Chengjiang is the name of the Cambrian fossil site in China famous for preserving soft-bodied organisms in extraordinary detail.
The Chengjiang fossil assemblage occurs mainly in the Maotianshan Shales of Yunnan Province. These deposits date to about 525–520 million years ago, during the Early Cambrian, only a few million years after the Sirius Passet deposits and at least 10 million years before the better-known Burgess Shale in Canada.
Rapid burial in fine sediment, probably through periodic turbidity currents in a shallow marine setting, helped preserve delicate tissues that normally disappear before fossilization. The fossils include arthropods, sponges, priapulids, trilobites with preserved appendages, and early chordates such as Haikouichthys and Myllokunmingia. Nearly half of the described animal species are arthropods, but only about 3% of the organisms have hard shells.
The key distinction is that Chengjiang is the fossil fauna or site commonly associated with the Chinese deposits, while Maotianshan Shales is the specific geological unit. Ediacara belongs to a much older pre-Cambrian fossil record, and Mazon Creek is a Carboniferous site in Illinois.