Journal of Earth Science, Vol. 29, No. 3, p. 695–706, June 2018 ISSN 1674-487X Printed in China https://doi.org/10.1007/s12583-017-0972-9 Luminescence Chronology and Radiocarbon Reservoir Age Determination of Lacustrine Sediments from the Heihai Lake, NE Qinghai-Tibetan Plateau and Its Paleoclimate Implications Fuyuan An *1, 2, 4, Zhongping Lai5, Xiangjun Liu1, 2, Yixuan Wang1, 3, Qiufang Chang1, Baoliang Lu1, Xiaoyun Yang5, 6 1. Key Laboratory of Comprehensive and Highly Efficient Utilization of Salt Lake Resources, Qinghai Institute of Salt Lakes, Chinese Academy of Sciences, Xining 810008, China 2. Qinghai Provincial Key Laboratory of Geology and Environment of Salt Lakes, Qinghai Institute of Salt Lakes, Chinese Academy of Sciences, Xining 810008, China 3. University of Chinese Academy of Sciences, Beijing 100049, China 4. State Key Laboratory of Cryosphere Sciences, Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences, Lanzhou 730000, China 5. School of Earth Sciences, China University of Geosciences, Wuhan 430074, China 6. Department of Geology, Baylor University, Waco 76798, USA Fuyuan An: https://orcid.org/0000-0003-3136-8847 ABSTRACT: The accurately determining the lake 14C reservoir age has a crucial significance for cli- matic reconstruction. In this study, the optically stimulated luminescence (OSL) dating method is em- ployed to date samples from highstand lacustrine sediments, palaeoshoreline, fluvial terrace, and the alluvial fan of the Heihai Lake catchment. Accelerator mass spectrometry (AMS) 14C dating was also used to date fossil plants from highstand lacustrine sediments. Based on the calculations of linear re- gression with OSL against radiocarbon ages for same layers of two sections, the quantitative 14C reser- voir ages were estimated to lie between 3 353 and 3 464 yr during the 1.8 to 2.4 ka, which showed tem- poral variation. The sources of old carbon are the dissolution of carbonate bedrocks distributed along the Kunlun Mountain. The OSL ages of the different members of the hydatogen sedimentary system at Heihai Lake catchment indicate that a stronger hydrologic condition occurred from 3.0±0.2 to 1.8±0.2 ka, with a maximum lake level of 9 m higher than present. This humid stage was widely recorded in different sediments on the QTP and Chinese Loess Plateau (CLP), indicating its broad synchronicity across the Asian Summer Monsoon region. The enhanced East Asian Summer Monsoon (EASM) and the Indian Summer Monsoon (ISM) resulted in the increase of moisture availability for the Heihai Lake area during this stage. KEY WORDS: luminescence and radiocarbon dating, 14C reservoir age, Heihai Lake, Qinghai-Tibetan Plateau (QTP), palaeoclimate implications. 0 INTRODUCTION 2016; Zeng et al., 2015; An Z S et al., 2012; Chen et al., 2008). The northern Qinghai-Tibetan Plateau (QTP) is a joint The QTP has changed the atmospheric and hydrological circu- area that was influenced by the East Asian Summer Monsoon lations and reshaped the local and global climate (Yang K et al., (EASM), Indian Summer Monsoon (ISM), and the mid-latitude 2014). Accurate and reliable dating of lacustrine deposits is Westerlies (Fig. 1a), and exerts a significant impact on the re- crucial for understanding these climate change patterns and its gional and global climate through a thermal and mechanical forcing mechanisms. Radiocarbon (14C) dating is the most forcing mechanism (An F Y et al., 2018, 2012; Wang et al., commonly applied method for establishing chronologies of lacustrine sediments. However, its application could be re- *Corresponding author: [email protected] stricted due to the ubiquitous hard water reservoir effect on © China University of Geosciences and Springer-Verlag GmbH young Holocene sediments, especially in the QTP (Mischke et Germany, Part of Springer Nature 2018 al., 2013; Hou et al., 2012a). The reservoir effect on lacustrine sediments in the QTP varies significantly, from 650 yr at Manuscript received April 24, 2017. Ahung Co to 6 670 yr at Bangong Co (Hou et al., 2012b). Thus, Manuscript accepted September 1, 2017. the accurate determination of the reservoir effect for 14C dating An, F. Y., La, Z. P., Liu, X. J., et al., 2018. Luminescence Chronology and Radiocarbon Reservoir Age Determination of Lacustrine Sediments from the Heihai Lake, NE Qinghai-Tibetan Plateau and Its Paleoclimate Implications. Journal of Earth Science, 29(3): 695–706. https://doi.org/10.1007/s12583-017-0972-9. http://en.earth-science.net 696 Fuyuan An, Zhongping Lai, Xiangjun Liu, Yixuan Wang, Qiufang Chang, Baoliang Lu and Xiaoyun Yang Figure 1. Map showing the location of the study area. (a) MSML represents Modern Summer Monsoon Limit; (d) the red dots represent the sample sites. HL. Heihai highstand lacustrine sediments; HP. Heihai paleoshoreline deposits; HF. Heihai alluvial fan deposits; HT. Heihai fluvial terrace deposits. is critical for establishing