Early Pleistocene Integration of the Yellow River I Detrital-Zircon Evidence from the North China Plain

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Palaeogeography, Palaeoclimatology, Palaeoecology 546 (2020) 109691

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Palaeogeography, Palaeoclimatology, Palaeoecology

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Early Pleistocene integration of the Yellow River I: Detrital-zircon evidence from the North China Plain T ⁎ ⁎⁎ Guoqiao Xiaoa,b, , Yuqi Suna, Jilong Yangc, , Qiuzhen Yind, Guillaume Dupont-Nivete,f,g, Alexis Lichth, Alan E. Kehewi, Yunzhuang Huc, Jianzhen Gengc, Gaowen Daia, Qingyu Zhaoa, Zhipeng Wua,d a State Key Laboratory of Biogeology and Environmental Geology, School of Earth Sciences, China University of Geosciences, Wuhan 430074, China b Hubei Key Laboratory of Critical Zone Evolution, School of Geography and Information Engineering, China University of Geosciences, Wuhan 430074, China c Tianjin Centre, China Geological Survey, Key Laboratory of Coast Geo-Environment, Tianjin 300170, China d Georges Lemaître Centre for Earth and Climate Research, Earth and Life Institute, Université Catholique de Louvain, Louvain-La-Neuve 1348, Belgium e Geosciences Rennes UMR 6118, CNRS-Université de Rennes 1, Campus de Beaulieu, 35042 Rennes Cedex, France f Institute of Earth and Environmental Science, Potsdam University, 14476 Potsdam, Germany g Key Laboratory of Orogenic Belts and Crustal Evolution, Ministry of Education, Peking University, Beijing 100871, China h Department of Earth and Space Sciences, University of Washington, Seattle, WA 98195, USA i Department of Geosciences, Western Michigan University, Kalamazoo, MI 49008, USA

ARTICLE INFO ABSTRACT

Editor: Paul Hesse The Yellow River (YR) is one of the longest and most sediment-laden rivers in the world. However, the timing Keywords: and mechanism of the integration of upstream and downstream reaches of the YR is still debated, with estimates Quaternary ranging from > 34 Ma to ~0.15 Ma. Here we address this debate by studying the detrital-zircon age spectra from Late Pliocene three boreholes that penetrate late Miocene sediment in the lower YR floodplain. Our results show a significant Sanmen Gorge provenance change between 1.6 and 1.5 Ma marking the input of new materials from the Middle Reach and/or Provenance the Upper Reach, suggesting the upstream and downstream parts of the YR were connected between 1.6 and River capture 1.5 Ma. This late establishment of the YR is not consistent with the timing of uplift of the northeastern Tibetan Sea level changes Plateau and surrounding mountain ranges and thus precludes a tectonic control; however, it follows the Plio- Pleistocene onset of large-amplitude sea level changes, associated with a worldwide increase of fluvial incision. We propose that Plio-Pleistocene base level fluctuations likely triggered fluvial erosion propagating upstream from the YR lower reach and were thus the main driving force for river integration.

1. Introduction history of the northeastern Tibetan Plateau in the Upper Reaches (Zhu, 1989; Li et al., 1996, 1997), the origin of the Chinese Loess Plateau in The 5464 km long Yellow River, or Huang He, is the 2nd longest the Middle Reaches (Nie et al., 2015), and the formation of the North river in China and the 6th longest river in the world. It originates on the China Plain and continental shelf in the Lower Reaches (Zhang et al., northeastern Tibetan Plateau, makes a great angular bend around the 2004; Yao et al., 2017). Ordos Block, flows out of the Sanmen Gorge and on to the North China Despite over a century of scientific investigations (Willis, 1907; Plain, and finally empties into the Bohai Sea (Fig. 1). It traverses a Wang, 1925; Barbour, 1933), there is still no agreement on the timing series of sedimentary basins and 30 consecutive gorges within its main of the integration of the YR, with estimates ranging from > 34 Ma to course. Previous studies suggested that the YR achieved its present ~0.15 Ma (Zhu, 1989; Lin et al., 2001; Zhang et al., 2004; Pan et al., geometry by integrating a series of ancestral local drainages in the 2005, 2011; Zheng et al., 2007; Li et al., 2017; Liu, 2017; Guo et al., Chinese Loess Plateau and northeastern Tibetan Plateau (Zhu, 1989; Li 2018; Shang et al., 2018). Lin et al. (2001) have proposed that a proto- et al., 1996; Pan et al., 2012; Craddock et al., 2010). Understanding the YR existed in the Eocene as an eastward-draining river running through integration timing of the YR is crucial as it has been linked to the uplift the course of the Weihe River directly to the Sanmen Gorge, and later

⁎ Correspondence to: G. Xiao, State Key Laboratory of Biogeology and Environmental Geology, School of Earth Sciences, China University of Geosciences, Wuhan 430074, China. ⁎⁎ Corresponding author. E-mail addresses: [email protected] (G. Xiao), [email protected] (J. Yang). https://doi.org/10.1016/j.palaeo.2020.109691 Received 20 December 2019; Received in revised form 27 February 2020; Accepted 28 February 2020 Available online 05 March 2020 0031-0182/ © 2020 Elsevier B.V. All rights reserved. G. Xiao, et al. Palaeogeography, Palaeoclimatology, Palaeoecology 546 (2020) 109691

