THE BURGESS SHALE LAGERSTATTEN AT THE WALCOTT QUARRY, YOHO NATIONAL PARK, CANADA

C.D. Walcott, head of the Smithsonian Institute, discovered the Walcott Quarry in 1909. The Smithsonian excavated from 1909-1924, and the quarry was subsequently expanded by Harvard (1924-1939), the Canadian Geological Survey (1966-67), and the Royal Ontario Museum (1975-2001). Approximately 250,000 fossils, including soft bodied forms, have been collected, making the Middle Cambrian Burgess Shale (508 Ma) a unique lagerstatten and an important representation of the Cambrian Explosion. The quarry is located on Fossil Ridge between Mounts Wapta and Field northeast of Field, British Columbia.

The fossils occur in the Stephen Formation at the base of the Cathedral Escarpment, a limestone reef prominent locally in the Canadian Rockies. The Walcott Quarry is composed of a thinly bedded sequence of shale, the depositional mechanism of which has led to debates about it's origin and whether the faunas are in situ or have been transported.

The diverse fossil assemblage represents the first well documented complete modern ecosystem. Walcott fit species into the classification system of the time, shoehorning them into existing groups, overlooking the abundance of unique body plans that dominate the assemblage. Modern understanding of Burgess Shale diversity began with Whittington's Cambridge research team re-examining Walcott's collections and realizing that many did not fit known classifications. These studies helped shape current understanding of early evolution of complex life on earth and the patterns of extinction and survival that would govern the next half billion years.

This Burgess Shale locality, while being the first Cambrian lagerstatten, sparked interest that resulted in others, both worldwide and locally. Globally significant sites include Chengjiang in China (520 Ma) and Sirius Passet in northern Greenland (520 Ma). Local sites include the slightly younger Marble Canyon deposit, potentially as diverse as the Walcott Quarry, but with a different faunal assemblage. These discoveries reveal that the Burgess Shale, while no longer unique, represents an invaluable look into a complex global Middle Cambrian ecosystem at a critical chapter in the evolution of life on earth.