Structure and geology of the continental shelf of the Laptev sea, eastern Russian Arctic

The Laptev Sea is of great significance for studying the processes of the i nitial breakup of continents. It is the southern termination of the Gakkel spreading ridge and thus the location of structural features resulting from a continental margin/spreading ridge intersection. The present-day underst anding of the Laptev Shelf geology is based on the Russian multichannel sei smic reflection data and extrapolation of the terrestrial geology. Geologic and plate-kinematic data are used to constrain the interpretation of the s eismic reflection data. The Laptev Rift System consists of several deep sub sided rifts and high standing blocks of the basement. From west to east the se are: the West Laptev and South Laptev rift basins, Ust' Lena Rift, East Laptev and Stolbovoi horsts, Bel'kov-Svyatoi Nos and Anisin rifts. The cent ral and eastern parts of the shelf have the greatest contrasts in the gravi ty field ranging from -60 mGal over the rifts to 50 mGal over the horsts. T he rifts contain up to five seismic stratigraphic units bounded by clear re gional reflectors and underlain by folded heterogeneous basement. They are suggested to be Late Cretaceous to Holocene in age and reflect different st ages of spreading ridge/continental margin interaction. The estimated total thickness of the rift-related sediments varies between 4 and 8-10 km while the sedimentary cover on the uplifts is significantly reduced and generall y does not exceed 1-2 km. An eastward decrease of the total thickness of th e sedimentary sections from about 10 km in the South Laptev Basin to 4-5 km in the Bel'kov-Svyatoi Nos Rift and the simplicity of the entire rift stru cture may indicate a rejuvenation of the rifts in the same direction. The e ntire rift system is covered by the uppermost seismic unit, which probably reflects a deceleration of the rifting during the last reorganization of th e North American/Eurasian plate interaction since about 2 Ma. (C) 1998 Else vier Science B.V. All rights reserved.