Geological Settings and Evolution of the South and North Kara Basins

Nikolay Malyshev, Valeriy Nikishin, Anatoly Nikishin, Victor Obmetko, Juriy Reydik, and Bulat Ikhsanov
Rosneft Oil Company, Moscow, Russian Federation.

The Kara Sea includes the area of two big sedimentary basins: South Kara Basin (SKB) and North Kara Basin (NKB), separated by the North Siberian Swell (NSS).

The SKB is located in the northern part of the West Siberia Megabasin (WSM). In the west it is surrounded by the Pay-Khoy and Novaya Zemlya fold belts and in the north-east - by NSS. The SKB is covered by 135500 line km of 2D seismic data and regional lines 2-AR and 3-AR. NKB is less explored as compared with SKB. Its area is covered by 8000 line km of 2D seismic data and regional lines 4-AR and 3-AR. No wells were drilled there. The 3-AR line links SKB to NKB and helps us to understand the features of the geological structure

The SKB is filled by Upper Triasic(?)-Cenosioc clastic sediments together with the Late Permian(?)-Mid Triassic synrift megasequence. The rifts base is tracked at the depth up to 11-12 km. Using new seismic data, we identify grabens and semi-grabens at the base of the basin. They are filled by partly deformed sediments. There are two major graben types: with deformations of synrift sediments and without. Grabens without deformations are located in the central part of the basin, grabens with deformations are close to the Novaya Zemla fold belt. They were formed by compressional/transpressional processes during the Middle Triassic time in the Barents-Kara region.

Generally, we do not know the age of sediment infilling and origin. From the analogy with the WSM grabens, we assume that the SK grabens have the same age of origin. Synrift basalts in WSM are of the Late Permian(?)-Early Triassic age. After rifting, the postrift subsidence started.

The South Kara basin is formed by a huge depression at the central part and a series of swells, surrounding it at the west border along the Novaya Zemlya and NSS. Big local structures are located at the steps and swells. There were two major periods of local structure formation. The first one took place in the Jurassic/Cretaceous boundary and the second one - in the Cenozoic time (post-Oligocene).

We assume that NKB have the Neoproterozoic basement. The sedimentary cover formations started from the Ordovician time. We refer Vendian(?)-Cambrian rocks to the acoustic basement on seismic data in the NK basin from the analogue with the Timan-Pechora basin.
The NKB combines a few narrow and extended depressions and ridges. Depressions are filled by about 12-16 km of the sedimentary sequence. The NK sea basin, possibly, includes the synrift, postrift and syninversional sedimentary complexes. The age of the synrift complex is unknown. Data on Severnaya Zemlya islands show that main unconformity is close to the Cambrian-Ordovician boundary. The Ordovician rift-related volcanism is displayed in the Severnaya Zemlya territory. It means that possible main rifting event in the NKB area took place during the Ordovician time. The main inversion event took place near the Triassic/Jurassic boundary.

 

AAPG Search and Discovery Article #90130©2011 3P Arctic, The Polar Petroleum Potential Conference & Exhibition, Halifax, Nova Scotia, Canada, 30 August-2 September, 2011.

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