Science China Earth Sciences

Dolomite genesis, Mg isotopes, Carbon and Oxygen isotopes, Xiaoerbulake Formation, Qigebulake Formation,Tarim Basin

Dolomite genesis is a century-old mystery in sedimentology, To reveal the mechanism of dolomite genesis, two coreproblems need to be addresed. The first is the origin and migration mechanism of Mg"-rich fluids during the dolomitizationprocess. The second is the kinetic barier caused by Mg"" hydration during dolomite precipitation at low temperatures. To addressthese problems, our study, based on detailed petrological., sedimentological, geochemical (major and trace elements), andisotopic (C-0-Mg) analysis, clarified the source and migration of Mg"-rich fluids and the kinetic bauier mechanism of lowtemperature dolomite precipitation in the Upper Sinian Qigebulake Formation and the Lower Cambrian Xiaoerbulake Formationin the Tarim Basin. First, we found that the Mg"-rich flhids required for the dolomitization of dolomite in the XiaoerbulakeFormation were primarily derived ftom the Early Cambrian marine fluid, At the interface ofthe sedimentary eycle. s"vg valuesfuctuated considerably, indicating that the seauence interface was the stating point and channel for the migration of dolomitizedfuids, Sea level variation plays a major role in controlling the dolomitization process ofthe Xiaoerbulake Formation. Second, theOigebulake Formation contains low-temperature dolomite with Mg"-rich fuids supplied by seawater, microorganisms, andsedimentary organic matter. Comprehensive analysis shows that the dolomite of the Oigebulake Formation was formed bymicrobial induction by anaerobic methane bacteria, Finally, the properties and sources ofdolomitization fuids and the fommationprocess of dolomite were the reasons for the difierence in the Mg isotope composition of dolomite during the Sinian-Cambriantransition. This study reveals the genetic mechanism of the simian-Cambran dolomite in the larim Basi and estabishes a newmethod to explain the genesis of microbial dolomite by C-0-Mg isotopes, providing a reference for the reconstruction of theforation and evolution ofdolomites.

66

2

334-357

1869-1897

SCI