Facies analysis of the Old Red Sandstone of Spitsbergen (Wood Bay Formation): Reconstruction of the depositional environments and implications of basin development

The object of this paper is to provide a facies guide that helps subsequent workers recognizing different facies and palaeoenvironments of the terrestrial Old Red Sandstone exposed in central N Spitsbergen. Sediments of the Early Devonian Wood Bay Formation represent continental molasse deposition under and to semi-arid climatic conditions in three main depositional environments (rivers, alluvial plains, perennial lakes) represented by characteristic lithologies, sedimentary structures and microfacies. River channel deposits, consisting of conglomerates, very coarse- to very fine-grained sandstones and sandy siltstones are generally arranged in successive fining-upward sequences marked by specific sedimentary structures in a particular order. The sediments reflect the bed, mixed and suspended load of low sinuosity braided to high sinuosity meandering rivers.Adjacent overbank areas (levees, crevasse splays) and extensive alluvial plains are represented by reddish-brown, fine-grained sandstones to sandy siltstones and silty mudstones. The sediments are the accumulated, mixed and suspended load of floodwaters, which recurrently inundated the lowlands. Various lithofacies types, facies associations and sequences reflect the local formation of palaeosols, ephemeral flood lakes and boggy areas with persistent high water tables.Multicoloured, calcareous successions and single limestone beds intercalated in the red beds represent the depositional products of perennial, low relief, low-energy lakes, which developed in topographic depressions of the alluvial plains. The sediments reflect deposition in deep-water, littoral and palustrine sub-environments, forming regressive, shallowing-upward sequences in the central lake areas.The overall arrangement of the various facies reflects a terrestrial basin that developed from a steep-sloped, high-energy, river-dominated molasse trough into a level, low-energy coastal plain, marked by broad mud flats and the formation of extensive perennial lakes.