reliable age control. generation (SAR) protocol (Murray and Wintle, 2000) has re- Approaches for estimating the reservoir age involves a sulted in extensive applications for dating lacustrine sediments modern calibration approach, linear extrapolation, geochemical (e.g., Fan et al., 2014; Liu and Lai, 2012; Long et al., 2011; Liu models, stratigraphic alignment, and independent age determi- et al., 2010; Shen et al., 2008), and it has been shown that nations (E et al., 2015; Hou et al., 2012b). Each of these meth- silt-sized lacustrine sediments have been adequately bleached ods has its own disadvantages for applications in lakes on the (Thomas et al., 2003). By comparing the OSL dating of silt QTP. The modern calibration and linear extrapolation ap- quartz and the 14C dating of organic matter for lake samples proaches only provide an estimate of the modern 14C reservoir with the same layers, the 14C reservoir age can be obtained age, and different ages can be obtained for samples from dif- (Long et al., 2011; Shen et al., 2008). In the current study, we ferent sites. Geochemical modeling is a theoretical method for try to evaluate the lake reservoir effect of 14C dating for Heihai determining reservoir age, but it is difficult to estimate the ini- Lake by comparing the radiocarbon and OSL ages for samples tial conditions and parameters of the models in the geological from the same lacustrine layers, and further discuss its paleo- time scale. Independent age determination is the most reliable climatic changes combining other hydatogen sedimentary sys- approach for estimating the past variations in the 14C reservoir tem at Heihai Lake catchment. age, thus this approach is widely used in determining the “old carbon” error in lacustrine sediments (Hou et al., 2012a, b; Liu 1 MATERIALS AND METHODS and Lai, 2012; Long et al., 2011; Shen et al., 2008). 1.1 Study Area Improvements in the optically stimulated luminescence The Heihai Lake (36°N, 93°15′E, 4 445 m a.s.l.) is located (OSL) dating method such as the use of the single aliquot re- in the Kunlun Mountains in the northern region of QTP (Figs. Luminescence Chronology and Radiocarbon Reservoir Age Determination of Lacustrine Sediments 697 1b, 1c, and 1d). This lake catchment is dominated by a large to avoid age underestimation (Lai and Brückner, 2008). The area of Triassic, Paleogene, and Carboniferous clastic rocks. purity of the isolated quartz was verified by infrared light Vast piedmont alluvial/fluvial fan sediments fill the catchment stimulation (830 nm) and no obvious IRSL was observed in all (Zhang et al., 2013). samples. The pure quartz samples were then mounted onto the The annual precipitation is 100–200 mm with the majority center (0.5 cm-diameter) of 0.97 cm-diameter stainless steel of the precipitation falling during the summer season in this discs with silicone oil. OSL measurements were carried out on region. The mean annual temperature is 2.0 oC. The mean an automated Risø TL/OSL-DA-20 reader. Stimulation was by January temperature at the Wudaoliang meteorological station blue LEDs at 130 °C for 40 s, and detection was through 7.5 (4 780 m a.s.l.), which is 50 km to the south, is -8.4 °C and the mm-thick U-340 filters. Preheat was performed using 260 °C mean July temperature is 12.1 °C (Zhang et al., 2013). The lake for 10 s for the regenerative dose, and cut-heat was 220 °C for is an open-basin lake. It is fed by two streams from the glacials 10 s for the test dose. The signals of the first 0.64 s stimulation and discharges into the Kunlun River, which finally flows into were integrated for growth curve construction after back- the Qarhan Salt Lake into the enclosed Qaidam Basin (QB). ground subtraction, which used the last 25 channels in the shine down curve. The concentrations of uranium (U), thorium 1.2 Section and Samples (Th) and potassium (K) were measured by neutron activation The HL1 section (35°57′28.95″N, 93°17′33.23″E, 4 446 m analysis in the Chinese Institute of Atomic Energy in Beijing. a.s.l.) is ~1.0 m higher than HL2 (35°57′42.30″N, For the 38–63 μm grains, the alpha efficiency value was taken 93°17′34.99″E, 4 445 m a.s.l.). The two sections are made up as 0.035±0.003 (Lai et al., 2008). The cosmic ray dose rate of six lacustrine sedimentary layers, which include an abun- was estimated for each sample as a function of depth, altitude, dance of interbedded aquatic plant species residues (Pota- and geomagnetic latitude (Prescott and Hutton, 1994). The mogeton sp.). Six plant residue samples for 14C dating and six water content was calculated based on moisture mass/dry mass lacustrine sediment samples for OSL dating were collected with (Aitken, 1985) and, taking into account the uncertainties dur- stratigraphic sequences to determine the chronology and the ing burial, an error of 5% was adopted for the water content to reservoir effect of 14C dating for the lake.