This is the author’s version of a work that was submitted/accepted for publication in the following source: Neupane, Bhupati, Ju, Yiwen, Allen, Charlotte M., Ulak, Prakash Das, & Han, Kui (2017) Petrography and provenance of Upper Cretaceous-Palaeogene sandstones in the foreland basin system of Central Nepal. International Geology Review, pp. 1-22. This file was downloaded from: https://eprints.qut.edu.au/108592/
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Group This is an electronic version of an article published in Bhupati Neupane, Yiwen Ju, Charlotte M. Allen, Prakash Das Ulak & Kui Han (2017): Petrography and provenance of Upper Cretaceous – Palaeogene sandstones in the foreland basin system of Central Nepal, International Geology Review, DOI:10.1080/00206814.2017.1312716. International Geology Review is available online at informaworldTM
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Petrography and provenance of Upper Cretaceous – Paleogene sandstones in the foreland
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basin system of the Central Nepal
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Bhupati Neupane1, 2, Yiwen Ju 1, 2, *, Charlotte M. Allen3, Prakash Das Ulak4, Kui Han 1, 2
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China
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College of Earth Science, University of Chinese Academy of Sciences, Beijing 100049, China
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Institute for Future Environments, Queensland University of Technology, Gardens Point
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Campus, 2 George Street, Brisbane, QLD 4000, Australia
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Key Lab of Computational Geodynamics of Chinese Academy of Sciences, Beijing 100049,
Department of Geology, Tri Chandra Multiple Campus, Tribhuvan University, Kathmandu,
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Nepal
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*Corresponding Author:
[email protected] (Y. Ju)
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E-mail Addresses:
[email protected] (B. Neupane),
[email protected] (Y. Ju),
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[email protected] (CM. Allen),
[email protected] (K. Han)
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ABSTRACT
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Sedimentary deposits of the Cretaceous to Miocene Tansen Group of Lesser Himalayan
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association in central Nepal record passive-margin sedimentation of the Indian Continent with
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direct deposition onto eroded Precambrian rocks (Sisne Formation onto Kaligandaki Supergroup
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rocks), succeeded by appearance of orogenic detritus from orogenesis as the Indian continent
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collided with Asia on a north-dipping subduction zone. Rock samples from two field traverses
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were examined petrographically and through detrital zircon U-Pb dating, one traverse being across
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the Tansen Group, and another across the Higher and Tethyan Himalaya. The Tansen Group
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depositional ages are well known through fossil assemblages. We examined samples from three
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units of the Tansen Group (Amile, Bhainskati, and Dumri Formations). Sedimentary petrographic
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data and Qt F L and Qm F Lt plots indicate their “Quartzose recycled” nature and classify Tansen
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sedimentary rocks as “recycled orogenic” suggesting Indian cratonic and Lower Lesser Himalayan
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(LLH) sediments as the likely source of sediments for the Amile Formation, the Tethyan Himalaya
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(TH) and Upper Lesser Himalaya (ULH) as the source for the Bhainskati Formation, and both the
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Tethyan and Higher Himalaya as the major sources for the Dumri Formation. The Cretaceous to
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Paleocene pre-collisional Amile Formation is dominated by a broad dertrital zircon U-Pb ~1830
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Ma age peak with neither Paleozoic nor Neoproterozoic zircons grains but hosts a significant
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proportion (23%) of syndepositional Cretaceous zircons (121 to 105 Ma) would be contributions
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from the Lower Lesser Himalayan volcanosedimentary arc, Gangdese batholith (including Xigaze
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forearc). The other formations of the Tansen Group are more similar to Tethyan units than to
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Higher Himalaya Crystalline (HHC). From the analyzed samples, there is a lack of distinctive
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evidence for Higher Himalayan detritus in the Tansen basin. Furthermore, the presence of ~23+/-
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1 Ma zircons from the Higher Himalaya unit suggests that they could not have been exposed until
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the earliest Miocene time.
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Keywords: Central Nepal; Foreland Basin; Optical Petrography; U-Pb Zircon Ages; Stratigraphy
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1. INTRODUCTION
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The world’s largest peripheral foreland basin, the Himalayan foredeep basin of India, Nepal, and
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western Pakistan, formed on the Paleozoic through early Cenozoic Tethyan continental margin of
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the Indian Plate (DeCelles, 2011; Gehrels et al., 2011; Vadlamani et al., 2011; Singh,2013). The
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Cretaceous – Paleogene sedimentary basin (Tansen Group), located in the southern part of the
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Lesser Himalaya, is one of the basins deposited on an eroded surface of Precambrian basement of
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the Lesser Himalaya (DeCelles et al., 1998; Sakai, 1983). The foreland basin sequences of the
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Nepal Himalaya are mostly continental deposits (some marine beds) developed first in a passive-
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margin setting succeeded by detritus from the collision of the Indian plate with the Asian plate
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about ca.60–50 Ma (e.g., Hu et al., 2016 and references therein). Whilst some recent studies have
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suggested that the initial India-Asia collision took place only at ~34 Ma (Aitchison et al., 2007;
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Aitchison et al., 2000; Gibbons et al., 2015; Hébert et al., 2012). Aitchison et al.(2011) proposed
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that an interoceanic arc (Zedong Terrane) collided with India, initially at ~55 Ma whereas Najman
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et al. (2017) suggests the terminal collision of India with Asia took place at 54 Ma.
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Since after the following collision the upliftment process of the mountain ranges of the Lesser
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Himalaya (LH), the Higher Himalaya (HH), and Tethys Himalaya (TH) took place and ultimately
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were weathered and eroded, and the foreland basin was over filled by their detritus (DeCelles et
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al., 1998). In the rocks of the Tansen Group, with the changing tectonics from passive-margin
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setting to a basin adjacent continental collision one can examine the changes in the sediment
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composition and style.
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Quartz, the essential mineral in sandstone derived from plutonic, volcanic, metamorphic, or
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sedimentary rocks is a potential indicator for provenance analysis (Pettijohn et al., 1987). Even
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though there are two different classification schemes to quantify sandstone framework, the Indiana
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method and the Gazzi-Dickinson (GD) method, we used the broadly used GD point counting
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method that was developed independently by Gazzi (1966) and Dickinson (1970) to minimize the
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effects of grain-size variations on sandstone composition. However, there are some limitations of
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the GD method that only apply to fine sand grains (