North Greenland Fold Belt Research Articles

Svalbard: a fragment of the Laurentian margin

Abstract The last decade of structural and isotope-age dating studies in Svalbard and East Greenland has provided strong support for the close correlation of these segments of the Caledonide Orogen, as had previously been inferred from stratigraphic evidence. Prior to Tertiary opening of the Norweigan-Greenland Sea, Svalbard’s Caledonian terranes were an essential part of the Laurentian margin, as witnessed not only by the Early Palaeozoic depositional environments and fauna, but also by the character of the Palaeoproterozoic basement, the Meso- to Neoproterozoic cover, the evidence of late Grenvillian tectono-thermal activity, Caledonian structural style and timing of movements, Caledonian granitic magmatism and Old Red Sandstone (ORS) deposition. Recently published maps of East Greenland show the hinterland allochthons of central East Greenland to strike out obliquely into the continental shelf. The hypothesis promoted here requires that they continue offshore northwards, extending to the northern edge of the NE Greenland shelf and that most of the Svalbard terranes were northerly continuations of the East Greenland Caledonides. Only along the west coast of central Spitsbergen are ‘foreign’ terranes exposed that have affinity with Pearya, having been located north of the North Greenland foldbelt, apparently unrelated to Laurentia, prior to Ellesmerian Orogeny. The unambiguous affinity of the Svalbardian and Greenlandian (Laurentian) Caledonides contrasts markedly with the Timanide evolution of northeastern Baltica. It confirms previous interpretations that an important Caledonian suture-zone transgresses northeast-wards across the Barents Sea, separating Laurentian domains in the NW from the Timanides of Baltica in the SE. The Timanides of northeastern Europe are truncated by, and terminate in the Barentsian Caledonides of the Barents Shelf.

The Citronen Fjord massive sulphide deposit, Peary Land, North Greenland: discovery, stratigraphy, mineralization and structural setting

The Citronen Fjord massive sulphide deposit in the Lower Palaeozoic of North Greenland is the world's most northerly base metal mineralization. Since discovery in 1993, it has been intensively investigated by geological and geophysical surveys, and by drilling. The deposit is generally flat lying with a thickness up to 50 m; it extends from outcrop level to depths of 300 m.
 Three main stratiform sulphide sheets occur within a 200 m thick stratigraphic sequence; these are composed of massive and bedded pyrite with variable amounts of sphalerite and minor galena. The proven mineralization is continuous over a strike length of at least 3 km with a maximum width of 500 m; an additional 5 km of mineralization along the same trend is suggested by geological mapping and gravity surveys. The total tonnage of sulphides is estimated to exceed 350 million tons. The overall base metal resource is estimated at 20 million tons of 7 per cent zinc, with a higher grade core of 7 million tons containing 9 per cent zinc and 1 per cent lead.
 The Citronen Fjord deposit is located at the eastern end of the Palaeozoic Franklinian Basin that extends through the Arctic Islands of Canada and across northern Greenland. Its discovery is an example of a successful exploration strategy based on regional evaluation, sparse but telltale surface mineralization observations and low-cost logistics: a skidoo-sledge expedition. The stratiform mineralization is hosted in the dark argillaceous rocks of the Amundsen Land Group of latest Ordovician to Early Silurian age that comprises a starved basin sequence of cherts and shales with siltstones and mudstones, punctuated by carbonate debris flow conglomerates derived from the nearby southern carbonate shelf. The Lower Palaeozoic strata at Citronen Fjord are part of the southern margin of the North Greenland Fold Belt characterized by southerly-facing folds and thrust faults.
 A new geological map of the Citronen Fjord area is presented featuring Cambrian, Ordovician and Silurian strata, with two north-south cross-sections illustrating the main structure. Twelve informally-named lithostratigraphic units are recognized and comments given on correlation to the regional stratigraphy. Tectonic contacts separate Lower Cambrian strata from the Ordovician-Silurian part of the succession. It is concluded that the Citronen Fjord stratigraphy could be of local development in a sub-basin controlled by syn-genetic faults.
 The lead-zinc deposit is interpreted to be of sedimentary-exhalative origin formed by the precipitation of sulphides from metal-bearing fluids introduced onto the sea-floor through underlying fractures. The significant components of this deposition model include the existence of a tensional tectonic regime, deep-seated fractures and a restricted sub-basin morphology. Massive to dendritic-textured pyrite is interpreted to represent vent-facies deposition while the bedded sulphides are taken to be the corresponding distal facies. The precise tectonic control of the fractures is debatable, as is the role of the so-called Navarana Fjord Escarpment - a palaeo-topographic feature marking the junction between shelf and trough that is assumed to lie immediately to the south of the Citronen Fjord.

