The mud banks are composed of a mixture of two basic micro-facies: (1) spiculitic wackestone with diverse fauna includingcryptostome and fenestellid bryozoans, crinoids, ostracodes, andbrachiopods; (2) fine-grained bioclastic wackestone and pack-stone containing crinoids, bryozoans, sponges, brachiopods,ostracodes, and corals. The mud banks developed during a rela-tive sea-level rise in an outer deep platform margin, and died asrelative sea-level fell evidenced from the bioclastic wackestoneand packstone overlying the banks. The mud banks at Longdian-shan are similar to typical Waulsortian mud mounds, as indicatedby the presence of bryozoans, crinoids, and sponges, mud gen-erations and spar-filled cavities