Fig. 5

Composition and texture of replacive layers in the carbonate concretions of Xiamaling Formation (Jizhentun section). a A green-yellow replacive layer (marked by R) interbedded in displacive layers (marked by D); b A BSE image showing that the replacive layer is composed of siliciclastic illite (Ill), chamosite (Ch), quartz (Q), K-feldspar (Kfs) and iron oxides (IO), and authigenic dolomite (Dol) and apatite (Ap); c and d “Cardhouse” structures (arrows) in the replacive layer; e SEM image of replaced mudstone horizon in a concretion, showing laminar clay minerals bended around an authigenic dolomite grain (dash line); f Green-yellow silty shale matrix adjacent to a concretion; g SEM image of panel f showing horizontal clay lamination (arrow); h SEM image with high magnification, showing horizontally distributed laminar clay minerals (arrow)