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U-Th dating of a Paleolithic site in Guanyindong Cave, Guizhou Province, southwestern China
Journal of Archaeological Science: Reports 27 (2019) 101996
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U-Th dating of a Paleolithic site in Guanyindong Cave, Guizhou Province, southwestern China
T
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Huiyi Suna, Jian-xin Zhaoa,b, , Guanjun Shena,c, Bo Caod, Xiaochao Chea, Dunyi Liua a
Beijing SHRIMP Centre, Institute of Geology, Chinese Academy of Geological Sciences, Beijing, 100037, China Radiogenic Isotope Facility, School of Earth & Environmental Sciences, The University of Queensland, Brisbane, QLD 4072, Australia c College of Geographical Sciences, Nanjing Normal University, Nanjing 210023, China d Guizhou Cultural Archaeological Institute, Guizhou 550003, China b
A R T I C LE I N FO
A B S T R A C T
Keywords: U-Th age Guanyindong cave Speleothem Fossil Paleolithic
Guanyindong Cave in southwestern China has received considerable attention in the investigation of Paleolithic hominin origins and evolution in China, due to its rich archaeological finds composed of thousands of stone artifacts and a unique fauna with 23 species of mammalian fossils found. However, despite earlier extensive excavations and descriptive studies, debates still centre around the conflict between previous radiometric age data and evidence from biostratigraphic correlations. In this study, we carried out detailed field investigations and sampling, and obtained 35 U-Th dates on flowstone layers and other datable materials from the cave. The age results from materials in stratigraphic context provide a robust chronological framework of the cave. The data suggest that the deposition of Group B sediments and fossil assemblages widely distributed within the cave should have occurred after ~370 ka but before ~70 ka, with the bulk of the sediments and associated fossils laid down during 200–140 ka. Our new U-Th dates of in situ flowstone layers intercalated with one rhinoceros tooth and several other fossil fragments near the Hall at the centre of the cave constrain the deposition ages of these mammalian fossils to the period between 469 ± 37 and 336 ± 7 ka. Combined our U-Th data with recent OSL dates of Hu et al. (2019), we suggest that Group A sediments and associated fossils were likely deposited episodically from ca. 90 ka to < 40 ka. Overall, our data indicate that the cave development started > 469 ± 37 ka ago, whilst the cave system framework took shape as we see today > 340 ± 10 ka ago. Subsequently, the cave might have experienced several flooding and washout events, resulting in recycling and mixing of older sediments and fossils into younger sequences, a hypothesis consistent with tight clustering of both U-Th ages of speleothems in this study and the OSL dates of clastic sediments (Hu et al., 2019). This would reconcile the contradiction between the great antiquity of mammalian fossils inferred from biostratigraphic correlation and the much younger radiometric dates of materials in stratigraphic context, and explain the lack of technological advance despite an apparently long presence of the “Guanyindong culture”, as well as the presence of the Levallois technologies. In this regard, our U/Th age data, combined with other recent studies, have resulted in an improved understanding of Paleolithic hominid evolution and stone technologies in south China.
1. Introduction The Paleolithic site in Guanyindong Cave is located ca. 25 km to the south of the town centre of Qianxi County in central Guizhou Province, southwestern China (26°51′26″ N, 105°58′7″ E). As its entrances were sealed by fallen rocks, the cave remained unknown until early 1950s, when some local villagers ventured into a mist-generating fissure and then found a cavern with a few fossils littering around its ground surface. Excavation of the cave was first carried out in 1964 by a joint team from Institute of Vertebrate Paleontology and Paleoanthropology,
⁎
Chinese Academy of Sciences, and Guizhou Provincial Museum, recovering hundreds of stone artifacts and a number of mammalian fossils. Subsequent fieldworks and excavations were organized in 1965, 1972 and 1973, respectively. In total, more than three thousand stone artifacts and an abundance of mammalian fossils representing 23 species were recovered (Pei et al., 1965; Li and Wen, 1978). Guanyindong Cave was the first ever excavated cave site in South China where mammalian fossils were discovered along with Paleolithic artifacts. Owing to not only the abundance of mammalian fossils but also the distinctive feature of the artifacts (Pei et al., 1965; Li and Wen,
Corresponding author. E-mail addresses: [email protected] (H. Sun), [email protected] (J.-x. Zhao).
https://doi.org/10.1016/j.jasrep.2019.101996 Received 12 October 2018; Received in revised form 1 August 2019; Accepted 18 August 2019 2352-409X/ © 2019 Elsevier Ltd. All rights reserved.
Journal of Archaeological Science: Reports 27 (2019) 101996
H. Sun, et al.
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Fig. 1. (a) Plan view of the Guanyindong cave. The shade represents the main excavated areas throughout the cave, where most of our samples were taken. The locations of Profiles (or cross-sections) 1, 2a, 2b, 3, 3b and 4 are also shown, respectively. Profiles 1, 2a, 3b and 4 are illustrated in detail in Figs. 2–5. (b) The stratigraphic sequence of the West Entrance of the main cave was subdivided into nine layers that can be attributed to three groups (Groups A: layers 1–2, B: layers 3–8, C: layer 9) (after Li and Wen, 1986).
composed of Triassic limestone, which has experienced extensive karstic processes. The main entrance of the cave opens to the west, and is ~1450 m above sea level and ~15 m higher than the adjacent small intermountain basin. The main corridor is ~90 m long, 2–4 m wide, and 2–8 m high. In the middle of the main corridor, two branch caves extend, respectively, to the north (~30 m long, 1–2 m wide, with an entrance opening to the north) and to the south (~15 m long, 1 m wide, an east-west direction sub-branch cave develops at its end). At the location, where Northern Branch Cave extends out, the Main Corridor expands into a hall (Fig. 1a). The entire deposits can be subdivided into three groups (Fig. 1b), as A (Layers 1–2), B (Layers 3–8) and C (Layer 9) (Pei et al., 1965; Li and Wen, 1978). Shen and Jin (1992) first sampled the cross sections or profiles (a term used in Hu et al., 2019), mainly speleothems and some tooth fossils, for U-Th dating by alpha spectrometry. In 2015 and 2016, we carried out further detailed survey and sampling within the cave. As the bulk of the fossiliferous deposits have been removed during previous excavations in the 1960–1980's, our sampling focuses on the remnants of the deposits, mainly flowstones, which are still attached to the cave corridor walls, as well as the walls of the excavation pits. Since previous excavations targeted only hominin remains and stone artifacts, unfortunately no other materials in stratigraphic sequences were curated for dating or other scientific analysis. Fig. 1b illustrates the cave floor plan and the profiles (or cross sections) reported in Pei et al. (1965), Li and Wen (1986) and Shen and Jin (1992), with our sample locations in either the floor plan or the profiles. Profile 1 is situated inside the West Entrance, against the north wall (Figs. 1b and 2). The elevation of loose sediment piles were the highest outside the entrance, getting progressively lower inside the entrance. Major excavations during 1960–1970's resulted in the removal of up to 8 m thick of sediment inside and outside the entrance (see Fig. 1b). Outside the entrance and at ~4.5 m above the current ground level (matching the elevation of the bottom of the excavations shown in Fig. 1b) occurs a small stalactite hanging over the cave ceiling. This stalactite is stained with red clay and its stratigraphical location is at about the same level as the red-clay layer (Layer 2 of Group A) (Fig. 2). The lowest tip of this stalactite was sampled as S27. Just inside the entrance and ~0.5 m lower than S27, there is another stalactite (also stained with red clay) on the ceiling, its lower tip was taken as sample S26. Inside the entrance, about 2.2 m above the current ground level (matching Layer 3 in Fig. 1b) occurs a shawl with unknown thickness on the cave wall, the outermost sublayer of which is taken as sample S21. Sample S22 was collected from a flowstone layer, quite pure and dense, at ~1.9 m above the current ground level, stratigraphically matching Layer 4 in Fig. 1b. Sample S23 was taken from a flowstone layer ~5 cm thick and with limited expanse, possibly representing synlayer post-deposition secondary calcite formation along fissure, which is located at ~1.1 m above the ground level (stratigraphically matching Layer 5 or 6 in Fig. 1b). Sample S24 was collected from a major flowstone layer, which is 1.3 m above the ground level (stratigraphically matching Layer 5 or 6 in Fig. 1b). Sample S25, a crystalline calcite formation, was taken from a 20 × 30 cm sediment-filled oblong cavity, which is developed inside a hole and it is stratigraphically about 0.3 m above sample S24 or 1.6 m above the current ground level (stratigraphically matching Layer 4 in Fig. 1b). A small stalagmite grown from the cave wall at an elevation equivalent to the bottom of Layer 8 was previously sampled as QGC-23 and analyzed by Shen and Jin (1992). The stratigraphical location of this specific sample was determined through digging a trench into the back-filled excavation pit of Pei et al.
