The environments of our planet, from topography to climate, are dictated by the movement of lithospheric plates. The relative motion associated with these large, rigid pieces of the Earth’s continental and oceanic crust results in convergence and collision or divergence and spreading. Our work attempts to unravel the long and complicated convergent and collisional history of the Eurasian High Arctic. We are seeking a new understanding of the geodynamic evolution and, in this context, Taymyr and Severnaya Zemlya play a central role.

Collision between the continental crust of the Siberian and the East European cratons in the late Palaeozoic (about 350 million years ago) resulted in the development of the Uralides, a mountain belt that defines the boundary between Asia and Europe today. One of the most prominent features of Eurasia is the deeply eroded Ural mountains, stretching 3 000 km from near the Aral Sea northwards to the Arctic shelf. The Uralian structures can be followed in to Novaya Zemlya, dividing the Barents from the Kara seas, from where they apparently curve back across the Kara Sea to Taymyr and then swing off-shore northeastwards and northwards via the Severnaya Zemlya islands to the edge of the High Arctic continental shelf. Yet in Taymyr and Severnaya Zemlya many of the characteristic features of the Uralian orogen are absent – the evidence of Palaeozoic oceans, subduction complexes and volcanic are magmatism that dominate the orogen further west.

Bedrock geology

Taymyr’s bedrock divides in to three E-W trending belts – the Northern, Central and Southern Belts. The Northern Belt is dominated by Neoproterozoic turbidites (deep water sandstones, siltstones and shales) which pass conformably up in to the Cambrian strata. They are intruded extensively by granites, some of which yield Carboniferous to Permian ages. The Central Belt is largely composed of Neoproterozoic sedimentary and volcanic rocks, including fragmented ophiolites and island are magmatic suites (Pease and Vernikovsky, in press); continental crust of Grenvillian age (Pease et al., in prep.) occurs as subordinate units intercalated within the Central Belt. These Proterozoic continental and oceanic rocks were folded and faulted together in the latest Neoproterozoic (Vendian), prior to the deposition of overlying late Vendian, Palaeozoic and early Mesozoic successions. Lower and middle Palaeozoic strata unconformably overlie the older rocks and are folded together with the latter in the latest Palaeozoic as parts of an S-vergent foldbelt (Inger et al., 1999). Taymyr’s Southern Belt is composed of Palaeozoic and early Mesozoic strata, including prominent Triassic volcanic rocks and mafic sills. The older strata occur along the northern margin of the Southern Belt where they are folded and thrust southwards on to the late Palaeozoic and Mesozoic rocks.

The Neoproterozoic successions of Taymyr can be followed from Cape Chelyuskin northwards to Bolshevik Island, in the eastern part of the Severnaya Zemlya archipelago. They also occur along the eastern coast of October Revolution Island, where they pass upwards in to the Palaeozoic. A turbidite facies gives way to middle Ordovician gypsiferous shales and limestones, and then thick Ashgill through Silurian limestones. Red beds appear toward the top of the Silurian and the early Devonian is developed in Old Red Standstone facies. The entire succession is folded on N-trending axes, the structure being upright to E-vergent with same thrusting and much disharmony in the gypsiferous formations.

Field-work

Thirteen geoscientists participated in the 1999 expedition. This group was divided in to two working parties, one on the Taymyr Peninsula and the other on October Revolution Island. The field season lasted from 22 July, when both teams were dropped-off by helicopter, to 18 August when a helicopter returned them to Dikson. Data and samples were collected on foot, sometimes requiring 25-30 km of hiking per day.

On Taymyr, research focussed on the eastern part of the Central Belt The team was led by V. Pease and included R. Eriksson, S. Inger, S. Kireev, E. Tagesson, and A Vernikovskaya. The field season was divided into three periods of roughly equal duration, corresponding to three base camps each more westerly than the last. Camp 1, the most easterly camp, was on the Stanovaya River and with the aid of a tracked vehicle we were able to relocate. Camp 2 was established at the confluence of the Zhdanova River and Krivoy Creek. Camp 3, our most westerly location, was at the confluence of the Zhdanova River and Cnezhnaya Creek. In this manner, we were able to obtain a regional picture of the stratigraphy and structure and to collect geochronological and geochemical samples over a wide area.

On October Revolution Island, the field-work work started in the central area with investigations concentrating on structure, stratigraphy, palaeontology (particularly Ordovician and Silurian), and palaeomagnetism. On 10 August, Russian helicopter support allowed the group to split in to two parties with Gee, Bogolepova, Gubanov, and Nilsson moving to the Kruzhilikha River and Proskurnin, Vernikovsky, and Meteolkin to the southeastern coast. This subdivision of the group allowed the western party to focus on the stratigraphy and structure of the late Cambrian to early-mid Ordovician successions. The south-eastern party Concentrated on mid -Ordovician volcanic rocks.

Preliminary results

The Central Belt of eastern Taymyr. In the Stanovaya River region ophiolitic rocks are in fault contact with fragmented remnants of continental crust (orthogneisses and paragneisses) and all rocks are metamorphosed to amphibolite facies. Deformed granites intrude the gneissic country rock and variably cut its foliation. Neoproterozoic (?) quartzite unconformably overlies both the granites and their host rocks. Relatively unmetamorphosed Paleozoic sediments overlie the basement gneisses, though the unconformable contact is not exposed. The basement (gneisses and intruding granites) is generally metamorphosed to greenschist or amphibolite facies, with abundant mafic dikes and local migmatization. Exposed near Camp 3 are polydeformed limestones, sandstones, and dikes adjacent to garnet amphibolite dikes, paragneisses, and foliated granites. Structural data, and samples for geochronology and geochemistry, were collected to facilitate our understanding of the deformation history of the Central Belt.

Our initial evaluation of structural and petrographic data indicates a deformational style similar to locations to the north and west, sampled in 1998 (Gee, 1999). The Palaeozoic successions have experienced low-grade regional metamorphism with relatively open folds and cleavage generally at high angles to bedding. In contrast, pre-Palaeozoic lithologies have experienced higher temperatures and pressures, with some polyphase deformation. The higher grade metamorphism and deformation of some of these units suggests that continental fragments in the eastern Central Belt may represent deeper crustal levels and are potentially also Grenville in age as in the Shrenk River region to the west (Pease et al., in prep.). Geochemical analyses of the granites are underway and will provide information regarding their genesis and tectonic setting. The separation of minerals for determining ages is complete; the next stage of isotopic analysis is now beginning.

October Revolution Island. The field studies on October Revolution Island included the collection of a wide range of material for laboratory analysis. It was also possible to better define the regional structure and analyze the significance of breaks in the stratigraphy. At least two unconformities have been referred to in the published literature, interrupting the Neoproterozoic and Palaeozoic successions. One, in the early Ordovician, is clearly of significance for October Revolution Island; its wider regional importance remains to be demonstrated. Another, between the mid and late Ordovician proved to be an hiatus only, the discordance reported previously being the result of structural complications in connection with flow-folding of gypsiferous shales. Our laboratory work on Ordovician faunas, palaeomagnetism, and the unconformities aims to define the tectonic relationships between the Severnaya Zemlya-Taymyr Northern Belt and adjacent terranes to the south in Central-South Taymyr.