Microfacies analysis and paleoenvironmental significance of palustrine carbonates in the Thakkhola-Mustang Graben (Nepal Himalaya) |
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| Institution: | 1. Department of Civil Engineering, Institute of Engineering, Tribhuvan University, Pulchowk Campus, Nepal;2. Center for Earth Sciences, Department for Geodynamics and Sedimentology, University of Vienna, Austria;1. Department of Geography, RWTH Aachen University, Templergraben 55, 52056 Aachen, Germany;2. Department of Earth Sciences, Freie Universität Berlin, Malteserstraße 74-100, 12249 Berlin, Germany;3. School of Geographic and Oceanographic Sciences, Nanjing University, Xianlin Avenue 163, 210023 Nanjing, China;1. University of Belgrade, Faculty of Mechanical Engineering, Kraljice Marije 16, 11120 Belgrade 35, Serbia;2. Ryerson University, Department of Mechanical & Industrial Engineering, 350 Victoria Street, Toronto, Canada;1. Division of Neurointerventional Radiology, Department of Radiology and Biomedical Imaging, University of California, San Francisco, San Francisco, CA, United States;2. Center for Cerebrovascular Research, Department of Anesthesia and Perioperative Care, University of California, San Francisco, San Francisco, CA, United States;3. Division of Experimental Medicine, Department of Medicine, University of California, San Francisco, San Francisco, CA, United States;1. Department of Geography, Ştefan cel Mare University, Str. Universitatii nr.13, 720229, Suceava, Romania;2. Institute for Geological and Geochemical Research, Research Centre for Astronomy and Earth Sciences, MTA, Budaorsi ut 45, H-1112, Budapest, Hungary;3. Hertelendi Laboratory of Environmental Studies, Institute for Nuclear Research, MTA, Bem ter, 18/c, H-4026, Debrecen, Hungary;4. Department of Mineralogy, Geochemistry and Petrology Faculty of Science and Informatics, University of Szeged, Egyetem street 2., H-6722, Szeged, Hungary |
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| Abstract: | The Thakkhola-Mustang Graben represents the extensional tectonic phase of the Tibetan Plateau uplift and whole Himalayan orogeny. It is situated at the northern side of the Dhaulagiri and Annapurna Ranges and south of the Yarlang Tsangpo Suture Zone. Stratigraphically, the oldest sedimentary units are the Tetang and Thakkhola Formations (Miocene), while the Sammargaon, Marpha and Kaligandaki Formations lying disconformably above these formations represent Plio-Pleistocene units. In this study, different lacustrine carbonates and calcretes were investigated within different lithological units and depositional environments to interpret the palaeoenvironmental and palaeoclimatological evolution of the area.Geological mapping, construction of columnar sections and carbonate sampling were carried out in the field, and stable oxygen and carbon isotope analyses and thin section analyses were done in the laboratory. Lacustrine facies contained abundant pelletal, charophytic algae, oncolitic algal micritic palustrine limestones with ostracods, and micritic mudstones with root traces. Stable carbon and oxygen isotope analysis from the carbonates show a range of δ13C values from −0.6‰ to 11.1‰ (V-PDB) and δ18O values from −13.5‰ to −25‰ (V-PDB).Discontinuous growth of oncolites and spherical pellets (25–40 μm in diameter) in micritic limestone, algal mats and charophyte algae indicate the presence of both shallow and deep water carbonates. Ostracods in dark micritic carbonates indicate quiet and calm water conditions. Microfabrics of the carbonates suggest that they were deposited in a flat and shallow lacustrine environment. The δ18O values of the investigated limestones of the Thakkhola-Mustang Graben suggest that it attained the current elevation level prior to the east-west extension of the Himalaya. |
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| Keywords: | Nepal Himalaya Thakkhola-Mustang Graben Carbonate sedimentology Stable isotopes |
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