1978; Hu et al., 2019), Guanyindong Cave plays an important role in the study of the origins and evolution of Paleolithic culture in China. Consequently, its precise chronological position is of great importance. Based on biostratigraphic evidence, Pei et al. (1965) attributed Guanyindong Cave to Middle or Late Pleistocene. However, using the faunal composition, particularly the presence of Gomphotheriidae fossils, generally accepted as extinct elephant-like species of Tertiary ages, Li and Wen (1978) assigned much greater ages to the site. They considered that the upper Group A and the lower Group B deposits were roughly contemporaneous with and slightly older than Locality 1 at Zhoukoudian, respectively. Yuan et al. (1986) dated the site by U-series (or called U-Th) dating of fossil teeth. Their results, in the range of 80–115 ka, are far too young compared with the previous age estimate of Li and Wen (1978). Li (1989) insisted, based on the biostratigraphic correlation, that “the Group B deposits in Guanyindong Cave can surely be attributed to earlier Middle Pleistocene”. Also he criticized the dates of Yuan et al. (1986) on fossil teeth as being self-contradictory. In an effort to reconcile the much younger U-series dates on fossil teeth with the last occurrence of Gomphotheriidae being no later than Middle Pleistocene, Han and Xu (1989) assigned an age range of the fossil finds spanning Late and Middle Pleistocene. Using alpha spectrometry, Shen and Jin (1992) carried out the first U-Th dating of flowstone layers intercalated in cultural deposits of Guanyindong Cave, obtaining ages in the range of 40–270 ka. As the validity of the U-Th dating of carefully selected, pure and dense cave calcites has been well demonstrated, this temporal frame has been widely cited in more recent literature (e.g., Li et al., 2009a, 2009b; Hu et al., 2019). However, classical alpha spectrometric U-Th dating is burdened with some intrinsic limitations. Notably, it needs a sample size of at least 10–20 g. In typical hominin cave sites, the interbedded flowstone layers are, more often than not, relatively thin and of mediocre or even poor purity. So some key horizons of a site cannot be dated because of the difficulty to obtain enough sample material, which is also the case of Guanyindong Cave. Besides, with important counting statistical error in the order of ~3%, the precision of the obtained dates is quite often insufficient to address some important issues, especially when the ages were > 300 ka (close to the limit of alpha spectrometric U-Th dating). In the past 30 years or so, important progresses in mass spectrometric technologies have revolutionized the U-series dating of speleothem carbonates. Now with TIMS or MC-ICPMS, 2δ precisions up to 0.2% can be achieved with small sample sizes of < 50 mg. Under such a circumstance, and considering the importance of the Guanyindong Cave in archaeological studies in China, a renewed chronological study of the site is warranted. Built upon the chronology of Shen and Jin (1992), Hu et al. (2019) reported a set of OSL dates for remnants of excavated profiles at the west entrance of the cave. The U-Th dates of the speleothems and the OSL dates of the sediments are broadly consistent for Group A and upper layers of Group B, but show some discrepancy in details, especially regarding the age limit of Group A. In this study, we will report a new set of U-Th dates for various types of speleothems systematically collected from the entire cave system, and attempt to synthesize the data to obtain an improved understanding of chronologies of the fossil records in context with the cave evolution history. 2. The site and samples in stratigraphic context The Guanyindong Cave is located at the middle axis of an anticline 3
Journal of Archaeological Science: Reports 27 (2019) 101996
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Fig. 2. Stratigraphic sequence of Profile (cross-section) 1 at West Entrance and sample photos showing speleothem sample localities (yellow dots) and their age results. Red circles with crosses denote the stratigraphic horizons where fossils were excavated. Zero level of the vertical scale bar represents the current ground level. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
ceiling, hanging ~2 m above the current ground level. This hanging sequence consists of four flowstone sub-layers, which were collected from top to bottom as samples S10-A, S10-B, S10-C, and S10-D, respectively. A strongly altered rhinoceros tooth fossil was found in the brown detrital deposits between flowstone sub-layers B and C. A few fossil debris can also be found between sub-layers C and D. At the intersection between the Main Corridor and the North Branch Cave (Fig. 1a), two samples (S12 and S38) were collected. Sample S12 was taken from the surface of a large (~2 m-long fallen, 0.3–0.5 m in diameter) stalactite the bottom of an excavation pit. Sample S38 was collected from the bottom of a stalagmite, which was attached to the wall and ~50 cm above ground (Fig. 1a). Profile 4 is situated at the end of the South Branch Cave (Fig. 5). This branch cave is only about a meter high at the end and the passage is even narrower. It took considerable efforts for us to reach its interior. The previous excavation focused mainly on the west end of the South Branch Cave, where we found two 5 cm-thick flowstone layers which
(1965) by Shen and Jin's team ~30 years ago. Profile 2a (Fig. 3) is located ~16 m inside the West Entrance. It is from a relatively well-preserved excavation pit. Above the pit occurs a large column composed of a giant stalactite and an underlying disproportionately small stalagmite. Samples S5 and S6 were collected from the lowermost and outermost parts of the stalactite, respectively. Sample S28 was taken from the central part of the stalagmite. Within the pit, some 2.1 m and 1.95 m below the current ground level, two in situ mushroom-shaped stalagmites were found and sampled as S1 and S3, respectively. Some 2.05 m and 0.75 m below the current ground level, two blocks of fallen speleothem formations were found and sampled as S2 and S4, respectively. Profile 3b is situated at the northwestern corner of the Hall (Fig. 4), ~10 m west of the original Profile 3 of Pei et al. (1965). This is a newly discovered and sampled sequence in this study. Profile 3b contains a number of flowstones interlayered with brown fossil-bearing deposits with a total thickness of ~40 cm. It was found loosely stuck to the cave 4
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Fig. 3. Stratigraphic sequence of Profile (cross-section) 2a and sample photos showing speleothem sample localities (yellow dots) and their U-Th ages. Red circles with crosses denote the stratigraphic horizons where fossils were excavated. Zero level of the vertical scale bar represents the current ground level. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
Radiogenic Isotope Facility (RIF), at the School of Earth and Environmental Sciences, the University of Queensland (UQ). The purest and densest possible portions of each sample were selected, cleaned, and broken into small chips or sands (1–2 mm) using a hand tool. The sample grains were examined carefully so as to remove any visible impurities. The pre-treated samples were then ultrasonicated for 20 min and rinsed with Milli-Q water for 3 times. The samples were dried on hotplate at 80 °C overnight. Upon dryness, the sample grains were then examined under a binocular microscope and further purified by hand picking to remove any grains with impure inclusions. The purpose of the sample vetting process is to increase the precision of dating results by physically removing and reducing non-radiogenic 230Th from non‑carbonate impurities. U-Th dating was carried out using a Nu Plasma multi-collector inductively-coupled plasma mass spectrometer (MC-ICP-MS) in the RIF Lab at UQ, following chemical treatment procedures and MC-ICP-MS analytical protocols described elsewhere (Zhao et al., 2001; Zhao et al., 2009; Clark et al., 2014). Pre-treated sample materials weighing 50–150 mg were spiked with a mixed 229Th-233U tracer and then completely dissolved in concentrated HNO3. After digestion, each sample was treated with H2O2 to decompose trace amounts of organic matters and to facilitate complete sample tracer homogenisation. U and Th were separated using conventional anion-exchange column chemistry using Bio-Rad AG 1-X8 resin. After stripping off the matrix from
were taken as samples S34 and S35. The stalagmite sample S29 was collected at ~10 cm above the sampling point of S35. Another stalagmite S37 was collected from the other side of the excavation site, slightly above sample S29. This small stalagmite is ~5 cm tall (~6 cm in diameter), its tip almost reaching to cave ceiling. About 10 m away from the entrance of the South Branch Cave, samples S36 and S18 were taken from ~5 cm thick flowstone layers attached to the ceiling. A small and pure stalagmite with a height of 6 cm and a diameter of 7 cm growing on the top of flowstone was sampled as S19. The North Branch Cave was poorly investigated comparing to the above profiles, because only a very small amount of deposits was left. About 20 m to the north entrance, flowstone layers were found on the west wall, and samples S39, S41and S43 were taken from different flowstone layers (Fig. 1a). S40 was taken from a small stalagmite slightly below sample S39. Sample S42 was collected from another stalagmite about 60 cm in length and 40 cm in diameter. In the North Branch Cave, about 10 m away from the Hall, sample S8 was taken from a stalagmite 10 cm in length and 6 cm in diameter (Fig. 1a). 3. Method and U-Th dating results 3.1. Method The speleothem samples were processed for U-Th dating in the 5
Journal of Archaeological Science: Reports 27 (2019) 101996
H. Sun, et al.
a
Fig.4b
7RRWK
%RQH
b
Fig. 4. Stratigraphic sequence of Profile (cross-section) 3b and sample photos showing speleothem sample localities (yellow dots) and their U-Th ages on a hanging wall at the Hall. Red circle with cross denotes the stratigraphic horizons where fossils were present. This is a new profile discovered and sampled in this study. Zero level of the vertical scale bar represents the current ground level. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
the column using double-distilled 7 N HNO3 as eluent, 3 ml of a 2% HNO3 solution mixed with trace amount of HF was used to elute both U and Th into a 3.5 ml pre-cleaned test tube, ready for MC-ICP-MS
analyses, without the need for further drying down and re-mixing. After column chemistry, the U-Th mixed solution was injected into the MCICP-MS through a DSN-100 desolvation nebuliser system with an 6
Journal of Archaeological Science: Reports 27 (2019) 101996
H. Sun, et al.
Fig. 5. Stratigraphic sequence of Profile (cross-section) 4 in the South Branch Cave and sample photos showing speleothem sample localities (yellow dots) and their U-Th ages. Red circle with cross denotes the stratigraphic horizon where fossils were excavated. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
uptake rate of around 0.07 ml per minute. U-Th isotopic ratio measurement was performed on the MC-ICP-MS using a detector configuration to allow simultaneous measurements of both U and Th isotopes (Zhou et al., 2011; Clark et al., 2014). The 230Th/238U and 234U/238U activity ratios of the samples were calculated using the decay constants given in Cheng et al. (2000).
speleothems are made of dense crystalline calcites without diagenesis or weathering.
3.2. Results
Based on the residual “red soil” stains characteristic of Group A sediments, it is likely that the stalactites hanging inside and outside the west entrance pre-date the fossiliferous Group A deposits of Li and Wen (1978, 1986) (see Fig. 2). Samples S26 and S27 from these stalactites yielded 230Th ages of 58 ± 4 ka and 71 ± 7 ka, respectively. On the other hand, using alpha spectrometry, Shen and Jin (1992) obtained detrital 230Th corrected U-Th ages of 53 ± 9 and 40 ± 6 ka (recalculated using Isoplot/EX 3.75 Program) for two sub-samples (QGC19-1 and QGC-19-2) from another “red-soil-stained” stalactite in a similar stratigraphic context. These age results together suggest the “redsoil-stained” stalactite clusters from similar stratigraphical horizons were developed over a period of 70–40 ka, and that the overlying Group A deposits, together with fossils and stone artifacts in Group A, could have been laid down rapidly after 40 ± 6 ka (i.e. after growth of the youngest stalactite tip), based on interpretation of Shen and Jin (1992). The alternative and more likely scenario is that Group A sediments may have been deposited progressively or episodically during the growth period of the stalactites (in other words, the stalactites of different ages were developed contemporaneously with the “red-soil” deposition). In
