Australia: The Land Where Time Began

A biography of the Australian continent 

The Burgess Shale - Middle Cambrian, 505 Ma

The animals comprising the Burgess Shale lived about 505 million years ago on and around Cathedral Escarpment, several hundred metres high, an algal reef in a warm, shallow sea at the edge of the then Laurentia, an ancient land mass centred on Hudson Bay. In such places periodic mud slides occur. These slides tend to bury creatures living on and near the sides of the escarpment and surrounding sea floor, carrying them to the base of the slope where they are entombed in the mud. The Burgess Shale fauna were deposited in a deep water basin near the base of the escarpment. The accumulation of these recurrent mud slides formed what became, after millions of years the Burgess Shale. During the Cambrian, Canada was situated just south of the equator.

175 million years ago mountain building and and seismic activity moved them to their present position on a mountain ridge, Burgess Pass, in the Yoho National Park, Canadian Rocky Mountains, British Columbia, where they were exposed by erosion

The fossil deposits are in shale deposits, part of the Stephen Formation, located in 2 quarries between Mt Wapta and Mt. Field. Walcott's Quarry is the upper one, containing the Phyllopod Bed. The lower is Raymond's Quarry, after Prof Piercy Raymond, who opened the quarry in 1924.

These shale deposits contain animals that originated in the Cambrian Explosion between about 545 and 525 million years ago. At this point in time life was confined to the oceans and rivers, it had still to make a move to dry land.

Unlike the usual mechanism of fossilisation, where a dead organism is gradually buried by sediment, the animals of this formation were buried instantly by mud slides, resulting in the organisms tumbling to the bottom of the slope so they ended up in random orientations, as opposed to being horizontal as they would be if buried while lying on the sea floor. An unusual feature of the Burgess Shale is that the organisms apparently died instantly. Dying invertebrates tend to curl up. These animals were still uncurled, as in life. Also, there is also no sign of them trying to burrow out of the encasing mud. This has led to the enhanced level of preservation found in the deposits, they were buried before they could begin to decay and disintegrate. As a result, the fossils often exhibit great detail.

The Burgess shale is an example of a taphonomic window, a snapshot of the life in a particular place at an instant in time.

The  Emu Bay Lower Cambrian shale, on Kangaroo Island, South Australia, dates to about 520 million years old, between the slightly older Chengjiang deposits of southern China and the slightly younger Burgess Shale. It differs from other Burgess Shale-type biotas in that it is believed to result from relatively shallow water deposition, as opposed to the deeper water deposition of the other known biotas of this type. Emu Bay remains are notable as the oldest known phosphatised muscle tissue and the first so far reported from the Cambrian. This mineralisation is rarely found  in other Burgess-Shale depomineralisation sites. 

The Burgess Shale features in the David Attenborough documentary First Life.

  1. The Burges Shale
  2. Discover the Burgess Shale
  3. A Burgess Shale Fossil Sampler
  4. Primitive soft-bodied cephalopods from the Cambrian

Sources & Further reading 

  1. Mary E. White, 1993, The Nature of Hidden Worlds: Animals and plants in prehistoric Australia and New Zealand, Reed
  2. Mikhail A. Fedonkin, James G. Gehling, Kathleen Grey, Guy M. Narbonne, Patricia Vickers-Rich, The Rise of Animals, Evolution and Diversification of the Kingdom Animalia, Johns Hopkins University Press, Baltimore, 2007
  3. The Emu Bay Shale biota, Kangaroo Island: Australia's unique window into the Cambrian world
Author: M. H. Monroe
Last Updated 05/11/2008


Emu Bay Shale

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