Abstract
Two separate and geologically and structurally different depositional basins (Kara and Laptev Seas) are distinguished in the middle Siberian Arctic shelf; both were formed by Neogene-Quaternary movements. These neotectonic basins are superposed discordantly on a Mesozoic-Cenozoic platform sedimentary cover which overlies peneplaned fold structures of circum-Pacific affinity. Intense tectonic movements in vast areas beyond the limits of the Circum-Pacific geosynclinal belt extended as far northwest as Severnaya Zemlya-Novaya Zemlya-Pay-Khoy, thus modifying the ancient structure of the Riphean (Proterozoic) Northern Asia platform, and the Caledonian and Hercynian fold structures adjacent to it. On recent rises, only fragments of intensely dislocated (by circum-Pacific tectogenesis) zones are exposed; they can be traced beneath the Mesozoic-Cenozoic cover by geophysical methods. Zones of intense dislocations are separated by relic blocks of the inner massif type. The age of the closing of the folding and orogenic processes within those zones becomes younger from west to east--from Late Permian to Early Cretaceous. The age of the basalt layer of the Mesozoic-Cenozoic platform cover changes according to the age of the latest folding. The inner structure of the platform is described in terms of (1) isometric areas with evenly downwarped basement, and (2) elongated swells and associated depressions. The swells and depressions correspond to buried, intensely dislocated zones. The isometric areas correspond to underlying relic blocks where platform conditions had been unchanged since basement consolidation and where several structural complexes had developed in the platform cover. In the upper beds of the Mesozoic-Cenozoic cover, the structural differences are less pronounced. With the use of geophysical methods, 4 classes of middle Siberian shelf areas can be outlined: (1) epi-Karelian (Riphean + Paleozoic + Meso-Cenozoic complex); (2) epi-Baikalian (Paleozoic + Meso-Cenozoic complexes); (3) epi-Caledonian (middle-upper Paleozoic + Meso-Cenozoic complexes); and (4) epi-circum-Pacific (meso-Cenozoic complexes). Type sections compiled from geologic and geophysical data for all classes indicate the thickness and composition of each complex. End_of_Article - Last_Page 2501------------
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