Fig. 4

Fabrics of the carbonate concretions of Xiamaling Formation. Displacive growth is marked with “D”, while replacive growth marked with “R”. a and b Polished concretions, showing offwhite zones of displacive growth, occurring within and adjacent to green-yellow zones of replaced mudstone that have been cemented and incorporated into the concretion fabric; c A concretion with curved lamination, showing that the displacive layer also occurred in a replacive layer concentrated zone; d and e Concretion with concentric ring structures. a and d were collected from Huangtugang section; the others were collected from Jizhentun section