干旱区生态环境知识资源中心

The age framework of Qarhan Salt Lake in arid western China is still controversial due in part to (1) age discrepancy between conventional C-14 and Th-230 dating results, and (2) no AMS C-14 ages of organic carbon from drilling cores in Qarhan Salt Lake were reported until now. In order to discuss these chronological problems, upper 54.50 m lacustrine sediments from a drilling core (ISL1A) recovered from Qarhan Salt Lake were dated based on Th-230 and AMS C-14 dating techniques. Results show that (1) AMS C-14 ages of total organic carbon (TOC) from 4.65 to 30.29 m are almost in stratigraphic order and consistent with Th-230 ages of halite in the corresponding layers; (2) AMS C-14 ages of TOC from 30.29 to 54.50 m are younger with increasing depth. This phenomenon was also found in Shell Bar in the study area, suggesting that AMS C-14 ages from upper 30.29 m are more reliable while those from lower 24.21 m in ISL1A may be underestimated; (3) Th-230 ages of halite from lower 24 m lacustrine sediments are obviously older than AMS C-14 ages of TOC in the corresponding layers, which results into different age framework of salt lake sediments in Qarhan Salt Lake; (4) if extrapolating these reliable AMS C-14 ages in ISL1A, similar age framework with Th-230 ages in this core confirms that Th-230 ages are much close to the true ages of these sediments, which suggests that the forming timing of the bottom salt layer is similar to 50 ka.