Sediments of large paleo-channels occur over a wide stratigraphic range in the Timan-Pechora region of northeast European Russia. The Paleozoic rivers flowed west to east with the source of supply on the west. The marine basin occupied the region of the future Ural-Novaya Zemlya fold belt. In Mesozoic and Cenozoic time the main marine basin was to the north of the Timan-Ural land area. Rivers then flowed largely to the north and northwest. For a long time there had been no direct confirmation of this direction of flow. Seismic surveys have now demonstrated that the linear depression zones known onshore, including the Denisov downwarp in the central part of the study area and the Khoreyver depression to its east, continue to the north as far as the junction with the South Barents depression. These depression zones appear to have been old river channels, and the area of junction with the South Barents depression was the site of delta formation. One such feature is predicted in the Lower Jurassic section.
At the beginning of the Jurassic the region of the Pechora sineklize was a low plain that was not experiencing significant downwarping. A minimum of lacustrine-alluvial deposits collected. Clastics from the Urals and Timan were transported across this plain into the marine basin on the north. Conditions were favorable for such transport along the north-south Denisov downwarp, where seismo-facies analysis has disclosed the position of a buried valley of an Earely Jurassic river.
The wave picture of the predominantly marine Jurassic sediments differs from that of the underlying predominantly continental Triassic sediments. Then there is a transitional seismic complex at the base of the Jurassic. The Barents part of this latter complex is typically marine with strong, persistent reflections. In the zone of junction with the Pechora sineklize is the above-mentioned deltaic complex. The Pechora part of this complex corresponds with a Lower-Middle Jurassic unit that has irregular reflections characteristic of continental deposits. On several profiles here that are sub-parallel to the paleo-shore line, lens-like seismic facies are recorded typical of shallow-water fluvial sections. These deposits are correlated with the base of the Jurassic.
In plan the fluvial seismic facies form a narrow belt 5-10 km wide,
which extends toward the paleo-sea. Thickness of this valley
section is close to 100 m near the mouth and only somewhat
less at a distance of 60 km "upstream" from it. The seismic
characteristics and position of the section indicate that these are
Early Jurassic alluvial deposits of a large river channel. It is
possible that several paleo-channels are represented here.
Taken from Shipel'kevich, 1988; digested in Petroleum Geology,
vol. 30, no. 2, p. 194-197, 1996; four seismic sections and one
structure map.
Copyright 2001 James Clarke. You are encouraged to print out this
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