Chronology of a lacustrine core from Lake Linggo Co using a combination of OSL, C-14 and Pb-210 dating: implications for the dating of lacustrine sediments from the Tibetan Plateau

Vast palaeolakes once occupied the Qinghai-Tibetan Plateau (TP). Analyses of the sedimentary records of these lakes could potentially provide an extensive dating archive. Many previously constructed age-depth models simulating lacustrine cores have been principally based on radiocarbon (C-14) dating. However, such dating could have been hampered by the so-called lake reservoir effect' (LRE) and the reworking of lakebed sediments, resulting in inaccurate C-14 age-depth models and limiting interpretations of existing lacustrine palaeoclimatic records. Lake Linggo Co is located on the central TP, in one of the coldest and most arid regions of Tibet. We dated a 9.87-m-long lacustrine core extracted from the lakebed at a water depth of similar to 60m using a combination of Pb-210, C-14 and optically stimulated luminescence (OSL) techniques. Some C-14 ages showed significant age reversals; all the C-14 ages were much older than the Pb-210 and OSL ages for the same depths. This could possibly be attributed to the presence of old, inherited carbon, causing the inherited C-14 age to appear unstable during the deposition period. The Pb-210 and OSL ages were roughly concordant, and were also consistent with the stratigraphical succession. We therefore suggest that C-14 dating may, on its own, be inadequate for accurate dating of lacustrine sediment sites on the TP, and that the OSL method should also be applied in order to evaluate the reliability of any C-14 ages. With this approach, we constructed an age-depth model, revealing sedimentation rates of 1.7, 0.8, 6.8 and 0.6mm a(-1) between 0-1.9, 1.9-4.2, 4.2-4.4 and 4.4-9.4 ka, respectively.