The Citronen Fjord massive sulphide deposit, Peary Land, North Greenland: discovery, stratigraphy, mineralization and structural setting

The Citronen Fjord massive sulphide deposit in the Lower Palaeozoic of North Greenland is the world's most northerly base metal mineralization. Since discovery in 1993, it has been intensively investigated by geological and geophysical surveys, and by drilling. The deposit is generally flat lying with a thickness up to 50 m; it extends from outcrop level to depths of 300 m.
 Three main stratiform sulphide sheets occur within a 200 m thick stratigraphic sequence; these are composed of massive and bedded pyrite with variable amounts of sphalerite and minor galena. The proven mineralization is continuous over a strike length of at least 3 km with a maximum width of 500 m; an additional 5 km of mineralization along the same trend is suggested by geological mapping and gravity surveys. The total tonnage of sulphides is estimated to exceed 350 million tons. The overall base metal resource is estimated at 20 million tons of 7 per cent zinc, with a higher grade core of 7 million tons containing 9 per cent zinc and 1 per cent lead.
 The Citronen Fjord deposit is located at the eastern end of the Palaeozoic Franklinian Basin that extends through the Arctic Islands of Canada and across northern Greenland. Its discovery is an example of a successful exploration strategy based on regional evaluation, sparse but telltale surface mineralization observations and low-cost logistics: a skidoo-sledge expedition. The stratiform mineralization is hosted in the dark argillaceous rocks of the Amundsen Land Group of latest Ordovician to Early Silurian age that comprises a starved basin sequence of cherts and shales with siltstones and mudstones, punctuated by carbonate debris flow conglomerates derived from the nearby southern carbonate shelf. The Lower Palaeozoic strata at Citronen Fjord are part of the southern margin of the North Greenland Fold Belt characterized by southerly-facing folds and thrust faults.
 A new geological map of the Citronen Fjord area is presented featuring Cambrian, Ordovician and Silurian strata, with two north-south cross-sections illustrating the main structure. Twelve informally-named lithostratigraphic units are recognized and comments given on correlation to the regional stratigraphy. Tectonic contacts separate Lower Cambrian strata from the Ordovician-Silurian part of the succession. It is concluded that the Citronen Fjord stratigraphy could be of local development in a sub-basin controlled by syn-genetic faults.
 The lead-zinc deposit is interpreted to be of sedimentary-exhalative origin formed by the precipitation of sulphides from metal-bearing fluids introduced onto the sea-floor through underlying fractures. The significant components of this deposition model include the existence of a tensional tectonic regime, deep-seated fractures and a restricted sub-basin morphology. Massive to dendritic-textured pyrite is interpreted to represent vent-facies deposition while the bedded sulphides are taken to be the corresponding distal facies. The precise tectonic control of the fractures is debatable, as is the role of the so-called Navarana Fjord Escarpment - a palaeo-topographic feature marking the junction between shelf and trough that is assumed to lie immediately to the south of the Citronen Fjord.

