Lower Devonian marine sediments are widespread in Arctic regions and are represented by different stratigraphic sequences. Until recently the boundary with underlying Silurian deposits was an arbitrary one. At present the boundary in graptolitic sections is drawn at the base of the Monograptus uniformis zone (in Pay-Khoy, Alaska, Yukon, and other sections). The correlation of the latter with carbonate sections bearing shelly faunas still is arbitrary. A detailed study of Ludlow and supra-Ludlow deposits (with Atrypella) found in the Urals, Vaygach, Novaya Zemlya, Canadian Arctic Archipelago, Greenland, and Alaska, and especially of deposits with Atrypella scheii characteristic of their upper part (the Greben horizon of the Soviet Arctic, part of the Read Bay Formation of he Canadian Arctic, and their age equivalents) may help solve this problem. The Lower Devonian deposits themselves are difficult to correlate. The most precise correlations are in the Emsian-Eifelian interval in the Soviet Arctic and the upper Eids and Blue Fiord Formations on Ellesmere and Bathurst Islands in the Canadian Archipelago.

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