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.

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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.

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