The Henson Gletscher Formation of North Greenland yields moderately diverse trilobite faunas which bracket the Cambrian Series 2-Series 3 boundary interval. A number of the trilobite taxa permit correlation into other parts of Laurentia and to other Cambrian continents, thus enhancing correlation within this stratigraphical interval of the traditional Lower-Middle Cambrian boundary. In particular, the occurrence of Ovatoryctocara granulata and O. yaxiensis substantially improves the intercontinental recognition of the O. granulata level, a prime GSSP candidate. In contrast, the level with Oryctocephalus indicus cannot be located in a number of Cambrian continents with sufficient precision, making this level unsuitable for the definition of a GSSP for the base of the Cambrian Series 3 and Stage 5. Further support for the correlation potential of the base of the range of Ovatoryctocara granulata comes from recent carbon isotope studies that indicate a striking negative excursion in sections of South China (ROECE event) that probably coincides with similar excursions in Laurentia. Four new trilobite species are described: Zacanthopsis blakeri sp. nov., Protoryctocephalus arcticus sp. nov., Eoptychoparia pearylandica sp. nov. and Onchocephalus? freucheni sp. nov.

NOTE: This article was published in a former series of GEUS Bulletin. Please use the original series name when citing this article, for example: Ineson, J. R., & Peel, J. S. (1997). Cambrian shelf stratigraphy of North Greenland. Geology of Greenland Survey Bulletin, 173, 1-120. https://doi.org/10.34194/ggub.v173.5024 _______________ The Lower Palaeozoic Franklinian Basin is extensively exposed in northern Greenland and the Canadian Arctic Islands. For much of the early Palaeozoic, the basin consisted of a southern shelf, bordering the craton, and a northern deep-water trough; the boundary between the shelf and the trough shifted southwards with time. In North Greenland, the evolution of the shelf during the Cambrian is recorded by the Skagen Group, the Portfjeld and Buen Formations and the Brønlund Fjord, Tavsens Iskappe and Ryder Gletscher Groups; the lithostratigraphy of these last three groups forms the main focus of this paper. The Skagen Group, a mixed carbonate-siliciclastic shelf succession of earliest Cambrian age was deposited prior to the development of a deep-water trough. The succeeding Portfjeld Formation represents an extensive shallow-water carbonate platform that covered much of the shelf; marked differentiation of the shelf and trough occurred at this time. Following exposure and karstification of this platform, the shelf was progressively transgressed and the siliciclastics of the Buen Formation were deposited. From the late Early Cambrian to the Early Ordovician, the shelf showed a terraced profile, with a flat-topped shallow-water carbonate platform in the south passing northwards via a carbonate slope apron into a deeper-water outer shelf region. The evolution of this platform and outer shelf system is recorded by the Brønlund Fjord, Tavsens Iskappe and Ryder Gletscher Groups. The dolomites, limestones and subordinate siliciclastics of the Brønlund Fjord and Tavsens Iskappe Groups represent platform margin to deep outer shelf environments. These groups are recognised in three discrete outcrop belts - the southern, northern and eastern outcrop belts. In the southern outcrop belt, from Warming Land to south-east Peary Land, the Brønlund Fjord Group (Lower-Middle Cambrian) is subdivided into eight formations while the Tavsens Iskappe Group (Middle Cambrian - lowermost Ordovician) comprises six formations. In the northern outcrop belt, from northern Nyeboe Land to north-west Peary Land, the Brønlund Fjord Group consists of two formations both defined in the southern outcrop belt, whereas a single formation makes up the Tavsens Iskappe Group. In the eastern outcrop area, a highly faulted terrane in north-east Peary Land, a dolomite-sandstone succession is referred to two formations of the Brønlund Fjord Group. The Ryder Gletscher Group is a thick succession of shallow-water, platform interior carbonates and siliciclastics that extends throughout North Greenland and ranges in age from latest Early Cambrian to Middle Ordovician. The Cambrian portion of this group between Warming Land and south-west Peary Land is formally subdivided into four formations.The Lower Palaeozoic Franklinian Basin is extensively exposed in northern Greenland and the Canadian Arctic Islands. For much of the early Palaeozoic, the basin consisted of a southern shelf, bordering the craton, and a northern deep-water trough; the boundary between the shelf and the trough shifted southwards with time. In North Greenland, the evolution of the shelf during the Cambrian is recorded by the Skagen Group, the Portfjeld and Buen Formations and the Brønlund Fjord, Tavsens Iskappe and Ryder Gletscher Groups; the lithostratigraphy of these last three groups forms the main focus of this paper. The Skagen Group, a mixed carbonate-siliciclastic shelf succession of earliest Cambrian age was deposited prior to the development of a deep-water trough. The succeeding Portfjeld Formation represents an extensive shallow-water carbonate platform that covered much of the shelf; marked differentiation of the shelf and trough occurred at this time. Following exposure and karstification of this platform, the shelf was progressively transgressed and the siliciclastics of the Buen Formation were deposited. From the late Early Cambrian to the Early Ordovician, the shelf showed a terraced profile, with a flat-topped shallow-water carbonate platform in the south passing northwards via a carbonate slope apron into a deeper-water outer shelf region. The evolution of this platform and outer shelf system is recorded by the Brønlund Fjord, Tavsens Iskappe and Ryder Gletscher Groups. The dolomites, limestones and subordinate siliciclastics of the Brønlund Fjord and Tavsens Iskappe Groups represent platform margin to deep outer shelf environments. These groups are recognised in three discrete outcrop belts - the southern, northern and eastern outcrop belts. In the southern outcrop belt, from Warming Land to south-east Peary Land, the Brønlund Fjord Group (Lower-Middle Cambrian) is subdivided into eight formations while the Tavsens Iskappe Group (Middle Cambrian - lowermost Ordovician) comprises six formations. In the northern outcrop belt, from northern Nyeboe Land to north-west Peary Land, the Brønlund Fjord Group consists of two formations both defined in the southern outcrop belt, whereas a single formation makes up the Tavsens Iskappe Group. In the eastern outcrop area, a highly faulted terrane in north-east Peary Land, a dolomite-sandstone succession is referred to two formations of the Brønlund Fjord Group. The Ryder Gletscher Group is a thick succession of shallow-water, platform interior carbonates and siliciclastics that extends throughout North Greenland and ranges in age from latest Early Cambrian to Middle Ordovician. The Cambrian portion of this group between Warming Land and south-west Peary Land is formally subdivided into four formations.