Fig. 1. Geotectonic setting and location of the Yellow River course. (a) Simplified geotectonic map of the drainage area of the Yellow River showing the principal source regions (modified after Yang et al., 2009 and Weislogel et al., 2010). The North China Craton (NCC) consists of the Eastern North China Craton (ENCC), the Trans-North China Orogen (TNCO), and the Western North China Craton (WNCC). OB—Ordos Block; CAOB—Central Asian Orogenic Belt; JB—Junggar Basin; TB—Tarim Block; QB—Qiangtang Block; Q&Q—Qilian and Qaidam; YC—Yangtze Craton; S-G—Songpan-Ganzi; Q-D—Qinling-Dabie. (b) Map of the Yellow River course (revised from Nie et al., 2015) and location of the studied boreholes (red squares). The Upper (U), Middle (M), and Lower (L) Reaches of the Yellow River are divided by black bold lines. The black dashed line denotes the modern watershed boundary. The green dots and numbers show the sites of published detrital-zircon samples cited in the Fig. 4(j) and (k) (see Table 1 for sample information), and the red triangles denote the previously studied sites and their estimates of the Yellow River age (see the text for details). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.) developed a 1500-km-long loop around the Ordos Block in late Mio- major dust supply for these loess deposits at least since 0.9 Ma (Shang cene–early Pliocene. However, dating of the uppermost fluvial terraces et al., 2018). A second line of evidence is from the sedimentary record lying along the Upper and Middle Reaches has yielded much younger of the Sanmen paleolake, a Cenozoic mega lake situated in the Fenwei and dissimilar ages for the integration of the YR (e.g., ~3.6 Ma or Graben to the west of the Sanmen Gorge (Fig. 1). The occurrence of 1.7 Ma at Linxia (Li et al., 1997; Nie et al., 2015) and Lanzhou (Li et al., some non-marine foraminiferal fauna and brackish ostracods in the 1996; Guo et al., 2018), 1.4–1.6 Ma in the Chinese Loess Plateau (Zhu, upper Neogene and lower Pleistocene deposits (Wang et al., 1982) in- 1989), ~8 Ma (Liu, 2017) or 3.7–1.2 Ma (Cheng et al., 2002; Pan et al., dicate that the Sanmen paleolake was once an endorheic basin. In- 2011; Hu et al., 2016) in the Jinshaan Gorge, Fig. 1). In addition, vestigations demonstrated that lacustrine deposition in the Sanmen Craddock et al. (2010) suggested that the development of the upper- paleolake terminated between 1.2 and 1.8 Ma and was followed by most reaches of the YR in northeastern Tibet did not occur earlier than loess deposition (Yue, 1996; Han et al., 1997; Wang et al., 2002a; Li 0.5 Ma. et al., 2004; Kong et al., 2014). The disappearance of the Sanmen pa- Exploring the timing of the YR integration requires age control on leolake is most likely related to incision of the Sanmen Gorge. However, the connection of the Upper and Middle Reaches to the Lower Reaches, others proposed that the termination of lacustrine deposition in the which was formerly blocked by the ~100 km-wide Xiaoshan Mountain Sanmen paleolake occurred later, at ~0.15 Ma (Wang et al., 2002b; uplift block (belongs to the southern part of the Taihang Mountains). Jiang et al., 2007). A third line of evidence for the incision of the The development of the Sanmen Gorge cut through Xiaoshan Mountain Sanmen Gorge is based on the ages of the regional planation surface and and connected the Upper and Middle Reaches to the Lower Reaches of the uppermost terrace along the gorge, which suggested the incision of YR (Fig. 1). Therefore, the incision timing of the Sanmen Gorge is the Sanmen Gorge occurred between 3.6 and 1.2 Ma (Pan et al., 2005; crucial to constraining the integration of the whole YR. However, its Kong et al., 2014; Hu et al., 2017). A fourth line of evidence is based on timing is still under debate. provenance studies from sedimentary cores in the Lower YR, which Four lines of evidence have been proposed as proxies for de- have suggested that the incision of the Sanmen Gorge occurred at least termining the excavation age of the Sanmen Gorge. First, some have ~0.8 Ma based on changes in lanthanum to samarium (La/Sm) ratios, proposed that incision occurred at ~0.24 or 0.15 Ma based on changes SreNd isotopic compositions, and clay mineral assemblages (Yao et al., in sedimentation rates, magnetic susceptibility values and grain-size in 2017; Zhang et al., 2019), as these signals probably reflected the input the loess deposits of Mangshan near the outlet of the gorge (Jiang et al., of large amount of loess materials from the Chinese Loess Plateau. 2007; Zheng et al., 2007), as these loess materials were likely trans- As the most sediment-laden river in the world (Saito et al., 2001), ported by the YR and sourced from the lower YR floodplain. However, a the YR has carried huge amounts of materials from the northeastern recent study suggested that the lower YR floodplain has served as a Tibetan Plateau and the Chinese Loess Plateau to the North China Plain

