Kotelny Island - Geology

Geology

Kotelny Island consists of sedimentary rocks and sediments ranging in age from Early Paleozoic to Late Cenozoic. The oldest rocks fossiliferous shallow- to deep-water marine, Ordovician to Early Devonian limestones and dolomites. Middle Devonian to Carboniferous interbedded limestones, dolomites, sandstones, and conglomerates overlie these sedimentary strata. The Permian to Jurassic strata exposed within Kotelny Island consist of interbedded, fossiliferous mudstones, siltstones, and sandstones. All of these sedimentary rocks are faulted, folded into complex anticlines and synclines, and intruded by thin diabase dikes. Pleistocene to Holocene fluvial sediments, which range in age from 1,500 to greater than 55,000 radiocarbon years BP, underlie stream terraces that lie within the Balyktakh and Dragotsennaya River valleys. Thick permafrost has developed in these sediments.

Within Bunge Land and the southwest corner of Kotelny Island, relatively unconsolidated sediments ranging in age from Early Cretaceous to Holocene overlie the above folded and faulted sedimentary rocks. The oldest of these sediments are Early Cretaceous alluvial clays, silts, and sands that contain layers of conglomerate, tuff, tuffaceous sandstone, coal, and, at top, rhyolite. The Late Cretaceous sediments are overlain by Late Eocene to Pliocene alluvial sands that contain layers of clay, silt, gravel, brown coal, and lignitized wood. The vast majority of Bunge Land is blanketed by Early Holocene marine sediments. Only in the central and southern parts of Bunge Land do either Late to Early Pleistocene marine sediments or very small patches of highly weathered Prequaternary deposits and bedrock underlie the surface.

The surface of Faddeyevsky Island is underlain by unconsolidated sediments ranging in age from Early Cretaceous to Pleistocene. Three very small and isolated exposures indicate that the Early Cretaceous strata are similar to those found in the southwest corner of Kotelny Island. Overlying the Early Cretaceous sediments are alluvial and lacustrine Eocene clays and silts that contains rare beds of sands, brown coal, and gravel. To the north these sediments grade laterally into nearshore marine clays with fossil pelecypods. The Eocene sediments are overlain by fossiliferous, terrestrial and marine Oligocene to Miocene sands that contain subordinate beds of mud, clay, gravel, and brown coal. The Oligocene-Miocene sands accumulated in alluvial, lacustrine, and nearshore marine environments. Overlying the Oligocene-Miocene sands are Pliocene alluvial, lacustrine, and nearshore marine, muds, silts, and sands.

Pleistocene deposits blanket most of the surface of Faddeyevsky Island. A layer of Late Pleistocene and Holocene alluvial and lacustrine deposits largely cover the central and southern parts of Faddeyevsky Island. Middle and Late Pleistocene deposits largely cover the northern part of this island. The permafrost is about 400 to 500 m thick. The central plain of Faddeyevsky Island has been highly altered by thermokarst processes. It contains numerous deep erosive cuts created by the seasonal melting of the permafrost. Numerous baydzharakhs, thermokarst mounds, dot landscape, They are the result of the melting of polygonal ice wedges within the permafrost.