BackgroundExceptionally preserved Palaeozoic faunas have yielded a plethora of trilobite-like arthropods, often referred to as lamellipedians. Among these, Artiopoda is supposed to contain taxa united by a distinctive appendage structure. This includes several well supported groups, Helmetiida, Nektaspida, and Trilobita, as well as a number of problematic taxa. Interrelationships remain unclear, and the position of the lamellipedian arthropods as a whole also remains the subject of debate.ResultsArthroaspis bergstroemi n. gen. n. sp., a new arthropod from the early Cambrian Sirius Passet Lagerstätte of North Greenland shows a striking combination of both dorsal and ventral characters of Helmetiida, Nektaspida, and Trilobita. Cladistic analysis with a broad taxon sampling of predominantly early Palaeozoic arthropods yields a monophyletic Lamellipedia as sister taxon to the Crustacea or Tetraconata. Artiopoda is resolved as paraphyletic, giving rise to the Marrellomorpha. Within Lamellipedia, a clade of pygidium bearing taxa is resolved that can be shown to have a broadly helmetiid-like tergite morphology in its ground pattern. This morphology is plesiomorphically retained in Helmetiida and in Arthroaspis, which falls basally into a clade containing Trilobita. The trilobite appendages, though similar to those of other lamellipedians in gross morphology, have a unique outward rotation of the anterior trunk appendages, resulting in a ‘hard wired’ lateral splay, different to that observed in other Lamellipedia.ConclusionsThe combination of helmetiid, trilobite, and nektaspid characters in Arthroaspis gives important hints concerning character polarisation within the trilobite-like arthropods. The distinctive tergite morphology of trilobites, with its sophisticated articulating devices, is derived from flanged edge-to-edge articulating tergites forming a shield similar to the helmetiids, previously considered autapomorphic for that group. The stereotypical lateral splay of the appendages of lamellipedians is a homoplastic character shown to be achieved by several groups independently.