2 G. Xiao, et al. Palaeogeography, Palaeoclimatology, Palaeoecology 546 (2020) 109691 and the Bohai Sea. Before the integration of the YR, the main sedi- To reveal the origin of the provenance change identified between mentary supply to the North China Plain and Bohai Sea must have come 1.6 and 1.5 Ma, we compared our data (Fig. 6a–f) with published zircon from the local ranges of Yanshan and Taihang Mountains, draining the age compilations from the two potential sediment sources for the YR Eastern North China Craton (ENCC) and Trans-North China Orogen lowermost floodplain: (1) local sources, i.e., the fluvial deposits derived (TNCO) respectively (Fig. 1). The integration of the YR would have from the Taihang and Yanshan Mountains (Fig. 6g), and (2) exotic brought additional material from the Ordos Block in the Middle sources, i.e., the northeastern Tibetan Plateau and Ordos Block in the Reaches and/or from the northeastern Tibetan Plateau in the Upper Upper and Middle Reaches of the YR, respectively (Fig. 6h–i). The Reaches. This source-to-sink relationship between the Upper, Middle 120–180 Ma age population observed in most core samples is com- and Lower Reaches provides an independent and convincing strategy pletely absent in the exotic sources and the modern YR (Fig. 6h–k) but for constraining the timing of integration of the YR (Yao et al., 2017; common in the bedrock of the Yanshan Mountains where the Early Zhang et al., 2019). Jurassic to Early Cretaceous igneous rocks are widespread (Yang et al., To better constrain the provenance changes of the Lower YR, we use 2006, 2009). The lack of 120–180 Ma zircons in the modern YR is due single-grain zircon ages as provenance tracers, which is a diagnostic to the lack of lower YR tributaries flowing from the Yanshan Mountains. tool to identify the source areas in East Asia (e.g., Stevens et al., 2013; They indicate that for the late Miocene onwards, our sampling area has Zheng et al., 2013; Licht et al., 2016). In this study, we carry out pro- been partly fed by the rivers flowing from the Yanshan Mountains. By venance studies based on detrital-zircon age spectra from three well- contrast, the 360–540 Ma zircon age population is very common in pre- dated late Miocene-Pleistocene boreholes in the lower YR floodplain. Cenozoic rocks of northeastern Tibetan Plateau and Ordos Block We compare our data with published detrital-zircon ages from the local (Fig. 6h and i), as well as in the modern YR sediments (Fig. 6j and k) but mountain ranges and the Upper and Middle Reaches of the YR to de- exceptionally rare (~1.5%) in modern fluvial sediment derived from termine when the river integrated. the local ranges (Fig. 6g). This suggests that the abrupt increase of the 360–540 Ma zircons in core samples after 1.6 Ma were derived from the 2. Materials and methods Ordos Block and/or the northeastern Tibetan Plateau, refl ecting an input of exotic sources from the Middle and/or Upper Reaches to the The three studied boreholes (G2, G3, and CK3) are located within Lower Reaches of the YR. This provenance change requires the incision the floodplain of the YR near the Bohai Sea (Fig. 1). Although other of the Sanmen Gorge, establishing the final connection between the local rivers also contribute to the sedimentary supply at these sites, Middle and Lower Reaches of the YR. This age is in agreement with the widespread and extremely frequent flood-induced lateral channel shifts recent estimates of 3.63–1.24 Ma for incision of the Sanmen Gorge in the Lower Reaches of the YR regularly bring the river main course to based on dating the planation surface and the uppermost terrace (Kong the borehole location (Saito et al., 2001; Chen et al., 2012). The sedi- et al., 2014; Hu et al., 2017) and also with the timing of the demise of mentary features and magnetostratigraphic results of these cores have the Sanmen paleolake in the early Pleistocene (Yue, 1996; Han et al., been reported in detail by our previous studies (Hu et al., 2014; Xiao 1997; Wang et al., 2002a; Li et al., 2004; Kong et al., 2014). et al., 2014; Zhou et al., 2018; Yang et al., 2020), and the basal ages of It is noteworthy that high-resolution records of clay minerals and the three boreholes G2 (1226 m, 117.62°E, 39.05°N), G3 (905 m, La/Sm ratios spanning the last 1.1 Ma from the Bohai and Yellow Seas 117.43°E, 38.83°N), and CK3 (500 m, 117.55°E, 38.16°N) are ~8.5 Ma, show a provenance shift at ~0.88 Ma (Yao et al., 2017), suggesting that 8.0 Ma, and 4.4 Ma, respectively (Fig. 2). The long age interval of these the integration of the YR occurred at least ~0.88 Ma ago. In addition, a cores makes them ideal targets to determine when the YR integrated, recent provenance study of a 300-m core (spanning last 3.5 Ma) re- and the results from these three boreholes can be tested for correlation. covered from the western South Yellow Sea shows a major change in To preclude potential contamination by fine zircons from aeolian dust clay mineral record and SreNd isotopic compositions at ~0.8 Ma, (with diameter commonly < 50 μm) deriving from the Asian inland via which has been attributed to the final integration of the YR in its pre- wind (Licht et al., 2016), all the 20 samples were collected from coarse sent form (Zhang et al., 2019). These ages for the provenance change in channel or floodplain deposits of these cores (Table 1), and only zircon the lower YR are much younger than our age based on detrital-zircon grains with diameters larger than 70 μm (commonly > 100 μm; Fig. 3) age data. This difference is probably due to the fact that the La/Sm were measured. ratio, clay mineral records, and SreNd isotopic data used in these Zircon grains were separated by standard heavy liquid techniques, studies are based on bulk sediment samples, and thus they may reflect selected randomly and analyzed by laser-ablation inductively coupled major changes in sediment sources, but they are not necessarily sensi- plasma–mass spectrometer at the China University of Geosciences tive to subtle changes in provenance. At the early stage of the Sanmen (Wuhan) and at the Tianjin Institute of Geology and Mineral Resources, Gorge opening, it is not likely that the YR could transport much sedi- following the analytical procedures of each laboratory (Hou et al., ments to the Bohai and Yellow Seas to influence significantly the signal 2009; Liu et al., 2010b). All the zircon grains were measured using a of bulk samples, as the gorge was probably not sufficiently deep and laser spot diameter of 32 μm(Fig. 3). The ages reported here are wide. However, our single grain zircon provenance analysis is more 206Pb/238U ages for zircons younger than 1000 Ma and 207Pb/206Pb diagnostic than the bulk mineralogical, elemental, and even isotopic ages for older grains. Individual zircons with < 90% concordance were approaches in tracing subtle changes in provenance (e.g., Stevens et al., rejected. The results are available from the Supplementary data. 2013; Zheng et al., 2013; Licht et al., 2016), and has detected an earlier change in provenance between 1.6 and 1.5 Ma. We speculate that the 3. Results and discussion ~0.8 Ma or ~0.88 Ma change in bulk clay minerals and SreNd isotopic records in the Bohai and Yellow Seas (Yao et al., 2017; Zhang et al., 3.1. The timing of integration of the Yellow River 2019) may reflect the input of large amount of loess materials eroded from the Chinese Loess Plateau and Tibetan Plateau to the sites when Kernel density estimation plots of the core samples are presented in the Sanmen Gorge became deeper and wider enough. Fig. 4. Samples exhibit four major age populations in the ranges of Incision of the Sanmen Gorge would have suddenly lowered the 120–180, 200–360, 1600–2200, and 2200–2700 Ma. In addition, a base level for the rivers in the Middle Reaches of YR by > 300 m, and significant age population of 360–540 Ma (6–14%) can be observed in would have significantly enhanced down-cutting and headward ero- the younger sediments (≤1.5 Ma) of these cores, but is conspicuously sion, resulting in subsequent rapid integration of the whole YR system. absent or sparse (mostly < 3%) in the older (≥1.6 Ma) sediments Several additional lines of evidence support a rapid river integration (Figs. 4–6). The appearance of this age population is abrupt and coeval quickly after 1.5 Ma. First, the upstream Jinshaan Gorge underwent in all the three cores between 1.6 and 1.5 Ma (Figs. 4 and 5). rapid incision (exceeding 170 m) starting at 1.2 Ma (Cheng et al., 2002;

3 .Xa,e al. et Xiao, G.

