Grain size, magnetic susceptibility and geochemical characteristics of the loess in the Chaohu lake basin: Implications for the origin, palaeoclimatic change and provenance

Journal of Asian Earth Sciences 117 (2016) 170–183

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Grain size, magnetic susceptibility and geochemical characteristics of the loess in the Chaohu lake basin: Implications for the origin, palaeoclimatic change and provenance Houchun Guan a,b,⇑, Cheng Zhu a,⇑, Tongxin Zhu c, Li Wu d, Yunhuai Li b a

School of Geographic and Oceanographic Sciences, Nanjing University, Nanjing 210093, China Anhui Institute of Geological Survey, Hefei 230001, China Department of Geography, Urban, Environment and Sustainability, University of Minnesota-Duluth, 329A Cina, Duluth, MN, USA d College of Territorial Resources and Tourism, Anhui Normal University, Wuhu 241003, China b c

a r t i c l e

i n f o

Article history: Received 20 April 2015 Received in revised form 4 December 2015 Accepted 14 December 2015 Available online 14 December 2015 Keywords: Loess Grain-size Magnetic susceptibility Geochemical weathering Provenance The Chaohu lake basin

a b s t r a c t Rare studies on the aeolian deposit located in north bank of the Yantgze River are documented. Recently, it is found in the field investigations and in bore sections that the loess in the Chaohu lake basin has the largest thickness of over 40 m. In this study, the probability cumulative curves, frequency distribution, the grain size distributions and the discriminant function of the grain size suggest that the loess in the Chaohu lake basin is of eolian origin. The magnetic susceptibility curves of the loess in the basin coincide perfectly with those of the loess in the northern China and the marine isotope stages (MIS), and show that paleoclimatic cycles and sub-cycles were documented since L3 during middle–late Pleistocene in the basin. The MS curve of Paleosol S1, Paleosol S2 and loess L3 in the basin coincide perfectly with MIS5, MIS-7 and MIS-8, respectively. The good correspondence indicates that the loess in the basin has given a sensitive response to the globe paleoclimatic change since L3. On the other hand, the climate changes in some stages recorded by the loess has regional characteristics obviously, which might be the result of the dual effect of globe climate changes and East-Asia monsoon climate changes. The result of geochemical characteristics suggests that the loess in the basin has undergone moderate to strong chemical weathering. Most elements are mobilized during chemical weathering; Na and Ca of the loess are markedly lost and the removal of K is also evident, and chemical weathering doesn’t evidently turn into the Si removal stage. The chemical weathering of the loess is more intensive than that of the loess deposits in northwestern China and the upper reaches of the Yantgze River. The intensive chemical weathering has been documented by the loess might be related to strong monsoon climate in Chaohu lake basin. The provenance of the loess also differs from that in northern China, and is discussed firstly with the lithofacies palaeogeography. The well-developed alluvial–lacustrine deposits in the Huaihe floodplain seem to be the major source materials of the loess. Ó 2015 Elsevier Ltd. All rights reserved.

1. Introduction A number of studies have been conducted on the loess deposits in the semi-arid continental monsoon climate regions of NW China, which provided a significant amount of information about their origin, source provenance, and paleoclimate conditions (Liu, 1985; Wen, 1989; Gallet et al., 1998; Ding et al., 1999, 2001; Gu et al., 2000; Chen et al., 1996, 1998, 2001; An et al., 2001; Jahn et al., 2001; Sun and An, 2002; Liu et al., 2002; Sun and Wang, ⇑ Corresponding author at: Anhui Institute of Geological Survey, No.19 Ningguo Road, Hefei 230001, China. E-mail address: [email protected] (H. Guan). http://dx.doi.org/10.1016/j.jseaes.2015.12.013 1367-9120/Ó 2015 Elsevier Ltd. All rights reserved.

2005; Liu et al., 2005, 2006; Stevens et al., 2006; Sun et al., 2008; Xiong et al., 2010). In order to obtain more detailed information about Quaternary environmental changes, and further catch East Asian winter monsoon activity and the consequent southward displacement of Northern Hemisphere westerlies (Liu, 1985; Yang et al., 1991; Hong et al., 2013), it is necessary to study the loess deposit of eastern and southern regions with relatively humid climate. The loess–paleosol sequences in the middle–lower reaches of the Yantgze River are fundamental geological records of environmental processes and have been powerful tools to study climate changes for the humid subtropical climate regions. In recent years, more attention has been paid to investigate the southern deposit of

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Middle–Late Pleistocene in these regions (Liu, 1985; Yang et al., 1991; Li et al., 1997, 2001; Wu et al., 1992; Qiao et al., 2003, 2011; Hao et al., 2010; Hong et al., 2010, 2013). Previous studies of the southern aeolian deposit have mostly focused on grainsize characteristic (Li et al., 1997, 2001; Qiao et al., 2003; Hu et al., 2005), chemical weathering (Yang et al., 2001,2004; Chen et al., 2008; Hong et al., 2010), environmental magnetism (Zhang et al., 2007; Qiao et al., 2003), isotopic compositions (Qiao et al., 2011; Hong et al., 2013; Liu et al., 2014) and provenance (Liu, 1985; Yang et al., 1991; Li et al., 1997, 2001; Hao et al., 2010; Qiao et al., 2011; Hong et al., 2013) in south of the middle–lower Yangtze River (e.g. Nanjing, Zhenjiang, Xuancheng, etc.), while, so far, rare relevant studies on the aeolian deposit in north of the river are documented. The occurrence of continuous loess deposits requires a sustained source of dust and adequate wind energy to transport the dust (Pye, 1995). There is no agreement on the source of the loess in southern China, among the existing studies (Liu, 1985; Yang et al., 1991; Li et al., 1997, 2001; Qiao et al., 2003). The predominant and traditional view is that the southern loess materials were mainly derived from the deserts of northern China (Yang et al., 1991; Li et al., 1997, 2001), while the others propose that finegrained floodplains in local river valleys or lake beds, exposed during glacial times, played an important role as the provenance areas (Wu et al., 1992; Qiao et al., 2003, 2011; Hao et al., 2010; Hong et al., 2013). The loess in the Chaohu lake basin of Anhui Province (Fig. 1a–c) is widely scattered in the Jianghuai plain in eastern China and has the largest thickness of over 40 m (Fig. 1d). There are two views about its origin. One is that the loess is fluvial (Xu, 1936), while the other proposes that it is eolian (Yu and Peng, 2008). Meanwhile, its chemical weathering intensity and provenance have not yet been carried out that would be particularly helpful to climate change. Thus, a study of the loess in the Chaohu lake basin is significant to the loess source and reconstruction of middle–late Pleistocene paleoenvironments in the northern subtropical region. Furthermore, the study on the provenance and Quaternary environmental changes is helpful to discuss the cause of the Chaohu lake which is still in suspense. Moreover, the Chaohu lake basin is bordered by the Dabie Mountains to the southwest, the Jianghuai hilly region to the northeast, the Huaihe floodplain to the northwest, and the South Anhui Mountains to the southeast (Fig. 1c) (Bureau of Geology and Mineral Exploration, 1990). Such geographic surroundings could have greatly promoted eolian deposition in the Chaohu lake basin via the strengthened East Asian Monsoon during the glacial periods of the mid-late Middle Pleistocene through the Late Pleistocene. Because the loess in the Chaohu lake basin has similar lithological characteristics to the Xiashu loess in the Nanjing and Zhenjiang regions in the Jiangsu Province, it was ever named ‘‘Xiashu Formation” (Regional Geological Survey Team of Anhui Province, 1988; Yu and Peng, 2008). Studies on the loess located in north of the middle–lower Yangtze River are very limited, although a considerable number of studies have been conducted on the Xiashu loess located in south of the middle–lower Yangtze River, such as Nanjing and Zhenjiang in the Jiangsu Province and Xuancheng in the Anhui Province (Li et al., 1997, 2001; Yang et al., 2001, 2004; Xia et al., 2007; Chen et al., 2008; Qiao et al., 2003, 2011; Hao et al., 2010). In this study, we selected a representative bore (ZK0711) to analyze grain-size, magnetic susceptibility and the geochemical characteristics of the loess in the Chaohu lake basin, East China. Specifically, the objectives are as follows: (1) the origin and source of the loess; (2) magnetic susceptibility curves, the chemical composition and their climatic significance.

