What is the Burgess Shale?

The Burgess Shale Formation is a rocky mountain range in British Columbia in northwestern Canada. American paleontologist Charles Doolittle Walcott first discovered it in 1909. The local geology is black shale. There are thousands of fossils in the shale. These fossil groups are famous for preserving biological soft tissues. They are mainly distributed in Field in Yoho National Park. One of the districts. The age is about 505 million years, which is equivalent to the middle Cambrian period. The rock formation is about 161 meters thick and is one of the earliest soft tissue fossil groups.

Burgess Shale

It is speculated that the animals in the Burgess Shale used to live on the sea floor and nearby areas.

The fossil-rich deposits of the Burgess Shale are associated with the Stephen formation. This stratum is a series of small dark-colored calcareous mudstone layers, about 505 million years old; the bottom of the stratum is located at the bottom of a cliff about 160 meters high, which is far below the strong waves caused by the storm. This vertical cliff is composed of a calcareous coral reef of the Cathedral Formation that may have formed shortly before the Burgess Shale. The detailed formation mechanism of the stratum is still unclear, but the most widely accepted hypothesis is that after the coral reef edge and other parts of the coral formation separated, they fell and were transported up to a few kilometers away from the coral reef edge. The strata were separated about 509 million years ago. This may leave a steep cliff protected at the bottom, because the limestone of the Cathedral Formation is difficult to be compressed by decompression from the plate. This protective effect further explains why the Cathedral Formation is unable to preserve the fossils, because the vertical compression of the plate compression rock layer causes the rock to break, causing the fossil to be cut vertically. These specializations were discovered at the Walcott quarry because these areas were close to the Stephen Formation, and the quarry did excavate very close to the edge of the Cambrian cliffs.

The original idea was that the Burgess shale was deposited in an anoxic environment, but continued research has shown that oxygen is always present in the sediment [9]. It was previously thought that the hypoxic environment not only preserved freshly dead organisms to avoid decay, but also produced a chemical environment suitable for the preservation of biological soft tissues. In addition, cave creatures have decreased significantly. Caves and footprints created by animals contain soft tissues of animals, although they are found, but they are rare and generally extend to a limited extent [5].

Burgess shale was discovered in 1909 by paleontologist Charles Dulit Walcott at the end of the season's field investigation. He returned to the area with his sons in 1910 and established a quarry to dig the fossils on the side now known as Fossil Ridge. The excavated fossils are well preserved in biological soft tissues, and their species are quite extensive, so Walcott knew this was an important new discovery in paleontology. Until he was 74 in 1924, he excavated almost every year; A total of 65,000 species were found. The description of the fossils of the Burgess Shale is a rather heavy task, and Walcott worked on fossil research after his discovery until his death in 1927. The prevailing scientific point of view in the Walcott era was to try to classify fossils into all existing biota. It was not until 1962 that Alberto Simonetta re-investigated the fossils. This led scientists to recognize the information that Walcott found in the Burgess Shale, and made it clear that these ancient organisms could not be clearly classified into existing biota.

The re-excavation of fossils at the Walcott quarry was persuaded by trilobite expert Harry Blackmore Whittington to be carried out by the Geological Survey of Canada. A new quarry, built by Harvard's Percy Raymond in 1924, is about 20 meters above the fossil ridge. Wellington and two Cambridge graduate students Derek Briggs and Simon Conway Morris started a complete resurvey of Burgess shale, also revealing the evolutionary differentiation of the Burgess fauna Broader and more specific than Walcott's research results [5]. Indeed, many of the fossils in the Burgess Shale have surprising structural features and are similar to only a few other known organisms. For example, the Obabin sea scorpion has 5 eyes and a snout similar to a vacuum cleaner hose. Nectocaris not only has fins similar to crustaceans, but also has a spine and a shell that are together. The state is upside down from the correct state and is mistaken for walking with symmetrical spines on both sides.

After the Parks Canada and UNESCO confirmed the historical value of the Burgess Shale, policies that began in the mid-1970s made it difficult to collect fossils. Fossil collection continues at the Royal Ontario Museum. The museum's curator, Desmond Collins, an expert in invertebrate paleontology, has identified a number of new outcrops that are higher or lower in the formation than in the Walcott quarry. These places continue to discover new species faster than scientists can study them.

Stephen Gould's book, The Wonderful Life, was published in 1989 and brought Burgess shale to the attention of the general public. Gould believes that the sharp differentiation of fossils shows that the life forms at that time were more differentiated than now, and many unique descendants are an attempt to extinct evolution. Gould's research on Cambrian fauna relies heavily on the results of Simon Conway Morris's re-examination of Walcott's publications. But Morris strongly opposed Gould's conclusion that Morris believed that almost all Cambrian fauna could be classified under the door of modern life.

The Burgess Shale Formation is composed of segments in 10 strata, the most famous being the Walcott quarry shale segment, which contains a large-scale leaf foot layer

At present, there are many Lagerst & auml; tte formations close to the Burgess Shale in the world, and the Cambrian age group is more than other ages. This is because the activities of biological excavations in caves are limited in scope. Because this kind of bio-perturbation has become common throughout the Cambrian, the environment for preserving biological soft tissues has become scarce.