Another Look at the Cambrian Explosion 

I came across THIS ARTICLE on the Earthlogs website, a favourite of mine. It describes recent work on the Cambrian of Chengjian County, Yunnan, China. It is based on THIS PAPER.

The Cambrian Explosion is always associated with the Burgess Shale in the Canadian Rockies. But there the fossils are not found in the environment where they lived. There extraordinary good preservation is due to their being moved by some underwater avalanche to an anoxic environment.

The Chengjian Biota has more species than any other Cambrian fossil locality. But here has been, up to now, no consensus about the environment of the deposit. This is probably due to the rocks being highly weathered. To settle (possibly!) the matter a 130m boehole was drilled through the deposit and the conclusion was that the rocks were laid down in a deltaic environment.

The best preserved fossils are found in the prodelta. Here there is rapid deposition where the beasties were buried quickly, preserving them from predation, and in an anoxic environment. The quick burial may have been due to river floods moving the animals from the delta front.