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2. Materials and methods 2.1. Materials The loess section of the ZK0711 bore (117°120 1100 E, 31°280 1300 N) with a surface elevation of 22.40 m in the Chaohu lake basin is a typical loess section in north of the middle–lower Yangtze River (Fig. 1a and b), and the lithology is mainly composed of yellow, brown silty clay (Fig. 2a and b). It is 35.2 m thick, with the Yicheng Formation underneath it and about 1 m thick cultivated soil on top of the loess (Fig. 2a). Based on the structure feature, color and high resolution of magnetic susceptibility (Fig. 3), the strata revealed in the ZK0711 bore from bottom to top are as follows: Layer 1: Yellow-colored silty clay, containing offwhite calcareous concretions and iron and manganese (Fe–Mn) nodules, 2.80 m thick. Layer 2: Yellow-colored silty clay, containing Fe–Mn nodules of 3–5%, 1.95 m thick. Layer 3: Gray yellow-colored silty clay, 3.55 m thick. Layer 4: Yellow-colored silty clay, containing Fe–Mn nodules of 5%, 3.90 m thick. Layer 5: Light brown-colored silty clay, containing few Fe–Mn nodules, 1.80 m thick. Layer 6: Ginger-colored silty clay, 3.30 m thick. Layer 7: Light brown-colored silty clay, 0.70 m thick. Layer 8: Yellow-colored silty clay, containing Fe–Mn nodules of 5%, 0.35 m thick. Layer 9: Ginger-colored silty clay, 2.20 m thick. Layer 10: Yellow-colored silty clay, containing Fe–Mn nodules of 6%, 2.65 m thick. Layer 11: Ginger-colored silty clay, 1.00 m thick. Layer 12: Yellow-colored silty clay, 0.60 m thick. Layer 13: Ginger-colored silty clay, containing few Fe–Mn nodules, 1.75 m thick. Layer 14: Yellow-colored silty clay, 2.35 m thick, corresponds to u1–u2 in Fig. 2b. Layer 15: Brown-colored silty clay, 2.40 m thick, corresponds to u3 in Fig. 2b. Layer 16: Gray yellow-colored silty clay, 1.9 m thick, corresponds to u4–u5 in Fig. 2b. Layer 17: Gray brown-colored silty clay, 0.9 m thick, corresponds to u6 in Fig. 2b. Layer 18: Gray yellow-colored silty clay, 1.1 m thick, corresponds to u7 in Fig. 2b. A total of 1696 samples were taken from this loess section, of which 10 samples were used for dating by optically stimulated luminescence (OSL), 92 samples for geochemical analysis collected at different interval, 889 samples for grain-size analysis taken at 4 cm interval, and 705 samples for magnetic susceptibility analysis collected at 5 cm interval.

2.2. Methods All the geochemical samples were air-dried and grounded to pass through a 200 mesh sieve. Samples for dating were analyzed by the Optical luminescence measuring instrument of Daybreak 2200 type in the Institute of Earth Environment, Chinese Academy of Sciences. The grain-size samples were analyzed at Nanjing Normal University after the pretreatment by a Mastersizer 2000 laser particle size analyzer made by the British Malvern company, with a

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Fig. 1. a and b. Location map of the loess sites in the Chaohu lake basin and other aeolian dust deposits loess mentioned. c. The mid-late Middle to Late Pleistocene lithofacies palaeogeography in Anhui Province (revised based on lithofacies palaeogeographical atlas in Anhui Province, 1990), East China. 1: Mountain; 2: hill; 3: river; 4: alluvial flat; 5: lake; 6: aeolian dust deposits; 7: sand; 8: silty clay; 9: clay; 10: lithologic boundary; 11: geomorphologic boundary; 12: Jianghuai Watershed. d. Isogram of distributed thickness of the Loess in Chaohu Lake basin. 1: Bedrock area; 2: erosion area (the Loess has been completely eroded by rivers); 3: Jianghuai Watershed; 4: bore disclosing thickness of the loess.

particle size range of 0.01–2000 lm and measurement error less than 2%. Magnetic susceptibility samples were analyzed in China University of Geosciences by KLY-3S kappa-bridge made in Czech with sensitivity of 2 ⁄ 108 (SI) and measurement error less than 0.5‰. The major elements including K2O, Na2O, CaO, MgO, SiO2, Fe2O3 and A12O3 were analyzed using the Axios advanced (PW4400) X-ray fluorescence method (XRF), and FeO is determined by potassium dichromate titration in the Hefei Center of the Supervision and Inspection on the Mine Resource, the Ministry of Land and Resource PRC. All these analyses were conducted following the

standard analysis procedure with relative error of less than ±2% for major elements. 3. Results and discussion 3.1. The origin of the loess: the evidence for fluvial or eolian? According to OSL dating, the age of the loess at the bottom of ZK0711 is about 287 ka B.P. (Figs. 2 and 3), which suggests that the initial depositing time of the loess in the Chaohu lake basin was in the late Middle Pleistocene.

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Fig. 2. a. Lithological pillar of ZK0711, 1: cultivated soil; 2: Xiashu Loess; 3: sands of Yicheng Formation. b. A man-made profile nearby ZK0711 during field investigation, u1: brown-yellow silty clay (unseen bottom); u2: yellow silty clay; u3: brown silty clay; u4: light yellow silty clay; u5: yellow silty clay; u6: dark brown silty clay; u7: brown silty clay; u8: brown-yellow cultivated soil. c. Drilled core, filed investigated Fe–Mn nodules. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

Fig. 3. Magnetic susceptibility (MS) strata of the loess in ZK0711 bore and their comparison to that of loess in Luochuan and marine isotope stages (MIS). a. The loess in Luochuan. b. SPECMAP. c. The loess in ZK0711 bore from the Chaohu basin.

3.1.1. Grain size composition The sand (>50 lm) content of samples is 0.29–58.61% with the large variation range, and the average content is 14.07% (Table 1), which is much larger than that of other aeolian dust deposits. Coarse silt (50–10 lm) is the most vulnerable to the activities and the most

easy to disperse by the action of the wind, and is the mode particle group of the loess in the northern China. The coarse silt content of the loess in ZK0711 bore section is 24.58–58.93%, and the average content is 44.54% that is similar to that of the loess in Luochuan. It indicates that the coarse silt is also the mode particle group of the

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Table 1 Grain-size contents of the loess from ZK0711 bore in the Chaohu lake basin and other aeolian dust deposits. Site

Category

Grain-size >50 lm

10–50 lm

5–10 lm

<5 lm

Loess of Chaohu lake basin

Max. of Xiashu loess Min. of Xiashu loess Avg. of Xiashu loess

58.61% 0.29% 14.07%

58.93% 24.58% 44.54%

25.50% 4.32% 16.15%

45.05% 5.58% 24.60%

Xiangyang section from Xuancheng (Li et al., 1997)

Loess Paleosoil Avg.

