Stratigraphic framework and continental weathering evolution of syn-glaciation, inter-glaciation, and post-glaciation during middle-late Neoproterozoic time in the southwestern Tarim Craton
Authors: Hu Haiyan , Liu Qian , Zhao Guochun , Lu Lihui , Shao Dong , Cao Xuyang , Jing Jiahao , Liu Jingyuan 
Published: March 2024

Two low-latitude glacial events (i.e. the Sturtian and Marinoan glaciations) occurred in the Cryogenian, both of which were known as the &#8220;Snowball Earth&#8221;. The sedimentary environment and continental chemical weathering recorded in the syn-glacial, inter-glacial, and post-glacial strata are of great significance to investigate the global glaciations and to establish the Earth&#8217;s environment evolution in the Neoproterozoic. Well-preserved middle-late Neoproterozoic sedimentary sequences (including the Yalaguzi, Bolong, Kelixi, Yutang, Kuerkake, and Kezisuhumu Formations from bottom to top) have been identified at the southwestern margin of the Tarim Craton. Nevertheless, there was ongoing debate regarding the evolution of sedimentary environments and their comparison to global glaciers. Furthermore, the sedimentary processes of glacial strata and continental chemical weathering remained obscure. This study conducted detailed field investigation, detrital zircon geochronology, and whole-rock major-element composition analysis. The sedimentary environment evolved from a continental to marine environment. The purplish red conglomerate of the Yalaguzi Formation represents alluvial fan facies, and the combination of diamictites and ice-raft debris depositions in the Bolong and Yutang Formations indicates glacial facies. After the deglaciation of the Bolong glaciation, the Kelixi Formation experienced the transition from neritic-littoral to fan delta-littoral. Afterwards, the sedimentary environment changed to the glacial facies of the Yutang Formation and evolved from a littoral-neritic to shore environment of the Kuerkake Formation. By using the mean age of the youngest two or more grains that overlap in age at 1&#963; (YC1&#963; (2+)), the maximum deposition age of the Kelixi Formation has been determined to be 662 Ma, which means that the Bolong and Yutang glaciations correspond to the Sturtian and Marinoan glaciations, respectively. The presence of relatively high corrected chemical index of alteration (CIAcorr) values in otherwise low CIA values documented in the Bolong Formation implies the existence of warm-humid intervals during the overall cold climate. The low CIAcorr values recorded in the Yutang Formation are consistent with a cold event in the Marinoan glaciation. The large variety of the CIAcorr values within the Kelixi Formation suggests that continental weathering during the interglacial period exhibited a tendency of (weakly)-strong-moderately-weakly-strong evolution. Notably, the dramatic fluctuation (from weak to strong continental weathering) recorded in the upper member of the Kelixi Formation implies the arrival of the Marinoan glaciation. A sharp CIAcorr increase is observed during the transition periods between the Bolong and Kelixi Formations, as well as the Yutang and Kuerkake Formations, indicating a huge increase in the chemical weathering intensity in the aftermath of the Sturtian and Marinoan glaciations. This suggests that the Sturtian and Marinoan deglaciation might have been associated with intense continental chemical weathering. This work was financially supported by the National Natural Science Foundation of China (grants 42272249 and 41972237) and the Hong Kong Research Grants Council General Research Fund (17307918).