4. Discussion 4.1. Chronology of Guanyindong cave deposits
The U-Th isotope ratios and 230Th ages of 35 speleothem samples are listed in Table 1, and presented in Figs. 1–5 with stratigraphic contexts for a majority of them. The rhinoceros tooth fossil in Profile 3 is strongly altered, unsuitable for U-Th dating. The dated samples have U concentrations ranging from 0.07 to 0.5 ppm, typical of speleothem calcites. > 70% of the dated samples have measured 230Th/232Th activity ratios > 10. For these samples, detrital or non-radiogenic 230Th corrections using the assumed bulkEarth 230Th/232Th value has relatively insignificant impact on the corrected 230Th ages. However, for the remaining ~30% with measured 230 Th/232Th activity ratios < 10, their corrected 230Th ages have large age uncertainties and should be treated with caution. Overall, all dated samples are within the dating limit of the U-series dating method, and they all plot above the secular equilibrium line on the 230Th/238U vs 234 U/238U evolution diagram (Fig. 6), suggesting even the oldest samples are in isotopically closed system without any visible U loss and thus the age results are reliable. This is also supported by the fact all dated 7
Material & type⁎
8
0.1170 0.0712 0.1044
0.02 m 0.75 m 0.01 m
0.1343 0.2980 0.5303 0.1356 0.1296 0.0771 0.10200
Walls (North branch cave) S8 Stalagmite (2) S39 Flowstone layer(1) S40 Stalagmite (2) S41(T) Flowstone layer(1) S41(B) Flowstone layer(1) S42 Stalagmite(4) S43 Flowstone layer(1) 0.0001 0.0001 0.0001 0.0000 0.0000 0.0000 0.0000
0.00010 0.0001 0.0003 0.0001 0.0001 0.0000 0.0000
0.0001 0.0001 0.0001 0.0000 0.0001 0.0001
0.0001 0.0000 0.0000
0.0001 0.0002
0.0001 0.0001
0.0001 0.0001 0.0000 0.0001 0.0005
0.0001 0.0001 0.0002
± 2δ
15.85 15.42 116.9 8.37 7.24 59.40 16.78
545 6.40 144.60 93.60 10.95 4.55 12.40
41.06 2.25 37.18 23.58 4.11 10.78
6.57 5.57 23.30
6.68 1.49
30.69 52.18
1.42 7.94 25.97 122.73 1.96
72.77 35.70 3.94
Th (ppb)
232
0.02 0.03 0.30 0.01 0.02 0.10 0.02
2.00 0.01 0.50 0.16 0.02 0.01 0.02
0.12 0.00 0.04 0.04 0.01 0.03
0.02 0.01 0.10
0.01 0.00
0.046 0.20
0.00 0.01 0.04 0.41 0.00
0.09 0.17 0.01
± 2δ
28.93 4.10 5.15 14.72 17.86 4.08 6.40
2.08 40.29 2.52 12.94 81.46 78.04 38.43
12.51 280.25 17.59 17.51 25.90 49.08
8.55 14.78 7.37
123.65 477.52
16.77 6.29
615.35 42.64 5.20 3.65 847.67
6.96 28.53 196.56
(230Th/232Th)
0.10 0.05 0.02 0.06 0.11 0.02 0.03
0.01 0.16 0.02 0.04 0.23 0.35 0.12
0.04 0.93 0.05 0.05 0.15 0.21
0.05 0.10 0.05
0.30 1.63
0.05 0.03
3.38 0.17 0.03 0.03 3.10
0.02 0.18 0.58
± 2δ
1.1250 0.0699 0.3739 0.2994 0.3287 1.0360 0.3473
1.1285 0.6326 1.1297 1.0310 0.9678 1.0669 0.9417
1.0692 1.0883 1.1205 1.1261 0.3169 0.9126
0.1583 0.3810 0.5419
0.9413 0.9124
1.0017 1.1174
1.0163 0.9581 0.4744 0.5688 1.0898
0.7118 0.9334 1.0067
(230Th/ 238 U)
0.0036 0.0008 0.0016 0.0011 0.0019 0.0035 0.0017
0.0063 0.0023 0.0057 0.0028 0.0024 0.0044 0.0026
0.0020 0.0029 0.0028 0.0025 0.0017 0.0033
0.0008 0.0024 0.0031
0.0018 0.0027
0.0026 0.0034
0.0046 0.0034 0.0022 0.0041 0.0032
0.0019 0.0042 0.0026
± 2δ
1.4459 1.1500 1.2055 1.1006 1.1018 1.0490 1.0709
1.0903 1.3141 1.0964 1.1939 1.1398 1.0868 1.1463
1.0974 1.1051 1.1171 1.1014 1.0923 1.1080
1.1351 1.1207 1.1724
1.0993 1.1071
1.1894 1.1215
1.0630 1.1128 1.0421 1.0479 1.0933
1.1415 1.1565 1.0688
(234U/238U)
0.0015 0.0017 0.0011 0.0009 0.0013 0.0017 0.0013
0.0014 0.0016 0.0019 0.0015 0.0009 0.0017 0.0014
0.0013 0.0014 0.0014 0.0011 0.0013 0.0012
0.0014 0.0017 0.0018
0.0009 0.0012
0.0013 0.0033
0.0009 0.0015 0.0017 0.0015 0.0011
0.0013 0.0013 0.0010
± 2δ
145.5 6.8 40.0 34.5 38.4 387.0 42.5
767 69.4 564 194.7 190.7 340.6 175.4
320.2 336.5 372.8 473 37.2 179.2
16.3 44.9 66.4
198.8 179.5
183.2 353.0
303.9 200.4 65.9 84.7 373.8
103.6 167.7 281.1
Uncorr. Age (ka)
1.0 0.1 0.2 0.1 0.3 14 0.3
456 0.4 82 1.6 1.3 9.9 1.3
4.3 6.5 8.2 18 0.2 1.6
0.1 0.4 0.5
1.2 1.4
1.3 11
7.3 2.1 0.5 0.9 9.3
0.5 1.8 3.6
± 2δ
143.4 5.5 34.6 32.8 36.9 365 37.9
735 68.4 532 189.2 189.8 339.5 173.6
313.8 336.2 368.4 469 36.2 177.8
14.9 42.9 60.8
198.2 179.3
179.1 340
303.8 198.7 57.8 70.6 373.7
95.6 165.4 280.7
Corr. age (ka)
1.9 0.7 2.6 0.8 0.8 35 2.3
5368 0.5 748 3.7 1.3 10.1 1.5
9.8 6.5 15.8 37 0.5 1.7
0.7 1.0 2.6
1.2 1.4
2.5 37
7.3 2.2 4.1 7.2 9.3
3.4 2.0 3.6
± 2δ
1.6905 1.1545 1.2410 1.1122 1.1147 1.174 1.0826
2.30 1.3860 1.69 1.3539 1.2413 1.2288 1.2437
1.2540 1.2724 1.3495 1.4020 1.1033 1.1811
1.1431 1.1392 1.2179
1.1748 1.1779
1.3302 1.371
1.1488 1.2014 1.0536 1.0670 1.2682
1.2024 1.2566 1.1525
Corr. initial (234U/238U)
0.0088 0.0021 0.0078 0.0014 0.0017 0.014 0.0025
19.3 0.0030 1.31 0.0094 0.0018 0.0060 0.0030
0.0059 0.0044 0.0107 0.0341 0.0015 0.0022
0.0019 0.0024 0.0073
0.0015 0.0019
0.0069 0.0024
0.0033 0.0029 0.0031 0.0054 0.0064
0.0091 0.0036 0.0021
± 2δ
Note: All ratios in parentheses are activity ratios. U-Th ages calculated using Isoplot/Ex 3.75 of Ludwig (2012). Corrected ages were calculated assuming non-radiogenic 230Th/232Th = 4.4 ± 2.2 × 10−6 (bulk-earth value), and 238U, 234U, 232Th and 230Th are in secular equilibrium. Non-radiogenic 230Th correction results in large age error magnification for samples with low measured 230Th/232Th ratios. ⁎ refers to distance from the current ground level of each site at the time of sample collection. It is different from the actual cave ground levels when the excavations took place ~50 years ago due to repeated digging, damage and erosion. ⁎ Based on their stratigraphic significance, the samples are divided into the following five groups: 1. capping flowstone layers and stalagmites on them, defining minimum age for the underlying deposits; 2. flowstone layers intercalated in detrital deposits and stalagmites developed in sediments, defining the maximum age of the overlying deposits and minimum age of the underlying deposits; 3. flowstone layers stuck on the ceiling, indicating filling-washingout event of the deposits inside the cave; 4. calcite shawl and stalactites buried by deposits (S5, S6, S26, S27), stalagmite on cave wall underlying the deposits, fallen calcite fragments (S2, S4), fallen stalactite (S12), representing the maximum age of their horizon; 5. calcite crystals in a cavity (S25), posteriorly formed, defining the minimum age of its horizon.
0.33192 0.1343 0.10611 0.3870 0.3038 0.1097 0.1668
0.1583 0.1906 0.1924 0.1208 0.1106 0.1910
0.2893 0.2563
−1.95 m −0.75 m
1.70 m 1.65 m 1.50 m 1.40 m
0.1694 0.0969
0.2826 0.1165 0.0938 0.2598 0.5034
1.3 m 1.6 m 4.0 m 4.5 m
−2.10 m −2.05 m
0.2346 0.3595 0.2536
U (ppm)
2.2 m 1.9 m 1.1 m
Distance ground⁎
Cross section 4 (South branch cave) S18 Flowstone layer (3) S19 Stalagmite (1) S29 Stalagmite (2) S34 Flowstone layer (2) S35 Flowstone layer (2) S36 Flowstone layer (3) S37 Stalagmite (1)
Cross section 3 (The Hall) S10-A Flowstone (3) S10-B Flowstone (3) S10-C Flowstone (3) S10-D Flowstone (3) S12 Fallen stalactite (4) S38 Stalagmite (2)
Cross section 2a (Excavation Pit) S1 Stalagmite (2) S2 Calcite fragment (4) S3 Stalagmite (2) S4 Calcite fragment (4) S5 Stalactite (4) S6 Stalactite (4) S28 Stalagmite (1)
Cross section 1 (West Entrance) S21 Shawl (4) S22 Flowstone layer (2) S23 Flowstone layer (2?) S24 Flowstone layer (2) S25 Cavity calcite (5) S26 Stalactite (4) S27 Stalactite (4) QGC23 Stalagmite (4)
Sample no.
Table 1 U-Th isotope data for speleothem samples from Guanyindong Cave, Guizhou Southwest China.
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Fig. 6. The 230Th/238U vs in this study.
234
down contemporaneously. All the nine ages appear to be in broad consistency with the OSL dates of 175 ± 32 to 161 ± 12 ka (age errors at 1δ) defined by six sediment samples from the main part of Group B at the West Entrance (Hu et al., 2019). The six OSL dates are analytically indistinguishable, with a weighted mean of 165 ± 11 ka. Sample S21 collected from the bottom of a shawl inside the West Entrance (Profile 1 in Figs. 1 and 2) yielded an age of 96 ± 3 ka. As all the fossiliferous sequence of Group B at this excavation site has been completely removed and the cave floor at the West Entrance was severely modified by floods and local villagers after excavations, it is difficult to envisage its corresponding stratigraphic location in Group B (Fig. 1). For instance, it is unclear whether its stratigraphic horizon matches to Layer 3 or 4 of Group B sediments. Based on its 2.2 m elevation above the current ground level, we suggest it should stratigraphically match with the lower part of Layer 3 of Group B in Fig. 1b, and thus its age may well define the maximum age of Layer 3. Based on their elevations above the current ground level, which is the bottom of the excavations at the West Entrance of the Main Cave (Fig. 1b), flowstone samples S23 and S24 (Fig. 2) appear to be from the upper sixth layer of Group B deposits at the West Entrance. Their ages of 281 ± 4 ka and 304 ± 7 ka indicate that the deposits found at this level should be at least 300 ka old, which is substantially older than the OSL dates for lower strata of the site (Hu et al., 2019). Stalagmite sample QGC-23 was collected by Shen and Jin (1992) from the basal 8th layer of Group B at the West Entrance. This sample gave an alpha-spectrometric age of 260 + 34/−26 ka (1δ) (Shen and Jin, 1992) and was redated by MC-ICP-MS in this study, yielding a more precise age of 374 ± 9 ka (2δ), making maximum age for Group B deposits. The large spread of speleothem ages as described above implies that the group-layer division of Li and Wen (1978, 1986) might not be consistent across the entire cave and should be treated with caution. The inconsistency of the depositional sequence is evidenced by the young age (36.2 ± 0.5 ka) of S12, a volumous fallen stalagtite apparently at a lower horizon of Group B. the deposits in North Branch Cave may also be quite young, as demonstrated by the ages on S40, S41, S42 and S43. Nevertheless, our U-Th age data do demonstrate that Group B sediments in the entire cave could have been deposited after 374 ± 9 ka (age of basal flowstone QGC-23 at West Entrance), but before 68 ± 5 ka (age of stalagmite sample S19 near South Branch Cave), with the bulk of sediment profiles laid down during ca. 199–143 ka. The great time-span of the fossiliferous Group B is also consistent with the presence in situ fossil-bearing deposits intercalated with in situ flowstone sub-layers of S10-A (314 ± 10 ka), S10-B (336 ± 6 ka), S10-C (368 ± 16 ka) and S10-D (469 ± 36 ka), attached to the ceiling in the Hall (see Fig. 4). Here one strongly altered rhinoceros tooth fossil was found in deposits between flowstone sub-layers B and C and a few fossils debris could also be found between sub-layers C and D. Thus the U-Th dates of the flowstones bracket the ages of the fossils here to between 469 and 336 ka. The age distribution of all dated speleothems (Fig. 7) suggest that the cave system was developed at least 469 ± 37 ka ago (age of S10D), and speleothem growth continued until Holocene or recent (the youngest date is 5.5 ± 0.7 ka from S39). Speleothem growth appears to be episodic, and tends to concentrate during the transition from interglacial to glacial periods. Few samples dated to the heights of full interglacials (possibly due to highest rainfall leading to intensified flooding). For instance, no samples dated to Marine Isotope Stage (MIS) 5e, 7 or 11. In addition, speleothems dated to > 340 ± 10 ka were found in all major sites of the cave, including the West Entrance (e.g. QGC23), Profile 2a (S2), the Hall (S10-C, S10-D), the North Branch Cave (S42) and the South Branch Cave (S36). This suggests that the entire cave system as we see today should have already been developed by that time.