4.76% 3.53% 4.16%

37.22% 33.56% 35.00%

18.49% 19.85% 19.46%

39.55% 43.06% 41.38%

Dagang section from Zhenjiang (Li et al., 2001)

Max. Min. Avg.

6.82% 0.00% 4.18%

58.40% 40.04% 49.36%

26.50% 15.20% 18.02%

33.99% 21.35% 28.44%

Luochuan section (Liu, 1985)

Malan loess Upper Lishi loess Lower Lishi loess Upper Lishi paleosoil Lower Lishi paleosoil

6.80% 10% 5.30% 7.10% 4.80%

53% 52.70% 50.30% 45.70% 45.70%

12.50% 11.00% 12.30% 12.70% 12.60%

27.40% 26.30% 31.20% 32.00% 37.80%

Fig. 4. Typical particle size frequency curves of the loess in ZK0711 bore.

loess in the Chaohu lake basin. Fine silt (5–10 lm) is transported in suspension form under the action of wind, and is the main component part of eolian sediments far away from the source of the northern deserts (Pye, 1987). The fine silt content of the loess in ZK0711 bore section is 4.32–25.50% with the average content of 16.15%. The average content is slightly higher than that of the loess in Luochuan, while lower than that of the loess in Zhenjiang and Xuancheng. Clay (<5 lm) is very difficult to raise. The clay content of ZK0711 is 5.58–45.05% with the average content of 24.60%,

therefore, it is the secondly mode particle group. The higher clay content indicates that the loess of Chaohu lake basin went through stronger weathering after deposition.

3.1.2. The typical particle size frequency curves and the probability cumulative curves Fig. 4 shows that typical particle size frequency curves are characterized by single mode, normal form, which suggests that the

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Y ¼ 3:5688M þ 3:7016r2  2:0766SK1 þ 3:1135KG

Fig. 5. The probability cumulative curves of the loess in ZK0711 bore.

sediment was fully sorted. The mode value is located near 6u that belongs to typical aeolian dust deposits. The probability cumulative curves present three sections (Fig. 5). The particle content less than 4U is very little, and only below 2%. On the other hand, the particle content more than 11U is rare, and also below 2%. The curves mainly indicates that the sediment dynamics is single, similar to those of the loess in Xifeng and Luochuan (Lu and An, 1999), which suggests that the origin of the loess in Chaohu lake basin is eolian. 3.1.3. Grain size distributions The C-M, A-M and L-M chart have been used to study the sediment environment. The application of them in the eolian deposition is to infer the origin and the sediment environment through comparing the projection area of the unknown samples and the known origin samples in the charts (Lu and An, 1999). Fig. 6 indicates that the origin of the loess in the Chaohu lake basin differs from that of the typical river deposit (Li et al., 2006, 2010; Zhan et al., 2010). A very small amount of sample situated in the projection area of the river deposit might result from that a little loess could be affected by the water transformation after deposition.

where M, r, SK1 and KG are mean grain-size, standard deviation, skewness and kurtosis, respectively. If Y is negative, it indicates aeolian sediments; Otherwise, it indicates aqueous sediment. Fig. 7 shows that most of the Y values from the loess in ZK0711 are negative, which suggests that most loess is eolian sediment. Very few Y values are positive, which indicates that a little loess could be affected by the water transformation after deposition. In addition, the eolian origin of the loess in Chaohu lake basin could be inferred by the space distribution features, sedimentary structures and major element contents. The loess is widely scattered in the Jianghuai plain in eastern China with the characteristics of continuity (Fig. 1b and d), and covers on the different geomorphic units including low hills, wavy plains, river valley plains and the bottom of the Chaohu Lake. The erosion area in Fig. 1d results from that the former loess has been completely eroded by the later rivers. Generally, the higher the terrain, the thicker the loess. Its coverage reaches Jianghuai Watershed with the nearly 100 m height. That the other dynamic except the wind power could not reach the characteristics of continuity and extensiveness (Li, 2001; Zheng et al., 2002) indicates that the origin of the loess in Chaohu lake basin is eolian. The loess in Chaohu lake basin is rich in columnar joint as well as Fe–Mn nodules (Fig. 2c). The aqueous bedding structure wasn’t found in the native loess strata. The alternation of the similar multi-layer loess and multi-layer paleosol was found in the loess section (Fig. 2b). The sedimentary structure is similar to that of the loess in northern China. Moreover, it can be concluded from Appendix A that the major elemental composition of the loess in the Chaohu lake basin is dominated by SiO2, Al2O3 and Fe2O3, with a mean value of 67.68% with variation range of 60.42–73.62%, 15.31% with variation range of 12.61–18.81%, and 5.8% with variation range of 4.35–7.40%, respectively. The total content of SiO2, Al2O3 and Fe2O3 is, on average, 88.79%, which is similar to those of the southern aeolian dust deposits, such as 84.15% of the loess in Wushan, 86.24% of Xiashu loess in Zhenjiang (Zhang et al., 2013), 86.86% of Xiashu loess from the Badou mountains in Nanjing (Li et al., 1999) and 89.03% of the loess in Xuancheng (Li et al., 1999). The characteristics of the sedimentary structure and the major elemental composition support the eolian origin.

3.2. Implications of magnetic susceptibility for environment changes 3.1.4. Sedimentary environment inferred from the discriminant function Sedimentary environment can be distinguished by the value of Y (Lu and An, 1999; Yu et al., 2006):

The variation range of the magnetic susceptibility (MS) curves is larger, and peak–valley cycles are also obvious. The MS curves show the situation of 3 peaks (S1, S2, S3) and 3 valleys (L1, L2,

Fig. 6. The charts of the grain size distributions of the loess in ZK0711 bore.

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Fig. 7. The value of Y to distinguish sedimentary environment of the loess in ZK0711 bore.