(a) G3 (b) G2 (c) CK3

Stratigraphy Inclination ( e ) Polarity GTS 2012 Polarity Inclination ( e ) Stratigraphy Stratigraphy Inclination ( e ) Polarity GTS 2012 -90 -45 0 45 90 Age (Ma) -90 -45 0 45 90 Depth (m) -90 -45 0 45 90 Age (Ma) SCCSS FSMS SCCS SFSMS SSCCSFSMS 0 0 0 0 0

N1 50 50 C1n N1 50 N1 C1n B 100 R1 R1 M N2 R1 100 N2 1 N2 100 1 J C1r1n 150 R2 C1r 1n

J R2 R2 200 N3 150 150 N3 R3 N3 R3 O N4 250 C2n 200 O C2n 2 2 R4 200 R3 N4 C2r 1n C2r1n 300 N5 R4 250 N4 M 350 250 N5 R4 R5 N5 G R5 C2An 1n 400 300 R5 C2An1n N6 N6 3 N7 R6 N6 3 300 C2An 2n K R7 450 C2An2n N8 R6 350 M C2An 3n R6 C2An3n R8 500 350 N7 N9 400 N7 R9 550 4 R7 Gi N10

4 N8 4 R10 400 R7 C3n 1n R8 N11 600 450 N9 C C3n1n R11 R9 C3n 2n C N12 N 650 450 N10 C3n2n 5 C3n 3n 500 R12 N8 R10 S C3n3n 700 C3n 4n 5 N13 R8 Th 500 550 N11 C3n4n R13 750 R11 Depth (m) 800

600 C3r Palaeogeography, Palaeoclimatology,Palaeoecology546(2020)109691 N14 N12 6 850 650 C3An1n Legend lithostratigraphy Legend magnetostratigraphy 900 R14 N15 B/M=Brunhes/Matuyama Detrital-zircon sample 700 C3An2n 950 M/G=Matuyama/Gauss R12 R15 Tuff bed 7 1000 Gi=Gilbert 750 N16 N13 C3Bn Silt clay Unreliable sample C3Br1n 1050 Clay silt R13 R16 800 C3Br2n Reversed polarity C4n1n 1100 Silt sand Fine sand Normal polarity N14 C4n2n Medium sand 850 8 N17 1150 Uncertain polarity R14 SCCSS FSMS C4r1n N15 R17 1200 900 1230 Depth (m)

Fig. 2. Lithology and magnetostratigraphy of the studied boreholes and comparison with GTS 2012 (Ogg, 2012). (a) Borehole G3 (Zhou et al., 2018; Yang et al., 2020). (b) Borehole G2 (Xiao et al., 2014). (c) Borehole CK3 (Hu et al., 2014). The red dots indicate the positions of samples used for detrital-zircon age analysis (Fig. 4). (For interpretation of the references to colour in this ﬁgure legend, the reader is referred to the web version of this article.) G. Xiao, et al. Palaeogeography, Palaeoclimatology, Palaeoecology 546 (2020) 109691

Table 1 Summary table for provenance samples used in this study.

Site Sample ID Longitude Latitude Description Reference

G2 G2-120 117.62°E 39.05°N 120 m, 0.9 Ma, fine sand This study G2 G2-194 117.62°E 39.05°N 194 m, 1.5 Ma, fine sand This study G2 G2-760 117.62°E 39.05°N 760 m, 6.5 Ma, silty fine sand This study G2 G2-1200 117.62°E 39.05°N 1200 m, 8.2 Ma, fine sand This study G3 G3-66.5 117.43°E 38.83°N 66.5 m, 0.6 Ma, fine sand This study G3 G3-100 117.43°E 38.83°N 100 m, 1.0 Ma, fine sand This study G3 G3-136 117.43°E 38.83°N 136 m, 1.3 Ma, fine sand This study G3 G3-150 117.43°E 38.83°N 150 m, 1.5 Ma, silty fine sand This study G3 G3-162 117.43°E 38.83°N 162 m, 1.6 Ma, fine sand This study G3 G3-187 117.43°E 38.83°N 187 m, 1.9 Ma, silty fine sand This study G3 G3-270 117.43°E 38.83°N 270 m, 3.1 Ma, fine sand This study G3 G3-360 117.43°E 38.83°N 360 m, 3.9 Ma, fine sand This study G3 G3-460 117.43°E 38.83°N 460 m, 4.9 Ma, fine sand This study G3 G3-560 117.43°E 38.83°N 560 m, 6.3 Ma, silty fine sand This study G3 G3-850 117.43°E 38.83°N 850 m, 7.7 Ma, fine sand This study CK3 CK3-71 117.55°E 38.16°N 71 m, 0.8 Ma, fine sand This study CK3 CK3-94 117.55°E 38.16°N 94 m, 1.2 Ma, fine sand This study CK3 CK3-112 117.55°E 38.16°N 112 m, 1.5 Ma, fine sand This study CK3 CK3-174 117.55°E 38.16°N 174 m, 2.5 Ma, silty fine sand This study CK3 CK3-288 117.55°E 38.16°N 288 m, 3.3 Ma, fine sand This study 1 CH12-17 98.17°E 34.89°N Modern YR fluvial sand, upper reach Nie et al., 2015 2 CH12-18 99.70°E 33.80°N Modern YR fluvial sand, upper reach Nie et al., 2015 3 CH12-19 102.46°E 33.53°N Modern YR fluvial sand, upper reach Nie et al., 2015 4 CH12-20 102.09°E 33.96°N Modern YR fluvial sand, upper reach Nie et al., 2015 5 CH12-16 100.17°E 35.50°N Modern YR fluvial sand, upper reach Nie et al., 2015 6 CH12-21 102.23°E 35.88°N Modern YR fluvial sand, upper reach Nie et al., 2015 7 YR-1 103.61°E 36.14°N Modern YR fluvial sand, upper reach Stevens et al., 2013 8 YR-9C 103.87°E 36.08°N Modern YR fluvial sand, upper reach Nie et al., 2015 9 CH11YR03-04 105.67°E 37.52°N Modern YR fluvial sand, upper reach Nie et al., 2015 10 13YELLOW01 106.74°E 39.41°N Modern YR fluvial sand, upper reach Licht et al., 2016 11 BY 106.72°E 39.93°N Modern YR fluvial sand, upper reach Nie et al., 2015 12 YL 108.77°E 40.59°N Modern YR fluvial sand, upper reach Nie et al., 2015 13 S4517A 115.11°E 35.43°N Modern YR fluvial sand, lower reach Nie et al., 2015 14 HH01SD 118.39°E 37.61°N Modern YR fluvial sand, lower reach Yang et al., 2009 15 S4520 119.16°E 37.76°N Modern YR fluvial sand, lower reach Nie et al., 2015 16 YDH01 116.23°E 39.76°N Modern Yongding River, fluvial sand Yang et al., 2009 17 LH01 118.76°E 39.73°N Modern Luanhe River, fluvial sand Yang et al., 2009

