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Fig. 8 | Journal of Palaeogeography

Fig. 8

From: Growth mechanisms and environmental implications of carbonate concretions from the ~ 1.4 Ga Xiamaling Formation, North China

Fig. 8

Schematic illustration of diagenetic environment with redox zones in marine sediment porewaters (adapted from Canfield and Thamdrup 2009), modeled aqueous REE patterns in sediment porewaters ranging from the oxic to methanic zones (adapted from Haley et al. 2004 and Kim et al. 2012), and possible growth model for the carbonate concretions of Xiamaling Formation. In different redox zones, different electron acceptors, including O2, NO2, NO3, MnO2, FeOOH, SO42− and CO2 are predominated, and different REE patterns of porewater appear with positive Ce anomaly in Mn reduction zone and enrichment of MREE in Fe reduction zone. The formation of carbonate concretions of Xiamaling Formation mainly occurred in the Mn reduction zone, and probably also extended to the upper nitrate and lower Fe reduction zones

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