Sedimentary features of terrigenous deposits (Late Aptian – Early Albian) in the northern Yamal

Relevance. The need to clarify the geological structure of Lower Cretaceous productive sediments in the northern part of the Yamal Peninsula with the ongoing N-field development. The Lower Cretaceous terrigenous deposition is characterized by a heterogeneous geology and lithofacies variability which specify the geological features and extent of the productive strata. The conducted lithofacial studies determine the depositional environment and specific features of sedimentary sequence changes in time and space, reveal the change succession of different facies as well as extent both formation and seals within the geological sections and the field area.

Aim. To reconstruct depositional environments and analyzing lithofacies variability of the Lower Cretaceous productive strata originated from the Late Aptian – Early Albian period (TP₁ and KhM₃ formations).

Methods. Geological interpretation of geophysical log data, lithofacies and ichnofacial analysis.

Results and conclusions. The core analysis and geophysical log data have revealed geological composition, structure-texture features, sediment composition, depositional environments. Facies were described; vertical and lateral facies variability were identified. It was stated that in the Late Aptian – Early Albian period the sedimentation was due to oscillatory seafloor movements in the northern part of the Yamal Peninsula. The section indicates the alternating transgressive and regressive sediment sequences. In the Late Aptian period, the terrigenous deposits of the Tanopchin Formation (TP₁ stratum) were accumulated due to marine transgression within the foreshore, shoreface and transitional zones of the shallow-marine beach. In the Early Albian period, the sequence formation between TP₁ and KhM₃ productive strata, composed of silty-clayey and clayey sediments accumulated within the far beach zone and the shelf remote from the shore, was associated with the maximum seafloor subsidence. The KhM₃ stratum was formed as the seashore regression increased within the far, transitional, shoreface and foreshore beach zones. Sandy material is genetically related to the ridge, central and slope parts and transgressive and regressive bar bottoms of the foreshore and shoreface, silty material is related to the transitional and far beach zones, clayey sediments are related to the deepened seabed areas of the far beach zone and the offshore shelf.