U/238U evolution diagram showing all U-Th data
this regard, it could be argued that Group A sediments were laid down from 70 ka to later than 40 ka. This interpretation appears to be broadly consistent with the OSL dates of Hu et al. (2019) (Note that age errors of the OSL dates were all reported at 1δ). Since Group A “red-soil” layer was only found near the West Entrance of the cave, whereas the underlying Group B deposits (mainly brown-coloured sediments) occur throughout the entire cave, it can be inferred that the two groups must have different origins and formation histories. When the cave was first excavated by Pei et al. (1965), a capping flowstone of 0.2 to 0.6 m in thickness, was reported to extend to the entire cave, which seems to overlie the upper fourth layer of Group B deposits inside the west entrance based on the stratigraphic division of Li and Wen (1978, 1986). It corresponds to the 2nd layer in Profile 1 and 2a, and the 1st layer in Profiles 2b, 3 and 4 reported in Pei et al. (1965). As the bulk of the fossiliferous deposits have been dug out, this capping flowstone is no longer existing and available for sampling. Because of this, it is difficult to assess if this capping flowstone is chronologically consistent across the entire cave. Sample S28 was collected from the mini-stalagmite growing below the large stalactite and above Profile 2a within the excavation pit inside the cave, ~15 m east of the West Entrance (Fig. 3). It yields an age of 61 ± 3 ka, whereas the lower (S5) and the upper (S6) parts of the large stalactite give ages of 14.9 ± 0.7 ka and 42.9 ± 1.0 ka, respectively. All fossiliferous Group B of Profile 2a below S28, must be older than 61 ± 3 ka, the age of the mini-stalagmite. Similarly, near the South Branch Cave (Fig. 1a), a small stalagmite (sample S19) appears to grow on top of the capping flowstone. It gives an age of 68 ± 5 ka, which marks the minimum age of the underlying (Profile 4). Based on above age constraints from Profiles 2a and 4, it can be inferred that Layer 3 sediments (uppermost layer of Group B) were deposited earlier than 61–68 ka (Fig. 1). Seven in situ speleothem samples, including samples S22 and S25 (within Profile 1), S8 (within North Branch Cave), S34-S35-S37 (within Profile 4), and S38 (within the Hall) were taken from the upper strata of Group B deposits across the entire cave system (Fig. 1a). They gave the following age results: 165 ± 2 ka, 199 ± 2 ka, 143 ± 2 ka, 189 ± 4 ka, 190 ± 1 ka, 175 ± 1 ka, and 178 ± 2 ka (Table 1, also see Figs. 1, 2, 5), respectively, indicating that the accumulation of the main part of Group B deposits started in the late Middle Pleistocene. The in situ mushroom-shaped small stalagmites S1 and S3 at ~2 m depth of the excavation pit as shown in Profile 2a gave ages of 179.1 ± 2.5 ka and 198.2 ± 1.2 ka, respectively. All together, these nine ages suggest that the upper strata of Group B sediments were laid 9
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the entire cave and the tight OSL date cluster of 160–170 ka (indistinguishable within 2δ errors, with a weighted mean of 165 ± 11 ka) for Layers 4–8 at the West Entrance (Hu et al., 2019), implying rapid accumulation of such thick sequences at their respective locations. It is also intriguing to note that 12 of the 13 OSL dates of Hu et al. (2019) clustered within three age groups (the OSL dates within each group are indistinguishable at their 2δ age uncertainties), with weighted means of 165 ± 11, 87 ± 7, and 42 ± 4 ka, respectively, separated by considerable age hiatuses. Such an age distribution pattern is consistent with separate flooding and fill-up/washout events being responsible for the rapid accumulation of the respective sediment sequences separated by long-term discontinuities. 4.3. Interpretations of Guanyindong stone artifacts The lithic assemblage of the site bears distinct features compared with the contemporaneous Paleolithic industries in Europe and in other regions in China (Hu et al., 2019). For marking its special status in archaeological studies, a term of “Guanyindong Culture” was proposed (Pei et al., 1965; Li and Wen , 1978; Li et al., 2009a, 2009b). According to the chronological frame given in this paper, the lithic industry of Guanyindong cave could have developed during a long period of time from > 470 ka to < 40 ka. The lack of detailed stratigraphic context for many of the artifacts renders it difficult to evaluate the trend of technological evolution. Nevertheless, detailed technological analyses did demonstrate that the Guanyindong industry remained largely unchanged over time (Li et al., 2009a, 2009b). This is also reflected by the fact that raw materials always came from a flint vein or from the gravelly bed of a small river within 3 km of the cave. Moreover, the débitage mode remained quite different from the concept of Levallois widely used in Europe, Near-East and Africa. However, the recent evidence of Levallois technology from the lithic assemblage of the Guanyindong Cave site challenges the existing model regarding the origins and spread of Levallois technologies in East Asia and its links to a Late Pleistocene dispersal of modern humans (Hu et al., 2019). It is unclear whether the Guanyindong industry did remain unchanged over such a long period, or those fossils and stone artifacts found in younger sequences were simply recycled from older deposits during a series of flood washout events. The fact that speleothem growth in the cave appears to be episodic, with few samples dated to the full interglacials, such as Marine Isotope Stage (MIS) 5e, 7 or 11 (Fig. 6) points to the possibility that cave flooding might have intensified during such fullinterglacial periods. The flooding hypothesis is also consistent with the tight clustering of the OSL dates of the fossiliferous sediment sequences, separated by considerable age hiatuses, as reported in Hu et al. (2019). Such repeated flooding and fill-up/washout events could have been responsible for the recycling and mixing of fossils and stone artifacts that may have different ages and origins. Nevertheless, more stringent temporal control of the site will help to provide useful evidence for exploring and interpreting the relationship between Paleolithic populations and stone artifacts.
Fig. 7. Relative probability plot of speleothem ages and δ18O record of benthic foraminifera is from Lisiecki and Raymo (2005).
4.2. Reconciling biostratigraphic correlation with isotope dating As described above, according to the ages of S10-A (314 ± 10 ka), S10-B (336 ± 6 ka), S10-C (368 ± 16 ka) and S10-D (469 ± 36 ka), samples from several in situ flowstone sub-layers intercalated with in situ fossil-bearing deposits (see Fig. 4) attached to the ceiling in the Hall, the cave should have been completely filled with deposits by 314 ± 10 ka. This inference is also supported by the age of S36 (340 ± 10 ka), a flowstone layer attached to the ceiling in South Branch Cave, with much younger speleothems developed underneath. The bulk of the hanging sequence collapsed and fell on the ground during our sample collection. There should be a considerable amount of older deposits below the hanging residual sequence, which have probably been washed away by subsequent floods. The fact that the hanging sequence has nearly reached the ceiling suggests that the original cave here was once almost completely filled. The present-day Hall could have been formed during a subsequent flood event(s) that washed out the bulk of the older deposits that once filled the pre-existing cave. A flood event washing away all the underlying deposits must have happened after emplacement of the rhinoceros tooth in between S10-B (dated to 336 ± 7 ka) and S10-C (dated to 368 ± 16 ka) in the Hall, or after the formation of S36 at 340 ± 10 ka in the South Branch Cave. The > 2 m thick washed-away deposits underneath S10-D (469 ± 36 ka) should be older than 469 ± 36 ka, probably early Middle Pleistocene in age. Based on faunal compositions, the Guanyindong site was once assigned with a much older age (e.g. Li and Wen, 1978, 1986). This is mainly based on the presence of Gomphotherium, generally considered as a Tertiary species. The discovery of an infilled cave being subsequently washed out by flood events points to the possibility that the Gomphotherium fossils may be recycled from deposits of a previous cycle, and somehow survived the washout event(s). Somehow this may reconcile the difference between faunal correlation and isotopic dating. Our hypothesis of repeated flooding and fill-up/washout events having occurred at least after the deposition of the earliest fossiliferous sediments well constrained to 336–469 ka is also supported by the relatively tight U-Th age cluster of 140–200 ka for all four profiles across
5. Conclusions Based on detailed field observations and systematic U-Th dating of speleothems collected from a number of excavation sites throughout the entire Guanyindong cave, Guizhou, southern China, combined with data reported in the literature, the following conclusions can be made: (1) The Guanyindong cave developed for at least half a million years, from early Middle Pleistocene till recent or present. (2) The present configuration of the cave system consisting of the West Entrance and the Main Cave Corridor, the Hall, the South Branch Cave, the North Branch Cave took shape probably ~340 ka ago or earlier. (3) The unconformably overlying red-coloured Group A sediments and 10
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Nengping and others during fieldworks in 2015 and 2016. This manuscript has benefited a lot from constructive comments and suggestions made by the Editor and the anonymous reviewer.
fossil assemblage of the excavated profile found mainly at the west cave entrance was likely deposited from 71 ka to later than 40 ka, constrained by the ages of the “red-clay-stained” stalactite clusters, their growths might be contemporaneous with the deposition of Group A sediments. This inference is broadly consistent with the OSL dates (87–42 ka) for this group. (4) The unconformably underlying brown-coloured Group B sediments and fossil assemblages widely distributed within the cave may have been laid down after ~370 ka but before ~70 ka, with the bulk of the sediments and associated fossils accumulated during 200–140 ka. (5) Our new U-Th dates of in situ flowstone layers intercalated with one rhinoceros tooth and several other fossil fragments near the Hall at the centre of the cave constrain the deposition ages of these mammalian fossils to the period between 469 ± 37 and 336 ± 7 ka. (6) The cave might have experienced one or several flooding and washout events, resulting in recycling and mixing of older fossils into younger sequences. This would explain the contradiction between the great antiquity of some mammalian fossils inferred from biostratigraphic correlation and younger radiometric dates of materials in stratigraphic context, as well as the apparent lack of technological advance despite an apparently long presence of the so-called “Guanyindong culture” (which is challenged by the discovery of the Levallois technologies according to Hu et al., 2019). In this regard, our U-Th chronology study of Guanyindong cave, combined with the recently reported OSL dates, leads to a better understanding of Paleolithic hominid evolution and stone technology in South China.
References Cheng, H., Edwards, R.L., Hoff, J., Gallup, C.D., Richards, D.A., Asmerom, Y., 2000. The half-lives of uranium-234 and thorium-230. Chem. Geol. 169, 17–33. Clark, T.R., Roff, G., Zhao, J.X., Feng, Y.X., Done, T.J., Pandolfi, J.M., 2014. Testing the precision and accuracy of the U–Th chronometer for dating coral mortality events in the last 100 years. Quat. Geochronol. 23, 35–45. Han, D.F., Xu, C.H., 1989. Quaternary Mammals in Southern China and the Primitive Human Living Environment. Early Humankind in China. Science Press, Beijing, pp. 338–364. Hu, Y., Marwick, B., Zhang, J.F., Rui, X., Hou, Y.M., Yue, J.P., Chen, W.R., Huang, W.W., Li, B., 2019. Late Middle Pleistocene Levallois stone-tool technology in southwest China. Nature 565, 82–85. Li, Y.X., 1989. Early Paleolithic Culture in Southern China. Early Humankind in China. Science Press, Beijing, pp. 159–192. Li, Y.X., Wen, B.H., 1978. Discovery of Palaeolithic industry at Guanyindong in Qianxi County, Guizhou Province, and its significance. In: Collected Papers on Palaeoanthropology. Science Press, Beijing, pp. 77–93. Li, Y.X., Wen, B.H., 1986. Guanyindong - A Lower Paleolithic Site at Qianxi County, Guizhou Province. Cultural Relics Publishing House, Beijing. Li, Y., Hou, Y.M., Boëda, E., 2009a. Mode of débitage and technical cognition of hominids at the Guanyindong site. Chin. Sci. Bull. 54, 3864–3871. Li, Y., Hou, Y.M., Boëda, E., 2009b. Methodological application of the Paleolithic technological research, a case study of a core from the Guanyindong Site (in Chinese). Acta Antropol. Sin. 28 (4), 356–362. Lisiecki, L.E., Raymo, M.E., 2005. A Pliocene e Pleistocene stack of 57 globally distributed benthic δ18O records. Paleoceanography PA1003 (20), 1–17. Ludwig, K.R., 2012. User's Manual for Isoplot 3.75: A Geochronological Toolkit for Microsoft Excel. United States of America, Berkeley Geochronology Centre, Berkeley. Pei, W.Z., Yuan, C.S., Lin, Y.P., Chang, Y.Y., 1965. Discovery of Palaeolithic chert artifacts in Kunyintung cave in chien-his-hsien of Kweichow province. Vertebrata PalAsiatica 9 (3), 270–279. Shen, G.J., Jin, L.H., 1992. U-series dating of speleothem samples from Guanyindong cave at Qianxi County, Guizhou Province (in Chinese). Acta Antropol. Sin. 1, 93–100. Yuan, S.X., Chen, T.M., Gao, S.J., 1986. Uranium series chronological sequence of some Paleolithic sites in South China (in Chinese). Acta Antropol. Sin. 5, 179–190. Zhao, J.X., Hu, K., Collerson, K.D., Xu, H.K., 2001. Thermal ionization mass spectrometry U-series dating of a hominid site near Nanjing, China. Geology 29, 27–30. Zhao, J.X., Yu, K.F., Feng, Y.X., 2009. High-precision 238U–234U–230Th disequilibrium dating of the recent past: a review. Quat. Geochronol. 4, 423–433. Zhou, H.Y., Zhao, J.X., Qing, W., Feng, Y.X., Tang, J., 2011. Speleothem-derived Asian summer monsoon variations in Central China, 54-46 ka. J. Quat. Sci. 26, 781–790.
