Observations on the geology of the northern part of North-East Land (Spitsbergen)

Abstract

Summary The paper describes the geology of the northern part of North-East Land, between 80° 30' N. and 80° N. and from 20° E. to 28° E., and refers also to rock outcrops on the east coast. The greater part of the interior is covered with land-ice. Oskar Kulling described the isoclinally folded succession of Hecla Hoek sediments in the north-west region, in which he found Lower Palaeozoic brachiopods near the top and a tillite below them, regarded as Eo-Cambrian. The subjacent beds are referred to the Pre-Cambrian and the succession known so far is more than 4000 metres thick; there are no strong unconformities. There was, therefore, Pre-Cambrian-Lower Palaeozoic continuity of deposition in the arctic part of the " Caledonian geosyncline ". The Hecla Hoek sediments are traced eastward in a pitching syncline between two anticlines, and the lowest divisions are identified. Fine-bedded shales and some other beds alternate with arenaceous rocks laid down in shallow water : some of the latter, low in the succession, bear ripple-marks and problematic impressions, some possibly of organic origin. Some of the shales display rhythmic bedding. The sediments as a whole accumulated in a neritic zone of a subsiding sea-floor, and the relative altitude of the land varied from time to time. The geosynclinal nature of the sea is evident, especially in the mountains of western Spitsbergen, built from its deposits at some time during the Lower Palaeozoic, and it is thought that the continental zone lay in the east, with its Archaean basement. In the mountains of Spitsbergen some rock-groups have arisen from the regional metamorphism of Hecla Hoek sediments, and they have been traced one into the other, notably by Fleming and Edmonds in Ny Friesland (North-East Spitsbergen). Granitization has also been invoked by Orvin and others. In North-East Land the lowest Hecla Hoek sediments are substantially without metamorphic grade. Beneath them lies a crystalline complex of schists and gneisses invaded by grey granites here regarded as granites sensu stricto , to be distinguished from pink-red granites—here recognized as felsic granodiorites—which penetrate not only the schists, gneisses and grey granites but at least the lower part of the Hecla Hoek sediments. The granodiorites are certainly pre-Upper Carboniferous; diorites may be associated with them, in addition to pegmatites and quartz veins. A broad classification and sequence of the igneous and metamorphic rocks is established. Thus it seems that in North-East Land the unaltered sediments are unconformable on the crystalline complex, from which rocks of low-grade metamorphism had previously been removed : the underlying rocks are, then, a core of greater age. An analogous core might have been present in Ny Friesland and have induced by its resistance to the stress of Lower Palaeozoic mountain-building the progressive grade of regional metamorphism in the adjacent Hecla Hoek sediments. There may thus be some comparison with structures in East Greenland. Obviously, not all metamorphic rocks in western Spitsbergen are Archaean, but consideration should be given to some dynamic function of already modified Archaean rocks in the Lower Palaeozoic (" Caledonian ") fold systems.