low-mid latitude carbonate environments (Adriatic Platform of Italy-Slovenia, Oman, Egypt, Libya, NW Somalia; Tewari et al., 2007, 2010; Scheibner & Speijer, 2008 and references therin). In contrast to west Tethys, corals are absent in Eastern Tethys (calcareous algae is present in SBZ3 and SBZ4 Biozone, Fig. 1) in the Meghalaya and other low-latitude eastern Tethys (Scheibner & Speijer, 2008). Carbonate ramp (shallow tidal flat ) carbonate environments were dominated by LBFs from Early to Late Paleocene (SBZ4, SBZ5, biozones; Fig. 1). It is interpreted that the collision of the Indian and Asian plates must have generated this difference in palaeobiodiversity by creating barriers, which prevented migration of certain LBFs (Nummulites) from west to east. Later, in the Early Eocene (SBZ6, SBZ7-SBZ8 biozones), recorded from younger Umlatodoh Limestone in the upper part gradually replaced by LBF dominated facies in the east, with highly diversified LBF species of Nummulites, Discocyclina, Discocylina jauhrii etc.), indicating stable shallow marine environmental conditions. Stable carbon and oxygen isotope analyses from Paleocene–Eocene Lakadong Limestone and Umlatodoh Limestone strongly supports a shallow marine carbonate platform deposition in Eastern Shallow Tethys, Meghalaya, India (Tewari et al., 2010)

3

Birds visiting flowers of erythrina suberosa: their abundance, frequency of visits and role as pollinators in a sub-tropical montane forest of Garhwal Himalaya

Khanduri Vinod Prasad

Polish Journal of Ecology

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2022

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Vol. 70, nr 2-3

117--127

EN

Bird pollination is specific among flowering plants which support mostly cross pollination and has been regarded as an important pollination syndrome. Frequency of bird pollinators visiting flowers of the corky coral tree Erythrina suberosa Roxb., was studied in a subtropical montane forest located in Garhwal Himalaya, India. Forty trees were selected randomly in the population and the observations on birds visitors were recorded for 10 days during peak flowering. In total 18 bird species were found visiting flowers of E. suberosa. The bird species belonging to Passeriformes, Piciformes, Psittaciformes, and Cuculiformes were observed most frequently. The highest bird frequency and abundance among flower-visiting birds were recorded for the red-billed blue magpie Urocissa erythrorhyncha (26 ± 3.2 individuals per hour per branch and 60 birds per tree, respectively), whereas the lowest – for the verditer flycatcher Eumyias thalassinus (2 ± 0.02 individuals per hour per branch and 6 individuals per tree, respectively). Majority of the bird species followed bimodal pattern of foraging on nectar in a day (mostly morning and evenings), which is consistent with other studies carried out for other ornithophilous tree species in the Himalayan region. The birds observed in this study are presumed to be pollinators, as the majority of birds foraged on nectar of properly opened flowers oriented upwards; however, possibility of nectar robbing cannot be excluded and requires further investigation in future studies.

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Hazard estimation of Kashmir Basin, NW Himalaya using probabilistic seismic hazard assessment

Yousuf Maqbool, Bukhari Kaiser

Acta Geophysica

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2020

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Vol. 68, no. 5

1295--1316

EN

This study presents hazard estimation of Kashmir Basin, NW Himalaya using regional ground motion relations, representing one of the most seismically active region in the Himalayan belt. Fault-level seismic recurrence parameters are determined from an updated earthquake catalogue spanning from 25 to 2018 AD for all possible seismic sources. The estimated hazard maps are presented for three ground motion parameters (PGA, short and long period spectral acceleration) for 50, 100, 500 and 2500 years return periods. Moreover, uniform hazard response spectrums and hazard curves are presented for all ten districts of the basin. The southern section of the basin consisting districts of Budgam, Shopian, Pulwama and Kulgam show higher hazard levels due to presence of numerous seismogenic structures in close vicinity. Our results highlight that the imposed seismic hazard in Kashmir basin is highly underestimated which need to be redressed by modifying the current provisional design standards.