L3). The sub-fluctuation cycles take place in each peak or valley, such as S1, S2 and L3 (Fig. 3). Since the early-1990s numerous researchers have suggested that MS should respond to climate (Zhou et al., 1990; Heller et al., 1991; Maher et al., 1994; Liu et al., 1995). Much of this work was done on the Chinese Loess Plateau (CLP) where it was clear that MS fluctuated with climate, particularly with glacial/interglacial transitions (Kukla et al., 1988). During the warm and humid climate, pedogenes is intensified, resulting in that fine ferromagnetic minerals enrich, which leads to increase of MS in the paleosoil. On the contrary, MS decreases in the loess during the cold and dry climate (Zhou et al., 1990; Maher and Thompson, 1991; Heller et al., 1991). Worldwidely, there is a general relationship between magnetic susceptibility and rainfall. As rainfall increases to about 1000–1200 mm/yr from tropical and temperate climate, MS increases and then decreases as rainfall continues to increase (Balsam et al., 2011). Therefore, MS is used as an alternative indicator of regional summer monsoon change, reflecting the paleoclimatic change (Zhou et al., 1990; Maher and Thompson, 1991). The sub-fluctuation cycles existed by turn in S1. MS of S1, similar to MIS5, consists of three peaks and two valleys, which indicates that two times dry/cold climatic fluctuation took place in the more humid and hot paleoclimatic background. The fluctuated climatic characters correspond to the sub-stages of MIS5 that are 5a, 5b, 5c, 5d and 5e. The sub-peaks of S1-1, S1-3 and S1-5 of the loess in the Chaohu lake basin correspond to the sub-stages of 5a, 5c and 5e in MIS5, indicating three more humid and hot paleoclimate, while the sub-peaks of S1-2 and S1-4 correspond to the sub-stages of 5b and 5d in MIS5, indicating two more dry and cold climate. In addition, three more humid and hot paleoclimatic grade is as follows, S1-5 > S1-3 > S1-1, which is consistent with that of 5e > 5c > 5a inferred by MIS5. This suggests that the loess in the basin has given a sensitive response to the globe paleoclimatic change in S1. Moreover, S2 of the loess in the Chaohu lake basin consisted of three sub-peaks (S2-1, S2-3 and S2-5) with two sub-valleys (S2-2 and S2-4), which indicates the climate went through three more humid and wet fluctuation and two more dry and cold one. The above phenomenon was equivalent to MIS7, and three sub-peaks of S2-1, S2-3 and S2-5 corresponded to sub-stages of 7a, 7c and 7e, while two sub-valleys of S2-2 and S2-4 corresponded to 7b and 7d. MS of S2 suggests that the humid and wet grades are as follows, S2-3 > S2-5 > S2-1 > S2-2 > S2-4. The grade of S2-3 > S2-5 > S2-1 > S2-4 is consistent with that of 7c > 7e > 7b > 7d inferred by

MIS7, which indicates that there are also consistencies between S2 and MIS7. On the other hand, that the grade of S2-1 differed from that of 7a in MIS7 suggests that the climate changes in some stages recorded by the loess in Chaohu lake basin has regional characteristics obviously, which might be the result of the dual effect of globe climate changes and East-Asia monsoon climate changes. In addition, the character of two sub-valleys with one peak could be compared with MIS8. Two sub-valleys of L3-1 and L3-3 corresponded to the sub-stages of 8a and 8c in MIS8. The dry and cold grade of the sub-valleys inferred by MS was equivalent, which is similar to that of 8a and 8c that was also equivalent. The sub-peak of L3-2 corresponded to 8b. Those all suggest that the loess in the basin has given a sensitive response to the globe paleoclimatic change in L3. The above features could compare with those of the loess in northwestern China, which are similar to the marine isotope stages (MIS). Whether the main or the sub-climatic fluctuation of S1 and L3 perfectly agrees with MIS5 and MIS8, respectively, which suggest that the loess in the basin has given a sensitive response to the globe paleoclimatic change in S1. On the other hand, that the grade of S2-1 differed from that of 7a in MIS7 suggests that the climate changes in some stages recorded by the loess in Chaohu lake basin has regional characteristics obviously. This difference might result from that the loess in Chaohu lake basin is located in the active area of East-Asia monsoon. The regional climate change is influenced by the monsoon climate and has distinctive regional characteristics. Therefore, the paleoclimatic change documented by MS in the basin might be the result of the dual effect of globe climate changes and East-Asia monsoon climate changes. The comparability between MS records of the loess in the Chaohu lake basin and MIS at some stages (such as S1 and S2) is even more than that of loess in Luochuan, which might result from the following factors. One is that the distance of the loess in the basin from the sea is nearer than that of the loess in Luochuan, and the climate is more directly and obviously influenced by the ocean climate change. The other is that the humid/wet and dry/cold fluctuation in the basin is more remarkable because of location in the mid latitude. 3.3. The chemical weathering and climate change The major element contents of the samples are given in Table 2 and Appendix A. The high correlation exists between the the Chemical Index of Alteration (CIA) and mean grain size (Shao et al., 2012). In order to avoid the grain-size effect, all collected samples were also ground to pass through a 200 mesh sieve (about 63.5 lm) after air drying and splitting, similar to the method of the corresponding references in Table 2. 3.3.1. Mobility of the major elements Changes of elements ratios are particularly useful to be applied to genetically related suites of materials such as weathering profiles. For example, if a particular element I is kept stable during pedogenesis, the percentage increase or decrease of any other element X in a sample (S), compared with its concentration in the parent (P), can be estimated by the percentage change (Chen et al., 1998; Nesbitt, 1979; Nesbitt et al., 1980; Mcfarlane, 1994):

D ð%Þ ¼ ððX s =Is Þ=ðX p =Ip Þ  1Þ  100 where Xs/Is and Xp/Ip are ratios of elements in the samples and parents, respectively. In this study, Al2O3 is used as the denominator. According to the color and magnetic susceptibility feature as well as the CIA values (Nesbitt, 1979; Nesbitt and Yong, 1982) of the ZK0711 bore, the least weathered loess (DH11) was used as the parent material to calculate the percentage changes of elements in the

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H. Guan et al. / Journal of Asian Earth Sciences 117 (2016) 170–183 Table 2 Ratios of major elements’ contents of the loess from ZK0711 bore in Chaohu lake basin and other aeolian dust deposits. Site

Sample

Statistical categories

CIA⁄

Na/K⁄

SiO2/Al2O⁄3

Loess of Chaohu lake basin

n = 92

Min Max Average CV

68.7 89.38 80.53 0.07

0.21 0.82 0.47 0.37

5.51 9.61 7.59 0.11

Ili loess (Li et al., 2006)

n = 56

Average CV

57.59 0.04

1.23 0.12

7.4 0.02

Xifeng loess (Liang et al., 2009)

n = 15

Min Max Average CV

61.21 65.95 63.25 0.02

0.81 1.16 1.01 0.09

7.31 8.58 8.05 0.04

Xiefeng soil (Liang et al., 2009)

n = 15

Min Max Average CV

63.79 68.95 66.26 0.02

0.75 1.07 0.91 0.1

7.3 8.5 7.78 0.04

Luochuan loess (Chen et al., 2001)

n = 21

Min Max Average CV

62.21 68.77 64.91 0.03

0.6 1.21 0.83 0.18

7 8.99 7.86 0.06

Wushan loess (Zhang et al., 2013)

n = 29

Average CV

66.85 0.04

0.82 0.09

8.42 0.06

Xuancheng loess (Li et al., 1999)

n=9

Average CV

88.45 0.04

0.18 0.31

9.02 0.15

UCC (Taylor and McLennan, 1985)

47.92

1.8

7.38

Terrestrial shale (Taylor and McLennan, 1985)

70.36

0.51

5.6

⁄

⁄

SiO2/Al2O⁄3

Note: (a) CIA , Na/K and represent molar ratio. (b) In Table 1, the data of the Ili loess are collected from Li et al. (2006), the data of the Xifeng loess and soil are collected from Liang et al. (2009), the data of the Wushan loess are collected from Zhang et al. (2013), the data of the Luochuan loess are collected from Chen et al. (2001), the data of the Zhenjiang loess are collected from Chen et al. (2008), and the data of the Xuancheng loess are collected from Li et al. (1999). Samples of above collected data were ground to 200 mesh after air drying and splitting. The data of both UCC and the terrestrial shale are quoted from Taylor and McLennan (1985).

