Место издания: Florence , Год издания: 2004

The Callovian marine transgression in West Siberia is one of the world's greatest geological events of such a type. It was preceded by prominent warming and aridisation of climate in adjacent southern territories. Water flow and sediment input into the basin were extremely reduced at the end of Bathonian and Early Callovian. The West Siberian Lowland has been denudated and underwent the "presubsidence" before the main marine transgression event. The equilibrium between sediment supply and the tectonic subsidence has been disrupted and the sediment input was not efficient enough to balance the tectonic subsidence. The proceeded transgression evoked resulted in replacement of fresh and brackish water environment by marine one. The transgression event was relatively instantaneous in the geological time scale. Since the Early-Middle Callovian boundary the sediment supply has started and continued persistently till the middle Late Oxfordian. In the continental conditions this period is represented by thinning-up series (Naunak Formation). Simultaneously, due to inversion process in the shore barrier zone, coarsening-up sequence has been precipitated in the marine basin. At the base of marine section there is a basal layer of specific aspect, composed of intercalation of carbonates, argillites, and siliceous sand rocks, rich in siderite concretions and carbonate oolites. This sequence is highly fossiliferous and bioturbated. It contains carbonized wood, pyrite, glauconite, etc. This layer is overlain by consolidated dark grey argillites, containing typical marine fossils. The appearance of silts and sands at the end of Callovian reflects an accelerating shoreline progradation with the maximum of regression at the end of the Early Oxfordian. The upper part of the series is consist of intercalated sand and clay rocks, which represent the transgressive part of the section (Middle-to-Late Oxfordian). The sediment input has diminished and the main factor controlling sedimentation is the tectonic subsidence again. At the end of Late Oxfordian the new sedimentation impulse took place and the whole of the process has repeated again. All substantial and structural features indicate the one-directional and irreversible course of events. The sedimentation impulse as a whole cannot be considered as a closed cycle. Therefore, the scenario of the basin development could not be described by sinusoidal curves, though there were sea level changes or something else.