Burgess shale

Burgess Shale Stratigraphic range: Cambrian Series 3 – ~508 Ma PreЄ Є O S D C P T J K Pg N ↓
Ottoia, a soft-bodied worm, abundant in the Burgess Shale. (From Smith et al. 2015)
Type	Geological formation
Unit of	Stephen Formation
Thickness	161 meters (528 ft)
Lithology
Primary	Shale
Location
Coordinates	51°26′N 116°28′W / 51.433°N 116.467°W / 51.433; -116.467
Region	Yoho National Park and Kootenay National Park
Country	Canada
Type section
Named for	Burgess Pass
Named by	Charles Doolittle Walcott, 1911
Map highlighting Yoho National Park in red

The Burgess Shale Formation is a fossil-bearing deposit exposed in the Canadian Rockies of British Columbia, Canada. It is famous for the exceptional preservation of the soft parts of its fossils. At 508 million years (Middle Cambrian) old, it is one of the earliest fossil beds containing soft-part imprints.

The rock unit is a black shale and crops out at a number of localities near the town of Field in Yoho National Park and the Kicking Horse Pass. Another outcrop is in Kootenay National Park 42 km to the south.

The Burgess Shale was discovered by palaeontologist Charles Walcott on 30 August 1909, towards the end of the season's fieldwork. He returned in 1910 with his sons, daughter, and wife, establishing a quarry on the flanks of Fossil Ridge. The significance of soft-bodied preservation, and the range of organisms he recognised as new to science, led him to return to the quarry almost every year until 1924. At that point, aged 74, he had amassed over 65,000 specimens. Describing the fossils was a vast task, pursued by Walcott until his death in 1927. Walcott, led by scientific opinion at the time, attempted to categorise all fossils into living taxa, and as a result, the fossils were regarded as little more than curiosities at the time. It was not until 1962 that a first-hand reinvestigation of the fossils was attempted, by Alberto Simonetta. This led scientists to recognise that Walcott had barely scratched the surface of information available in the Burgess Shale, and also made it clear that the organisms did not fit comfortably into modern groups.

Excavations were resumed at the Walcott Quarry by the Geological Survey of Canada under the persuasion of trilobite expert Harry Blackmore Whittington, and a new quarry, the Raymond, was established about 20 metres higher up Fossil Ridge. Whittington, with the help of research students Derek Briggs and Simon Conway Morris of the University of Cambridge, began a thorough reassessment of the Burgess Shale, and revealed that the fauna represented were much more diverse and unusual than Walcott had recognized. Indeed, many of the animals present had bizarre anatomical features and only the slightest resemblance to other known animals. Examples include Opabinia, with five eyes and a snout like a vacuum cleaner hose and Hallucigenia, which was originally reconstructed upside down, walking on bilaterally symmetrical spines.