Fig. 8. Percentage changes of major elements relative to Al2O3 for the Loess from sediment of ZK0711 bore in Chaohu lake basin.

loess. The variation in percentage of each element was calculated by using Al as the stable element. Fig. 8 shows that the order of the activity for the major element of the loess in the Chaohu lake basin is Na2O > MgO > CaO > K2O > FeO > SiO2 > Al2O3 > Fe2O3, which is consistent with that of the Xiashu loess in Zhenjiang (Li et al., 2001). In the loess sequence from the Chaohu lake basin, FeO did not migrate and its variation reflects the change of the valence state, i.e. Fe2+ converting into Fe3+, instead of the element itself, which can be proved by the fact that many Fe–Mn nodules were found in the field investigations and in bore sections of the loess from the Chaohu lake basin (Fig. 2c). 3.3.2. Chemical weathering intensity Weathering processes are sequentially characterized by the early Na and Ca removal stage, the intermediate K removal stage and the more advanced Si removal stage (Nesbitt et al., 1980). Fig. 8 shows that Na and Ca of the loess in the Chaohu lake basin

Fig. 9. Scatter diagram of CIA vs Na/K molar ratio of the loess in the Chaohu lake basin and other aeolian dust deposits loess. Loess⁄ = the loess in the Chaohu lake basin.

are markedly lost, removal of K is also obvious, and the intensity of chemical weathering doesn’t evidently turn into the Si removal stage, which suggests that the intensity of chemical weathering is stronger than that of the loess in Zhenjiang, in which the removal of Na and Ca is obvious while the removal of K is not apparent (Yang et al., 2001), and is also stronger than that of the loess in northern China that still belongs to the feebler Na and Ca removal stage (Chen et al., 1998). Chemical index of alteration (CIA) is widely used to evaluate the chemical weathering of terrestrial sediments. CIA is defined as Al2O3/(Al2O3 + CaO⁄ + Na2O + K2O)  100 (in molar proportions),

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Fig. 10. A–CN–K diagram showing the trends of chemical weathering of the loess in the Chaohu lake basin and other aeolian dust deposits loess. A = Al2O3; CN = CaO⁄ + Na2O; K = K2O; Ka: kaolinite; Sm: smectite; IL: illite; Mu: muscovite; Pl: plagioclase; Ks: K-feldspar. Loess⁄ = the loess in the Chaohu Lake basin.

where the oxide is given in molar ratio and CaO⁄ represents its content in silicate, excluding CaO in carbonate and phosphate. All the CaO⁄ values in this study are calculated according to McLennan’s method (McLennan, 1993). CIA can reflect the chemical weathering degree of the silicate mineral and feldspar. The mineralogical and chemical composition of the loess in the Chaohu lake basin and other aeolian dust deposits will reflect the intensity of weathering because highly aluminous minerals, especially kaolinites, are produced in quantity during intensive weathering and such sediments will have correspondingly high CIA values. Mass wasting of profiles in glacial conditions, may result in fine grained detrital sediment containing less aluminous clay minerals (smectites and illites) and a high proportion of plagioclase and K-feldspar (Fig. 9). The degree of chemical weathering increases with the increase of CIA values (Nesbitt and Yong, 1982; Guo et al., 1996; Wu and He, 2003; Feng et al., 2003; Li and Song, 2011). Otherwise, size sorting during transportation and deposition generally results in some degree of mineralogical differentiation which may modify the value of CIA (Nesbitt and Yong, 1982; Shao et al., 2012). We have therefore restricted the grain size of the samples in this study and all cited data to less than 63.5 lm. The CIA values of the 92 samples from the ZK0711 bore section range from 68.70 to 89.38, with a mean value of 80.53 (Table 2, Appendix A). This mean value is significantly higher than 47.92 of the upper continental crust (UCC) (Taylor and McLennan, 1985), 57.59 of the loess in Ili of Xinjiang (Li and Song, 2011), 66.85 of the loess in Wushan (Zhang et al., 2013), 70.36 of terrestrial shale, 70.19 of the loess from the Dagang section in Zhenjiang (Chen et al., 2008), but considerably lower than 88.45 of the aeolian Xiashu loess–soil sequence from the Xiangyang section in Xuancheng (Li et al., 1999). Fig. 9 shows that the loess in Chaohu lake basin has undergone moderate to strong chemical weathering intensity. Na/K molar ratios are in inverse proportion to the chemical weathering intensity (Kang and Mu, 1998; Chen et al., 2001; Li and Song, 2011). CIA versus Na/K for loess (soils) from different regions is then plotted in Fig. 9. Clearly, Na/K ratios are in inverse proportion to CIA for all the samples, which also indicates the same chemical weathering intensity. Nesbitt and Yong (1982) had developed an A–CN–K (Al2O3–CaO⁄ + Na2O–K2O) triangle model to reflect the chemical weathering intensity, and changes of major elements and minerals, which has been successfully applied

Fig. 11. Geochemical coefficients of variation from the loess in the Chaohu lake basin and other aeolian dust deposits loess. Loess⁄ = Loess in the Chaohu lake basin.

(Jahn et al., 2001; Yang et al., 2004; Qiao et al., 2011; Li and Song, 2011). The direction from UCC to terrestrial shale on the diagram represents the typical trend of continental chemical weathering (Gallet et al., 1996, 1998; Zheng, 1999; Li et al., 2001; Li and Song, 2011). The chemical weathering process of the loess in the Chaohu lake basin is between the loess in Xuancheng and the loess in Zhenjiang, showing that Na and Ca of the loess in the basin are markedly lost, and the removal of K is also obvious (Fig. 10). The intensive chemical weathering has been documented by the loess might be related to strong monsoon climate in Chaohu lake basin. 3.4. Provenance of the loess in the Chaohu lake basin The evidence described in the following sections indicates that the provenance of the loess in the Chaohu lake basin does not support the traditional viewpoint that the southern loess has the same provenance as the loess deposited in the NW region of China, which was derived from the deserts in northern China. 3.4.1. Geochemistry It is known that fine silt of 5–10 lm is transported long distance in suspension form under the excitation of wind forces, and is the main component part of eolian sediments far away from the source of the deserts in northern China (Pye, 1987). The Chaohu Lake basin and Zhenjiang are both in the middle and lower reaches of the Yangtze River and the distances from the deserts in northern China are almost the same, and the geochemical coefficients of variation should be similar in the two locations if the northern deserts are their main provenance. However, it is shown from Table 2 and Fig. 11 that coefficients of variation in CIA, Na/K and SiO2/Al2O3 of the loess in the Chaohu lake basin are all much greater than those of the Zhenjian loess which are similar to the NW loess. It can be inferred that the loess from the Chaohu lake basin wasn’t only derived from the deserts in northern China (Liu, 1985; Zheng, 1999; Li et al., 2001, 2006). Moreover, the average CIA value of the loess in the basin, 80.53, with an average annual temperature and an average precipitation of 15.7 °C and 1000 mm, is greater than that of the Zhenjiang Xiashu loess, 70.19, with an average annual temperature and an average precipitation of 15.4 °C and 1066 mm. It also suggests that the provenance of the loess in the Chaohu Lake basin differed from that of the loess in Zhenjiang (Liu, 1985; Zheng, 1999; Li et al., 2001, 2006).