Acknowledgments This work was financially supported by the Basic Scientific Research Foundations of the Institute of Geology, Chinese Academy of Geological Sciences (Project No. A1403). Sun and Che thank Beijing SHRIMP Centre for supporting their visit to the Radiogenic Isotope Facility (RIF) at the University of Queensland, and the RIF Lab team for their help and friendship. We appreciate the assistance from You Qian-sheng, Shen
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U-Th dating of a Paleolithic site in Guanyindong Cave, Guizhou Province, southwestern China
T
⁎
Huiyi Suna, Jian-xin Zhaoa,b, , Guanjun Shena,c, Bo Caod, Xiaochao Chea, Dunyi Liua a
Beijing SHRIMP Centre, Institute of Geology, Chinese Academy of Geological Sciences, Beijing, 100037, China Radiogenic Isotope Facility, School of Earth & Environmental Sciences, The University of Queensland, Brisbane, QLD 4072, Australia c College of Geographical Sciences, Nanjing Normal University, Nanjing 210023, China d Guizhou Cultural Archaeological Institute, Guizhou 550003, China b
A R T I C LE I N FO
A B S T R A C T
Keywords: U-Th age Guanyindong cave Speleothem Fossil Paleolithic
Guanyindong Cave in southwestern China has received considerable attention in the investigation of Paleolithic hominin origins and evolution in China, due to its rich archaeological finds composed of thousands of stone artifacts and a unique fauna with 23 species of mammalian fossils found. However, despite earlier extensive excavations and descriptive studies, debates still centre around the conflict between previous radiometric age data and evidence from biostratigraphic correlations. In this study, we carried out detailed field investigations and sampling, and obtained 35 U-Th dates on flowstone layers and other datable materials from the cave. The age results from materials in stratigraphic context provide a robust chronological framework of the cave. The data suggest that the deposition of Group B sediments and fossil assemblages widely distributed within the cave should have occurred after ~370 ka but before ~70 ka, with the bulk of the sediments and associated fossils laid down during 200–140 ka. Our new U-Th dates of in situ flowstone layers intercalated with one rhinoceros tooth and several other fossil fragments near the Hall at the centre of the cave constrain the deposition ages of these mammalian fossils to the period between 469 ± 37 and 336 ± 7 ka. Combined our U-Th data with recent OSL dates of Hu et al. (2019), we suggest that Group A sediments and associated fossils were likely deposited episodically from ca. 90 ka to < 40 ka. Overall, our data indicate that the cave development started > 469 ± 37 ka ago, whilst the cave system framework took shape as we see today > 340 ± 10 ka ago. Subsequently, the cave might have experienced several flooding and washout events, resulting in recycling and mixing of older sediments and fossils into younger sequences, a hypothesis consistent with tight clustering of both U-Th ages of speleothems in this study and the OSL dates of clastic sediments (Hu et al., 2019). This would reconcile the contradiction between the great antiquity of mammalian fossils inferred from biostratigraphic correlation and the much younger radiometric dates of materials in stratigraphic context, and explain the lack of technological advance despite an apparently long presence of the “Guanyindong culture”, as well as the presence of the Levallois technologies. In this regard, our U/Th age data, combined with other recent studies, have resulted in an improved understanding of Paleolithic hominid evolution and stone technologies in south China.
1. Introduction The Paleolithic site in Guanyindong Cave is located ca. 25 km to the south of the town centre of Qianxi County in central Guizhou Province, southwestern China (26°51′26″ N, 105°58′7″ E). As its entrances were sealed by fallen rocks, the cave remained unknown until early 1950s, when some local villagers ventured into a mist-generating fissure and then found a cavern with a few fossils littering around its ground surface. Excavation of the cave was first carried out in 1964 by a joint team from Institute of Vertebrate Paleontology and Paleoanthropology,
⁎
Chinese Academy of Sciences, and Guizhou Provincial Museum, recovering hundreds of stone artifacts and a number of mammalian fossils. Subsequent fieldworks and excavations were organized in 1965, 1972 and 1973, respectively. In total, more than three thousand stone artifacts and an abundance of mammalian fossils representing 23 species were recovered (Pei et al., 1965; Li and Wen, 1978). Guanyindong Cave was the first ever excavated cave site in South China where mammalian fossils were discovered along with Paleolithic artifacts. Owing to not only the abundance of mammalian fossils but also the distinctive feature of the artifacts (Pei et al., 1965; Li and Wen,
Corresponding author. E-mail addresses: [email protected] (H. Sun), [email protected] (J.-x. Zhao).
https://doi.org/10.1016/j.jasrep.2019.101996 Received 12 October 2018; Received in revised form 1 August 2019; Accepted 18 August 2019 2352-409X/ © 2019 Elsevier Ltd. All rights reserved.
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Fig. 1. (a) Plan view of the Guanyindong cave. The shade represents the main excavated areas throughout the cave, where most of our samples were taken. The locations of Profiles (or cross-sections) 1, 2a, 2b, 3, 3b and 4 are also shown, respectively. Profiles 1, 2a, 3b and 4 are illustrated in detail in Figs. 2–5. (b) The stratigraphic sequence of the West Entrance of the main cave was subdivided into nine layers that can be attributed to three groups (Groups A: layers 1–2, B: layers 3–8, C: layer 9) (after Li and Wen, 1986).
composed of Triassic limestone, which has experienced extensive karstic processes. The main entrance of the cave opens to the west, and is ~1450 m above sea level and ~15 m higher than the adjacent small intermountain basin. The main corridor is ~90 m long, 2–4 m wide, and 2–8 m high. In the middle of the main corridor, two branch caves extend, respectively, to the north (~30 m long, 1–2 m wide, with an entrance opening to the north) and to the south (~15 m long, 1 m wide, an east-west direction sub-branch cave develops at its end). At the location, where Northern Branch Cave extends out, the Main Corridor expands into a hall (Fig. 1a). The entire deposits can be subdivided into three groups (Fig. 1b), as A (Layers 1–2), B (Layers 3–8) and C (Layer 9) (Pei et al., 1965; Li and Wen, 1978). Shen and Jin (1992) first sampled the cross sections or profiles (a term used in Hu et al., 2019), mainly speleothems and some tooth fossils, for U-Th dating by alpha spectrometry. In 2015 and 2016, we carried out further detailed survey and sampling within the cave. As the bulk of the fossiliferous deposits have been removed during previous excavations in the 1960–1980's, our sampling focuses on the remnants of the deposits, mainly flowstones, which are still attached to the cave corridor walls, as well as the walls of the excavation pits. Since previous excavations targeted only hominin remains and stone artifacts, unfortunately no other materials in stratigraphic sequences were curated for dating or other scientific analysis. Fig. 1b illustrates the cave floor plan and the profiles (or cross sections) reported in Pei et al. (1965), Li and Wen (1986) and Shen and Jin (1992), with our sample locations in either the floor plan or the profiles. Profile 1 is situated inside the West Entrance, against the north wall (Figs. 1b and 2). The elevation of loose sediment piles were the highest outside the entrance, getting progressively lower inside the entrance. Major excavations during 1960–1970's resulted in the removal of up to 8 m thick of sediment inside and outside the entrance (see Fig. 1b). Outside the entrance and at ~4.5 m above the current ground level (matching the elevation of the bottom of the excavations shown in Fig. 1b) occurs a small stalactite hanging over the cave ceiling. This stalactite is stained with red clay and its stratigraphical location is at about the same level as the red-clay layer (Layer 2 of Group A) (Fig. 2). The lowest tip of this stalactite was sampled as S27. Just inside the entrance and ~0.5 m lower than S27, there is another stalactite (also stained with red clay) on the ceiling, its lower tip was taken as sample S26. Inside the entrance, about 2.2 m above the current ground level (matching Layer 3 in Fig. 1b) occurs a shawl with unknown thickness on the cave wall, the outermost sublayer of which is taken as sample S21. Sample S22 was collected from a flowstone layer, quite pure and dense, at ~1.9 m above the current ground level, stratigraphically matching Layer 4 in Fig. 1b. Sample S23 was taken from a flowstone layer ~5 cm thick and with limited expanse, possibly representing synlayer post-deposition secondary calcite formation along fissure, which is located at ~1.1 m above the ground level (stratigraphically matching Layer 5 or 6 in Fig. 1b). Sample S24 was collected from a major flowstone layer, which is 1.3 m above the ground level (stratigraphically matching Layer 5 or 6 in Fig. 1b). Sample S25, a crystalline calcite formation, was taken from a 20 × 30 cm sediment-filled oblong cavity, which is developed inside a hole and it is stratigraphically about 0.3 m above sample S24 or 1.6 m above the current ground level (stratigraphically matching Layer 4 in Fig. 1b). A small stalagmite grown from the cave wall at an elevation equivalent to the bottom of Layer 8 was previously sampled as QGC-23 and analyzed by Shen and Jin (1992). The stratigraphical location of this specific sample was determined through digging a trench into the back-filled excavation pit of Pei et al.
