The Cretaceous of Northeastern Siberia (Laptev Sea region): Stratigraphy and Sedimentary Successions

Boris Nikitenko

The most detailed stratigraphic schemes of the Cretaceous and palaeoenvironment reconstructions for Arctic areas of Russia are developed on the basis of the materials from Laptev Sea region (northeastern Siberia). The uppermost Jurassic and the Cretaceous are here represented by the most complete sedimentary successions and exposed in several outcrops characterizing by different facies. Abundant macro- and microfauna and palynomorphs provide the high-resolution biostratigraphic subdivision of the sections. It allows the definition of several isochronous levels characterizing by specific features in different facial areas. New biostratigraphic data on foraminifers, ostracodes, dinocysts and terrestrial palynomorphs are the basis for the revision and the more precise definition of the stratigraphic extends of some lithostratigraphic units in northeastern Siberia. A number of marker levels on foraminifers related to the migration of several species from southern seas and taxanomic changes of foraminiferal communities as well as some dinocyst bioevents allow the Panboreal correlations. The Early Cretaceous is characterized by two stages of the evolution of sedimentary basins in the northeastern Siberia: 1) the Boreal Berriasian (Ryazanian) - first half of the Hauterivian (predominately marine sedimentation); 2) the latest Hauterivian - Albian (predominately continental sedimentation). Seven facies-controlled areas are established in this region. The sections of western and eastern areas are characterized by wide distribution of sands and silts, while the sections of central areas mainly consist of relatively deep-water silts and clays. In the eastern areas of studied region, subcontinental and continental regime set in the end of the Valanginian and Early Hauterivian. In the west, marine conditions continued in the Late earliest Hauterivian, and accumulation of fully continental deposits began only in the latest Barremian - Aptian. The Upper Cretaceous sediments are of local distribution and represented by alternation of mainly continental sands and clays. The marine and lagoon conditions occurred only in the Santonian- Campanian. Stratigraphic position of the base of the Cretaceous in the northeastern Siberia in regard to Standard Stratigraphic Scale is problematic. From one point of view, it should be located at the top of the Upper Volgian (chetae/sibiricus Ammonite Zones). Other widespread opinion is the correlation of the base of the Cretaceous to the Upper Volgian base (boundary of variabilis/okensis Zones boundary). Taking into consideration new data on magnetostratigraphy, Jurassic/Cretaceous boundary can be established within the taimyrensis Zone of the Upper Volgian. Considerable changes in taxonomic composition of foraminiferal and dinocyst assemblages occur somewhat higher these levels. Microfossil assemblages are dominated by typically Cretaceous taxa since the upper part of sibiricus ammonite zone of the Boreal Berriasian.

AAPG Search and Discovery Article #90177©3P Arctic, Polar Petroleum Potential Conference & Exhibition, Stavanger, Norway, October 15-18, 2013