The Sirius Passet Lagerstätte (Early Cambrian) of North Greenland  

The Sirius Passet biota is the oldest major Cambrian lagerstätte in Laurentia.  The occurrence of the trilobite Buenellus places it in the Nevadella Zone (Montezuman Stage of the Waucoban Series) of the North American standard, equivalent to series 2, stage 3 of the developing chronostratigraphic scale for the Cambrian.  The locality on the northern coast of Greenland (82°47.6' N, 42°13.7' W) preserves an assemblage of about 40 species, dominated by weakly sclerotized arthropods, including Buenaspis, Kleptothule, Pauliterminus and Isoxys; the lobopodians Kerygmachela, Pambdelurion and Hadranax; and a number of species under publication or awaiting description.  Worms include the annelid Phragmochaeta and palaeoscolecidans.  Buenellus, Halkieria evangelista and rare hyolithids and archeocyathids are the only calcareous forms.  With the exception of large Choia, the sponge fauna is undescribed; brachiopods are rare. 

Fine details of soft tissues, such as mineralized digestive glands and muscle fibres; gut traces; and limbs, are often visible. Their preservation is variable within specimens, and within and between taxa, reflecting the different life styles and taphonomic histories of the various faunal elements. 

The Sirius Passet locality lies at the transition between the southern shelf and the northern deep water trough of the trans-arctic Franklinian Basin.  The depositional setting of the lagerstätte is reminiscent of the younger Burgess Shale: the fossiliferous, fine-grained, siliciclastic sediments of the Buen Formation accumulated in close proximity to the degraded, abrupt scarp of an extensive aggradational carbonate platform (the Portfjeld Formation). Following exposure and karstification, with shedding of extensive sheets of debris and olistoliths into the trough, the carbonate platform was transgressed in the early Cambrian, with the fine-grained Sirius Passet sediments accumulating in an oxygen-deficient, sheltered pocket in the upper slope coarse-sediment bypass zone.  As the basin expanded, continued subsidence and accompanying eustatic sea-level rise caused the siliciclastic Buen Formation to drape the platform. 

The northern deep water trough of the Franklinian Basin forms the locus of Ellesmerian deformation with the Sirius Passet locality lying within a zone of southerly directed thrusts and folds; as suggested for the Burgess Shale, proximity to the carbonate platform probably shielded the Sirius Passet lagerstätte from pervasive deformation.  Chloritoid porphyroblasts indicate temperatures in excess of 300 ˚C.