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Global Cooling and Enhanced Eocene Asian Mid-Latitude Interior Aridity

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Global Cooling and Enhanced Eocene Asian Mid-Latitude Interior Aridity ARTICLE DOI: 10.1038/s41467-018-05415-x OPEN Global cooling and enhanced Eocene Asian mid-latitude interior aridity J.X. Li1,2, L.P. Yue2,3, A.P. Roberts4, A.M. Hirt 5, F. Pan1,2, Lin Guo1,Y.Xu1, R.G. Xi1, Lei Guo1, X.K. Qiang3, C.C. Gai6,7, Z.X. Jiang4,7,8, Z.M. Sun9 & Q.S. Liu 10 Tibetan Plateau uplift has been suggested as the main driving force for mid-latitude Asian inland aridity (AIA) and for deposition of thick aeolian sequences in northern China since the 1234567890():,; Miocene. However, the relationship between earlier AIA and Tibetan Plateau mountain building is uncertain because of a lack of corresponding thick aeolian sequences with accurate age constraints. We here present results for a continuous aeolian sequence that spans the interval from >51 to 39 Ma from the eastern Xorkol Basin, Altun Shan, northeastern Tibetan Plateau. The basal age of the studied sequence postdates initial uplift of the Tibetan Plateau by several million years. Our results indicate that the local palaeoclimate was tele- connected strongly to the overall global cooling pattern, so that local enhanced aridification recorded by the studied aeolian sequence is dominantly a response to global climatic forcing rather than plateau uplift. 1 Research Center for Orogenic Geology, Xi’an Center of Geological Survey, China Geological Survey, Xi’an 710054, China. 2 State Key Laboratory for Continental Dynamics, Department of Geology, Northwest University, Xi’an 710127, China. 3 State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi’an 710061, China. 4 Research School of Earth Sciences, Australian National University, Canberra 2601 ACT, Australia. 5 Institute of Geophysics, Eidgenössische Technische Hochschule Zürich, CH-8092 Zürich, Switzerland. 6 State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China. 7 Laboratory for Marine Geology, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266237, China. 8 College of Marine Geosciences, Ocean University of China, Qingdao 266100, China. 9 Laboratory of Paleomagnetism, Institute of Geomechanics, Chinese Academy of Geological Sciences, Beijing 100081, China. 10 Department of Ocean Science and Engineering, Southern University of Science and Technology, Shenzhen 518055, China. Correspondence and requests for materials should be addressed to Q.S.L. (email: [email protected]) NATURE COMMUNICATIONS | (2018) 9:3026 | DOI: 10.1038/s41467-018-05415-x | www.nature.com/naturecommunications 1 ARTICLE NATURE COMMUNICATIONS | DOI: 10.1038/s41467-018-05415-x sian inland aridity (AIA) has been linked strongly with Results Asurface Tibetan Plateau uplift1–7. Details of late Eocene Evidence for aeolian dust. Most terrestrial clastic sediments with and early Miocene uplift history have been reported silt-clay size particles are transported by either water or wind. widely from different methods8–10. Recent studies trace an initial Following typical studies of aeolian dust on the Chinese Andean-like Tibetan Plateau to the early Eocene11–13, but no Loess Plateau (CLP) and surrounding areas2,16–18, we interpret related long AIA records are available for that time period. This the studied red clay sediments as aeolian deposits for the fol- hampers the understanding of any potential causality between lowing six main reasons. First, the fine-grained sediment fraction early Tibetan Plateau uplift and AIA. Aeolian deposits, such as (<100 μm) that can be transported in suspension by wind19 loess and red clay, are particularly valuable as indicators of dry consists of up to 92% of the total sediment, which is within the land evolution because sizeable deserts are needed as sources for typical range for aeolian dust from the CLP20. Second, aeolian aeolian deposits2,14,15. Therefore, long (semi-) continuous aeolian dust on the CLP is well sorted due to long-distance transportation deposits have been used widely to trace the history of AIA. and accumulated at low and relatively stable rates. Chinese loess Reworked and discrete aeolian deposits are also helpful for is, thus, homogenous and devoid of stratification and lamina- palaeoclimate reconstructions16–18. tion21. The studied red clay also lacks bedding, but has pseudo- To trace early stages of AIA development and its underlying bedding (Fig. 2a, Supplementary Figure 3; Supplementary Note 2) mechanisms, we here investigated a 95.8-m red clay sequence associated with calcareous nodules derived from leaching of from the Xorkol Basin (91°31′45″ E, 38°54′42″ N), which is a primary clay. Layer-cutting spindle-like calcareous nodules in Cenozoic Basin within the Altun Shan, northeastern Tibetan some “layers” distinguish pseudobedding from periodic climatic Plateau (Fig. 1; Supplementary Figures 