1978; Hu et al., 2019), Guanyindong Cave plays an important role in the study of the origins and evolution of Paleolithic culture in China. Consequently, its precise chronological position is of great importance. Based on biostratigraphic evidence, Pei et al. (1965) attributed Guanyindong Cave to Middle or Late Pleistocene. However, using the faunal composition, particularly the presence of Gomphotheriidae fossils, generally accepted as extinct elephant-like species of Tertiary ages, Li and Wen (1978) assigned much greater ages to the site. They considered that the upper Group A and the lower Group B deposits were roughly contemporaneous with and slightly older than Locality 1 at Zhoukoudian, respectively. Yuan et al. (1986) dated the site by U-series (or called U-Th) dating of fossil teeth. Their results, in the range of 80–115 ka, are far too young compared with the previous age estimate of Li and Wen (1978). Li (1989) insisted, based on the biostratigraphic correlation, that “the Group B deposits in Guanyindong Cave can surely be attributed to earlier Middle Pleistocene”. Also he criticized the dates of Yuan et al. (1986) on fossil teeth as being self-contradictory. In an effort to reconcile the much younger U-series dates on fossil teeth with the last occurrence of Gomphotheriidae being no later than Middle Pleistocene, Han and Xu (1989) assigned an age range of the fossil finds spanning Late and Middle Pleistocene. Using alpha spectrometry, Shen and Jin (1992) carried out the first U-Th dating of flowstone layers intercalated in cultural deposits of Guanyindong Cave, obtaining ages in the range of 40–270 ka. As the validity of the U-Th dating of carefully selected, pure and dense cave calcites has been well demonstrated, this temporal frame has been widely cited in more recent literature (e.g., Li et al., 2009a, 2009b; Hu et al., 2019). However, classical alpha spectrometric U-Th dating is burdened with some intrinsic limitations. Notably, it needs a sample size of at least 10–20 g. In typical hominin cave sites, the interbedded flowstone layers are, more often than not, relatively thin and of mediocre or even poor purity. So some key horizons of a site cannot be dated because of the difficulty to obtain enough sample material, which is also the case of Guanyindong Cave. Besides, with important counting statistical error in the order of ~3%, the precision of the obtained dates is quite often insufficient to address some important issues, especially when the ages were > 300 ka (close to the limit of alpha spectrometric U-Th dating). In the past 30 years or so, important progresses in mass spectrometric technologies have revolutionized the U-series dating of speleothem carbonates. Now with TIMS or MC-ICPMS, 2δ precisions up to 0.2% can be achieved with small sample sizes of < 50 mg. Under such a circumstance, and considering the importance of the Guanyindong Cave in archaeological studies in China, a renewed chronological study of the site is warranted. Built upon the chronology of Shen and Jin (1992), Hu et al. (2019) reported a set of OSL dates for remnants of excavated profiles at the west entrance of the cave. The U-Th dates of the speleothems and the OSL dates of the sediments are broadly consistent for Group A and upper layers of Group B, but show some discrepancy in details, especially regarding the age limit of Group A. In this study, we will report a new set of U-Th dates for various types of speleothems systematically collected from the entire cave system, and attempt to synthesize the data to obtain an improved understanding of chronologies of the fossil records in context with the cave evolution history. 2. The site and samples in stratigraphic context The Guanyindong Cave is located at the middle axis of an anticline 3
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Fig. 2. Stratigraphic sequence of Profile (cross-section) 1 at West Entrance and sample photos showing speleothem sample localities (yellow dots) and their age results. Red circles with crosses denote the stratigraphic horizons where fossils were excavated. Zero level of the vertical scale bar represents the current ground level. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
ceiling, hanging ~2 m above the current ground level. This hanging sequence consists of four flowstone sub-layers, which were collected from top to bottom as samples S10-A, S10-B, S10-C, and S10-D, respectively. A strongly altered rhinoceros tooth fossil was found in the brown detrital deposits between flowstone sub-layers B and C. A few fossil debris can also be found between sub-layers C and D. At the intersection between the Main Corridor and the North Branch Cave (Fig. 1a), two samples (S12 and S38) were collected. Sample S12 was taken from the surface of a large (~2 m-long fallen, 0.3–0.5 m in diameter) stalactite the bottom of an excavation pit. Sample S38 was collected from the bottom of a stalagmite, which was attached to the wall and ~50 cm above ground (Fig. 1a). Profile 4 is situated at the end of the South Branch Cave (Fig. 5). This branch cave is only about a meter high at the end and the passage is even narrower. It took considerable efforts for us to reach its interior. The previous excavation focused mainly on the west end of the South Branch Cave, where we found two 5 cm-thick flowstone layers which
(1965) by Shen and Jin's team ~30 years ago. Profile 2a (Fig. 3) is located ~16 m inside the West Entrance. It is from a relatively well-preserved excavation pit. Above the pit occurs a large column composed of a giant stalactite and an underlying disproportionately small stalagmite. Samples S5 and S6 were collected from the lowermost and outermost parts of the stalactite, respectively. Sample S28 was taken from the central part of the stalagmite. Within the pit, some 2.1 m and 1.95 m below the current ground level, two in situ mushroom-shaped stalagmites were found and sampled as S1 and S3, respectively. Some 2.05 m and 0.75 m below the current ground level, two blocks of fallen speleothem formations were found and sampled as S2 and S4, respectively. Profile 3b is situated at the northwestern corner of the Hall (Fig. 4), ~10 m west of the original Profile 3 of Pei et al. (1965). This is a newly discovered and sampled sequence in this study. Profile 3b contains a number of flowstones interlayered with brown fossil-bearing deposits with a total thickness of ~40 cm. It was found loosely stuck to the cave 4
Journal of Archaeological Science: Reports 27 (2019) 101996
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Fig. 3. Stratigraphic sequence of Profile (cross-section) 2a and sample photos showing speleothem sample localities (yellow dots) and their U-Th ages. Red circles with crosses denote the stratigraphic horizons where fossils were excavated. Zero level of the vertical scale bar represents the current ground level. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
Radiogenic Isotope Facility (RIF), at the School of Earth and Environmental Sciences, the University of Queensland (UQ). The purest and densest possible portions of each sample were selected, cleaned, and broken into small chips or sands (1–2 mm) using a hand tool. The sample grains were examined carefully so as to remove any visible impurities. The pre-treated samples were then ultrasonicated for 20 min and rinsed with Milli-Q water for 3 times. The samples were dried on hotplate at 80 °C overnight. Upon dryness, the sample grains were then examined under a binocular microscope and further purified by hand picking to remove any grains with impure inclusions. The purpose of the sample vetting process is to increase the precision of dating results by physically removing and reducing non-radiogenic 230Th from non‑carbonate impurities. U-Th dating was carried out using a Nu Plasma multi-collector inductively-coupled plasma mass spectrometer (MC-ICP-MS) in the RIF Lab at UQ, following chemical treatment procedures and MC-ICP-MS analytical protocols described elsewhere (Zhao et al., 2001; Zhao et al., 2009; Clark et al., 2014). Pre-treated sample materials weighing 50–150 mg were spiked with a mixed 229Th-233U tracer and then completely dissolved in concentrated HNO3. After digestion, each sample was treated with H2O2 to decompose trace amounts of organic matters and to facilitate complete sample tracer homogenisation. U and Th were separated using conventional anion-exchange column chemistry using Bio-Rad AG 1-X8 resin. After stripping off the matrix from
were taken as samples S34 and S35. The stalagmite sample S29 was collected at ~10 cm above the sampling point of S35. Another stalagmite S37 was collected from the other side of the excavation site, slightly above sample S29. This small stalagmite is ~5 cm tall (~6 cm in diameter), its tip almost reaching to cave ceiling. About 10 m away from the entrance of the South Branch Cave, samples S36 and S18 were taken from ~5 cm thick flowstone layers attached to the ceiling. A small and pure stalagmite with a height of 6 cm and a diameter of 7 cm growing on the top of flowstone was sampled as S19. The North Branch Cave was poorly investigated comparing to the above profiles, because only a very small amount of deposits was left. About 20 m to the north entrance, flowstone layers were found on the west wall, and samples S39, S41and S43 were taken from different flowstone layers (Fig. 1a). S40 was taken from a small stalagmite slightly below sample S39. Sample S42 was collected from another stalagmite about 60 cm in length and 40 cm in diameter. In the North Branch Cave, about 10 m away from the Hall, sample S8 was taken from a stalagmite 10 cm in length and 6 cm in diameter (Fig. 1a). 3. Method and U-Th dating results 3.1. Method The speleothem samples were processed for U-Th dating in the 5
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a
Fig.4b
7RRWK
%RQH
b
Fig. 4. Stratigraphic sequence of Profile (cross-section) 3b and sample photos showing speleothem sample localities (yellow dots) and their U-Th ages on a hanging wall at the Hall. Red circle with cross denotes the stratigraphic horizons where fossils were present. This is a new profile discovered and sampled in this study. Zero level of the vertical scale bar represents the current ground level. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
the column using double-distilled 7 N HNO3 as eluent, 3 ml of a 2% HNO3 solution mixed with trace amount of HF was used to elute both U and Th into a 3.5 ml pre-cleaned test tube, ready for MC-ICP-MS
analyses, without the need for further drying down and re-mixing. After column chemistry, the U-Th mixed solution was injected into the MCICP-MS through a DSN-100 desolvation nebuliser system with an 6
Journal of Archaeological Science: Reports 27 (2019) 101996
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Fig. 5. Stratigraphic sequence of Profile (cross-section) 4 in the South Branch Cave and sample photos showing speleothem sample localities (yellow dots) and their U-Th ages. Red circle with cross denotes the stratigraphic horizon where fossils were excavated. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
uptake rate of around 0.07 ml per minute. U-Th isotopic ratio measurement was performed on the MC-ICP-MS using a detector configuration to allow simultaneous measurements of both U and Th isotopes (Zhou et al., 2011; Clark et al., 2014). The 230Th/238U and 234U/238U activity ratios of the samples were calculated using the decay constants given in Cheng et al. (2000).
speleothems are made of dense crystalline calcites without diagenesis or weathering.
