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.

Abstract In carbonate sequence stratigraphy, carbonate megabreccias have acquired particular significance, being deemed characteristic of the lowstand systems tract (LST) or the forced regressive systems tract (FRST). Large-scale mass-wastage can, however, result from factors other than sea-level change and it is rare that the sequence stratigraphic significance of megabreccias can be rigorously tested. In the Cambrian of North Greenland, erection of a robust sequence stratigraphic framework is facilitated by extensive fjord-wall exposures of the platform to deep shelf transect and by a well-developed carbonate-silici-clastic reciprocal sedimentation pattern within off-platform strata. On the basis of this independent framework, megabreccias are represented locally within the LST and the highstand systems tract (HST), but occur systematically above the HST. These HST-capping megabreccias are composite sheets tens of metres thick that extend up to 50 km distally and flank the platform for up to 400 km along strike. They comprise debris derived from the highstand platform margin and slope and are directly overlain by mixed carbonate-siliciclastic sediments of the succeeding LST. The HST-capping megabreccias are assigned to the FRST; they record extensive failure of the platform margin and upper slope during relative fall of sea-level and prior to the onset of lowstand sedimentation. Although the LST megabreccias are compositionally distinctive, the sole example of an intra-HST megabreccia differs from those of the FRST only in terms of areal extent. In the absence of an independent framework, therefore, the sequence stratigraphic affinities of megabreccias may be ambiguous.

Abstract The northeastern margin of Laurentia formed an important part of the Iapetus Ocean and includes the development of the Franklinian Basin in North Greenland and Arctic Canada. The uninterrupted continental margin bordering the North American craton is represented by well-exposed successions in Northeast and eastern North Greenland, together with Svalbard and Bjørnøya. Physiographically, the northeastern margin of Laurentia during the early Paleozoic history of Greenland was a northward extension of the passive rifted continental margin of the Caledonian continental edge of Laurentia. It was a transform-rifted margin and represents the part of the Laurentian margin that borders the Arctic part of the North Atlantic Ocean. Geologically, the northwestern segment of the continental margin has a somewhat different setting and development from farther south in the Northeast Greenland–Svalbard segment but both regions overlie a thick and extensive package of Neoproterozoic rocks and were affected by the Caledonian orogeny.

The East Greenland Caledonides, which make up an ∼1300-km-long stretch of North-East Greenland, were formed by the collision of Laurentia and Baltica in mid-Silurian time. Geological mapping and research in this remote and poorly accessible segment of the circum-Atlantic Caledonide orogen began in connection with geographical exploration voyages in the early part of the nineteenth century. The first regional geological mapping took place during the long series of “The Danish Expeditions to North-East Greenland” between 1926 and 1958. Modern geological research and regional mapping by the Geological Survey of Denmark and Greenland between 1968 and 1998 have resulted in the publication of a series of 1:500,000 geological maps of the orogen, and an overview geological map at 1:1,000,000 scale, which accompanies this volume. This article reviews the history of geological research and the evolution of interpretations of the orogen. The recent systematic studies by the Geological Survey of Denmark and Greenland supplement and build on the considerable existing published literature and demonstrate that the North-East Greenland segment of the Caledonide orogen consists of a westward-propagating thrust sheet pile, with displacements estimated at 300–500 km. The thrust sheets incorporate major segments of reworked Laurentian gneiss basement, and a thick succession of Neoproterozoic to Ordovician sediments that accumulated in a major basin originally located outboard of the present coastline.

A geological map of the Caledonian orogen in East Greenland at the scale of 1:1,000,000 accompanies this volume. The map sheet is a compilation of lithostructural data, and it includes cross sections and inset synoptic tectonic maps with profiles. The ∼1300 km length of the N-S–trending Caledonian orogen in East Greenland is divided into three lithostructural domains—the Caledonian foreland, which is partly exposed in the west, a western marginal thrust belt with foreland windows exposed in anticlinal culminations, and an eastern thick-skinned thrust belt that incorporates major segments of reworked Laurentian gneiss basement in major thrust sheets. Caledonian migmatites and granite intrusions are widespread in the southern part of the orogen. Transport directions of the major thrusts are to the west-northwest, and restoration indicates total displacements on the order of 200–400 km, with estimated shortening of 40%–60%. Archean and Paleoproterozoic gneiss complexes, reworked during Caledonian orogenesis, are widespread. In the south, they are overlain by late Mesoproterozoic metasedimentary rocks. Overlying Neoproterozoic and Lower Paleozoic sediments laid down at the margin of Iapetus reach ∼20 km in thickness. In the north, the Paleoproterozoic basement gneisses are overlain by late Paleoproterozoic to early Mesoproterozoic quartzites interbedded with basaltic rocks and cut by doleritic dikes and sills. Overlying Neoproterozoic and Lower Paleozoic sedimentary rocks relate to developments on the south side of the Franklinian Basin, which extends across North Greenland and into Arctic Canada.

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.