The Late Jurassic—Early Cretaceous Synorogenic Foreland Basin in the Shelf of Laptev Sea

Alexander Kuzmichev and Maria Danukalova
Geological Institute of RAS, Moscow, Russia.

The three southern islands of the New Siberian archipelago are underlain mostly by Jurassic-Cretaceous sandstones and shales. They constitute the synorogenic foreland basin that lay to the north of the South Anyui orogen. The initial stage of basin formation is represented by deposits in southeastern Big Lyakhov Island where they are partly tectonically buried under the allochthonous ophiolitic assemblage (Kuzmichev et al., 2006). Clastic successions of the main stage of deposition underlie Small Lyakhov and Stolbovoi Islands. These deposits were studied in 2007 field season on Stolbovoi Island, which is almost completely surrounded by excellent sea cliff exposures. The deposits are represented by sand-rich distal turbidites, which preserve all their original sedimentary features. The thickness of measured section is about 1200 m. A notable feature of the turbidite complex is the presence of light-colored, amalgamated sandstone units up to 25 meter-thick. The rest of the complex consists mostly of mud-rich rhythmically bedded, dark-colored sandstones. Shale-silt intervals with abundant ripples represent a lesser part of the sequence. The massive sand units are interpreted as redeposited in deep water after accumulation on an outer shelf. The dark sandstones are the sediments directly transported from land across a narrow shelf into deep water. Sole marks indicate the sediments transport from south to north. Ripple marks indicate current directions towards the northeast. The last direction is a result of the deviation of low-density suspension by along-basin currents. Sandstone composition and grains angularity together with fresh K-feldspar and biotite point to proximal orogenic sources. Buchia fossils were found in numerous locations. They were identified by V.A.Zakharov and specify a Late Volgian (Tithonian) to Early Valanginian age. The existence of above foreland basin should be taken into consideration in the course of seismic prospecting in Laptev Sea. The Jurassic—Cretaceous strata are gently folded and look in seismic profiles in the vicinity of Stolbovoi Island as traceable layered sequence. Sand-rich turbidite complexes can contain hydrocarbons although the studied sandstones show poor porosity due to postdepositional cementation. It can be supposed that cementation would diminish in a distance of the South Anyui orogen.

AAPG Search and Discover Article #90096©2009 AAPG 3-P Arctic Conference and Exhibition, Moscow, Russia