The Precession Cycles in East Asian Stalagmite Records Before the MPT Constrained by Carbonate U-Pb Dating

The U-Pb geochronology of carbonates holds significant application value and potential in the field of geoscience. The Isotope Laboratory at Xi'an Jiaotong University has pioneered the development of Carbonate Laser Ablation and Dilution (LA&ID-MC-ICPMS) U-Pb dating techniques, based on research into Quaternary cave secondary carbonate geochronology. By combining the high spatial resolution and rapid analysis speed of the laser method with the controllable sample volume and high testing accuracy of the dilution method, a comprehensive system for Carbonate U-Pb geochronology testing has been established.

 

Moreover, with advancements in in-situ laser and isotopic dilution techniques for Carbonate U-Pb dating, we conducted tests using the laser method on various carbonate standards, both domestic and international, achieving U-Pb age results consistent with standard values within the error range. This laboratory also reported, for the first time in China, high-precision laser U-Pb dating results for Quaternary cave secondary carbonates, in alignment with ages obtained via dilution methods in foreign laboratories. Furthermore, our laboratory's entire Pb background is currently at a world-class level (~10 pg), and the testing results for cave secondary carbonates are consistent within the error range with dilution methods abroad and the laser method in our laboratory, validating its accuracy.

 

The laboratory has developed robust, high-precision laser and isotopic dilution techniques for Carbonate U-Pb dating, surpassing the limitations of U-Th dating. Through U-Pb dating and oxygen isotope analysis of stalagmite SB20 obtained from Sanbao Cave in Shennongjia, Hubei, our investigation reveals that SB20's growth period spans from 1.25 to 1.50 million years ago, depicting roughly 10 orbital cycles in δ¹⁸O. Consequently, we have established East Asia's inaugural δ¹⁸O record within the monsoon region, preceding the Mid-Pleistocene Transition (MPT). This novel stalagmite record affirms the predominant influence of low-latitude monsoons, driven by solar radiation forcing, on the East Asian region, showcasing discernible precession cycles. The current emphasis on global climate change research is substantial. By amalgamating prior scientific accomplishments, the interplay between the thermodynamic circulation system governed by ice volume in higher latitudes and the dynamic circulation system regulated by low-latitude monsoons shapes a multifaceted Earth scientific framework. This study furnishes pivotal evidence for the comprehensive exploration of a "high-low latitude" climate circulation theory in the context of climate orbital dynamics.

 

Keywords: Carbonate U-Pb geochronology; MPT; Stalagmite records; precession cycles