Sirius Passet is a Cambrian Lagerstätte located in Peary Land, Greenland. The site was named after the Sirius sledge patrol, which operates in North Greenland. It includes six locations in Nansen Land, on the east side of J.P. Koch Fjord in northern Greenland. The site was discovered in 1984 by A. Higgins of the Geological Survey of Greenland. An early report about Sirius Passet was published in 1987 by Simon Conway Morris and others. Expeditions led by J. S. Peel and Simon Conway Morris have visited the site multiple times from 1989 to the present. A collection of about 10,000 fossil specimens has been gathered there. Sirius Passet is part of the Buen Formation.
Age
The fauna is often compared to that of the Burgess Shale, even though it is likely 10 to 15 million years older—518 million years ago compared to 508 million years ago. It is also more similar in age to the fauna found in the Maotianshan shales from Chengjiang, which are dated to 518 million years ago.
Preservation
The preservation of the Sirius Passet fossils is usually thought to involve silicification, a process linked to a type of preservation called a "death mask," similar to how fossils from the Precambrian Ediacara biota are preserved. However, a 2022 study proposed that the original preservation method was phosphatisation, which later changed due to low-grade metamorphism. This process reached a peak temperature of about 409 ± 50 °C (768 ± 90 °F) during the Devonian Ellesmerian orogeny, causing widespread replacement of the original minerals in the fossils.
Geochemical analysis suggests that the organisms lived near the edge of an oxygen minimum zone, an area with very low oxygen levels. This indicates they may have been preserved during periods when oxygen was extremely scarce.
IUGS geological heritage site
Because of their importance in helping scientists understand the Cambrian Explosion, the Sirius Passet site was added by the International Union of Geological Sciences (IUGS) to its list of 100 "geological heritage sites" worldwide. This list was published in October 2022. The IUGS describes a "geological heritage site" as an important place with geological features or processes that are scientifically significant worldwide. These sites are used as references and have made important contributions to the development of geological science throughout history.
Fauna
Although scientists have not yet fully described the animal life, it is known to include a moderate number of arthropods and sponges, as well as rare members of other groups. The area has included the difficult-to-classify taxon Halkieria, and the Panarthropods Kerygmachela and Pambdelurion. These organisms have played important roles in discussions about the origins of modern animal groups.