Early Diagenetic Dolomite as a Potential Archive of Paleoredox Fluctuations in an Early Tonian Marine Basin?  

作　　者：KANG Junyao LI Chenqing DONG Lin XIAO Shuhai 

机构地区：[1]Key Laboratory of Orogenic Belts and Crustal Evolution,MOE,Beijing 100871,China [2]School of Earth and Space Sciences,Peking University,Beijing 100871,China [3]Department of Geosciences,Virginia Tech,Blacksburg,VA 24060,U.S.A.

出　　处：《Acta Geologica Sinica(English Edition)》2022年第2期607-620,共14页地质学报（英文版）

基　　金：supported by Natural Science Foundation of China(Grant No.41672334);US National Science Foundation(Grant No.EAR-2021207)。

摘　　要：The Tonian Period witnessed important environmental changes and critical evolutionary innovations. Published iron speciation data suggest a global redox transition of mid-depth seawaters from euxinic to ferruginous in early Tonian, but details of this transition remain unknown. This study explores Tonian stromatolitic carbonates as a possible archive of paleoenvironmental changes, through the investigation of dolomitic limestones and dolostones associated with stromatolites of the Weiji Formation in the Huaibei region of North China. Three types of dolomitization are recognized on the basis of petrographic and geochemical data. Type Ⅰ and Ⅱ dolomitization resulted in dolomitic limestones characterized by LREE depletions, MREE enrichments, positive yttrium anomalies, and a lack of europium anomalies, indicating early diagenetic dolomitization, possibly in the iron reduction zone and under the influence of bottom seawater. The lack of cerium anomalies in these carbonates suggests anoxia in shallow marine environments. The coexistence of ferroan/non-ferroan dolomite crystals and overgrowth bands is interpreted as possible evidence for rapid fluctuations between iron-rich and iron-depleted conditions in pore-waters or seawaters. In contrast, type Ⅲdolomitization resulted in pervasively dolomitized stromatolitic carbonates and likely represents late diagenetic processes. This study highlights the potential of early diagenetic dolomite as an archive for paleoenvironmental investigations.

关 键 词：redox early diagenesis rare earth elements DOLOMITE NEOPROTEROZOIC North China 

分 类 号：P53[天文地球—古生物学与地层学] P588.245[天文地球—地质学]