Cambrian sites

From Palaeos.org

Cambrian period 542-488
Terreneuvian 542-521		Series 2 521-510		Series 3 510-499			Furongian 499-488
Fortunian 542-528	Stage 2 528-521	Stage 3 521-515	Stage 4 515-510	Stage 5 510-506	Drumian 506-503	Guzhangian 503-499	Paibian 499-496	Stage 9 496-492	Stage 10 492-488

1) Chengjiang

This site is discussed at Chengjiang, and the diverse faunal assemblage is listed at Chengjiang biota. The English spellings are somewhat variable, "Chenjiang" being another popular variant. The correct spelling seems to be 澄江. It might be better to referred to as the Maotianshan Shale. This is less accurate (it is more properly the Qiongzhusi Formation), but seems least likely to be misspelled by ignorant foreigners, such as ourselves. The Chengjiang fossils are dated at 525-520 Mya, or perhaps a bit younger, corresponding most nearly to the Botomian Age in our system [1]. Outcrops of the Qiongzhusi occur in scattered locations south of Kunming in eastern Yunnan Province, Chengjiang County, near the towns of Chengjiang and Ercai. Additional sites have now been opened further south. Of all the sites mentioned here, Chengjiang is geologically the oldest and historically the youngest. The fossil potential of the region was discovered by Dr. Hou Xianguang in 1984. Many of the fossils have been recovered - and many lost forever - in connection with phosphate mining in the area that continues unabated. The incredible soft-tissue preservation of the fossils here seems to have resulted from rapid burial, complete sediment anoxia, and replacement of organic remains with pyrite or phosphates - nothing magical, except the absolutely unreasonable number of such sites, of varying ages, in Yunnan Province.

The faunal list from Chengjiang is a virtually complete census of the major metazoan taxa of the time, and includes our personal favorite of all early chordates, Haikouella. There seems to be little selectivity. There are now Chengjiang fossil images all over the web. However, many of the Chengjiang organisms remain undescribed, simply for lack of competent describers, and new specimens are being discovered at an extraordinary rate. Many species have undergone revisions, and contention among scientists about interpretations is commonplace.

2) The Burgess Shale

The Burgess Shale is slightly younger than Chengjiang. The Shale is located near the town of Field, in southeastern British Columbia, high in the Canadian Rockies. The closest major town is Banff, about 90 km to the east. The site was discovered by Charles Walcott of the Smithsonian Institution in 1909, and the Walcott Quarry is named after him. The deposits are deepwater, benthic sediments, but the fauna probably represent a reef community swept off the reef and buried in an anoxic bottom by a mudslide. The Burgess is actually far less spectacular than Chengjiang, but it attained great fame (ironically, just at the time that Chengjiang was starting to produce large quantities of fossils) due in part to Stephen Jay Gould's book, Wonderful Life.

The Burgess Shale's influence on paleontology has been, in part, due to the fact that Gould chose this book to set out some of his most interesting and controversial ideas about evolution, and in a manner readable by almost everyone. Gould argued that the end results of evolution were essentially random because the process was chaotic [2]. Thus even the tiniest change in Proterozoic conditions might have resulted in an entirely different modern fauna. His proof was the diversity of phyla in the Shale, hinting at an enormous initial diversity in the Cambrian Explosion which was quickly pruned away, largely by happenstance. As it has turned out, Gould was certainly wrong about the Burgess Shale. Chengjiang - and closer examination of the Burgess fauna - have shown that Walcott was more correct than Gould. The great majority of Burgess animals can now be assigned with confidence to well-known phyla. However, his ideas about evolution may well be correct, if the pruning process actually occurred in the lower Early Cambrian or even before metazoans became morphologically recognizable.

notes:
[1] We use the Russian-Kazakhian stages until the ICS gets around to finally giving these Early Cambrian ages some names. As of this date (100406), the ICS age corresponding to the Botomian is still unnamed.

[2] We use chaotic in its mathematical sense, meaning that the end state of a closed system is extremely sensitive to initial conditions. The classical example is from meteorology, in which the occurrence of a hurricane is supposedly determined by the wing beat of a butterfly six months earlier and ten thousand miles away.

Palaeos com - Paleozoic

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