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Estimated casualties in possible future earthquakes south and west of the M7.8 Gorkha earthquake of 2015

Wyss Max, Chamlagain Deepak

Acta Geophysica

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2019

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Vol. 67, no. 2

423--429

EN

The 2015 M7.8 Gorkha earthquake has moved the upper, unbroken, part of the Main Himalayan Thrust (MHT) and the neighboring sections of this fault closer to failure. Using the program and data set of QLARM, which has been correct in fatality estimates of past Himalayan earthquakes, we estimate quantitatively the numbers of fatalities, injured and strongly affected people when assumed ruptures along these two sections will happen. In the Kathmandu up-dip scenario with M8.1, we estimate that more than 100,000 people may perish, about half a million may be injured, and 19 million are likely to be affected strongly, if we assume the high virtual attenuation observed for the 2015 Gorkha earthquake exists here also. Likewise, if the 100 km underthrusting segment west of Gorkha ruptures, we quantitatively estimate that 12,000–62,000 people may perish and 4 million to 8 million will be strongly affected, in a down-dip (lower half of the thrust plane) and an up-dip rupture (upper half) scenario, respectively. If the up-dip part of the MHT cannot rupture by itself, and greater earthquakes are required to generate the several meters of displacement observed in trenches across the MHT, then our estimates are minima.

6

Assessment of slope instability and its impact on land status: a case study from Central Himalaya, India

Pande A.

Landform Analysis

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2016

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Vol. 32

27--43

EN

Tectonic instability, geological sensitivity along with human intrusion in Himalaya has greatly exacerbated the occurrence of hazardous situation. Dynamics of slope instability have been evaluated under three processes leading to geomorphic instability, viz. i. erosion ii. mass wasting and iii. anthropogenic. Their causative factors have been identified under Ghuniyoli Gad watershed. The measurement of the intensity, magnitude and nature of instability factors were done within the units of 1 km2 under 21 units of watershed. Each unit was evaluated in terms of type, extent and corresponding degree of instability along with their potential assessment. The stage of erosion reveals that Ghuniyoli Gad watershed experiences instability. Maximum units fall under instability of degree 1 and degree 2 (38% and 38%) while minimum units belong to instability of degree 4 (4.76%). The instability of degree 3 contributes only about 19.04%. Appropriate mitigation measures to overcome hazardous calamities are needed to be introduced therein.

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Site-specific Probabilistic Seismic Hazard Map of Himachal Pradesh, India. Part I. Site-specific Ground Motion Relations

Muthuganeisan P., Raghukanth S. T. G.

Acta Geophysica

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2016

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Vol. 64, no. 2

336--361

EN

This article presents four regional site-specific ground motion relations developed for the state of Himachal Pradesh in northwest Himalaya, situated in a seismically active region. These relations are developed from synthetic free surface ground motion databases obtained from a calibrated stochastic seismological model considering the characteristic properties of this specific region. The adopted methodology incorporates the site effects characterised through active MASW tests conducted in 22 important cities. The estimated ground motion levels from the developed relations are found to be in reasonable agreement with the recorded data.

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Site-specific Probabilistic Seismic Hazard Map of Himachal Pradesh, India. Part II. Hazard Estimation

Muthuganeisan P., Raghukanth S. T. G.

Acta Geophysica

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2016

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Vol. 64, no. 4

853--884

EN

This article presents site-specific probable seismic hazard of the Himachal Pradesh province, situated in a seismically active region of northwest Himalaya, using the ground motion relations presented in a companion article. Seismic recurrence parameters for all the documented probable sources are established from an updated earthquake catalogue. The contour maps of probable spectral acceleration at 0, 0.2, and 1 s (5% damping) are presented for 475 and 2475 years return periods. Also, the hazard curves and uniform hazard response spectrums are presented for all the important cities in this province. Results indicate that the present codal provision underestimates the seismic hazard at cities of Bilaspur, Shimla, Hamirpur, Chamba, Mandi, and Solan. In addition, regions near Bilaspur and Chamba exhibit higher hazard levels than what is reported in literature

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Statistical analysis on yearly seismic moment release data to demarcate the source zone for an impending earthquake in the Himalaya

Mukhopadhyay B., Acharyya A., Dasgupta S.

Acta Geophysica

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2009

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Vol. 57, no. 2

387-399

EN

Tectonism in the Himalayan fold-thrust belt had generated great earthquakes in the past and will spawn more in the future. Sequential cumulative moment release data of macroearthquakes (Mb ≥ 4.5) over the years 1964–2006 in four zones of the Himalaya was analysed by nonparametric RUD method. The Z values of RUD analysis had neither rejected nor supported the null hypothesis of randomness. However, the Hurst analysis and plot, a statistical procedure to identify clustering of low and high values in a time series, brought out a pattern for earthquake prognostication. The pattern was a negative sloping segment representing a sluggish moment release over years, followed by a positive sloping segment indicating a sudden high moment release with occurrence of medium/large size earthquake(s). In recent past, such a negative sloping has been found in Zones B (1992–2006) and D (1998–2006), indicating an impending moderate/mega earthquake event in near future.