Abstract Five stratigraphic successions are recognized in the Sauk megasequence in the Canadian Arctic Islands. The Lower Cambrian succession was deposited on a distally steepened carbonate ramp that overlaid thick Lower Cambrian siliciclastics. The second Middle Cambrian succession is composed of oolitic grainstone, microbial boundstone, lime mudstone, and mixed carbonate-siliciclastic facies assemblages that developed on a platform. The second and third successions are separated by an unconformity that spanned most of the Steptoean. The third succession includes mixed carbonate-siliciclastic strata and spans the Sunwaptan Prosaukia Biozone to the Cordylodus proavus Biozone. This succession was terminated by the Cambrian–Ordovician unconformity. The shelf had a ramplike configuration during this time. The fourth succession starts above the Cambrian-Ordovician unconformity with a widespread shelf sandstone that spans the C. proavus to C. lindstromi Zones. This was followed by a rapid deepening in the earliest Ordovician (Iopetognathus fluctivagus Zone) marked by the deposition of open-marine carbonates. A progressive shallowing culminated in evaporite units in the Stairsian. A marked change in basin architecture occured during this fourth succession. Distinctive shelf-margin units appeared consisting of fenestral mudstone, shoal deposits, and common karst breccias. The shelf margin during this interval was very steep, and carbonate was not transported into the deep water. The platform also changed configuration during this time, with the development of an intraplat-formal basin. Evaporites accumulated in this silled basin. Strata in the intraplatformal basin are thicker than those at the shelf margin. The fifth succession (Tulean–Blackhillsian) consists of shallow subtidal carbonates. The first two sequences in the Arctic Islands correspond closely to Sauk I and II elsewhere in Laurentia. Strata in the Arctic that are equivalent to the standard Sauk III supersequence contain three unconformity-bounded stratigraphic assemblages. This reflects local tectonic conditions that resulted from the change from a passive-margin setting in the Early Cambrian– earliest Ordovician to convergence later in the Early Ordovician. The downgoing slab, interpreted to be dipping below Laurentia, affected carbonate sedimentation along northwestern Laurentia during this time.

Abstract Ordovician strata in Greenland are extensively exposed in North Greenland and northern East Greenland; additional small traces (loose blocks) are recorded from the craton of West Greenland. The western North Greenland succession is nearly identical to that of the Franklinian Basin exposed on Ellesmere Island, Arctic Canada; the eastern North Greenland represents the (present) northeastern corner of Laurentia and provides the connection to the East Greenland Caledonian platform. The northern East Greenland succession is the natural northern extension of the Caledonian platform of northern Europe and the Appalachian platform of eastern North America. During the Ordovician Greenland occupied a palaeogeographical subtropical to tropical position with a faunal assemblage typical of Laurentia. A prominent faunal peak of diversification occurred in the Late Ordovician. The stratigraphical succession of Greenland is summarized and age relationships are discussed with reference to the fossil faunas and breaks in the successions and correlation between the locations and regions are provided.

The Iapetus margin of Laurentia is preserved, with varying degrees of deformation, along a belt that extends for 1300 km along the eastern coast of Greenland, from Scoresby Sund in the south to Kronprins Christian Land at the northernmost extent of the Caledonian–Appalachian orogen. Along the length of the Greenland Caledonides, deformation is restricted to a single orogenic phase, the Scandian, at around 425 Ma, which represents the continent-continent collision of Laurentia and Baltica. The Lower Paleozoic stratigraphy can be closely correlated with the palinspastically contiguous terranes of NE Spitsbergen, Bjørnøya, and NW Scotland, and, farther to the south, that of western Newfoundland. In Greenland itself, Lower Paleozoic sediments are present in the foreland, parautochthon, and the highest allochthonous sheet of the orogen, the Franz Joseph allochthon. In the Franklinian Basin of eastern North Greenland, unconformity-bounded Lower Cambrian sediments can be correlated with the Sauk I sequence of cratonic North America. These Cambrian sediments are separated from younger units by a significant hiatus, the sub–Wandel Valley unconformity, but above that surface, the succession extends without major breaks from the major flooding event at the base of Sauk IV (Early Ordovician) through to the early Wenlock. The carbonate platform in this region foundered from late Llandovery time onward due to loading by thrust sheets, and turbidite deposition replaced platform carbonate deposition. Caledonian thrusts truncate the youngest preserved sediments, which are of early Wenlock age. The punctuated, attenuated stratigraphy seen in Kronprins Christian Land continues southward along the length of the parautochthon, through Lambert Land, Nørreland, and Dronning Louise Land, to a series of tectonic windows in the southern part of the Greenland Caledonides. In contrast to the stratigraphy seen in the parautochthon, the Franz Joseph allochthon contains one of the thickest Cambrian–Middle Ordovician successions in Laurentia, including a complete succession from Sauk I to Tippecanoe II.