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modified saltation. Based on the analysis of the Loess Plateau, a coarse particle doesn’t primarily exist in paleosols, but is concentrated in the periphery of the loess and desert in northern China, which should be closely related to the advance and retreat of the desert. In the ZK0711 bore, the content of particles larger than 50 lm in loess is 14.7%, which is much higher than others (Table 1) and varies considerably, suggesting that they were unlikely to have been transported for a long distance by wind (Wu et al., 1992; Qiao et al., 2003; Hong et al., 2013). It indicates that they were derived from the nearby sources.

Fig. 12. Spatial changes in SiO2/Al2O3 ratios plotted against longitude and latitude for samples from the Chaohu lake basin and other aeolian dust deposits. Loess⁄ = loess in the Chaohu lake basin.

Furthermore, Si and Al remain unchanged during the weathering of loess deposits on the NW loess (Gallet et al., 1996; Jahn et al., 2001; Chen et al., 2001). The SiO2/Al2O3 ratio has been proposed as a proxy to study the grain-size of original eolian particles. Sedimentary sorting tends to lead to the enrichment of the coarse fractions of weathering-resistant quartz which is a major component in loess detrital minerals (Hao et al., 2010), while Al tends to be enriched in the finer fractions (Hao et al., 2010; Jahn et al., 2001). Thus, sedimentary sorting would lead to a decrease in the SiO2/Al2O3 ratio with increasing transport distances away from the source area. Any weathering that may have occurred would have led to depletion rather than enrichment in Si (Hao et al., 2010). Based on the moderate-strong chemical weathering intensity, about 8% of the samples have SiO2/Al2O3 ratios that are larger than the maximum value of the loess in Luochuan and Xifeng, 8.99 (Table 2 and Fig. 12). The SiO2/Al2O3 ratio should be more concentrated after the sediment was transported long-distance and sorted. However, Fig. 12 shows that the SiO2/Al2O3 ratios of the loess in the basin and the Xuancheng loess are more dispersed than those of the loess in northern China. The above results also indicate that the northern deserts weren’t the main origin of the loess from the Chaohu Lake basin. 3.4.2. Grain-size Granularity is the most basic of the sediment physical characteristics, and grain-size composition is the basis of clastic sediment classification and nomenclature. The grain-size characteristics include the particle sizes and their distribution which are controlled by the parent source, carrying medium, mode of transport, depositional environment and others. Thus, particle size analysis is one of the most important research means for studying sedimentary environments, transport processes and mechanisms (Liu et al., 1993; Pye, 1987). In recent decades, grain-size analysis has been successfully used to study sedimentary environments of eolian origin (Li et al., 1997, 2001; Lu et al., 2001; Xiong et al., 2002; Prins et al., 2007, 2009; Xu and Wang, 2011; Liang et al., 2013). Theoretically, by the action of the wind, sand material of more than 50 lm is only transported from the source region to the accumulation area in the form of saltation because of its coarse grain size. It is also difficult to transport the coarse material long distance in suspension in the wind (Bagnold, 1959). Pye (1987) thinks that, under medium storm conditions, the main transport models of a particle larger than 50 lm are peristalsis, saltation, and

3.4.3. Depositional rate Depositional rate provides a proxy measure of continental aridity (Rea and Leinen, 1988; Pye, 1995), and is used to test whether the loess in Chaohu lake basin has the same provenance as the loess in Zhenjiang and northern China or not. The average depositional rate of the Zhenjiang loess is 0.079 m/ka, and the ones of the loess in Weinan and Xifeng are 0.1 m/ka, 0.093 m/ka, respectively. The thickness of the loess section of ZK0711 is 35.2 m, and the age of the bottom is about 287 ka B.P. Thus, it can be calculated that its average depositional rate is at least 0.123 m/ka. The loess in northern China was mainly derived from the northwest deserts. If it was partly derived from the northern deserts and from the aeolian dust deposits of the deserts in northern China, the loess in the Chaohu Lake basin, located in the northern subtropical area, which is far away from the northern deserts, should have a lower depositional rate than that of the NW loess which is closer to the provenance. If so, the phenomenon that the continental aridity of the Chaohu lake basin located in the Northern subtropical area is greater than that of the northwest area is incredible (Pye, 1995). Thus the depositional rate provides evidence that the provenance of the loess in the basin differs from the loess in Zhenjiang and northern China. 3.4.4. Discussion of provenance area The occurrence of continuous loess deposits requires the existence of provenance regions and winds strong enough to carry dust particles (Wu et al., 1992; Qiao et al., 2003; Hao et al., 2010). Fig. 1c shows the sedimentary facies of the Huaihe floodplain that are mainly occupied by rivers, lakes and littoral. The abundant fine sediments (clay, silty clay, sand, etc.) in those sedimentary areas are the potential source material for the loess in the Chaohu lake basin during glacial periods. It has been well accepted that the East Asian monsoon was strengthened in the Middle Pleistocene as seen from evidence in the loess in northern China (Guo et al., 1993; Xiao and An, 1999; Hao et al., 2010), and the climate turned into the aridity and cooling in the northern subtropical area, the intensified cooling of the high northern latitudes induced a strengthened winter monsoon by strengthening the Siberian High Pressure, leading to a colder and drier climate during glacial periods (Hao et al., 2010). Accordingly, the precipitation and the sea level in the northern subtropical area would decrease, which would result in a decline in the water levels of the rivers and lakes, and the degradation of vegetation in the area (Yang and Li, 2000; Hao et al., 2010; Qiao et al., 2011). Those would result in an enlarged area of exposed river valleys, lake beds, and littoral deposits. The multiperiod relatively arid and cold climates in the nearby area were recorded by sporopollen and ostracod fossils of the Panji Formation and the Maotao Formation in the Huaibei stratigraphic division during the mid-late Middle Pleistocene through the Late Pleistocene period (Regional Geological Survey Team of Anhui Province, 1988; Yu, 1988; Yu and huang, 1993), and by the sporopollen fossils from Xiashu loess section near Nanjing (Huang et al., 1988) and the Subei Basin (Xiao et al., 2005; Shu et al., 2010) of the same periods. During glacial periods, the Huaihe floodplain with its sparse vegetation cover would be easily deflated by strong wind and might have become the provenance regions.

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Fe2O3. Na and Ca of the Loess are markedly lost and the removal of K is also obvious, but the intensity of chemical weathering doesn’t evidently turn into the Si removal stage. The loess in the Chaohu lake basin had undergone the moderate-strong chemical weathering intensity, which might be related to strong monsoon climate in Chaohu lake basin. (4) The provenance of the loess in the Chaohu lake basin differs from the loess in northern China. The northwest deserts weren’t the main origin of sources. Instead, the abundant fine sediment from rivers, lakes and littoral sedimentary areas in floodplain of the Huaihe River seems to be the important source materials.

