第九届青年地学论坛

Calcareous root tubes (CRTs), which are formed by the encrustation of roots with pedogenic carbonate, serve as an archive for paleoclimate reconstructions. However, controversies remain regarding the formation age of CRT carbonate and the quantitative tracing of its sources in the hinterland of the desert. In this study, 13 CRT samples were obtained from 11 sites in the Tengger Desert of northwestern China. Samples were described using X-ray micro-tomography Scanning (Micro-CT), and their ¹⁴C ages, δ¹³C, and ⁸⁷Sr/⁸⁶Sr values were measured. The results show that more than 99.84% of pore diameters in the precipitated carbonate layer were less than 1mm, which was much smaller than the plant roots in this region. Moreover, the root residues from poor cementation CRT were dated at 151−431 cal yr BP, which was significantly younger than the carbonate age of other complete cemented CRTs. Thus, most of the root residues found within completely cemented CRTs may invade after the CRT formation and their ¹⁴C ages cannot represent the CRT formation period, while the carbonate ¹⁴C dating results can indicate the CRT formation period. ⁸⁷Sr/⁸⁶Sr values of CRTs occurred at 0.71152−0.71189, indicating that the main source of calcium in CRTs was the dissolution of carbonate in rhizosphere soil. δ¹³C values of CRTs varied between -5.4‰ and -3.2‰. Using the end-member mixing model, carbon sources from CRT can be divided into rhizosphere soil respiration CO₂ (81−82%) and atmospheric CO₂ (18−19%). Hence, δ¹³C values of CRTs may derive the δ¹³C signal from soil and record paleoenvironment conditions. This study enhances our understanding of the formation mechanism of pedogenic carbonate and provides an important aspect in assisting paleoenvironmental reconstructions.

Pedogenic carbonate,Dune soil,Micro-CT Scanning,Radiocarbon,Desert