Seismogeological analysis of the pre-Jurassic sediment complexes of the South Kara syneclise in connection with the tectonic zoning of the sedimentary cover

We present new data on the structure of deep horizons of the sedimentary cover of the South Kara syneclise, based on an integrated interpretation of data from modern seismic prospecting and data on the geologic structure of the adjacent folded areas. A network of seismic base profiles reprocessed with up-to-date programs is used to determine the structure of the wave fields of the pre-Jurassic sediments of the South Kara syneclise. The interpretation of the wave fields with the use of the network of seismic base profiles shows that the wave fields of the Pai-Khoi-Novaya Zemlya monoclise and the Novaya Zemlya-Taimyr terrace are fundamentally different from those of the South Kara central area of depressions and uplifts. We substantiate a new structural and tectonic zonation of the northern West Siberian Plate, with areas of Hercynian and Early Cimmerian consolidation. The geologic evolution of the South Kara syneclise and adjacent areas in the Late Paleozoic-Early Jurassic is considered. The studies show that the Hercynides of the northern Taimyr Peninsula occupy the deepest central part of the South Kara syneclise, including the North Siberian step. They are separated from the coeval sediments of the surface part of the northern West Siberian Plate by the Early Cimmerian folded area of the Yamal-Pai-Khoi saddle, which joins the Early Cimmerian West Taimyr folded area to the Early Cimmerides of Pai-Khoi and Novaya Zemlya.The Permo-Triassic rifts distinguished in central West Siberia have no shelf extension. Areal structural studies along the surface of the acoustic basement and analysis of wave fields showed that the structures of the South Kara syneclise were semiconcentric and concentric intermontane depressions and troughs in the Permian and Lower-Middle Triassic. They formed at the orogenic stage of evolution of the Hercynides. In the Devonian-Carboniferous, the South Kara syneclise was an intracontinental block structure. It is presumed that elevated blocks consist of carbonate sediments, whereas the separating troughs consist of bathyal terrigenous sediments. The Hercynian folding, which affected mainly deep-water sediment complexes, was followed by an inversion of the troughs, their uplifting and disintegration. The intermontane depressions which formed instead of carbonate shelf in the Permian were filled with sediments from the uplifts which formed instead of the troughs.A well-grounded conclusion is made about the hydrocarbon potential of the pre-Jurassic basement of the South Kara syneclise. The layered seismic record of the pre-Jurassic sediments suggests their heterogeneous composition, i.e., the presence of sand and clay series (reservoirs and caps). The pools might be of the arch-bedded and lithologic (traps which formed in the case of the toplap of beds onto the eroded surface) types or be localized along the line of pinching-out of the Triassic sediments. The largest number of Paleozoic structures is concentrated on the Rogozinskii and Vilkitsky arches, in the Monskaya and Matusevich saddles, and in the northern Rusanov-Skuratov arch.© 2014, V.S. Sobolev IGM, Siberian Branch of the RAS. Published by Elsevier B.V. All rights reserved.