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Comparative stratigraphic schemes of Arunachal Pradesh proposed by different researchers. Vertical lines temporally differentiating different members and groups are somewhat arbitrary.
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The Early Permian marine strata exposed at the Siang and Subansiri districts, Arunachal Pradesh are known for brachiopod and molluscan fossils. A stratigraphic review and palaeoenvironmental, palaeoecological, and palaeobiogeographic interpretation of these Early Permian fossils have been dealt here on the basis of additional fossil and rock materi...
Citations
... The climate discrimination diagram and sedimentary lithofacies suggest cold climatic conditions. Mondal et al. (2021) report Sakmarian and younger bivalve and brachiopods of Gondwana affinity from the Bichom Formations. These belong to suspension feeding groups representing an oxic, soft substrate of a shallow shelf environment. ...
82 publications by Indian geoscientists pertaining to the Proterozoic–Phanerozoic have come out during the last four years (2020–2024). Guide Books for the IGC 2020, GSI publication on the Precambrian sequences and a publication on the evolution of the Lesser Himalaya provide glimpses of regional geology. Other publications deal with geochemistry, sedimentology, isotope geology, palaeontology, and stratigraphy. A succinct summary of the publications is presented with short comments where necessary.
... They are found in association with quartzites and carbonaceous shales of the Bichom-Bhareli Formation (Sharma et al. 2018). The studies conducted on the faunal and palynofloral assemblages of the Bichom and Bhareli Formations have yielded a Lower Permian age for the formations (Dutta et al. 1988;Srivastava and Bhattacharya 1996;Mondal et al. 2021). Thus, the Bichom-Bhareli Formations are categorised under the Gondwana Group (Mondal et al. 2021). ...
... The studies conducted on the faunal and palynofloral assemblages of the Bichom and Bhareli Formations have yielded a Lower Permian age for the formations (Dutta et al. 1988;Srivastava and Bhattacharya 1996;Mondal et al. 2021). Thus, the Bichom-Bhareli Formations are categorised under the Gondwana Group (Mondal et al. 2021). The MBT separates these Gondwana sediments along with the associated Lichi volcanics from the micaceous sandstones of the Dafla Formation of the Siwalik Group (Sharma et al. 2018). ...
The Lichi volcanics are a suite of mafic-intermediate-felsic rocks and are considered coeval with the Abor volcanics (~132 Ma) of the Siang window in the Eastern Himalaya. Here, we present the first report of trachytic rocks from the Lichi volcanics, which are exposed in the Ranga valley, along the Kimin-Yazali road section in the Eastern Himalayan Region, Northeast India. The trachytes occur in close association with sandstones of the Gondwana Group of rocks and are characterised based on field, petrographical, and geochemical investigations. These fine-grained trachytes are composed of alkali feldspar, biotite, plagioclase, sodic-amphibole, apatite, illmenite, and titanite. The REE profiles of the evolved trachytic rocks (higher SiO2 content) display fractionated trends. The fractionation of accessory mineral phases, like apatite and titanite, was possibly responsible for the strongly fractionated REE patterns of the evolved samples. The trachytic rocks demonstrate high apatite saturation temperatures of 988 ± 14 °C (1σ, n = 8). The Aluminium Saturation Index (< 1.1) and binary discrimination diagrams of these peralkaline trachytes define their affinity with A-type granitoids. Elemental ratios like Y/Nb, Nb/U, and Ce/Pb signify that the Lichi trachytes are differentiated products of mantle-derived ocean island basalts. Trace elemental discrimination diagrams Th/Yb versus Nb/Yb, Y versus Nb, and Y + Nb versus Rb reflect a within-plate tectonic regime for the trachytes. From the results presented in this work, we infer that the development of rifting events during the breakup of eastern Gondwana due to the onset of Kerguelen plume activity further led to underplating of basic magma in lower crustal levels. These parental basaltic magmas underwent fractionation processes forming differentiated trachyandesites and trachytes. Taking into consideration the similarities recorded between the Lichi volcanics and Abor volcanics, this study supports the idea that Kerguelen plume activities resulted in the emplacement of these volcanics in the Eastern Himalayas.
