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Erg Deposition and Development of the Ancestral Taklimakan Desert (Western China) Between 12.2 and 7.0 Ma Richard V

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Erg Deposition and Development of the Ancestral Taklimakan Desert (Western China) Between 12.2 and 7.0 Ma Richard V https://doi.org/10.1130/G45085.1 Manuscript received 27 April 2018 Revised manuscript received 24 July 2018 Manuscript accepted 16 August 2018 © 2018 The Authors. Gold Open Access: This paper is published under the terms of the CC-BY license. Published online 11 September 2018 Erg deposition and development of the ancestral Taklimakan Desert (western China) between 12.2 and 7.0 Ma Richard V. Heermance1, Jozi Pearson1, Annelisa Moe1, Liu Langtao2, Xu Jianhong3, Chen Jie3, Fabiana Richter4, Carmala N. Garzione4, Nie Junsheng5, and Scott Bogue6 1Department of Geological Sciences, California State University Northridge, Northridge, California 91330-8266, USA 2Department of Prospecting Engineering, Hebei University of Engineering, Handan, Hebei, 056038, China 3State Key Laboratory of Earthquake Dynamics, Institute of Geology, China Earthquake Administration, P.O. Box 9803, Chaoyang District, Beijing, 100029, China 4Department of Earth & Environmental Sciences, University of Rochester, Rochester, New York 14627, USA 5Key Laboratory of Western China’s Environment System (Ministry of Education), College of Earth and Environmental Sciences, Lanzhou University, Lanzhou, Gansu 730000, China 6Department of Geology, Occidental College, Los Angeles, California 90041, USA ABSTRACT development behind the Pamir and Tian Shan at The Taklimakan Desert in western China contains the second largest shifting sand des- the Oligocene-Miocene and Miocene-Pliocene ert on earth. The onset of this desert formation has been debated between the Eocene, early boundaries (e.g., Sun et al., 2011; Bosboom Miocene, late Miocene, or Pliocene, with each hypothesis having profound implications for et al., 2014; Licht et al., 2014; Carrapa et the climatic and tectonic evolution of this region. We provide stratigraphic evidence for des- al., 2015; Zheng et al., 2015; Bougeois et al., ert formation based on a new 3800-m-thick stratigraphic section in the northwestern Tarim 2018). Mountain uplift would block westerly Basin. Magnetostratigraphy defines 50 magnetozones and constrains the age of these strata airflow and moisture, producing a rain shadow to between ca. 15.1 and 1.5 Ma. Fluvial and lacustrine strata at the base of the section change within the Tarim Basin (e.g., Caves et al., 2015). abruptly to eolian sandstone (~1100 m thick) at 12.2 Ma and persist until 7.0 Ma, implying Although parts of the Pamir may have been high development of an erg system that represents the ancestral Taklimakan Desert. The appear- prior to 35 Ma, northward indentation and uplift ance of sand dunes at 12.2 Ma has no global climate parallel, and resulted from aridification was most pronounced after ca. 25 Ma, with in the rain-shadow behind a growing Tian Shan and Pamir that isolated the Tarim Basin. pulsed episodes from 21–13 Ma, 20–16 Ma, 20–8 Ma, 25–16 Ma, and 6–0 Ma, depending INTRODUCTION dunes are interpreted to be between 26.7 and on location (Sobel and Dumitru, 1997; Amidon The Tarim Basin in northwest China contains 22.6 Ma at the Aertashi section in the southwest- and Hynek, 2010; Bershaw et al., 2012; Lukens the Taklimakan Desert, one of the largest erg ern Tarim Basin (Zheng et al., 2015), and Wang et al., 2012; Thompson et al., 2015; Blayney systems on Earth. Ergs, also known as sand seas, et al. (2014) interpret eolian strata intermittently et al., 2016). Similarly, the southwestern Tian are large regions (100–106 km2) where sand cov- throughout the Miocene in the Pamir-Tian Shan Shan had pulsed deformation and uplift initiat- ers >20% of land area, and are typically unveg- convergence zone (Fig. 1A). The first evidence ing at 25–20 Ma, with southward migration of etated and arid desert environments (Wilson, of thick eolian successions, however, don’t deformation at 16.3, 13.5, and 4 Ma (Sobel et 1973). The Tarim Basin formed between the appear until 7.0 Ma or 4.2 Ma at the Mazatagh al., 2006; Heermance et al., 2007). This study Tibetan Plateau, Pamir, and Tian Shan orogens, section (M in Fig. 1A; Sun et al., 2009., 2011). provides new age constraints on eolian strata and contains a 3–8-km-thick Cenozoic stratig- Shifts to eolian deposition resulted from the from the Tarim Basin, to test the hypothesis raphy. Since the early Miocene, the fluvial and retreat of the Tethys seaway and/or global cli- that growth of the Tian Shan and Pamir are lacustrine Wuqia Group, Atushi Formation and mate change in the late Eocene, or rain-shadow linked to desert development. Xiyu Formation have been deposited there (ie. Heermance et al., 2007; Zheng et al., 2015), but A 42°N B 77.25˚ 77.5˚ 77.75˚ Tian Shan P there is little evidence for thick eolian deposits WK (this study) iqiang Faul WK section 40˚ similar to that being deposited today, and thus UL Tarim Basin Kashgar