The Early Cambrian Sirius Passet Lagerstätte of North Greenland occurs in marine mudstones (Buen Formation) deposited in a slope environment along the eroded scarp of a pre-existing carbonate platform. The shallow-water platform is represented by dolostones of the Portfjeld Formation (Neoproterozoic – earliest Cambrian), which record a belt of tide-swept subtidal ooid shoals and microbial patch reefs at the outer edge of the platform. Solution features and meteoric cements attest to exposure of the platform, accompanied by fracturing, mass wastage and erosional retreat of the escarpment producing slope talus, and extensive debris sheets and olistoliths in basinal deposits. The marine mud-dominated siliciclastics of the Buen Formation, deposited in slope and shelf environments, record the transgression and onlap of the degraded platform in the Early Cambrian. The Sirius Passet Lagerstätte has yielded an arthropod-dominated fossil assemblage of over 40 species, many showing exceptional preservation of soft tissues; the finely laminated mudstones hosting this fauna accumulated from suspension in a poorly oxygenated slope sub-environment, such as an erosional embayment or abandoned slope gully. Although taphonomic features suggest that the fauna is mainly parautochthonous, some components (e.g., sponges, worms, the halkieriids and certain sightless arthropods) may be truly autochthonous. Comparison of the Sirius Passet locality with the renowned Middle Cambrian Burgess Shale of western Canada reveals similarities in overall depositional and tectonic setting: both accumulated in deep water adjacent to the steep, eroded margins of carbonate platforms — settings that subsequently sheltered the faunas from tectonic and metamorphic obliteration.

The diverse metazoan fauna from the upper member of the Buen Formation of North Greenland is described as a complement to published descriptions of the exceptionally preserved fauna of the Sirius Passet Lagerstätte which occurs in the lowest beds of the formation. Considered together with organic‐walled microfossils, which are absent from the Sirius Passet Lagerstätte on account of regional metamorphism, the fauna from the upper member provides an extended picture of the Buen Formation biota (Cambrian, Series 2, Stages 3–4; Montezuman–Dyeran of Laurentian usage). Although dominated numerically by specimens of the olenelline trilobites Limniphacos and Mesolenellus, the oldest assemblages (Montezuma–Dyeran boundary) from the upper member of the Buen Formation are characterized by a high diversity of hyoliths which often occur as partial associations of conch, operculum and helens in the dark mudstones; hyoliths are rare in the Sirius Passet Lagerstätte. Sponges are rare in the upper Buen Formation but diverse at Sirius Passet. Unlike the Sirius Passet Lagerstätte, fossil remains of non‐mineralized metazoans with limbs and other details of internal anatomy do not occur in the upper Buen Formation, although organic tubes assigned to a new selkirkiid stem group priapulid (Sullulika) are common. New taxa: Alutella siku sp. nov., Sullulika broenlundi gen. et sp. nov., Nevadotheca boerglumensis sp. nov., Kalaallitia myliuserichseni gen. et sp. nov., Nasaaraqia hyptiotheciformis gen. et sp. nov., Trapezovitus malinkyi sp. nov., Decoritheca? hageni sp. nov.

The marine offshore shelf mudstones of the Early Cambrian Buen Formation at Sirius Passet, North Greenland, contain a rich Konservat-Lagerstätte which includes abundant well-preserved material of the bivalved arthropod Isoxys volucris new species. The new material confirms Isoxys Walcott, 1890 as a component of the earliest arthropod faunas worldwide. Isoxys species are known from the Early Cambrian of Spain, Siberia, South Australia and Southwest China and also from the Early to Middle Cambrian of Laurentian North America. Isoxys occurs in the Redlichiid, Bigotinid and Olenellid trilobite faunal realms but is restricted to within tropical/subtropical regions, attesting to possible paleolatitudinal controls on its distribution. Isoxys resembles some phyllocarid and bradoriid arthropods but without knowledge of its soft-parts the affinity of the genus remains uncertain.

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