SIRIUS PASSET - NEW DATA FROM AN EXCEPTIONAL FOSSIL LAGERSTÄTTE (Invited Presentation)

Sirius Passet is an Early Cambrian fossil Lagerstätte, discovered in North Greenland in 1984. Expeditions in 1989-1994 recovered several thousand fossils from the tallus slopes, which included several important groups, which have changed our understanding of evolution and the nature of the Cambrian Explosion. More recent expeditions in 2009, 2011 and 2016 have focused on collections from the outcrop and detailed catalogues of where fossils occur, coupled with sedimentology and geochemistry. Here I will present results from our recent expeditions, including new fossil groups and novel data that elucidate the taphonomy and paleo-ecology of the site. We show that preservation is uniquely exceptional in that both intestines and muscle tissue routinely preserve in a number of taxa, reflective films preserve both as carbonaceous impressions and clay mineral templates, which is most likely metamorphic in origin. Microbial mats are frequent in Sirius Passet, which is likely responsible for the early mineralisation through phosphatisation. Preservation quality and taxon abundance varies between beds. More importantly, the exploration of fresh rock surface rather than the tallus have revealed a plethora of new taxa with little relief, but that are identified by their preservation as reflective films. These include polychaetes, priapulids, lobopods, nectocaridids among others. While the diversity of Sirius Passet is much smaller than the Burgess Shale and the Chengjiang Biota, the frequency of fossils on slabs are unique and new taxa occur frequently, which likely will bring the diversity closer to these other sites with time. Hence, considering the limited exploration of the Sirius Passet and the recognition that the preservation is better than hitherto appreciated sets it apart as a unique Lagerstätte with many grave secrets remaining to be told.