... (Pascoe, 1968;Mukhopadhyay et al. 2010;Varshney & Bhattacharya, 2023). Marine fossil assemblages have been recorded from several basins in Peninsular India where the Talchir Formation crops out, as well as along the Tethyan margin (Venkatachala & Tiwari, 1987;Ghosh, 2003;Mukhopadhyay et al. 2010;Bharti & Chakraborty, 2014;Mondal et al. 2021). However, supposedly glacial sediments and Early Permian marine fossils together occur nowhere in India except in the study area near Manendragarh (Bose et al. 1992;Chakraborty, 1993;Mukhopadhyay & Bhattacharya, 1994;Bhattacharya et al. 2004;Bhattacharya & Bhattacharya, 2015;Varshney & Bhattacharya, 2023). ...
Among the vast swathes of Gondwanan sedimentary rocks in India, exposures of the Lower Permian Talchir Formation at Manendragarh in India are exceptional for their cold marine faunal assemblage and muddy conglomerates of possible glacial origin. They may represent a record of the late Palaeozoic glaciation that affected Gondwana in the Permo-Carboniferous. Although the fossil record is relatively well documented, the sedimentology of this area is not well understood. This paper intends to fill the gap in knowledge regarding palaeogeography and
the palaeoenvironmental changes within the basin through space and time. We distinguish conglomerates that are formed by glacial and mass flow processes. The lateral variation in facies associations along a NNE-SSW transect in the study area identifies the depositional basin as an interior sea that formed when the sea spilled over a steep basement ridge during a transgression. The benthic organisms remained confined to the seaward basin margin where they only flourished in the initial stage of basin filling. Locally derived, bioclastic storm beds are limited to
the seaward flank of the basin. Alternating phases of glaciation and interglaciation resulted in an interbedded succession of grey shales and interglacial density flow deposits. The channels that fed these density flows are preserved closest to the landward margin of the basin. Co-existence of glacial diamictites and interglacial density flow deposits highlights the climatic changes in this part of Gondwana during the Late Palaeozoic.
The present study describes a late Permian marine faunal assemblage dominated by brachiopods from Arunachal Pradesh, NE
India and analyses its importance for the global Permian palaeobiogeography. Previous studies suggested that Tethyan sediments
are absent from Arunachal Pradesh east of the Siang river and therefore late Permian marine fossils in Arunachal Pradesh
remained ambiguous and at best poorly known. In the Dalbuing area, a fossiliferous, brown-coloured shale unit of the Yamne
Formation is found to host late Permian brachiopods and bivalves. It is overlain by Eocene nummulitic limestone of the Dalbuing
Formation of the Yinkiong Group. This late Permian brachiopod fauna from Dalbuing is dominated by chonetids and includes
typical Permian Himalayan taxa like Spiriferella and Neochonetes and Tethyan genera like Tethychonetes. Their preservation is
relatively poor because ofmultiple episodes of deformation, but an overall similarity with typical late Permian fossil assemblages
can be observed. The late Permian brachiopod assemblages from Tibet and south China are also characterised by the dominance
of rugosochonetids. All twenty-two brachiopod and bivalve genera collected from the Yamne Formation were subjected to a
palaeobiogeographic study by analysing whether these taxa were also present in twelve locations representing the seven Permian
biogeographic provinces using a cluster analysis and NMDS . The results reveal the highest similarity of Arunachal taxa
with faunas in China and the Himalayan Province, comprising of Tibet, Nepal, Pamir, Pakistan, Sikkim and North India. This
suggest mixing of the taxa in peri-Gondwanan areas with Cathaysian elements in the late Permian due to climatic amelioration
and the northward drift of Gondwanaland.