Age of low-grade regional metamorphism in the North Greenland fold belt: mineralogical and Rb–Sr-isotope evidence from pelitic metasediments

Established isotopic sediment-dating techniques have been used to date the time of deformation and metamorphism of the lower Palaeozoic rocks within the North Greenland fold belt. Fine mineral fractions < 2 μm have been separated from pelitic sediments at widely distributed localities and analysed using X-ray diffraction, isotope, and geochemical techniques.The mineralogical study identified two slightly different mineral parageneses of low greenschist facies. One assemblage without the sodium mica paragonite is confined to calcareous lithologies of the Amundsen Land and Vølvedal groups. The second assemblage includes paragonite and is found in noncalcareous lithologies of the Polkorridoren Group.Rb–Sr isotope dating of the mineral fractions yielded isochron ages in the range 318–346 Ma, which shows that final uplift and cooling associated with Ellesmerian tectonism in North Greenland occurred in the Mississippian. The results suggest that, although the metamorphism was of regional scale, recrystallization and isotopic homogenization occurred in closed systems of local extent.

A new siluro‐Devonian paleopole from Early Paleozoic rocks of the Franklinian basin, North Greenland Fold Belt

Demagnetization of dolomitic shales, dolomites, and carbonate breccias of the Cambro‐Ordovician Kap Stanton Formation within the Franklinian basin sequence of the North Greenland Fold Belt yields a characteristic direction (declination/inclination is 16/−16, tilt corrected) from 14 of the 28 sites. A negative breccia test and positive local and regional fold tests bracket the age of the magnetization as postdepositional but pre‐Ellesmerian (pre‐Carboniferous). After rotating the corresponding paleopole (1°N, 302°E) to account for the Cretaceous‐Tertiary opening of the Labrador Sea, the Greenland pole remains removed by approximately 20° from the existing North American Apparent Polar Wander Path (APWP). However, the rotated paleopole (2°S, 284°E in North American coordinates) is similar to British Silurian and Devonian paleopoles in a Bullard et al. (1965) reconstruction (pole is 2°S, 322°E in British coordinates). We interpret our new paleopole as Late Silurian to Early Devonian in age, requiring a modification of previously published APWPs for Laurentia. If the age assignment is correct, the new paleopath for North America/Greenland and that for Great Britain can be brought into good agreement by closing the Atlantic Ocean, thus indicating that North America, Greenland, and Great Britain were assembled in a supercontinent in Late Silurian to Early Devonian time.

Lithostratigraphy and structure of the North Greenland fold belt in Nansen Land

Field work in Nansen Land and adjacent areas in 1985 has largely confirmed the provisional lithostratigraphy of the Paradisfjeld Group and Polkorridoren Group previously established; both are Lower Cambrian deep-water sequences. Some units of the Polkorridoren Group show marked thickness variations. Two major phases of Ellesmerian (Devonian-Carboniferous) deformation are recognised, whereas Eurekan (CretaceousTertiary) events are limited to relatively minor structures, and several phases of dyke intrusion.

A shallow detachment beneath the North Greenland fold belt: implications for sedimentation and tectonics

AbstractIn northern Greenland in early Palaeozoic time a turbidite trough (the eastward extension of the Hazen trough of Arctic Canada) was flanked to the south by a carbonate platform. The trough was deformed during the mid-Palaeozoic Ellesmerian orogeny to form the E–W trending North Greenland fold belt. This fold belt was deformed further by Eurekan (Tertiary) structures, important among which is a major fault complex, the Harder Fjord fault zone (HFFZ). The suggestion has been made that this fault zone controlled early Cambrian sedimentation, even though the fault trace does not coincide with the trough–platform facies transition in sediments of that age; this has led to some controversy.We report new information from a mapping programme by the Geological Survey of Greenland which has established the thin-skinned nature of Ellesmerian deformation at the trough-platform transition and implies that much of the fold belt is underlain by a shallow detachment. This in turn implies that the HFFZ exists in the hanging-wall of the detachment while the early Cambrian trough-platform transition is located autochthonously in the foot-wall. We adduce evidence to show that the latter was probably controlled by syndepositional faulting with actively eroding fault scarps and suggest that these basement structures were reactivated in a dextral strike-slip mode in early Tertiary time to form the HFFZ as now observed.