3.2. Results
Based on the residual “red soil” stains characteristic of Group A sediments, it is likely that the stalactites hanging inside and outside the west entrance pre-date the fossiliferous Group A deposits of Li and Wen (1978, 1986) (see Fig. 2). Samples S26 and S27 from these stalactites yielded 230Th ages of 58 ± 4 ka and 71 ± 7 ka, respectively. On the other hand, using alpha spectrometry, Shen and Jin (1992) obtained detrital 230Th corrected U-Th ages of 53 ± 9 and 40 ± 6 ka (recalculated using Isoplot/EX 3.75 Program) for two sub-samples (QGC19-1 and QGC-19-2) from another “red-soil-stained” stalactite in a similar stratigraphic context. These age results together suggest the “redsoil-stained” stalactite clusters from similar stratigraphical horizons were developed over a period of 70–40 ka, and that the overlying Group A deposits, together with fossils and stone artifacts in Group A, could have been laid down rapidly after 40 ± 6 ka (i.e. after growth of the youngest stalactite tip), based on interpretation of Shen and Jin (1992). The alternative and more likely scenario is that Group A sediments may have been deposited progressively or episodically during the growth period of the stalactites (in other words, the stalactites of different ages were developed contemporaneously with the “red-soil” deposition). In
4. Discussion 4.1. Chronology of Guanyindong cave deposits
The U-Th isotope ratios and 230Th ages of 35 speleothem samples are listed in Table 1, and presented in Figs. 1–5 with stratigraphic contexts for a majority of them. The rhinoceros tooth fossil in Profile 3 is strongly altered, unsuitable for U-Th dating. The dated samples have U concentrations ranging from 0.07 to 0.5 ppm, typical of speleothem calcites. > 70% of the dated samples have measured 230Th/232Th activity ratios > 10. For these samples, detrital or non-radiogenic 230Th corrections using the assumed bulkEarth 230Th/232Th value has relatively insignificant impact on the corrected 230Th ages. However, for the remaining ~30% with measured 230 Th/232Th activity ratios < 10, their corrected 230Th ages have large age uncertainties and should be treated with caution. Overall, all dated samples are within the dating limit of the U-series dating method, and they all plot above the secular equilibrium line on the 230Th/238U vs 234 U/238U evolution diagram (Fig. 6), suggesting even the oldest samples are in isotopically closed system without any visible U loss and thus the age results are reliable. This is also supported by the fact all dated 7
Material & type⁎
8
0.1170 0.0712 0.1044
0.02 m 0.75 m 0.01 m
0.1343 0.2980 0.5303 0.1356 0.1296 0.0771 0.10200
Walls (North branch cave) S8 Stalagmite (2) S39 Flowstone layer(1) S40 Stalagmite (2) S41(T) Flowstone layer(1) S41(B) Flowstone layer(1) S42 Stalagmite(4) S43 Flowstone layer(1) 0.0001 0.0001 0.0001 0.0000 0.0000 0.0000 0.0000
0.00010 0.0001 0.0003 0.0001 0.0001 0.0000 0.0000
0.0001 0.0001 0.0001 0.0000 0.0001 0.0001
0.0001 0.0000 0.0000
0.0001 0.0002
0.0001 0.0001
0.0001 0.0001 0.0000 0.0001 0.0005
0.0001 0.0001 0.0002
± 2δ
15.85 15.42 116.9 8.37 7.24 59.40 16.78
545 6.40 144.60 93.60 10.95 4.55 12.40
41.06 2.25 37.18 23.58 4.11 10.78
6.57 5.57 23.30
6.68 1.49
30.69 52.18
1.42 7.94 25.97 122.73 1.96
72.77 35.70 3.94
Th (ppb)
232
0.02 0.03 0.30 0.01 0.02 0.10 0.02
2.00 0.01 0.50 0.16 0.02 0.01 0.02
0.12 0.00 0.04 0.04 0.01 0.03
0.02 0.01 0.10
0.01 0.00
0.046 0.20
0.00 0.01 0.04 0.41 0.00
0.09 0.17 0.01
± 2δ
28.93 4.10 5.15 14.72 17.86 4.08 6.40
2.08 40.29 2.52 12.94 81.46 78.04 38.43
12.51 280.25 17.59 17.51 25.90 49.08
8.55 14.78 7.37
123.65 477.52
16.77 6.29
615.35 42.64 5.20 3.65 847.67
6.96 28.53 196.56
(230Th/232Th)
0.10 0.05 0.02 0.06 0.11 0.02 0.03
0.01 0.16 0.02 0.04 0.23 0.35 0.12
0.04 0.93 0.05 0.05 0.15 0.21
0.05 0.10 0.05
0.30 1.63
0.05 0.03
3.38 0.17 0.03 0.03 3.10
0.02 0.18 0.58
± 2δ
1.1250 0.0699 0.3739 0.2994 0.3287 1.0360 0.3473
1.1285 0.6326 1.1297 1.0310 0.9678 1.0669 0.9417
1.0692 1.0883 1.1205 1.1261 0.3169 0.9126
0.1583 0.3810 0.5419
0.9413 0.9124
1.0017 1.1174
1.0163 0.9581 0.4744 0.5688 1.0898
0.7118 0.9334 1.0067
(230Th/ 238 U)
0.0036 0.0008 0.0016 0.0011 0.0019 0.0035 0.0017
0.0063 0.0023 0.0057 0.0028 0.0024 0.0044 0.0026
0.0020 0.0029 0.0028 0.0025 0.0017 0.0033
0.0008 0.0024 0.0031
0.0018 0.0027
0.0026 0.0034
0.0046 0.0034 0.0022 0.0041 0.0032
0.0019 0.0042 0.0026
± 2δ
1.4459 1.1500 1.2055 1.1006 1.1018 1.0490 1.0709
1.0903 1.3141 1.0964 1.1939 1.1398 1.0868 1.1463
1.0974 1.1051 1.1171 1.1014 1.0923 1.1080
1.1351 1.1207 1.1724
1.0993 1.1071
1.1894 1.1215
1.0630 1.1128 1.0421 1.0479 1.0933
1.1415 1.1565 1.0688
(234U/238U)
0.0015 0.0017 0.0011 0.0009 0.0013 0.0017 0.0013
0.0014 0.0016 0.0019 0.0015 0.0009 0.0017 0.0014
0.0013 0.0014 0.0014 0.0011 0.0013 0.0012
0.0014 0.0017 0.0018
0.0009 0.0012
0.0013 0.0033
0.0009 0.0015 0.0017 0.0015 0.0011
0.0013 0.0013 0.0010
± 2δ
145.5 6.8 40.0 34.5 38.4 387.0 42.5
767 69.4 564 194.7 190.7 340.6 175.4
320.2 336.5 372.8 473 37.2 179.2
16.3 44.9 66.4
198.8 179.5
183.2 353.0
303.9 200.4 65.9 84.7 373.8
103.6 167.7 281.1
Uncorr. Age (ka)
1.0 0.1 0.2 0.1 0.3 14 0.3
456 0.4 82 1.6 1.3 9.9 1.3
4.3 6.5 8.2 18 0.2 1.6
0.1 0.4 0.5
1.2 1.4
1.3 11
7.3 2.1 0.5 0.9 9.3
0.5 1.8 3.6
± 2δ
143.4 5.5 34.6 32.8 36.9 365 37.9
735 68.4 532 189.2 189.8 339.5 173.6
313.8 336.2 368.4 469 36.2 177.8
14.9 42.9 60.8
198.2 179.3
179.1 340
303.8 198.7 57.8 70.6 373.7
95.6 165.4 280.7
Corr. age (ka)
1.9 0.7 2.6 0.8 0.8 35 2.3
5368 0.5 748 3.7 1.3 10.1 1.5
9.8 6.5 15.8 37 0.5 1.7
0.7 1.0 2.6
1.2 1.4
2.5 37
7.3 2.2 4.1 7.2 9.3
3.4 2.0 3.6
± 2δ
1.6905 1.1545 1.2410 1.1122 1.1147 1.174 1.0826
2.30 1.3860 1.69 1.3539 1.2413 1.2288 1.2437
1.2540 1.2724 1.3495 1.4020 1.1033 1.1811
1.1431 1.1392 1.2179
1.1748 1.1779
1.3302 1.371
1.1488 1.2014 1.0536 1.0670 1.2682
1.2024 1.2566 1.1525
Corr. initial (234U/238U)
0.0088 0.0021 0.0078 0.0014 0.0017 0.014 0.0025
19.3 0.0030 1.31 0.0094 0.0018 0.0060 0.0030
0.0059 0.0044 0.0107 0.0341 0.0015 0.0022
0.0019 0.0024 0.0073
0.0015 0.0019
0.0069 0.0024
0.0033 0.0029 0.0031 0.0054 0.0064
0.0091 0.0036 0.0021
± 2δ
Note: All ratios in parentheses are activity ratios. U-Th ages calculated using Isoplot/Ex 3.75 of Ludwig (2012). Corrected ages were calculated assuming non-radiogenic 230Th/232Th = 4.4 ± 2.2 × 10−6 (bulk-earth value), and 238U, 234U, 232Th and 230Th are in secular equilibrium. Non-radiogenic 230Th correction results in large age error magnification for samples with low measured 230Th/232Th ratios. ⁎ refers to distance from the current ground level of each site at the time of sample collection. It is different from the actual cave ground levels when the excavations took place ~50 years ago due to repeated digging, damage and erosion. ⁎ Based on their stratigraphic significance, the samples are divided into the following five groups: 1. capping flowstone layers and stalagmites on them, defining minimum age for the underlying deposits; 2. flowstone layers intercalated in detrital deposits and stalagmites developed in sediments, defining the maximum age of the overlying deposits and minimum age of the underlying deposits; 3. flowstone layers stuck on the ceiling, indicating filling-washingout event of the deposits inside the cave; 4. calcite shawl and stalactites buried by deposits (S5, S6, S26, S27), stalagmite on cave wall underlying the deposits, fallen calcite fragments (S2, S4), fallen stalactite (S12), representing the maximum age of their horizon; 5. calcite crystals in a cavity (S25), posteriorly formed, defining the minimum age of its horizon.
0.33192 0.1343 0.10611 0.3870 0.3038 0.1097 0.1668
0.1583 0.1906 0.1924 0.1208 0.1106 0.1910
0.2893 0.2563
−1.95 m −0.75 m
1.70 m 1.65 m 1.50 m 1.40 m
0.1694 0.0969
0.2826 0.1165 0.0938 0.2598 0.5034
1.3 m 1.6 m 4.0 m 4.5 m
−2.10 m −2.05 m
0.2346 0.3595 0.2536
U (ppm)
2.2 m 1.9 m 1.1 m
Distance ground⁎
Cross section 4 (South branch cave) S18 Flowstone layer (3) S19 Stalagmite (1) S29 Stalagmite (2) S34 Flowstone layer (2) S35 Flowstone layer (2) S36 Flowstone layer (3) S37 Stalagmite (1)
Cross section 3 (The Hall) S10-A Flowstone (3) S10-B Flowstone (3) S10-C Flowstone (3) S10-D Flowstone (3) S12 Fallen stalactite (4) S38 Stalagmite (2)
Cross section 2a (Excavation Pit) S1 Stalagmite (2) S2 Calcite fragment (4) S3 Stalagmite (2) S4 Calcite fragment (4) S5 Stalactite (4) S6 Stalactite (4) S28 Stalagmite (1)
Cross section 1 (West Entrance) S21 Shawl (4) S22 Flowstone layer (2) S23 Flowstone layer (2?) S24 Flowstone layer (2) S25 Cavity calcite (5) S26 Stalactite (4) S27 Stalactite (4) QGC23 Stalagmite (4)
Sample no.
Table 1 U-Th isotope data for speleothem samples from Guanyindong Cave, Guizhou Southwest China.
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Fig. 6. The 230Th/238U vs in this study.
234
down contemporaneously. All the nine ages appear to be in broad consistency with the OSL dates of 175 ± 32 to 161 ± 12 ka (age errors at 1δ) defined by six sediment samples from the main part of Group B at the West Entrance (Hu et al., 2019). The six OSL dates are analytically indistinguishable, with a weighted mean of 165 ± 11 ka. Sample S21 collected from the bottom of a shawl inside the West Entrance (Profile 1 in Figs. 1 and 2) yielded an age of 96 ± 3 ka. As all the fossiliferous sequence of Group B at this excavation site has been completely removed and the cave floor at the West Entrance was severely modified by floods and local villagers after excavations, it is difficult to envisage its corresponding stratigraphic location in Group B (Fig. 1). For instance, it is unclear whether its stratigraphic horizon matches to Layer 3 or 4 of Group B sediments. Based on its 2.2 m elevation above the current ground level, we suggest it should stratigraphically match with the lower part of Layer 3 of Group B in Fig. 1b, and thus its age may well define the maximum age of Layer 3. Based on their elevations above the current ground level, which is the bottom of the excavations at the West Entrance of the Main Cave (Fig. 1b), flowstone samples S23 and S24 (Fig. 2) appear to be from the upper sixth layer of Group B deposits at the West Entrance. Their ages of 281 ± 4 ka and 304 ± 7 ka indicate that the deposits found at this level should be at least 300 ka old, which is substantially older than the OSL dates for lower strata of the site (Hu et al., 2019). Stalagmite sample QGC-23 was collected by Shen and Jin (1992) from the basal 8th layer of Group B at the West Entrance. This sample gave an alpha-spectrometric age of 260 + 34/−26 ka (1δ) (Shen and Jin, 1992) and was redated by MC-ICP-MS in this study, yielding a more precise age of 374 ± 9 ka (2δ), making maximum age for Group B deposits. The large spread of speleothem ages as described above implies that the group-layer division of Li and Wen (1978, 1986) might not be consistent across the entire cave and should be treated with caution. The inconsistency of the depositional sequence is evidenced by the young age (36.2 ± 0.5 ka) of S12, a volumous fallen stalagtite apparently at a lower horizon of Group B. the deposits in North Branch Cave may also be quite young, as demonstrated by the ages on S40, S41, S42 and S43. Nevertheless, our U-Th age data do demonstrate that Group B sediments in the entire cave could have been deposited after 374 ± 9 ka (age of basal flowstone QGC-23 at West Entrance), but before 68 ± 5 ka (age of stalagmite sample S19 near South Branch Cave), with the bulk of sediment profiles laid down during ca. 199–143 ka. The great time-span of the fossiliferous Group B is also consistent with the presence in situ fossil-bearing deposits intercalated with in situ flowstone sub-layers of S10-A (314 ± 10 ka), S10-B (336 ± 6 ka), S10-C (368 ± 16 ka) and S10-D (469 ± 36 ka), attached to the ceiling in the Hall (see Fig. 4). Here one strongly altered rhinoceros tooth fossil was found in deposits between flowstone sub-layers B and C and a few fossils debris could also be found between sub-layers C and D. Thus the U-Th dates of the flowstones bracket the ages of the fossils here to between 469 and 336 ka. The age distribution of all dated speleothems (Fig. 7) suggest that the cave system was developed at least 469 ± 37 ka ago (age of S10D), and speleothem growth continued until Holocene or recent (the youngest date is 5.5 ± 0.7 ka from S39). Speleothem growth appears to be episodic, and tends to concentrate during the transition from interglacial to glacial periods. Few samples dated to the heights of full interglacials (possibly due to highest rainfall leading to intensified flooding). For instance, no samples dated to Marine Isotope Stage (MIS) 5e, 7 or 11. In addition, speleothems dated to > 340 ± 10 ka were found in all major sites of the cave, including the West Entrance (e.g. QGC23), Profile 2a (S2), the Hall (S10-C, S10-D), the North Branch Cave (S42) and the South Branch Cave (S36). This suggests that the entire cave system as we see today should have already been developed by that time.