Pan et al., 2011; Hu et al., 2016); the Weihe River, largest tributary of 3.2. Possible mechanisms for the integration of the Yellow River the YR, cut through the Liupan Mountains at ~1.4 Ma and rapidly propagated upstream to the Longxi region at ~1.1 Ma (Gao et al., 2016, The evolution of the major rivers in Asia is generally attributed to 2017). Further, flow direction reconstructions indicate that the paleo- tectonically driven topographic changes associated with Tibetan river systems in the northern Jinshaan Gorge (Pan et al., 2012) and Plateau growth (e.g., Li et al., 1996; Brookfield, 1998; Clark et al., Huangshui River (Miao et al., 2008) underwent a flow reversal between 2004; Zheng et al., 2013, 2017; Robinson et al., 2014). Previous studies 1.5 and 1.2 Ma (Fig. 7b). In addition, the observed provenance changes have suggested that the uplift of the northeastern Tibetan Plateau has at ~0.8 Ma in the Bohai and Yellow Seas (Yao et al., 2017; Zhang et al., been the main forcing for the integration of the YR (e.g., Zhu, 1989; Li 2019) may be a response to deepening and widening of the gorge and et al., 1996, 1997). However, our results suggest that the integration of increased erosion in the Middle and Upper Reaches of the YR. the YR significantly lags the major uplift stages (e.g., ~22 Ma, ~14 Ma,

Fig. 3. Representative CL images of analyzed zircon grains. The measured zircon grains are mostly with diameter > 100 μm in size. The circles and numbers denote the spots of LA-ICP-MS analysis.

5 G. Xiao, et al. Palaeogeography, Palaeoclimatology, Palaeoecology 546 (2020) 109691

(a) G2 (b) G3

23.6% 1.8% 44.1% 47.5% G2-120, 0.9 Ma, n=55 9.1% 65.5% G3-66.5, 0.6 Ma, n=59

8.5%

1 5 3.5% .8% 28.1% G3-100, 1.0 Ma, n=57 14% G2-194, 1.5 Ma, n=57 63.2% 66.7% 8.8%

30.9% G2-760, 6.5 Ma, n=55 G3-136, 1.3 Ma, n=66 37.9% 59.1% 67.3% 1.5% 1.8% 1.5%

5.7% 1 41.8% G2-1200, 8.2 Ma, n=51 G3-150, 1.5 Ma, n=110 51.8% 84.3%

3.5% 6.4% 2.7% 250 500 750 1000 1250 1500 1750 2000 2250 2500 2750 Age (Ma) G3-162, 1.6 Ma, n=113 93.8%

1.7%

CK3-71, 0.8 Ma, n=57 17.5%8.8% 68.4% G3-270, 3.1 Ma, n=58 50% 50% 5.3%

51.8% 33.9% 12.5% CK3-94, 1.1 Ma, n=56 G3-360, 3.9 Ma, n=56 39.3% 60.7%

1.8%

28.8% CK3-112, 1.5 Ma, n=111 35.8% 60.4% 9.9% G3-460, 4.9 Ma, n=53 64.2%

0.9%

3.6% 20.5% 40.7% CK3-174, 2.5 Ma, n=112 G3-560, 6.3 Ma, n=59 57.6% 75.9%

1.7% 1.7%

16.9% G3-850, 7.7 Ma, n=45 37.8% CK3-288, 3.3 Ma, n=59 62.2% 81.4%

250 500 750 1000 1250 1500 1750 2000 2250 2500 2750 Age (Ma) 250 500 750 1000 1250 1500 1750 2000 2250 2500 2750 Age (Ma)