Comparative studies of gravity tectonics in Quaternary sediments and sedimentary rocks related to fold belts

Summary Two different modes of gravity tectonics have been active as deformation mechanisms in the Quaternary of Denmark, namely ‘gravity gliding’ and ‘gravity spreading’. Examples of gravity gliding can be found in the fairly slowly moving coherent landslides which characterize many coastal cliffs with lithologies intercalated with Tertiary marine clay or Quaternary interglacial clay. The gravity spreading mechanism generated folds and dislocation structures characteristic of glacial tectonics, mainly during the Weichselian glacier advances of the Pleistocene glaciation. Imbricate dislocation structures formed by diapiric rise of water-saturated clay into sand occur. This structure type is proposed to be characteristic for the gravity spreading model. Analysis of these gravity deformed Quaternary deposits serve as a model for structures occurring in large-scale tectonic settings. Among the megascopic tectonic settings mentioned, two regions are discussed. Firstly, the transverse thin-skinned thrust fault belt in the southern part of the North Greenland Fold Belt is demonstrated to contain the characteristics of a gravity gliding system. Secondly, the gravity spreading structures of the glacio-dynamic deformations in Denmark are suggested to have a megascopic equivalent in the plate-tectonic convergence zone of the Barbados Ridge.

Topographical and geological maps of Hall Land, North Greenland. Description of a computer- supported photogrammetrical research programme for production of new maps, and the Lower Palaeozoic and surficial geology

Topographical and geological map sheets covering the northern part of Hall Land (81-82°N) are presented – an area of about 3000 km2. The maps are the products of a research programme in which newly developed photogrammetric techniques have been used in the interpretation and compilation of the topography and the geology (both solid and surficial). The topographical map has been constructed with a minimum of geodetic ground control. The topographic contours have been calculated from a digital elevation model using computer programmes, and automatically plotted out. The geological map has been hand-drawn from 74 manuscript sheets compiled from aerial photograph models on second-order analog stereo-plotting instruments with computer facilities. The maps, the photogrammetric programme and the solid and surficial geology are described in seven chapters. The first two provide an introductory background that explains the motivation for the research, summarises the history of cartographic, geodetic and geologic work and provides a status of research at the start of the programme. The third chapter discusses the various aspects of the photogrammetric programme, instrumentation and the on-line computer facilities utilised, and is followed by a chapter dealing with compilation method, map presentation and assessment of cartographic accuracy compared to previous maps and modern geodetic ground data. The next chapter describes the topography and geomorphology and relates the three main physiographic provinces to the solid and surficial geology. The penultimate chapter outlines the stratigraphy and structure of the Upper Ordovician-Silurian (Llandovery-Pridoli) section through the E-W trending Franklinian basin. In Ordovician-earliest Silurian time, the map area was part of the carbonate platform; in the Llandovery a major shift southwards of the deep-water basin occurred. The Silurian succession displays a regional facies change from platform carbonates in the south, through a major reef belt on the shelf and upper slope to, in the north, clastic turbidites of the lower slope and trough. Facies transitions and interdigitation of shelf-slope-trough lithologies are complex. The northern part of the map exposes the autochthonous margin of the mid-Palaeozoic North Greenland fold belt characterised by E-W folds. The regional structure is an asymmetric synclinorium; a decollement zone probably occurs in the shale sequence that overlies the Lower Silurian carbonate platform. The final chapter describes eight groups of Quaternary deposits and features: moraine, fluviatile-glaciofluvial, marine, lacustrine, colluvial, solifluction, aeolian and periglacial. Hall Land was formerly entirely ice covered, and deposits of several ice advances are preserved; six major marginal moraine systems are defined. Marine deposits are prominent and terrace levels and raised shorelines are well preserved; the Holocene marine limit is at least 125 m above present sea level. Major events are placed within a Pleistocene-Holocene chronostratigraphic framework. Comments on place names are given in an appendix.

