Applied Geochemistry

Mg isotope;Dolomitization;Diagenetic alteration;Hydrothermal activities;Qiulitage formation;Tarim basin

Recovering the Mg isotopic composition of seawater using penecontemporaneous dolomite is possible; howeverthe Mg isotopic composition of dolomite may be changed by later diagenesis and hydrothermal activities, Solvingthis problem requires further research on the behavior of Mg isotopes in dolomitization systems, Diagenesis andhydrothermal fluids have significantly altered the considerable amount of dolomites in the Lower CambrianQiulitage Formation in the Gucheng region of the Tarim Basin. Thus, this formation is excellent for examining thebehavior of dolomite Mg isotopes after diagnostic and hydrothermal alterations. The results of major and traceelements and C-0-Mg isotope analysis show that the dolomite of Qiulitage Formation is penecontemporaneousdolomite, and the Mg in dolomite is mainly from the Early Cambrian seawater. The dolomites of the QiulitageFormation in the Gucheng area are formed by carbonate platform facies. The stratigraphic variability of Mgisotopes is small, averaging -2.08%+ 0.23%, which indicates that the Mg isotope of the dolomitized fluid in thelarge-scale dolomitization process of the carbonate platform is uniform and balanced with the seawater in thesame period. In addition, the Mg isotopic composition of dolomite is stable, and the $?6ig value is not affectedby burial diagenesis and hydrothermal fluid activities. we found that the Mg isotopic composition and stratigraphic age of the dolomites of the Lower Cambrian Qiulitage Formation are consistent with the simulated results, the S*'vig value of the ancient seawater in the Early Cambrian is estimated to be about -0.08%+0.23%This study shows that the S"oMg of penecontemporaneous massive dolomite may have been used to invert the Mgisotopic composition of seawater during the same period, within a confidence range of +0.2%, using massivedolomite, and provided a new idea for quantitatively reconstructing the marine Mg cycle in the geologicahistory.

148

105540

1872-9134

SCI