0-360 Ma 360-540 Ma 540-1000 Ma >1000 Ma

Fig. 4. Kernel density estimation plots of zircon UePb ages from the studied boreholes. (a) borehole G2. (b) borehole G3. (b) borehole CK3. Note that the post-1.5 Ma appearance of the 360–540 Ma population is indicated by a vertical pink band. The pie charts show the proportions of zircon grains within different age ranges indicated by colors defined in the lower panel. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.) and ~8 Ma) of uplift of the northeastern Tibetan Plateau (Lu et al., accelerated exhumation of the Taihang and Lvliang Mountains occurred 2004; Lease et al., 2007, 2012; Wang et al., 2011). On the other hand, at ~23 Ma and ~6 Ma (Meng et al., 2015; Zhao et al., 2016; Pan et al., several lines of evidence have suggested that the northeastern Tibetan 2018). These regional tectonisms were much earlier than 1.5 Ma, thus Plateau experienced a recent uplift between 1.2 and 0.8 Ma (e.g., Cui not likely the main factors for the integration of the YR. Nevertheless, et al., 1998; Sun and Liu, 2000; Liu et al., 2010a), which has been re- these regional tectonisms could have affected the base level of the ferred to the “Kunlun-Yellow River Tectonic Movement” (Cui et al., Middle YR and influenced the topography around the Sanmen Lake, and 1998). Our results show that the integration of the YR is prior to the thus may have played a delayed role in YR integration, which needs to onset of this late tectonic event by at least 0.3 Ma. Therefore, the in- be further evaluated. tegration of the YR could not be attributed to this late and distant A climate driver has been suggested by recent studies, which have tectonic event in the northeastern Tibetan Plateau either. proposed that the YR was formed by lake expansion and spillover into Tectonic activity in regions closer to the Sanmen Gorge, such as downstream basins that initiated fluvial incision under cooling climates extension and normal faulting in the Weihe Graben (e.g., Zhang et al., during the early Pleistocene (Craddock et al., 2010; Kong et al., 2014). 2003; Rao et al., 2014), or uplift of the Lvliang and Taihang (including However, this scenario conflicts with many pieces of evidence for the the Xiaoshan) Mountains (Meng et al., 2015; Zhao et al., 2016; Pan enhanced aridification observed in the course of the YR, associated with et al., 2018) could have played a role. However, normal faulting in the the expansion of the Northern Hemisphere ice volume during the Weihe Graben did not extend into Xiaoshan Mountain along the Quaternary (Sun et al., 2012). Lithologic features and pollen records Sanmen Gorge (Zhang et al., 2003; Rao et al., 2014); and studies on the from the Sanmen paleolake also indicate a drying trend from late tectono-sedimentary evolution of the Weihe Graben suggested that Pliocene to early Pleistocene, with the depositional environment gra- three major extensions occurred during the periods of late Eocene-early dually changing from shallow lacustrine conditions in late Pliocene to a Oligocene, mid-late Miocene, and latest Miocene to late Pliocene, re- fluvial setting containing water-reworked loess deposits in the early spectively (Zhang et al., 2003, and references therein). Further, Pleistocene (Han et al., 1997). The absence of deep lacustrine facies in

6 G. Xiao, et al. Palaeogeography, Palaeoclimatology, Palaeoecology 546 (2020) 109691

Zircons of 360-540 Ma (%) Herman et al., 2013; Herman and Champagnac, 2016). Given that the initial dissection of the regional planation surface near the Sanmen 0 3691215 Gorge occurred at ~3.7 Ma (Pan et al., 2011; Hu et al., 2016, 2017), coeval with the onset of an extremely unstable climate in the late 0 Pliocene (Lisiecki and Raymo, 2005), we propose that such a climate state could have significantly enhanced erosion of the former drainage divide between the Middle and Lower Reaches of the YR (Xiaoshan 1 Mountain). The late Pliocene onset of this accelerated headward erosion may have finally cut through the ~100 km-wide Xiaoshan Input of exotic sources at ~1.5 Ma Mountain and subsequently integrated the whole YR system in the early 2 Pleistocene. Although river capture events can also happen in stable climate states, we emphasize that the onset of this extremely unstable 3 climate would undoubtedly accelerate this process. Interestingly, it seems that the more erosive climate since the late Pliocene has induced the onset of worldwide rapid fluvial incision, 4 suggesting that the integration of the YR was probably related to this global mechanism. In the tectonically inactive Yangtze Block of East China, terrace dating indicates that > 500 m of incision occurred in the 5 Three Gorges of the Yangtze River over the past 2 Ma (Li et al., 2001). In North America, chronology and inferred incision data indicate that the eastern Grand Canyon underwent fast incision and rapid headward Sample age (Ma) Sample age 6 Legend erosion since ~3.7 Ma (Polyak et al., 2008), which notably lagged the significant uplift of the Colorado Plateau (Flowers et al., 2008). In 7 G2 South America, thermochronological results from the eastern Andean Plateau indicate accelerated canyon incision starting at 4 to 3 Ma (Lease G3 and Ehlers, 2013), notably lagging regional tectonism (Garzione et al., 8 2017) and arguably linked to late Pliocene climate changes. In addition, CK3 a comparison of the fluvial terrace sequences from around the world 9 reveals that further acceleration of global fluvial incision occurred at the time of the middle Pleistocene transition (Bridgland and Westaway, Fig. 5. The percentage of zircon ages in the range of 360–540 Ma for each 2008), when the dominant periodicity of global climate variations sample from the studied boreholes. Note that an abrupt increase of the changed from 40 ka during the Pliocene and early Pleistocene to 100 ka 360–540 Ma population occurred at ~1.5 Ma indicated by an arrow. The ver- during the past 0.7 Ma (Clark et al., 2006), and which was accompanied tical dashed line shows the percentage of the 360–540 Ma zircons (~1.5%) by an increase in amplitude of glacial-interglacial climate and sea level sourced from the North China Craton, and the gray band indicates the variation changes (Lisiecki and Raymo, 2005; Miller et al., 2005). range of the percentage of the 360–540 Ma zircons in the pre-1.5 Ma samples. 3.3. Implications for the development of the Yellow River drainage system the late Pliocene and early Pleistocene sediments of the Sanmen paleolake (Yue, 1996; Han et al., 1997; Wang et al., 2002a; Li et al., 2004; Our results suggest that the timing of integration of the YR is much Kong et al., 2014) precludes the possibility that the incision of the younger than some previous estimates (Lin et al., 2001; Pan et al., 2011; Sanmen Gorge was caused by lake expansion and spillover. In addition, Nie et al., 2015; Liu, 2017; Guo et al., 2018). Studies have demon- the height of the youngest lacustrine sediment, at least 80 m lower than strated that the ages of the uppermost fluvial terrace of the YR and its the height of planation surface (the paleo-watershed) near the Sanmen tributaries, such as Jinshaan Gorge (Lin et al., 2001; Liu, 2017), Gorge (Kong et al., 2014; Hu et al., 2017), also precludes the lake Huangshui River (Lu et al., 2004; Miao et al., 2008), Weihe River (Sun, spillover hypothesis. 2005), and Daxia River (Nie et al., 2015), were asynchronous and much A simple lowering of the base level, either by tectonic uplift or by older than 1.5 Ma. These results are consistent with our proposed model sea-level drop during glacial periods could induce significant incision (Fig. 7a) that these older terraces would have belonged to ancient and headward erosion of the fluvial system (Davis, 1902; Schumm, drainage networks, likely endorheic. This view is supported by the 1993; Xu et al., 2019). In contrast to tectonically induced base level occurrence of some non-marine foraminiferal fauna and brackish os- lowering, climatically induced base level lowering is more rapid and tracods in the late Neogene and early Pleistocene deposits indicating can result in large magnitude cyclical fluvial incision at orbital and endorheic conditions in the Hetao and Fenwei Grabens (Wang et al., millennial timescales (Reusser et al., 2004; Xu et al., 2019), therefore 1982; Yuan et al., 1992). The post-1.5 Ma incision of the Sanmen Gorge potentially playing a key role in fluvial evolution (Davis, 1902; likely united these ancient drainages to form the YR (Fig. 7b). In this Schumm, 1993). Since the late Pliocene, the global climate entered a sense, using the ages of the uppermost fluvial terrace as the sole in- cooler and more variable state (Lisiecki and Raymo, 2005), with glacial- dicator seems unsatisfactory to estimate the timing of the formation of interglacial changes of global sea level exceeding 100 m (Miller et al., the YR. 2005) that have significantly influenced the development of fluvial It has been previously suggested that the YR did not extend a great systems (Schumm, 1993; Reusser et al., 2004). It is noteworthy that a distance into the northeastern Tibetan Plateau before 0.5 Ma (Craddock rapidly fluctuating climate would prevent fluvial systems from estab- et al., 2010). This suggestion is confirmed by our results that the lishing equilibrium states (Zhang et al., 2001; Molnar, 2004), and the 540–1000 Ma zircon grains are almost absent in our cores up to the disequilibrium condition in a river system would enhance erosion of the youngest samples ca. 0.6 Ma (Fig. 4). This zircon population is rather drainage divides and result in lowering and migrating of the drainage limited in the local ranges and the pre-Cenozoic rocks of the Ordos divides and even river capture (Willett et al., 2014). It has been sug- Block (< 2%, Fig. 6h) but well expressed in the Mesozoic Songpan- gested that the rapidly fluctuating climate since the Late Pliocene has Ganzi complex (Fig. 6i) located in the uppermost reaches of the YR deep resulted in globally rapid erosion (Zhang et al., 2001; Molnar, 2004; into northeastern Tibet. Because the modern YR sediments contain a significant proportion (> 7%, Fig. 6j and k) of this zircon population,

