Peter R. Dawes

Organic-walled microfossils from the Proterozoic Thule Supergroup, Northwest Greenland

Abstract The Proterozoic rocks of the intracratonic Thule Basin on the northern margin of the Canadian–Greenlandic shield have recently been referred to as the Thule Supergroup. The succession comprises unmetamorphosed, unfolded sedimentary and magmatic rocks, which are, with few exceptions, not deformed. Five groups have been defined and fine-grained siliciclastic samples from the uppermost three (Baffin Bay, Dundas and Narssârssuk groups), yielded moderately well-preserved acanthomorphic and non-acanthomorphic acritarchs, prasinophytes and filamentous microfossils. The age of the supergroup is quite poorly constrained, at the base by a 1268xa0Ma basaltic sill, and at the top by a basic dyke swarm with a K/Ar age range between 630 and 725xa0Ma, that cuts the entire succession. Biostratigraphical studies further constrain the age of the Thule Supergroup and suggest that the succession is of a late Mesoproterozoic/earliest Neoproterozoic age. This age assignment is corroborated by independent stable isotope data and correlation with the Bylot Supergroup to the south. This leads us to propose that the Thule Supergroup was deposited between c. 1300 and c. 1200xa0Ma. Microfossil taxa previously interpreted as exclusively occurring in pre-Varangerian, Neoproterozoic rocks (i.e. Simia annulare Jankauskas, Tasmanites rifejicus Jankauskas and possibly Vandalosphaeridium varangeri Vidal) are consequently re-evaluated. Process-bearing acritarchs, herein attributed under open nomenclature to ?Comasphaeridium sp., `Trachyhystrichosphaera truncata and ?Vandalosphaeridium sp., are of special palaeobiological importance since acanthomorphic acritarchs have rarely been reported from pre-Neoproterozoic successions.

North Atlantic spreading axes terminate in the continental cul-de-sacs of Baffin Bay and the Laptev Sea

In conventional plate-tectonic models, an independent Greenland plate is supposed to have drifted in the Paleogene along a transform fault through Nares Strait that links the two branches of the North Atlantic spreading system. However, this postulated structurexa0— widely known as the Wegener Faultxa0— cannot be detected by any means in the southern part of the strait. The mapped geology flanking this part of the strait is identical, with no evidence whatsoever of any strike-slip displacement or compressional deformation, and geophysical data provide no support for the existence of such tectonism offshore. We analyse the serious drawback of having a major transform located within a Precambrian crustal block stable since the Paleozoic and emphasize that the extinct Labrador – Baffin Bay spreading axis is but a mirror image of the active North Atlantic – Gakkel Ridge that terminates in a continental cul-de-sac in the Laptev Sea. We conclude that, in the Baffin Bayxa0– Nares Strait region, there is only one plate...

Copper–gold occurrences in the Palaeoproterozoic Inglefield mobile belt, northwest Greenland: a new mineralisation style?

Abstract Inglefield Land in northwest Greenland is an ice-free 7000 km 2 region underlain by the Palaeoproterozoic Inglefield mobile belt, composed of quartzo-feldspathic gneisses, meta-igneous and supracrustal rocks. These rocks are unconformably overlain by an unmetamorphosed cover of sedimentary and igneous rocks of the Mesoproterozoic Thule Basin and the Lower Palaeozoic Franklinian Basin. Mineralisation in Inglefield Land is characterised by a copper–gold metal association that can be classified in terms of the hosting rocks, namely: garnet–sillimanite paragneiss-hosted, orthogneiss-hosted and mafic–ultramafic-hosted. The paragneiss-hosted mineralisation, the topic of this paper, is essentially confined within a NE-trending structural corridor and consists of bands of sulphide±graphite-bearing, hydrothermally altered, quartzo-feldspathic gneiss, called “rust zones”. These are commonly parallel to the paragneiss main foliation, suggesting a close relationship. The rust zones have strike lengths from a few metres to more than 5 km, and widths ranging from a few centimetres to 200 m. Sulphides mainly include pyrrhotite, pyrite and chalcopyrite. The sulphides form disseminations, up to 30% by volume, but in places they form massive pods or lenses up to 20–30 m, and about 0.1–0.5 m wide. Graphite contents are up to 5 vol.%. Rust zones typically consist of a quartz–plagioclase mosaic associated with a late generation of red-brown biotite, sericite, chlorite and epidote. Mylonitic or cataclastic textures are locally recognisable. XRD analyses of graphite indicate temperatures of between 650 and 700 °C. Sulphur isotope analyses show δ 34 S values ranging from −6.2‰ to +9.3‰. An ore genesis model is proposed in which the Palaeoproterozoic precursor sandstone–carbonaceous shale succession is polydeformed and polymetamorphosed to granulite facies quartzo-feldspathic and pelitic gneisses, with transposition of layering to axial plane of folds, followed by ductile shearing and mylonitisation, from which future rust zones were derived. The mylonitic zones were infiltrated by fluids, whose origin can be ascribed to deep-penetrating surface waters and/or external brines. In our ore genesis model, we envisage that brines derived from the overlying Lower Palaeozoic Franklinian succession infiltrated the basement into the structural channels provided by the shear/mylonitic zones. At the regional scale, this infiltration was facilitated by a NE-trending corridor, postulated to be a deep structure.

