Sirius Passet

Sirius Passet is a Cambrian Lagerstätte in Peary Land, Greenland. The Sirius Passet Lagerstätte was named after the Sirius sledge patrol that operates in North Greenland. It comprises six places in Nansen Land, on the east shore of J.P. Koch Fjord in the far north of Greenland.^[1] It was discovered in 1984 by A. Higgins of the Geological Survey of Greenland. A preliminary account was published by Simon Conway Morris and others in 1987 and expeditions led by J. S. Peel and Conway Morris have returned to the site several times between 1989 and the present. A field collection of perhaps 10,000 fossil specimens has been amassed. It is a part of the Buen Formation.

Sirius Passet
Stratigraphic range: Cambrian Series 2 ~523–518 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
Halkieria evangelista, an iconic fossil of the Sirius Passet
Type	Geological formation
Lithology
Primary	Mudstone
Location
Coordinates	82°47.6′N 42°13.7′W
Region	Northern Greenland
Country	Greenland
Type section
Named for	Sirius sledge patrol
Named by	A. Higgins
Location	J.P. Koch Fjord
Year defined	1987
Coordinates	82°47.6′N 42°13.7′W
Country	Greenland
Geologic Map with the Buen and the Portfjeld formations, and the Polkorridoren Group.

Age

Location of Sirius Passet during the early Cambrian

The fauna is inevitably compared to that of the Burgess Shale, although it is probably ten to fifteen million years older – 518 million years ago vs. 508 million years ago^[2]) – and more closely contemporaneous with the fauna of the Maotianshan shales from Chengjiang, which are dated to 518 million years ago.

Preservation

The preservation of the Sirius Passet is traditionally considered to represent silicification associated with a death mask,^[3] recalling the 'Ediacara-type' preservation of the Precambrian Ediacara biota.^[4] A 2022 study suggested that the original preservation mode was phosphatisation that was later altered by low-grade metamorphism with a peak temperature of 409 ± 50 °C (768 ± 90 °F) during the Devonian Ellesmerian orogeny, which resulted in widespread mineral replacement.^[5]

Geochemical analysis indicates that the fossils lived close to the boundary of an oxygen minimum zone, possibly being preserved in oxygen-starved periods.^[6]

IUGS geological heritage site

In respect of the importance of the exceptionally preserved fossils in our understanding of the event, the 'Cambrian Explosion in Sirius Passet' was included by the International Union of Geological Sciences (IUGS) in its assemblage of 100 'geological heritage sites' around the world in a listing published in October 2022. The organisation defines an 'IUGS Geological Heritage Site' as 'a key place with geological elements and/or processes of international scientific relevance, used as a reference, and/or with a substantial contribution to the development of geological sciences through history.'^[7]

Fauna

Although the fauna has not yet been fully described, it is known to consist of a moderate number of arthropods and sponges, and rare representatives of other groups. It has yielded the problematic taxon Halkieria, and the Panarthropods Kerygmachela and Pambdelurion, all of which have played prominent roles in discussions about the origins of the modern animal phyla.

Taxa from the Sirius Passet fauna

After^[8]

Arthropods

Arthropods
Genus	Species	Notes	Images
Aaveqaspis[9]	A. inesoni	An arthropod of uncertain affinitiies
Arthroaspis	A. bergstroemi	A member of Artiopoda
Buenaspis	B. forteyi	A nektaspid artiopod
Buenellus	B. higginsi	A trilobite
Campanamuta	C. mantoni	An artiopod
Kleptothule	K. rasmusseni	A trilobite
Molaria	M. steini	An artiopod
Sidneyia?	Indeterminate	A vicissicaudatan artiopod, later authors have stated that the assignment to the genus is equivocal.[10]	Life restoration of Sidneyia inexpectans from the Burgess Shale to which the Sirius Passet form has been considered closely related
Thulaspis	T. tholops	A basal artiopodan closely related to Squamacula.
Siriocaris	S. trollae	A possible member of Lamellipedia
Isoxys	I. volucris, I. sp	A bivalved, freely swimming arthropod
Kiisortoqia	K. soperi	A basal arthropod with large frontal appendages
Kerygmachela	K. kierkegaardi	A "gilled lobopodian" closely related to arthropods
Pambdelurion	P. whittingtoni	A "gilled lobopodian" closely related to arthropods
Tamisiocaris	T. borealis	A filter feeding radiodont
Amplectobeluidae[11]	Indeterminate	Predatory radiodont
Pauloterminus	P. spinodorsalis	A shrimp-like arthropod, possibly a member of Hymenocarina

Other animals

Non-arthropod animals
Genus	Species	Notes	Images
Ooedigera[12]	O. peeli	A vetulicolian, another indeterminate vetulicolian is also present
Chordata[11]	Indeterminate	Vertebrate-like chordate
Hadranax	H. augustus	A lobopodian
Halkieria	H. evangelista	A basal mollusc
Xystoscolex	X. boreogyrus	A palaeoscolecid worm
Chalazoscolex	C. pharkus	A palaeoscolecid worm
Timorebestia[11]	T. koprii	A giant stem-group chaetognath
Chaetognatha[11]	Indeterminate	Small-sized form
Pygocirrus	P. butyricampum	An annelid worm
Phragmochaeta[13]	P. canicularis	A polychaete worm
Singuuriqia	S. simony	A priapulid worm
Sirilorica	S. carlsbergi, S. pustulosa	a stem-group Loricifera or a scalidophoran
Hyolithus	H. cf. tenuis	A hyolith
Trapezovitus	Indeterminate
Orthothecida
Hyolithida
Archaeocyatha	Indeterminate	A sponge
Choia	C. cf. carteri	A sponge
Constellatispongia	C. canismajorii	A sponge
Crassicoactum	C. cucumis	A sponge
Demospongiae	Indeterminate	A sponge
Fieldospongia	F. bellineata	A sponge
Hamptonia	H. limatula	A sponge
Lenica	L. cf. unica L. hindei, L. perverse	A sponge
Saetaspongia	S. cf. densa S. procera	A sponge
Salactiniella	S. cf. plumata	A sponge
Stephanella?	Indeterminate	A sponge

See also

• Matground