1 and 2; Supplementary stratification and lamination (Fig. 2a, Supplementary Figure 3). Table 1; Supplementary Note 1). Our study demonstrates that the Third, mineral assemblages and geochemical features of the stu- studied sequence spans the ~51–39 Ma time interval. The basal died red clay are comparable to those of aeolian red clay from the age of the studied sequence postdates initial uplift of the Tibetan CLP (Fig. 2b–d). Fourth, grain size distributions of the clastic Plateau by several million years. Our results indicate that component in the red clay have bimodal distributions (~30–100 enhanced Eocene AIA was mainly driven by global palaeoclimatic μm and ~1–10 μm for the coarse and fine fractions, respectively) changes rather than being a direct response to the plateau uplift. and remain relatively stable throughout the profile (Fig. 2e). The a 45 N Tarim Basin 39 15′ Studied locality Fault 40 Paratethys in the middle Eocene Xorkol Basin 38 45′ Qaidam Basin 91 00′ 91 30′ 92 00′ 35 Eocene Tibetan Plateau 30 0 400 km 25 70 E 80 90 100 110 b 6000 6000 4000 4000 Modern 2000 topography Eocene Rain shadow 2000 profile topography profile area (m) (m) 250 500 750 1000 1250 1500 1750 Along-section distance (km) Fig. 1 Topographic map of the study location and surrounding region. a Present day topography of the Tibetan Plateau and location of the study site. The sub-figure is focused on the Altun Shan and surrounding area. Also shown in a are the estimated extent of the Paratethys Sea60 and the estimated extent of the Tibetan Plateau in the Eocene13. b Topographic profiles across the Tibetan Plateau for the present day and early Eocene periods. The star indicates the location of the studied stratigraphic sequence. The early Eocene reconstruction is from ref. 13. The digital elevation data are from http://www.gscloud.cn/ 2 NATURE COMMUNICATIONS | (2018) 9:3026 | DOI: 10.1038/s41467-018-05415-x | www.nature.com/naturecommunications NATURE COMMUNICATIONS | DOI: 10.1038/s41467-018-05415-x ARTICLE a b Q Q: Quartz Chl: Chlorite Or: Orthoclase Gao: Kaolinite 12 Eocene red clay Ab: Albite It: illite Cal: Dolomite I/S: illite/smectite SL loess Do: Hematite Te: Amphibole 10 SL red clay SL paleosol Q PS) Q Q Q Q 8 Chl It Gao Ab Chl Or 6 I/S Intensity (C 4 Do Te Hem 2 ×103 10 20 30 40 50 2 (°) c 100 d 1000 SiO2 Ba Eocene red clay Eocene red clay Rb Zr Al2O3 10 100 Sr Fe O 2 3 Y CaO K2O .) Ni MgO Pb Li Th Nb Na O Sc 1 2 10 Co Hf Cs TiO2 Be U Content (wt%) Content (p.p.m Ta P2O5 0.1 1 Bi MnO Qinan red clay Qinan red clay 0.01 0.1 0.01 0.11 10 100 0.11 10 100 1000 Content (wt%) Content (p.p.m.) e f 8.0 %) 6.0 4.0 Frequency percentage ( 2.0 10 μm JEOL 10/11/2016 0 X 180010.0 kV SEILM WD 8.0 mm 14 : 49 :49 0.1 1 10 100 1000 Content (mm) Fig. 2 Evidence for an aeolian origin of the studied red clay. a Field photograph of alternating reddish-brown clay and grey caliche nodule layers. b Mineral composition from X-ray diffraction results from bulk sediments for the studied red clay in Altun Shan, compared with Quaternary loess and red clay from Shilou61 (SL) on the Chinese Loess Plateau. c, d Average major and trace element distributions for the studied red clay from Altun Shan compared with red clay from Qin’an62. e Grain size distributions for the studied red clay from Altun Shan. f Scanning electron microscope image of representative quartz grains that illustrate the angular morphology of the grains bimodal distribution is strikingly similar to Miocene-Quaternary collisions and preserves the original shape of quartz grains from CLP aeolian deposits that were transported by two wind the source area. Sixth, elemental signatures of the studied Eocene systems22,23 and to aeolian deposits in the NE Tibetan Plateau red clay are similar to the average composition of upper con- (Fig. 2e)16. Fifth, quartz grains, which comprise the main granular tinental crust, which indicates that the sediments were derived mineral of the studied red clay, have irregular and angular shapes, from well-mixed sedimentary protoliths that underwent repeated with most having sharp edges (Fig. 2f), low-relief and conchoidal upper crustal recycling (Supplementary Figure 4)26. The sediment fracture. This is because fine particles are transported in must, therefore, be derived from widely mixed areas, such as suspension24,25, which decreases grain–grain and grain–bed Asian deserts, because local sources have more specific NATURE COMMUNICATIONS | (2018) 9:3026 | DOI: 10.1038/s41467-018-05415-x | www.nature.com/naturecommunications 3 ARTICLE NATURE COMMUNICATIONS | DOI: 10.1038/s41467-018-05415-x geochemical signatures. All of the above sedimentological and oceanic moisture sources and highly evaporative conditions. geochemical evidence attests to an aeolian origin for the studied Given that the Tibetan Plateau was already elevated to altitudes red clay deposits (Supplementary Notes 3 and 4).
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