The particles of exposed river valleys, lake beds, and littoral deposits were carried and mixed by the strengthened winter winds and local winds (Zhang et al., 2012). They were then deposited in the nearby regions, and the particles formed the southern loess in the present-day northern subtropical area, such as in the Chaohu lake basin. 4. Conclusions This paper discussed the origin, the paleoclimatic cycles and sub-cycles, the chemical weathering intensity and the provenance of the loess in the Chaohu lake basin. (1) The grain size character, space distribution features, sedimentary structures and major element contents all suggest that the loess in the Chaohu lake basin is of eolian origin. (2) The paleoclimatic cycles and sub-cycles documented by MS since L3 during middle–late Pleistocene in the basin can be compared with that of Luochuan and MIS. The MS curve of Paleosol S1, Paleosol S2 and loess L3 in the basin coincide perfectly with MIS5, MIS-7 and MIS-8, respectively, which indicates that the loess in the basin has given a sensitive response to the globe paleoclimatic change. On the other hand, the climate changes in some stages recorded by the loess has regional characteristics obviously. Those might be the result of the dual effect of globe climate changes and East-Asia monsoon climate changes. (3) The activity for the major elements of the loess increases in the order of Na2O > MgO > CaO > K2O > FeO > SiO2 > A2O3 >

Acknowledgments This work was supported by Land and Resources Survey Project from China Geological Survey Bureau (Grant Nos. 1212010610608, 12120113067800), Natural Science Foundation of China (Grant Nos. 41401216), Open Foundation of State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences (Grant Nos. SKLLQG1206), Major Program of National Social Science Foundation of China (Grant Nos. 11 & ZD183), National Science Support Program (Grant Nos. 2013BAK08B02). We are grateful to Profs. Dai S.Q., Tong J. S. and Chu D.R. for their help in the field investigations. Special thanks to the anonymous reviewers for their valuable comments on the manuscript and checking the English.

Appendix A. Contents (%) and ratios of major elements in the loess from ZK0711 bore in Chaohu Lake Basin Depth (cm)

Sample

K2O

Na2O

CaO

MgO

SiO2

Fe2O3

Al2O3

FeO

CIA⁄

Na/K⁄

SiO2/Al2O⁄3

124.40 164.60 203.95 240.70 281.75 320.65 337.95 376.90 419.55 456.95 495.25 540.15 577.55 617.70 659.25 700.80 742.35 763.10 823.85 853.25 882.55 911.95 941.30 970.65 995.15 1035.20 1077.40 1119.55

0711-DH1 0711-DH2 0711-DH3 0711-DH4 0711-DH5 0711-DH6 0711-DH7 0711-DH8 0711-DH9 0711-DH10 0711-DH11 0711-DH12 0711-DH13 0711-DH14 0711-DH15 0711-DH16 0711-DH17 0711-DH18 0711-DH20 0711-DH21 0711-DH22 0711-DH23 0711-DH24 0711-DH25 0711-DH26 0711-DH27 0711-DH28 0711-DH29

2.22 2.28 2.17 1.80 1.63 1.96 2.11 2.20 2.35 2.39 2.44 2.28 2.23 2.26 2.26 2.08 1.88 1.96 1.82 2.10 1.74 1.72 1.76 1.73 1.81 1.80 1.86 1.51

0.92 1.05 1.06 0.92 0.69 0.71 0.82 0.94 1.07 1.11 1.18 1.17 1.09 1.11 1.10 1.08 0.93 0.69 0.88 0.84 0.86 0.77 0.67 0.58 0.44 0.32 0.58 0.38

0.96 0.90 0.92 0.84 0.79 0.91 0.93 0.99 1.09 1.11 1.12 1.09 1.03 1.02 0.99 0.87 0.74 0.82 0.80 0.90 0.74 0.69 0.70 0.70 0.68 0.78 0.60 0.78

1.34 1.34 1.32 1.04 0.99 1.28 1.40 1.49 1.60 1.65 1.72 1.56 1.45 1.48 1.48 1.25 1.01 1.13 1.08 1.34 1.00 0.96 1.01 1.03 1.09 1.16 1.09 0.92

66.06 66.63 66.99 68.98 66.43 64.96 65.27 65.92 65.84 65.96 66.66 68.03 67.50 67.55 67.77 69.45 70.64 65.81 68.90 66.89 71.31 71.01 68.42 66.69 65.60 61.51 67.80 70.81

5.69 6.02 5.95 6.03 6.43 5.89 5.86 5.71 5.83 5.72 5.50 5.29 5.45 5.53 5.36 5.20 5.29 6.23 5.32 6.14 5.57 5.66 5.75 6.62 6.95 7.39 6.62 7.34

15.22 14.98 14.53 13.53 15.42 16.49 16.01 15.41 15.06 14.90 14.62 14.29 14.44 14.56 14.49 13.82 13.21 15.75 14.39 14.94 12.61 13.17 14.66 15.18 15.99 18.47 14.56 12.88

0.22 0.13 0.17 0.10 0.14 0.15 0.18 0.17 0.06 0.15 0.17 0.19 0.13 0.14 0.15 0.13 0.14 0.13 0.13 0.09 0.17 0.14 0.12 0.12 0.10 0.08 0.54 0.08

73.34 71.74 71.34 72.83 78.92 78.40 75.93 73.41 70.84 70.04 68.70 68.88 70.18 70.14 70.27 70.85 72.67 77.88 74.48 74.43 72.85 74.80 77.77 79.76 82.15 85.92 78.49 81.37

0.65 0.73 0.77 0.80 0.66 0.57 0.61 0.67 0.72 0.73 0.76 0.81 0.77 0.77 0.77 0.82 0.77 0.55 0.76 0.63 0.77 0.70 0.60 0.52 0.38 0.27 0.49 0.40

7.38 7.56 7.84 8.66 7.32 6.70 6.93 7.27 7.43 7.52 7.75 8.09 7.95 7.89 7.95 8.55 9.09 7.10 8.14 7.61 9.61 9.17 7.93 7.47 6.97 5.66 7.91 9.34

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Appendix A (continued) Depth (cm)

Sample

K2O

Na2O

CaO

MgO

SiO2

Fe2O3

Al2O3

FeO

CIA⁄

Na/K⁄

SiO2/Al2O⁄3

1161.75 1203.95 1242.70 1278.05 1313.35 1348.70 1380.10 1435.20 1462.00 1475.30 1532.00 1565.30 1599.50 1652.55 1686.70 1720.80 1788.10 1821.60 1855.10 1888.60 1922.10 1955.60 1991.00 2027.00 2063.00 2099.00 2135.00 2163.00 2199.45 2235.95 2272.45 2308.95 2383.25 2420.55 2457.75 2495.00 2532.25 2569.45 2580.60 2634.00 2700.60 2734.00 2767.30 2800.65 2838.45 2877.85 2917.25 2956.65 2996.05 3035.45 3090.75 3117.35 3143.85 3170.45 3197.05 3223.55 3246.65 3280.50 3384.15 3417.85 3451.55

0711-DH30 0711-DH31 0711-DH32 0711-DH33 0711-DH34 0711-DH35 0711-DH36 0711-DH38 0711-DH39 0711-DH40 0711-DH41 0711-DH42 0711-DH43 0711-DH44 0711-DH45 0711-DH46 0711-DH47 0711-DH49 0711-DH50 0711-DH51 0711-DH52 0711-DH53 0711-DH54 0711-DH55 0711-DH56 0711-DH57 0711-DH58 0711-DH59 0711-DH60 0711-DH61 0711-DH62 0711-DH63 0711-DH64 0711-DH66 0711-DH67 0711-DH68 0711-DH69 0711-DH70 0711-DH71 0711-DH72 0711-DH73 0711-DH75 0711-DH76 0711-DH77 0711-DH78 0711-DH79 0711-DH80 0711-DH81 0711-DH82 0711-DH83 0711-DH84 0711-DH86 0711-DH87 0711-DH88 0711-DH89 0711-DH90 0711-DH91 0711-DH92 0711-DH93 0711-DH95 0711-DH96