The rotations opening the Central and Northern Atlantic Ocean: compilation, drift lines, and flow lines (Int J Earth Sci 102:1357–1376)

Strait and marked the Wegener Fault. Figure 1b depicts the present-day geography and geology of the region modified from Dawes (2009, Fig. 9). The mismatch between Ellesmere Island and Greenland in Fig. 1a is immediately apparent from the disruption of the two sedimentary basins—the Mesoproterozoic Thule and Paleozoic Franklinian—that straddle nares Strait. The component of the Thule Basin on Greenland is displaced from that on Ellesmere Island. The regional architecture of the Franklinian Basin depicted in Fig. 1b by cambrian to Devonian markers in Ellesmere Island and Greenland is destroyed and the cambro-Silurian, folded, deep-water trough of the Franklinian Basin on Greenland strikes into Paleoproterozoic gneiss on Ellesmere Island. Other misfits on a more detailed scale are listed by Dawes (2009). In addition, closure of the major seaways flanking Devon Island (Lancaster and Jones Sounds) likewise results in gross mismatches within canadian geology. Similar problems arising from the undoing of harmonious geology mar Greiner and neugebauer’s reconstructions at 84 and 52.65 Ma. Saalmann et al. (2005) described a Paleogene, nEtrending, strike-slip fault zone and later SE-directed thrusting on land in a 100-km-long stretch of the nE Ellesmere Island coastline. They considered this deformation to be a manifestation of the Wegener Transform Fault and plate boundary but admitted that the fault could not be traced farther south through southern nares Strait into Baffin Bay. Greiner and neugebauer have used Saalmann et al.’s findings to support their case for convergence of Greenland and Ellesmere Island and large-scale displacement along the Wegener Fault but fail to acknowledge that these Paleogene tectonic features are of limited regional significance and that, in any event, the amount of strike slip recorded on land is insufficient to account for the separation of Greenland from north America by spreading in Baffin Bay. Greiner and neugebauer (2013) have modeled the opening of the central and northern Atlantic Ocean using a computer program that generates paleogeographic reconstructions based on Euler rotational data, which in turn are derived from magnetic anomalies flanking oceanic spreading ridges. Here, we confine ourselves to a critique of Greiner and neugebauer’s results for the nares Strait—northern Baffin Bay region bordered by Greenland and the eastern canadian High Arctic. Reconstructions at or before 175, 84, and 52.65 Ma are shown in Greiner and neugebauer’s Figures 5, 6, 9, and 10. All these are strictly paleogeographic representations; none shows any surface geological feature. Greiner and neugebauer a priori consider Greenland to be an independent tectonic plate separated from Ellesmere Island—part of the north American plate—by a transform fault, the Wegener Fault, running through nares Strait. They accept the Wegener Fault as a proven structure and overlook abundant evidence that it is hypothetical (Oakey and Damaske 2006; Harrison 2006; Dawes 2009; Hansen et al. 2011; Rasmussen and Dawes 2011). They cite only one reference to geology relevant to their reconstructions, viz. Saalmann et al. (2005), to which we will return below. Figure 1a is a reproduction of part of Greiner and neugebauer’s Fig. 9 (reconstruction before 175 Ma) with four geological provinces shown, as well as their postulated north American plate boundary coinciding with nares

Epilithic Lichen Communities in High Arctic Greenland: Physical, Environmental, and Geological Aspects of Their Ecology in Inglefield Land (78°–79°N)

Abstract The present investigation of High Arctic epilithic lichens and their substrate is based on field observations in Inglefield Land, North-West Greenland, mainly in 1999, with subsidiary observations from 1995. Eighteen rock samples, all glacial erratics, were specifically selected on the basis of macroscopic mineralization features such as iron and copper staining, vein and breccia structures, and ore minerals. The samples are representative of the crystalline shield, and their lithologies can be matched with exposures in Inglefield Land. Seven lichen communities are recognized, viz. Pleopsidium chlorophanum c., Xanthoria elegans var. splendens c., Dimelaena oreina–Physcia caesia–Xanthoria elegans c., Xanthoria elegans–Umbilicaria virginis c., Orphniospora moriopsis c., Porpidia flavicunda c., and Tremolecia atrata c. The studied material on the 18 samples reveals no conspicuous correlation between metal concentrations in the rock samples and the lichen communities and, broadly speaking, it can be stated that the lichens reflect more the properties of the rock surface, such as, for example, nitrogen- and iron-bearing weathering crusts, than the mineralogical composition of the rocks. However, there is a very close affinity between the Orphniospora moriopsis community and one variety of syenitic rocks with elevated magnetite and phosphorus.