Sedimentary environment and petrological features of organic-rich fine sediments in shallow water overlapping deposits: A case study of Cambrian Yuertus Formation in northwestern Tarim Basin, NW China

JIN Zhimin,TAN Xiucheng,TANG Hao,SHEN Anjiang,QIAO Zhanfeng,ZHENG Jianfeng,LI Fei,ZHANG Shixuan,CHEN Lei,ZHOU Chenggang

Fig. 7. Vertical karst sequence characteristics of the Yuertus Formation on Shiairike section. (a) Macroscopic characteristics of typical vertical karst sequence on the Shiairike section; (b) Gray-green mudstone, near-surface breccia, and sac-like karst cave above the exposed surface; gray-green shale in the near-horizontal dissolved fractures and calcite fillings in the karst cave; (c) Macrocrystalline calcite and percolated hematite in the sac-like caves; (d) Near-surface and near-in-situ breccias; (e) Gray-green argillaceous breccia, with near-horizontal dissolved fractures filled with purple-red mud; (f) Near-in-situ breccia (yellow arrow), with pseudo-breccia cut by dominant karst channels. A—gray-green mudstone; B—gray-green argillaceous filling in karst fractures; C—calcite in sac-like karst cave; D—macrocrystalline calcite in near-horizontal karst cave; E—red iron ore; F—near-surface breccia. Scale bar: geological hammer length: 30 cm, lighter length: 8 cm, marker length: 10 cm.