An alpine meadow soil chronology based on OSL and radiocarbon dating, Qinghai Lake, northeastern Tibetan Plateau

摘要

Extensive alpine meadow soil on the Tibetan Plateau (TP) plays a core role in the local ecological system, however, its ages of formation and pedogenic processes are relatively poorly understood. In this study, we reconstructed a soil development chronology for two alpine meadow soil sections on Riyue Mountain, southeast of Qinghai Lake (QHL), using quartz optically stimulated luminescence (OSL) and potassium-rich feldspar (K-feldspar) post-infrared infrared stimulated luminescence (post-IR IRSL, pIRIR) techniques. In addition, accelerator mass spectrometry C-14 analysis of soil organic matter (SOM) was used to date alpine meadow soil profiles on Xiangpi Mountain, southwest of QHL. Bulk samples were collected from Riyue Mountain profiles for determination of soil grain size and magnetic susceptibility. The results show: (1) Consistency of quartz OSL and K-feldspar pIRIR ages, indicating both the quartz OSL and K-feldspar pIRIR signal for alpine meadow soil samples are well bleached before burial. (2) SOM radiocarbon ages most likely underestimate sample age due to modern organic contamination from plant roots. (3) A lower limit on alpine meadow soil development after the last deglaciation based on OSL dating of bottom deposits, and an upper limit of before 1450 +/- 80 cal BP from radiocarbon dating of the upper SOM; alpine meadow soils developed mainly during the late Holocene (4-0 ka) on the mountains around QHL. (4) The grain size characteristics of alpine meadow soil are similar to atmospheric dust and loess at QHL; the rapid aeolian accumulation in the late Holocene implies conditions of relative arid and cold climate.