7 G. Xiao, et al. Palaeogeography, Palaeoclimatology, Palaeoecology 546 (2020) 109691

Fig. 6. Comparison of detrital-zircon UePb 0 250 500 750 1000 1250 1500 1750 2000 2250 2500 2750 Age (Ma) age distributions from the studied boreholes with their potential sources. (a) and (b) show data from borehole G2; (c) and (d) %6.1

(a) G2, Post-1.5 Ma, n=112 25.9% 1 show data from borehole G3; (e) and (f) show data from borehole CK3. (g), (h), and 9. % 8 52.7% (i) show the compilation of published data from their potential source areas of (g) the local Taihang and Yanshan Mountains

%0 (Yang et al., 2009), (h) the pre-Cenozoic

1 rocks of Ordos Block (Diwu et al., 2012; (b) G2, Pre-1.5 Ma, n=106 6 %6. 0.9% Stevens et al., 2013; Licht et al., 2016), and yaB 75.5% (i) the Songpan-Ganzi complex (Weislogel

iah et al., 2010; Ding et al., 2013), respectively. (j) and (k) show data from the Upper o

B fo tsaoc t tsaoc fo B (Stevens et al., 2013; Nie et al., 2015; Licht 23.3% et al., 2016) and Lower (Yang et al., 2009; (c) G3, Post-1.5 Ma, n=292 40.1% Nie et al., 2015) Reaches of modern YR 28.4% sediments, respectively. Borehole samples

7.2% ≤ 1.0% were grouped into two families ( 1.5 s

ew eht eht ew and > 1.5 Ma) that display strikingly different features. Note that the post-1.5 Ma (d) G3, Pre-1.5 Ma, n=442 26.5% appearance of the 360–540 Ma population 63.8% 8.6% n is indicated by a vertical pink band. Plots of i se i individual samples are shown in Fig. 4. The 1.1% l pie charts show the proportions of zircon oheroB 3.6% grains within different age ranges indicated by colors defined in the lower panel. (For (e) CK3, Post-1.5 Ma, n=224 23.7% interpretation of the references to colour in 60.3% 10.3% this figure legend, the reader is referred to the web version of this article.) 2.2% 0.6%

18.7% (f) CK3, Pre-1.5 Ma, n=171 2.9%

77.8%

3.6%

(g) ENCC and TNCO, n=194 20.1% 1.5% 0.5% 74.2% Local sources 0.7%

(h) Pre-Cenozoic rocks of Ordos Block, n=687 24.2% 62.9% 10.5%

1.7%

(i) Pre-Cenozoic rocks of Songpan-Ganzi complex 22.5% 44.4% Exotic sources n=3228 18.6%

14.5%

(j) Modern Yellow River, Upper Reaches, n=1955 33.8% 25.9%

%7. 25.8% 31

(k) Modern Yellow River, Lower Reaches, n=403 21.3% 52.6% 17.6% Modern Yellow River Modern Yellow 7

. 9

0 250 500 750 1000 1250 1500 1750 2000 2250 2500 2750 Age (Ma)

0-180 Ma 180-360 Ma 360-540 Ma 540-1000 Ma >1000 Ma

8 G. Xiao, et al. Palaeogeography, Palaeoclimatology, Palaeoecology 546 (2020) 109691

(a) Pre-1.5Ma Yinchuan-Hetao Graben

Bohai Sea Xining Basin 1.55-14Ma Lu et al., 2004; Miao et al., 2008 8-3.7Ma Liu, 2017 Pan et al., 2011 3.6Ma 3.6Ma 2.5Ma Guo et al., 2018 Nie et al., 2015 Weihe Graben Sun, 2005

