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 III dolomitization 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.

KANG Junyao;LI Chenqing;DONG Lin;XIAO Shuhai

Key Laboratory of Orogenic Belts and Crustal Evolution,MOE,Beijing 100871,China;School of Earth and Space Sciences,Peking University,Beijing 100871,China;Department of Geosciences,Virginia Tech,Blacksburg,VA 24060,U.S.A.

地质学报（英文版）

[1]KANG Junyao;LI Chenqing;DONG Lin;XIAO Shuhai-.Early Diagenetic Dolomite as a Potential Archive of Paleo-redox Fluctuations in an Early Tonian Marine Basin?)[J].地质学报（英文版）,2022(02):607-620

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