CHENGJIANG: A WINDOW INTO THE DAWN OF LIFE

Maotianshania cylindrica

High in the mist-softened hills of Yunnan Province, China, a band of ochre and grey shale holds one of Earth’s most extraordinary archives—a fossil record so exquisitely preserved that even the gills, antennae, and gut tracts of animals from over 518 million years ago remain visible. 

This is Chengjiang, a UNESCO World Heritage Site and one of the most important early Cambrian Lagerstätten on the planet.

Here, at the base of the Maotianshan shales, paleontologists have uncovered a moment of evolutionary ignition: the rapid diversification of complex animal life known as the Cambrian Explosion.

The Geological Setting: Maotianshan Shales

The Chengjiang fossil exposures occur within the Yu’anshan Member of the Heilinpu Formation, deposited in a quiet, offshore marine environment during the Cambrian. 

These fine-grained mudstones accumulated under low-oxygen conditions—an essential factor that inhibited decay and burrowing, allowing soft tissues to fossilize with remarkable fidelity.

Key geological features:

• Age: ~518–520 Ma
• Depositional environment: Distal, oxygen-poor shelf
• Sediment: Fine mudstones and shales ideal for preserving delicate structures
• Taphonomy: Rapid burial via storm-induced sediment flows, sealing organisms beneath thin laminae

It is this marriage of rapid burial and anoxic bottom waters that created one of Earth’s rare Konservat-Lagerstätten, preserving not only bones and shells but organs, musculature, and entire life assemblages.

Lead Image Credit: Maotianshania cylindrica. Phylum: Nematomorpha Early Cambrian Chengjiang, Maotianshan Shales, SNP. Released under the GNU Free Documentation License