The Burgess Shale

What is the geological significance of the Burgess Shale:
• The Burgess Shale is famous for its fossils of soft-bodied organisms. It is exceptional to find complete animals preserved, especially ones that had only soft tissues and no mineralized structures. (Typically it is only the hard parts of organisms - shell or bone - that become fossils.)
• When this happens palaeontologists can gain a vast amount of ecological and biological information about a particular time in Earth's history. The Burgess Shale is such a site, providing the best window on animal communities during the end of the Cambrian Explosion.

When was it deposited:
• The story of the Burgess Shale begins more than 500 million years ago. Shortly before the Burgess Shale animals lived, there was an evolutionary “Big-Bang” called the Cambrian Explosion.
• These fossils are approximately 530 million years old, and represent an array of life-forms present during the early-middle years of the Cambrian period (545-495 million years ago).

What kind of organisms were fossilised:
Approximately 120 species are found in the Burgess Shale, including familiar forms as well as several species belonging to previously unknown phyla. Some of the fossilized species are members of groups (phylum) that still exist. These species can be categorized as members of the phyla Porifora (sponges), Annelida (segmented marine flatworms), Arthropoda (insects, crabs, and trilobites), and Echinodermata (sea urchins, sea fans, and sea lilies), and one species is the earliest representative of the phylum Chordata (which includes vertebrates). Most of these animals were scavengers, and a few were predators. Of these Burgess Shale animals, the aptly named Hallucigenia (phyla Annelida) is probably one of the most famous for its bizarre morphology. Seven pairs of stiltlike legs support its long, cylindrical body. It is hard to tell for certain which end is "head" and which end is "tail," but most scientists designate the head end by the bulbous projection that is prominent on one end of its body. • Algae
• Cyanobacteria
• Arthropoda
• Brachiopoda
• Chordata
• Cnidaria
• Ctenophora
• Echinodermata
• Hemichordata
• Mollusca
• Onychophora (Lobopoda)
• Porifera Why were the fossils so well preserved (what conditions)/what was the paleoenvironment:
At the time the sediments of the Burgess Shale were being deposited, western Canada lay near the equator and formed the northern continental margin of what would become North America. At the edge of the continental shelf, a massive algal reef developed into a near-vertical cliff of limestone several hundred meters high, called the Cathedral Escarpment. Periodically, ocean currents would generate underwater landslides, called turbidity flows, which would sweep up any animals in their paths and bury them along with the animals living in the deep water muds at the base of the cliff.
The hapless animals were completely buried in fine sand, silt, and mud. The turbulence forced fine-grained clay particles into every crack and crevice of the animals, outlining features rarely preserved in other fossils. Tightly packed in clay, the animals were protected from scavengers and from decomposition by bacteria. As a result, their complete forms along with details such as gut contents, appendage hairs, and antennae are often preserved, making these fossils extremely valuable to palaeontologists.