0.01-1.2Ma (b) Post-1.5Ma Hobq Pan et al., 2011, 2012 Desert

~1.5Ma (This study) Mu Us 0.01-1.2Ma Tengger Desert Bohai Sea Lu et al., 2004; Desert Miao et al., 2008

0.01-1.5Ma Li et al., 1996 1.2Ma; Pan et al., 2005

0.002-0.5Ma 0.01-1.4Ma 1.24-3.63Ma Craddock et al., 2011 Li et al., 1997 0.01-1.6Ma Zhu, 1989 Kong et al., 2014; Hu et al., 2017

Fig. 7. A conceptual model for the Yellow River integrated over time. (a) the distribution of endorheic river basins in North China before 1.5 Ma. (b) integration of the Yellow River after 1.5 Ma. Red dots denote the studied sites and their estimates of the local rivers or Yellow River history based on ages of terraces. Note that the flow direction of the paleo-river systems in the northern Jinshaan Gorge and Huangshui River underwent a reversal (white curved arrows) between 1.5 and 1.2 Ma (Miao et al., 2008; Pan et al., 2012). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.) its absence in the core sediments (< 3% in most samples, see Fig. 4) and indicates a much younger integration age for the Yellow River via likely indicates that headward incision of the YR did not propagate headward erosion of the Sanmen Gorge, significantly different from upstream to the Songpan-Ganzi complex until at least 0.6 Ma. previously proposed scenarios (Li et al., 1997; Hu et al., 2017). This late integration of the Yellow River lags the major stages of uplift of the 3.4. Implications for the aridification of the northwestern China northeastern Tibetan Plateau and other regional tectonic events, pre- cluding a dominant tectonic control. The incision of the Sanmen Gorge The integration of the YR drained the basins located in the arid- and the subsequent integration of the whole Yellow River system are fl semiarid Upper Reaches (Fig. 7) and thus could have caused the re- coeval with the worldwide acceleration of uvial incision and head- gional environment to begin to deteriorate. Interestingly, the ~1.5 Ma water erosion since the late Pliocene, implying that a global mechanism fl incision of the Sanmen Gorge was temporally followed by an abrupt such as climate change most likely triggered the uvial erosion. We expansion of desert environment across northwestern China at ~1.2 Ma suggest that the integration of the Yellow River is most likely a response (Fig. 7b), including in the Mu Us (Ding et al., 2005), Tengger (Li et al., to the onset of large-amplitude and high-frequency sea level changes 2014), and Hobq Deserts (Li et al., 2017). However, there is no such associated with increasing climate instability since late Pliocene. desert expansion further west in Central Asia (Ding et al., 2002), nor abrupt global cooling (Lisiecki and Raymo, 2005) at ~1.2 Ma. There- Declaration of competing interest fore, this desert expansion is best interpreted as a regional hydrological and geomorphological response to the emptying of the Yinchuan-Hetao The authors declare that they have no known competing financial Graben, a megabasin situated between the Tengger, Hobq, and Mu Us interests or personal relationships that could have appeared to influ- Deserts (Fig. 7). However, the linkage between environmental dete- ence the work reported in this paper. rioration of northwestern China at ~1.2 Ma and the integration of the YR requires further study. Acknowledgments

4. Conclusions We are grateful to professors Sean Willett, William H. Craddock, Yuanbao Wu, and two anonymous reviewers for their thorough and This study provides a detailed detrital-zircon age record from three valuable comments on an early version. We are grateful to Drs. Zhaochu long sediment cores recovered in the Lower Reaches of the Yellow River Hu, Keqing Zong, and Zhixiang Wang for laboratory assistance. This

9 G. Xiao, et al. Palaeogeography, Palaeoclimatology, Palaeoecology 546 (2020) 109691 study is supported by the National Science Foundation of China (Grant Herman, F., Seward, D., Valla, P.G., Carter, A., Kohn, B., Willett, S.D., Ehlers, T.A., 2013. nos. 41672338, 41972196, 41830319), the Foundation of the Worldwide acceleration of mountain erosion under a cooling climate. Nature 504, 423–426. Geological Survey of China (Grant nos. 121201006000182401, Hou, K., Li, Y., Tian, Y., 2009. In situ U-Pb zircon dating using laser ablation-multi ion DD20190035), the 111 Project (Grant no. B08030). G. Xiao acknowl- counting ICP-MS. Mineral. Deposita 28, 481–492 (in Chinese with English abstract). edges the support from the China Scholarship Council under the file Hu, Y.Z., Xu, Q.M., Yuan, G.B., Pei, J.L., Yang, J.L., Zhang, Y.F., Wang, Q., 2014. Magnetostratigraphy of Borehole CK3 and record of the Quaternary volcanic activ- number 201806415003. G. D.-N. acknowledges support from Horizon eties in Xiaoshan of Haixing, Hebei Province. J. Palaeogeogr. 16, 411–426 (in Chinese 2020 ERC grant 649081 ‘MAGIC’, ANR DSP-Tibet and the Cai Yuanpei with English abstract). programme of the French ministry of foreign affairs. Q. Yin acknowl- Hu, Z., Pan, B., Guo, L., Vandenberghe, J., Liu, X., Wang, J., Fan, Y., Mao, J., Gao, H., Hu, fl edges the support from the Fonds de la Recherche Scientifique - FNRS X., 2016. Rapid uvial incision and headward erosion by the Yellow River along the Jinshaan gorge during the past 1.2 Ma as a result of tectonic extension. Quat. Sci. under grant MIS F.4529.18. Rev. 133, 1–14. Hu, Z., Pan, B., Bridgland, D., Vandenberghe, J., Guo, L., Fan, Y., Westaway, R., 2017. The Appendix A. Supplementary data linking of the upper-middle and lower reaches of the Yellow River as a result of fluvial entrenchment. Quat. Sci. Rev. 166, 324–338. Jiang, F.C., Fu, J.L., Wang, S.B., Sun, D.H., Zhao, Z.Z., 2007. 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