the age of desert formation and associated arid- PE M A t ification is unresolved. Thin (<100 m) eolian Pamir S eolian strata north Dashenkou lt strata appeared as early as 39 Ma in the Tajik 36°N Fau Valley base of ntage Tibetan Plateau Cenozoic Kepi Basin (Tajikistan; Carrapa et al., 2015), isolated 70E° 74E° 78E° 82E° 76.75˚ 10 km 77˚ 77.25˚ 77.75˚ CITATION: Heermance, R.V., Pearson, J., Moe, A., Figure 1. A: Regional map showing the study area (WK section), previous work (white stars), and Langtao, L., Jianhong, X., Jie, C., Richter, F., Garzione, the location of Kashgar Town (northwestern China), located just south of the Kashgar section C.N., Junsheng, N., and Bogue, S., 2018, Erg deposi- (Heermance et al., 2007). A—Aertashi section (Zheng et al., 2015); M—Mazatagh section (Sun et tion and development of the ancestral Taklimakan Des- al., 2009, 2011); PE—PE section (Carrapa et al., 2015); S—Sanju section (Sun and Liu, 2006); UL— ert (western China) between 12.2 and 7.0 Ma: Geology, Ulugqat section (Wang et al., 2014). B: Google Earth™ image of study area (outlined in A) showing v. 46, p. 919–922, https://doi.org/10.1130 /G45085.1 sample locations (black dots), major faults (red-lines with barbs on hanging wall), base of Miocene strata (green line), Dashenkou Valley (blue line), and the extent of the described eolian strata. Geological Society of America | GEOLOGY | Volume 46 | Number 10 | www.gsapubs.org 919 Downloaded from http://pubs.geoscienceworld.org/gsa/geology/article-pdf/46/10/919/4338820/919.pdf by guest on 23 September 2021 METHODS p . strat.ht. r. paleoflow 3800 m of continuous Miocene–Quaternary (m) Fm Mb direction Mag ATNTS Grou lithology Decl. Incl. stratigraphy were measured and described from 3800 strat. 2012 N R R N the West Kepintagh (WK) section in the north- n=27 0 west Tarim Basin (39.9°N, 77.3°E; Fig. 1B). We conducted 138 paleocurrent measurements, Xiyu 1 including planar and trough cross-stratification, n=10 imbricated clasts, ripples, and channel margins 2.2 Ma 2 (Table DR1 in the GSA Data Repository1) from 16 stratigraphic levels, and processed 486 ori- 3000 3 ented samples from 460 sites (8.3 m average sample spacing; Table DR2) for paleomagne- 4 tism at the Occidental College (California, USA) Paleomagnetic Laboratory using the methods 5 described in the Data Repository. Atushi n=29 6 RESULTS 7 Stratigraphy 2000 Five of six described lithostratigraphic units within the WK section correlate with strata from 8 the Kashgar Basin, and we define lithofacies 7.0 Ma after Heermance et al. (2007) (Fig. 1A). Details n=15 9 on stratigraphy are provided in the Data Reposi- tory and in Figure 2. Units include: 0–270 m: 10 Wuqia Group Unit B, interpreted as meandering n=9 fluvial deposition; 270–318 m: Wuqia Group 11 Unit C, interpreted as shallow lacustrine and p 1000 playa; 318–525 m: Wuqia Group Pakabulake Eolian Mbr. n=15 12 Formation, interpreted as meandering river Pakabulake and floodplain; 1698–3285 m: Atushi Forma- 13 tion (also called the Artux Formation), inter- Wuqia Grou 12.2 Ma preted as channelized fluvial and floodplain; 14 n=25 3285–3800 m: Xiyu Formation, interpreted as 13.3 Ma braided stream and alluvial fan. unit C 13.6 Ma 15 Between 525 and 1698 m, the stratigra- unit B n=6 phy changes dramatically to well-sorted, pale- 0 17.5 Ma 16 m s f m c g 0˚ 180˚ -90˚ 0˚ 90˚ red, fine-grained sandstone characterized by (Ma) >1-m-thick, planar, continuous beds with meter- sand scale cross-bedding (Fig. 3A). Sand grains are Figure 2. Stratigraphy of the West Kepintagh (WK) section in the northwest Tarim well-sorted, rounded, and show evidence of pits, Basin (color-coded by Formation), and magnetostratigraphy, including paleocurrent directions. Black = unidirectional fluvial data; gray = bidirectional fluvial data; red = depressions and upturned plates (Fig. 3B; Figs. eolian data. ATNTS—Astronomically Tuned Neogene Time Scale (Ogg, 2012). Black DR1 and DR2). Beds contain 0.2–1.5-m-ampli- polarity zone = normal; white polarity zones = reversed; gray zones = ambiguous. tude tabular cross-bedding (Figs. DR3A–DR3F) strat.ht.—stratigraphic height; Fm.—Formation; Mbr.—Member; Decl.—declination; and have 1–3 mm upward-coarsening laminations Incl.—inclination. Sand grain sizes: f—fine; m—medium; c—coarse; m—mud; s—silt. (Fig. DR2). These strata are interpreted as eolian dune deposits based on the following rationale: (1) The pitted sand grain textures are diag- represent the passage of dunes across draas nostic of grain impacts in wind-blown sand (very large-scale dune bedforms; Fig. 3A; Fig. (Krinsley and Doornkamp, 1973). DR5B). In contrast, the lower contacts of fluvial 1 GSA Data Repository item 2018342, DR Text: (2) Reverse-graded laminations imply grain- channel sandstones are laterally discontinuous Paleomagnetic methods and discussion, stratigraphic flow on the slip face of eolian dunes (Kocurek and show scour into the underlying mudstone descriptions, grain-size analysis; Table DR1: Paleo- current data; Table DR2: Paleomagnetic sites and and Dott, 1981).
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