Geology of central and eastern North Greenland

A historical review of geological research in North Greenland is followed by a summary of the main results of the 1978-80 GGU expeditions to the region. New outcrops of Archaean and early Proterozoic crystalline rocks are recorded only as xenoliths in dykes and volcanic centres. A revised stratigraphy is applied to the middle Proterozoic Independence Fjord Group sandstones, while petrographic and isotopic studies have been made of the cross-cutting Midsommersø dolerites and the overlying Zig-Zag Dal Basalt Formation. No convincing evidence has been found of a Carolinidian orogenic episode separating these units from succeeding late Proterozoic sedimentary sequences. Lower Palaeozoic sediments dominate North Greenland and are divided into southern shelf and northern trough successions; new or revised stratigraphies are now applied in both settings. The shelf-trough boundary can be shown to have moved south with time, and a major early Silurian expansion of the trough is related to shelf subsidence and a new phase of turbidite deposition derived from the rising East Greenland Caledonian mountains. Devonian - Middle Carboniferous (Ellesmerian) deformation brought deposition to a close and created the North Greenland fold belt, in which deformation intensity and metamorphic grade increase northwards. Thin-skinned thrusting in association with west or south-facing folds is important in southern areas; this is one of the main differences in interpretation compared to earlier work in the fold belt. New outcrops of post-ElIesmerian sediments (Wandel Sea Basin) have mainly been recorded as fault or thrust bounded sequences; a new stratigraphy is applied to the Wandel Sea Basin succession. Cretaceous - Tertiary events include a suite of volcanic centres, dyke swarms, the Kap Washington Group volcanics, and faults and thrusts of Tertiary (Eurekan) age; all have been studied anew, as have the Quaternary deposits.

A transverse, thin-skinned, thrust-fault belt in the Paleozoic North Greenland Fold Belt

The southern part of the North Greenland Fold Belt in Peary Land has been affected by two widely different orogenic events: an Early to Middle Devonian, westward-directed, thrust-fault deformation and a Late Devonian to an early Carboniferous folding on east-west axes that folded the earlier thrust faults. The deformation in this part of the North Greenland Fold Belt affected an ∼5-km-thick pile of lower Paleozoic shales, turbidites, and conglomerates deposited in the Franklinian–North Greenland, clastic trough. The thrust-fault belt is separated from the northern part of the North Greenland Fold Belt by the east-west–trending transcurrent Harder Fjord fault zone, north of which no westward-directed thrust faults have been recognized. The thrust fault region covers an area of 3,000 km 2 , and the main transport direction was toward the west with a refraction toward southwest along the sideland to the south. The thrust fault region is rimmed by a frontal thrust fault and fold zone. Behind the frontal zone, the uppermost stratigraphical unit, the Silurian flysch, forms an allochthonous mega-cover, draping imbricate thrust structures in the Ordovician units below. The central part of the thrust-fault belt consists of a western, north-south–striking, imbricate, thrust-fault fan and an eastern and southern area characterized by flat-lying, coherent thrust sheets. The imbricate fan is formed by 20 steeply east-dipping thrust sheets with an individual thickness of 500 m. The flat-lying thrust sheets are 100–300 m thick, and the relative displacement along individual thrust faults is in the order of 1–10 km. The subhinterland or proximal thrust zone is situated in the eastern part of the thrust-fault region and is dominated by the Cambrian Frigg Fjord Mudstones. This zone is regarded as a peel-off area from which the Ordovician and Silurian sediments were removed and displaced toward the west. The Frigg Fjord Mudstones compose the lowermost unit exposed in the region and contain the main decollement zone for the thrust faulting. The cumulative effect of the thrusting is a total transport of ∼100 km from east to west. The thrust fault deformation is herein named the “Volvedal orogeny” and is interpreted as a foreland deformation related to the Caledonian Mobile Belt, which involved gravity gliding in the hinterland of the thrust-fault belt.

The North Greenland fold belt in eastern Nansen Land

Field work in 1984 shows that Nansen Land consists of clastic rocks of the carbonaceous Paradisfjeld Group and terrigeneous rocks of the Polkorridoren Group; both are lower Cambrian in age and deposited in a slope and fan environment. Two major Ellesmerian (Devonian to Carboniferous) phases of deformation gave rise to east-west trending folds and schistosities. Three phases of Eurekan (upper Cretaceous to Tertiary) deformation, associated with dyke intrusion, are recognised. The second of these may be related to transpression on the Harder Fjord fault zone, though no major strike-slip movement seems to have taken place.