1.65 1.81 1.91 1.85 1.72 2.15 2.29 2.29 2.01 1.56 1.67 1.73 1.66 1.78 1.70 1.59 1.95 2.13 2.11 2.26 2.22 2.14 1.75 1.58 1.33 1.37 1.40 1.35 1.22 1.18 1.25 1.63 1.75 1.76 1.59 1.61 1.26 1.26 1.09 1.07 1.17 1.77 1.69 1.64 1.69 2.10 1.55 1.49 1.46 1.18 1.21 1.09 1.57 1.80 1.84 1.94 2.01 2.05 1.86 1.07 1.03

0.26 0.33 0.58 0.35 0.29 0.48 0.63 0.64 0.62 0.43 0.39 0.40 0.30 0.29 0.39 0.36 0.46 0.37 0.41 0.30 0.32 0.54 0.58 0.46 0.32 0.30 0.28 0.26 0.26 0.26 0.25 0.45 0.33 0.35 0.33 0.36 0.24 0.23 0.22 0.21 0.21 0.39 0.40 0.33 0.42 0.63 0.35 0.41 0.42 0.36 0.32 0.27 0.43 0.49 0.45 0.62 0.69 0.80 0.85 0.39 0.37

0.76 0.72 0.55 0.66 0.73 0.65 0.59 0.73 0.67 0.54 0.64 0.70 0.74 0.77 0.70 0.71 0.70 0.78 0.73 0.86 0.87 0.80 0.64 0.64 0.62 0.67 0.70 0.68 0.67 0.68 0.72 0.72 0.83 0.79 0.70 0.75 0.70 0.75 0.66 0.68 0.77 0.68 0.79 0.85 0.80 0.91 0.82 0.77 0.75 0.69 0.75 0.82 0.77 0.94 0.97 0.96 0.94 0.94 0.97 1.12 1.98

1.06 1.14 1.02 1.07 1.08 1.23 1.18 1.26 1.12 0.77 0.89 0.96 1.03 1.11 1.03 1.04 1.21 1.24 1.09 1.30 1.33 1.31 0.91 0.79 0.79 0.91 0.94 0.92 0.89 0.88 0.90 0.96 1.13 1.12 1.01 1.11 0.95 0.96 0.87 0.88 0.99 1.19 1.17 1.13 1.14 1.56 1.21 1.15 1.17 1.01 1.04 1.02 1.18 1.51 1.54 1.57 1.59 1.59 1.50 1.09 1.15

61.22 62.41 69.50 64.99 63.08 65.42 67.89 68.22 70.41 72.90 70.01 69.01 63.28 61.89 67.69 66.69 67.62 64.19 66.99 61.00 60.42 66.02 73.43 73.62 71.95 71.15 69.37 69.22 69.73 69.97 68.98 71.70 67.01 68.85 70.77 70.16 70.35 67.96 71.13 69.69 66.88 67.28 68.42 66.91 68.70 67.29 65.20 69.55 70.61 70.90 69.86 66.97 66.44 66.47 65.17 66.60 67.72 68.76 70.30 68.74 65.85

7.08 7.40 6.09 7.09 6.58 6.04 5.91 6.01 5.34 5.54 5.45 5.54 7.04 6.91 6.09 6.33 5.89 7.06 5.70 7.35 6.92 5.75 4.42 4.35 5.17 5.14 5.37 5.41 5.26 4.88 4.80 4.95 5.98 5.64 5.21 5.49 5.32 5.64 5.09 5.51 5.99 5.72 5.86 5.86 5.48 5.79 5.70 5.19 5.34 5.14 5.44 6.00 5.99 6.07 6.14 6.02 5.82 5.63 5.14 5.41 6.60

18.65 17.72 14.52 16.71 18.17 16.62 15.40 14.88 14.16 13.04 14.98 15.57 17.14 18.49 15.73 15.58 15.62 16.56 16.40 18.81 18.27 16.37 13.80 13.85 13.88 14.87 15.81 15.80 15.43 15.77 16.67 14.42 15.86 15.22 14.51 14.45 15.09 15.76 14.41 15.24 16.58 15.82 14.98 15.94 14.99 15.13 15.46 14.49 14.36 13.99 14.88 15.65 16.06 15.74 16.04 15.14 14.99 14.43 13.99 14.96 15.33

0.12 0.10 0.12 0.09 0.08 0.13 0.10 0.13 0.08 0.05 0.08 0.59 0.17 0.06 0.06 0.10 0.06 0.10 0.10 0.32 0.08 0.18 0.12 0.10 0.10 0.12 0.15 0.12 0.14 0.10 0.08 0.10 0.08 0.09 0.08 0.10 0.08 0.13 0.08 0.09 0.08 0.08 0.14 0.28 0.05 0.06 0.08 0.09 0.06 0.06 0.06 0.08 0.08 0.08 0.44 0.06 0.06 0.17 0.06 0.06 0.05

87.50 85.23 78.21 83.86 86.48 80.71 76.91 76.16 76.75 80.44 82.60 82.72 85.91 86.42 83.15 84.00 80.89 82.22 81.61 84.48 84.01 79.75 78.08 80.79 84.68 85.67 86.57 87.14 87.56 88.00 88.38 81.31 84.07 83.00 83.50 82.85 87.43 88.07 88.25 89.10 89.38 82.90 82.35 84.51 82.06 77.39 84.24 82.76 82.62 84.75 86.20 88.24 83.46 81.26 81.92 78.22 76.81 74.48 74.02 85.68 86.51

0.24 0.28 0.48 0.30 0.26 0.35 0.43 0.44 0.48 0.43 0.37 0.37 0.28 0.25 0.36 0.36 0.37 0.28 0.31 0.21 0.22 0.40 0.52 0.46 0.37 0.34 0.31 0.30 0.33 0.34 0.31 0.43 0.29 0.32 0.33 0.35 0.29 0.28 0.31 0.30 0.28 0.35 0.37 0.32 0.39 0.47 0.36 0.44 0.46 0.48 0.41 0.38 0.43 0.43 0.39 0.50 0.54 0.61 0.72 0.58 0.57

5.58 5.99 8.13 6.61 5.90 6.69 7.50 7.79 8.46 9.50 7.94 7.53 6.28 5.69 7.32 7.28 7.36 6.59 6.94 5.51 5.62 6.86 9.05 9.03 8.81 8.13 7.46 7.45 7.68 7.54 7.03 8.45 7.18 7.69 8.29 8.26 7.93 7.33 8.39 7.77 6.86 7.23 7.76 7.14 7.79 7.56 7.17 8.16 8.36 8.62 7.98 7.27 7.03 7.18 6.91 7.48 7.68 8.10 8.54 7.81 7.30

(continued on next page)

182

H. Guan et al. / Journal of Asian Earth Sciences 117 (2016) 170–183

Appendix A (continued) Depth (cm)

Sample

K2O

Na2O

CaO

MgO

SiO2

Fe2O3

Al2O3

FeO

CIA⁄

Na/K⁄

SiO2/Al2O⁄3

3501.75 3536.55 3583.75

0711-DH97 0711-DH98 0711-DH99

0.91 1.18 1.75

0.36 0.58 0.83

3.45 0.77 0.84

1.17 1.21 1.47

65.13 68.15 67.78

4.98 4.55 4.71

15.21 15.39 14.97

0.23 0.05 0.08

87.23 82.56 76.02

0.63 0.77 0.74

7.28 7.53 7.70

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