U/238U evolution diagram showing all U-Th data
this regard, it could be argued that Group A sediments were laid down from 70 ka to later than 40 ka. This interpretation appears to be broadly consistent with the OSL dates of Hu et al. (2019) (Note that age errors of the OSL dates were all reported at 1δ). Since Group A “red-soil” layer was only found near the West Entrance of the cave, whereas the underlying Group B deposits (mainly brown-coloured sediments) occur throughout the entire cave, it can be inferred that the two groups must have different origins and formation histories. When the cave was first excavated by Pei et al. (1965), a capping flowstone of 0.2 to 0.6 m in thickness, was reported to extend to the entire cave, which seems to overlie the upper fourth layer of Group B deposits inside the west entrance based on the stratigraphic division of Li and Wen (1978, 1986). It corresponds to the 2nd layer in Profile 1 and 2a, and the 1st layer in Profiles 2b, 3 and 4 reported in Pei et al. (1965). As the bulk of the fossiliferous deposits have been dug out, this capping flowstone is no longer existing and available for sampling. Because of this, it is difficult to assess if this capping flowstone is chronologically consistent across the entire cave. Sample S28 was collected from the mini-stalagmite growing below the large stalactite and above Profile 2a within the excavation pit inside the cave, ~15 m east of the West Entrance (Fig. 3). It yields an age of 61 ± 3 ka, whereas the lower (S5) and the upper (S6) parts of the large stalactite give ages of 14.9 ± 0.7 ka and 42.9 ± 1.0 ka, respectively. All fossiliferous Group B of Profile 2a below S28, must be older than 61 ± 3 ka, the age of the mini-stalagmite. Similarly, near the South Branch Cave (Fig. 1a), a small stalagmite (sample S19) appears to grow on top of the capping flowstone. It gives an age of 68 ± 5 ka, which marks the minimum age of the underlying (Profile 4). Based on above age constraints from Profiles 2a and 4, it can be inferred that Layer 3 sediments (uppermost layer of Group B) were deposited earlier than 61–68 ka (Fig. 1). Seven in situ speleothem samples, including samples S22 and S25 (within Profile 1), S8 (within North Branch Cave), S34-S35-S37 (within Profile 4), and S38 (within the Hall) were taken from the upper strata of Group B deposits across the entire cave system (Fig. 1a). They gave the following age results: 165 ± 2 ka, 199 ± 2 ka, 143 ± 2 ka, 189 ± 4 ka, 190 ± 1 ka, 175 ± 1 ka, and 178 ± 2 ka (Table 1, also see Figs. 1, 2, 5), respectively, indicating that the accumulation of the main part of Group B deposits started in the late Middle Pleistocene. The in situ mushroom-shaped small stalagmites S1 and S3 at ~2 m depth of the excavation pit as shown in Profile 2a gave ages of 179.1 ± 2.5 ka and 198.2 ± 1.2 ka, respectively. All together, these nine ages suggest that the upper strata of Group B sediments were laid 9
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the entire cave and the tight OSL date cluster of 160–170 ka (indistinguishable within 2δ errors, with a weighted mean of 165 ± 11 ka) for Layers 4–8 at the West Entrance (Hu et al., 2019), implying rapid accumulation of such thick sequences at their respective locations. It is also intriguing to note that 12 of the 13 OSL dates of Hu et al. (2019) clustered within three age groups (the OSL dates within each group are indistinguishable at their 2δ age uncertainties), with weighted means of 165 ± 11, 87 ± 7, and 42 ± 4 ka, respectively, separated by considerable age hiatuses. Such an age distribution pattern is consistent with separate flooding and fill-up/washout events being responsible for the rapid accumulation of the respective sediment sequences separated by long-term discontinuities. 4.3. Interpretations of Guanyindong stone artifacts The lithic assemblage of the site bears distinct features compared with the contemporaneous Paleolithic industries in Europe and in other regions in China (Hu et al., 2019). For marking its special status in archaeological studies, a term of “Guanyindong Culture” was proposed (Pei et al., 1965; Li and Wen , 1978; Li et al., 2009a, 2009b). According to the chronological frame given in this paper, the lithic industry of Guanyindong cave could have developed during a long period of time from > 470 ka to < 40 ka. The lack of detailed stratigraphic context for many of the artifacts renders it difficult to evaluate the trend of technological evolution. Nevertheless, detailed technological analyses did demonstrate that the Guanyindong industry remained largely unchanged over time (Li et al., 2009a, 2009b). This is also reflected by the fact that raw materials always came from a flint vein or from the gravelly bed of a small river within 3 km of the cave. Moreover, the débitage mode remained quite different from the concept of Levallois widely used in Europe, Near-East and Africa. However, the recent evidence of Levallois technology from the lithic assemblage of the Guanyindong Cave site challenges the existing model regarding the origins and spread of Levallois technologies in East Asia and its links to a Late Pleistocene dispersal of modern humans (Hu et al., 2019). It is unclear whether the Guanyindong industry did remain unchanged over such a long period, or those fossils and stone artifacts found in younger sequences were simply recycled from older deposits during a series of flood washout events. The fact that speleothem growth in the cave appears to be episodic, with few samples dated to the full interglacials, such as Marine Isotope Stage (MIS) 5e, 7 or 11 (Fig. 6) points to the possibility that cave flooding might have intensified during such fullinterglacial periods. The flooding hypothesis is also consistent with the tight clustering of the OSL dates of the fossiliferous sediment sequences, separated by considerable age hiatuses, as reported in Hu et al. (2019). Such repeated flooding and fill-up/washout events could have been responsible for the recycling and mixing of fossils and stone artifacts that may have different ages and origins. Nevertheless, more stringent temporal control of the site will help to provide useful evidence for exploring and interpreting the relationship between Paleolithic populations and stone artifacts.
Fig. 7. Relative probability plot of speleothem ages and δ18O record of benthic foraminifera is from Lisiecki and Raymo (2005).
4.2. Reconciling biostratigraphic correlation with isotope dating As described above, according to the ages of S10-A (314 ± 10 ka), S10-B (336 ± 6 ka), S10-C (368 ± 16 ka) and S10-D (469 ± 36 ka), samples from several in situ flowstone sub-layers intercalated with in situ fossil-bearing deposits (see Fig. 4) attached to the ceiling in the Hall, the cave should have been completely filled with deposits by 314 ± 10 ka. This inference is also supported by the age of S36 (340 ± 10 ka), a flowstone layer attached to the ceiling in South Branch Cave, with much younger speleothems developed underneath. The bulk of the hanging sequence collapsed and fell on the ground during our sample collection. There should be a considerable amount of older deposits below the hanging residual sequence, which have probably been washed away by subsequent floods. The fact that the hanging sequence has nearly reached the ceiling suggests that the original cave here was once almost completely filled. The present-day Hall could have been formed during a subsequent flood event(s) that washed out the bulk of the older deposits that once filled the pre-existing cave. A flood event washing away all the underlying deposits must have happened after emplacement of the rhinoceros tooth in between S10-B (dated to 336 ± 7 ka) and S10-C (dated to 368 ± 16 ka) in the Hall, or after the formation of S36 at 340 ± 10 ka in the South Branch Cave. The > 2 m thick washed-away deposits underneath S10-D (469 ± 36 ka) should be older than 469 ± 36 ka, probably early Middle Pleistocene in age. Based on faunal compositions, the Guanyindong site was once assigned with a much older age (e.g. Li and Wen, 1978, 1986). This is mainly based on the presence of Gomphotherium, generally considered as a Tertiary species. The discovery of an infilled cave being subsequently washed out by flood events points to the possibility that the Gomphotherium fossils may be recycled from deposits of a previous cycle, and somehow survived the washout event(s). Somehow this may reconcile the difference between faunal correlation and isotopic dating. Our hypothesis of repeated flooding and fill-up/washout events having occurred at least after the deposition of the earliest fossiliferous sediments well constrained to 336–469 ka is also supported by the relatively tight U-Th age cluster of 140–200 ka for all four profiles across
5. Conclusions Based on detailed field observations and systematic U-Th dating of speleothems collected from a number of excavation sites throughout the entire Guanyindong cave, Guizhou, southern China, combined with data reported in the literature, the following conclusions can be made: (1) The Guanyindong cave developed for at least half a million years, from early Middle Pleistocene till recent or present. (2) The present configuration of the cave system consisting of the West Entrance and the Main Cave Corridor, the Hall, the South Branch Cave, the North Branch Cave took shape probably ~340 ka ago or earlier. (3) The unconformably overlying red-coloured Group A sediments and 10
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Nengping and others during fieldworks in 2015 and 2016. This manuscript has benefited a lot from constructive comments and suggestions made by the Editor and the anonymous reviewer.
fossil assemblage of the excavated profile found mainly at the west cave entrance was likely deposited from 71 ka to later than 40 ka, constrained by the ages of the “red-clay-stained” stalactite clusters, their growths might be contemporaneous with the deposition of Group A sediments. This inference is broadly consistent with the OSL dates (87–42 ka) for this group. (4) The unconformably underlying brown-coloured Group B sediments and fossil assemblages widely distributed within the cave may have been laid down after ~370 ka but before ~70 ka, with the bulk of the sediments and associated fossils accumulated during 200–140 ka. (5) Our new U-Th dates of in situ flowstone layers intercalated with one rhinoceros tooth and several other fossil fragments near the Hall at the centre of the cave constrain the deposition ages of these mammalian fossils to the period between 469 ± 37 and 336 ± 7 ka. (6) The cave might have experienced one or several flooding and washout events, resulting in recycling and mixing of older fossils into younger sequences. This would explain the contradiction between the great antiquity of some mammalian fossils inferred from biostratigraphic correlation and younger radiometric dates of materials in stratigraphic context, as well as the apparent lack of technological advance despite an apparently long presence of the so-called “Guanyindong culture” (which is challenged by the discovery of the Levallois technologies according to Hu et al., 2019). In this regard, our U-Th chronology study of Guanyindong cave, combined with the recently reported OSL dates, leads to a better understanding of Paleolithic hominid evolution and stone technology in South China.
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Acknowledgments This work was financially supported by the Basic Scientific Research Foundations of the Institute of Geology, Chinese Academy of Geological Sciences (Project No. A1403). Sun and Che thank Beijing SHRIMP Centre for supporting their visit to the Radiogenic Isotope Facility (RIF) at the University of Queensland, and the RIF Lab team for their help and friendship. We appreciate the assistance from You Qian-sheng, Shen
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