Thin-skinned structures at the basin-shelf transition in North Greenland

Description is given of the structural pattern in the southern part of the North Greenland fold belt between northern Nyeboe Land and Adolf Jensen Fjord. The structures prove to be of thin-skinned fold-and-thrust type with southeriy vergence, quite distinct from that of the north-verging, multiply deforrned orthotectonic zone to the north.

Tectonic Significance of Kanayut Conglomerate and Related Middle Paleozoic Deposits, Brooks Range, Alaska: ABSTRACT

The Upper Devonian and Lower Mississippian(?) Kanayut Conglomerate, which crops out for a distance of 950 km across the Brooks Range, is significant for understanding of the tectonic history of northern Alaska in relation to the geology of the circum-Arctic region. The Kanayut Conglomerate is as thick as 3,000 m and consists chiefly of conglomeratic fluvial strata that were deposited as a result of southwestward progradation of a large and coarse-grained fluvial-dominated delta. Underlying and overlying shallow marine and prodeltaic strata record the advance and retreat of the delta. The Kanayut and related deposits crop out in a series of thrust sheets in which the Paleozoic rocks were detached in the late Mesozoic from an unknown basement and transported at least severa hundred kilometers northward. Detailed sedimentologic studies and measured sections in the Kanayut Conglomerate permit estimates to be made of the amount of displacement on the thrust sheets and suggest that the source area of the allochthonous middle Paleozoic deltaic deposits was the underlying autochthonous upper Precambrian and lower Paleozoic basement rocks of the North Slope. The Kanayut Conglomerate is not palinspastically compatible with other middle Paleozoic successions in Alaska, in the cordillera of western Canada, in the conterminous western U.S., or in the Canadian Arctic Islands. The strata do, however, resemble fluvial deposits of the Old Red Sandstone in Svalbard and East Greenland. They and their associated autochthonous basement may have been displaced from an original position contiguous with the North Greenland foldbelt by post-Early Mississippian strike-slip faulting and thus indicate an early phase of circum-Arctic tectonic displacement prior to that associated with the opening of the modern Canada basin in the late Mesozoic. End_of_Article - Last_Page 673------------

Routine K/Ar age determination on post-Silurian dolerite dykes, North Greenland fold belt

This note documents results of routine K/Ar isotopic age determination of dolerite dykes from the North Greenland fold belt. All the material was collected in 1969 by two of us (P.R.D. and N.J.S.) during the Joint Services Expedition to Peary Land; the isotopic analyses have been undertaken by D.C.R. in the geologicallaboratories of the University of Leeds. In view of the renewed interest in the tectonic and magmatic history of the Peary Land region stemming from the systematic field studies carried out by GGU in 1978-1980 (see GGU Rapport 88, 99 and 106), the results of this early dating programme are listed here as a contribution to this discussion. Recently, some reference has been made in the literature to these hitherto unpublished results (Dawes & Soper, 1979; Higgins et al., 1981; Håkansson & Pedersen, 1982).

The significance of a Middle Devonian Kl Ar age of an intrusive rock in the southern part of the North Greenland Fold Belt

A Kl Ar age of 380 ± 5 Ma has been obtained from an intrusive body in the· southern part of the North Greenland Fold Belt in Peary Land. This age dates the first major deformation event in the North Greenland Fold Belt, and it is inferred that a correlation exists between the North Greenland Fold Belt and the Northern Ellesmerian Fold Complex of the Arctic Canadian archipelago. The dating furthermore casts serious doubt on the proposed genetic link between the intrusive rocks of the southern part of the North Greenland Fold Belt and the Late Cretaceous Kap Washington volcanics and the N-S trending dyke swarms W of Peary Land.

