From: "James Clarke" Subject: MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit X-Priority: 3 X-MSMail-Priority: Normal X-Unsent: 1 X-MimeOLE: Produced By Microsoft MimeOLE V4.72.3110.3 From: "James Clarke" Subject: MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit X-Priority: 3 X-MSMail-Priority: Normal X-Unsent: 1 X-MimeOLE: Produced By Microsoft MimeOLE V4.72.3110.3 Cyclicity in Sediment Deposition on Siberian Craton

Cyclicity in Sediment Deposition on Siberian Craton
Internet Geology News Letter No. 168, September 23, 2002

Three stages are recognized in the sedimentary history of the Siberian craton (East Siberian oil-gas province): aulacogen (Riphean), homogen (Vendian-Early-Middle Paleozoic), and heterogen (subdivided into denudational-accumulative of Late Paleozoic - Early Mesozoic age and essentially denudational of Mesozoic-Cenozoic age).

Most of the deposition in the basin was in the homogen stage, which constituted a mega-cycle of about 450 million years (700-250 m. y. age span). This mega-cycle consisted of two large cycles, each about 225 m. y. in duration. The boundary between them was at the end of the Early Ordovician. These cycles are in turn subdivided into segments of 112, 56, 28, and 14 m. y. segments. Cycles of the third order, that is, those of 56 m. y. duration, have four phases: transgression, inundation, regression, emersion. Cycles of the first order (225 m. y.) correspond with a "galactic year", whereas those of the third order may be compared to a "galactic season".

Seven cycles of the third order are recognized. The sediments of the first cycle are Lower Vendian and are largely clastics, rarely carbonates. Smaller-scale cycles are rare here. The rocks of the next three third-order cycles extend fro the upper part of the Lower Vendian to the Ordovician. They are very widely distributed, are very thick, and constitute the main volume of sedimentary rocks of the mega-basin. Practically all types are present from detrital facies to evaporites. The main commercial oil and gas pools of the mega-basin are in the rocks of these cycles. Cycles of fourth and fifth order are also clearly recognized with these third-order cycles.

The three upper cycles of the third order extend from the Middle Ordovician to the Early Carboniferous and have a clay- carbonate, silt-clay, carbonate, and clay-carbonate-sulfate composition. Only thin beds of sandstone are present. No commercial hydrocarbon deposits have been found here. Transgressive units enriched in organic matter are the Lower Vendian Khatysput Formation of the Olenek high, argillite members of the lower Moty Formation of Vendian age, most of the upper Moty of Late Vendian-Early Cambrian age and its analogs, the lower Chopkotin Formation of the Late Cambrian, Middle and Upper Ordovician clay-carbonate rocks, Silurian graptolitic shales, and the Koktin Formation of Givetian age.

Regressive units enriched in organic matter are the middle Moty Formation, Lower-Middle Cambrian Kuonam Formation, Upper Cambrian Turin Formation, Upper Silurian clayey dolomites, and Upper Devonian Kalargon Formation.

Taken from Bazhanova, 1986; digested in Petroleum Geology, vol. 23, no. 11/12, two stratigraphic charts. Copyright 2002, James Clarke. You are encouraged to print out this News Letter and to forward it to others. Earlier News Letters are available at: http://geocities.com/internetgeology/ This News Letter is distributed without charge in the interest of our science of petroleum geology. To be added to the mailing list please send your e-mail address to: jamesclarke@erols.com For information on the journal Petroleum Geology please telephone 703 759-4487 or FAX 703 759-3754. Man has developed beyond other animals because his erect posture freed his hands for graspinf things - Anaxagoras, 5th Century B. C. 1