Radiocarbon and Luminescence Dating of Lacustrine Sediments in Zhari Namco, Southern Tibetan Plateau

Lu Cong,Tianyuan Chen,Donglin Gao,Fuyuan An,Yixuan Wang,Xiying Zhang

doi:10.3389/feart.2021.640172

Abstract

There are more than 1,000 lakes within the Tibetan Plateau (TP), all of which are sensitive to changes in regional climate and local hydrology. Lacustrine sediments within these lakes preserve a good record of these changes. However, determining their precise ages is difficult due to the complex nature of lake reservoir effects (LRE), which limit our understanding of paleoenvironmental changes. Focusing on an exposed 600 cm thick lacustrine sediment profile located in western Zhari Namco, we used a combination of both radiocarbon and optically stimulated luminescence (OSL) dating methods in order to evaluate the carbon reservoirs of bulk organic matter (BOM) and aquatic plant remnants (APR), and to explore the age differences between 14C and OSL and their respective reliability. We demonstrated that (i) OSL ages were changed in stratigraphic order, and the OSL age just below the beach gravel layer was consistent with previously reported paleoshoreline ages; (ii) 14C ages were divergent between BOM and grass leaves; (iii) 14C ages of BOM were older than 14C ages of APR; and (iv) all 14C ages were older than OSL ages. This could be attributed to changing LRE in the past, causing the 14C ages to appear unstable during the deposition period. Although the 14C ages of terrestrial plant remnants (TPR) were not affected by LRE, an analyzed twig nonetheless returned a 14C age older than its respective layer’s OSL age, suggesting it may have been preserved on land prior to transportation into the lake. Our study suggests that OSL ages are more reliable than 14C ages with respect to Zhari Namco lacustrine sediments. We recommend caution when interpreting paleoenvironmental changes based on lacustrine sediment 14C ages alone.

Highlights

The Tibetan Plateau (TP) is the largest and highest plateau on Earth, often regarded as the “Third Pole” due to both its high elevations and expansive c. 2.5 million km2 coverage (Yao et al, 2012; Liu et al, 2019)
Our results showed that the ages for all five optically stimulated luminescence (OSL) samples increased with respect to their depth within the section, indicating that these lacustrine sediments were deposited between 5 and 2 ka BP (Table 2)
Radiocarbon and OSL dating were used to date lacustrine sediments from Zhari Namco Lake in the southern Tibetan Plateau

Summary

INTRODUCTION

The Tibetan Plateau (TP) is the largest and highest plateau on Earth, often regarded as the “Third Pole” due to both its high elevations and expansive c. 2.5 million km coverage (Yao et al, 2012; Liu et al, 2019). For OSL age calculation, because the sediments in nearby lakes within the TP did not experience long-distance transport or multiple sedimentation-transportation cycles, samples drawn from these lakes may be partially bleached, and the stimulated signal intensities will be low when compared with sediments from other regions, such as the Chinese Loess Plateau (Lee et al, 2009). To reduce this impact, CQ1–90 removed one test aliquot with abnormal data, CQ2–60 and CQ2–26 removed two test aliquots with abnormal data.

RESULTS AND DISCUSSION

DATA AVAILABILITY STATEMENT

CONCLUSION