The relationship between Caledonian nappe tectonics and Silurian turbidite deposition in North Greenland

The relationship between the northern part of the Caledonian fold belt of East Greenland and the North Greenland fold belt is explored within the context of Silurian sedimentation and tectonics. A model is developed relating the Caledonian nappes of eastern North Greenland to major tectonic and sedimentological features of the Silurian of the remainder of North Greenland. The abrupt change from a thin succession of predominantly slowly deposited muds to a thick succession of rapidly deposited sandstone turbidites at the Ordovician/Silurian boundary, in the deep-water basin N of the carbonate platform in North Greenland, is directly related to uplift and westerly directed nappe emplacement in the eastern Caledonides. It is suggested that uplift to the E of North Greenland, which commenced in the late Ordovician or early Silurian, provided the main source of the Silurian turbidites of North Greenland. This is corroborated by the dominant westerly transport direction of the Silurian turbidites. Nappe emplacement during the latest Llandovery (Silurian), and foundering of the whole of the carbonate platform of eastern North Greenland E of the Victoria Fjord Arch (approximately 60 000 km 2 ), is marked by the replacement of shallow water carbonates by basin turbidites. These events were directly related to isostatic readjustments as the nappes advanced onto the eastern fringe of the platform.

A Late Permian flora of Pechora affinity in North Greenland

Late Permian plant impressions comprising six taxa have been obtained from the North Greenland fold belt. Rhipidopsis, a probable ginkgophyte, occurs together with the fems Prynadaeopteris venusta Radczenko and Pecopteris (Asterotheca?) cf. P. (A?) helenaeana Zalessky, the sphenophyte Sphenophyllum cf. S. biarnicum Zalessky the cordaitean Cordaites cf. C. sylovaensis (Neuburg) Meyen and a possibie conifer branch fragment. The assemblage invites comparison with the Pechora flora of the northem Pre-Urals, and also with that of Mongolia and north-eastern China. These may be warm temperate floras on approximately the same palaeolatitude.

The Nyeboe Land fault zone: a major dislocation on the Greenland coast along northern Nares Strait

The name Nyeboe Land fault zone is proposed for a major dislocation zone in the western part of the North Greenland fold belt, traceable along the outer coast for 300 km. Two other names are introduced: 1) the Hand Bugt fault, a reverse fault that juxtaposes strata at least as old as Cambrian to the north, against Silurian rocks to the south, and 2) the Wulff Land anticline, a major fold structure that parallels the fault zone and the outer coast. The Wulff Land anticline is regarded as having formed during the main diastrophism of the Franklinian geosyncline in Devonian time; the Nyeboe Land fault zone is considered an expression of later Tertiary reactivation.
 Stratigraphic data are presented that define more accurately than hitherto the Franklinian Cambro-Ordovician platform margin. This roughly coincides with the Nyeboe Land fault zone that probably had a history dating back at least to the early Palaeozoic. The location of a steep Bouguer gravity gradient in the coastal area of Nyeboe Land suggests that a deep-seated crustal structure controlled the margin of the Franklinian trough and the site of the Nyeboe Land fault zone.
 The Nyeboe Land fault zone, the Wulff Land anticline and the platform margin can be correlated across Nares Strait with on-line features on Judge Daly Promontory within the central Ellesmere fold belt. This indicates that any strike-slip movement along Nares Strait has only resulted in minor net displacement between Greenland and Ellesmere Island.
 The Nyeboe Land fault zone is correlated with the Judge Daly fault zone of Ellesmere Island to define an extensive fracture line that is oblique to Nares Strait. It is concluded that main crustal displacements in the late Phanerozoic probably took place along fracture systems oblique to Nares Strait rather than affecting the separation of Greenland and Ellesmere Island as separate plates.

Preliminary Rb-Sr age determinations from the North Greenland fold belt, Johannes V Jensen Land, with comments on the metamorphic grade

This report presents the first Rb-Sr age determinations obtained on low-grade metasediments within the eastern part of the North Greenland fold belt. Samples were collected during the 1979 field mapping in eastem Johannes V. Jensen Land, the results ofwhich have been published elsewhere (Soper et al., 1980). Material selected for this study was taken from moderately folded rocks of the Polkorridoren Group and from the northem part of the fold belt where deformation is intense and sedimentary structures are rarely preserved (fig. 23). The principles and methods of isotopic dating of sedimentary rocks applied in this study have been treated in a recent paper by Clauer (1979).