Accumulation of the Paleocene-Eocene sediments in Magadan basin on the north shelf of the Sea of Okhotsk was under relatively low sea level conditions accompanying the intensive tectonic movements of the opening of the rift depressions. This complex is present in all the downwarps, pinching out on adjacent highs. It consists largely of sub-continental deposits of lake, rarely lagoonal or near-shore marine origin. Sandstone and conglomerate predominate; some coal, argillite, and siltstone are present. Near-shore marine facies predominate in the upper part of this complex in Zav'yalov downwarp and on adjacent Magadan high. There is a change from deltaic cones, turbidites, and volcano- clastics on the borders of the basins to more monotonous finer- grained deposits in axial areas of the downwarps.
Deposition of the lower Oligocene sediments took place under shallow-water marine and lagoonal conditions. The area where these deposits collected was less than that of the Paleocene- Eocene complex due to depletion of the source of supply (Shestakov and Lisyan highs) on the south and interception of sediment arriving from the continent on the north by the Kavin-Tauysk depressions which formed in the early Paleogene. This complex consists of rhythmically bedded rocks from conglomerates to sand-silt, argillite, and coal beds. Introduction of clastic material was by lateral transport along the axis of the downwarps and by a system of submarine cones and deltaic fans.
The areas of syn-rift sedimentation in Magadan basin include a wide spectrum of types of deposits, and along with high rates of sedimentation at 100-300 cm per year conditions were favorable for formation of reservoirs and source beds. Total thickness of the syn-rift Paleocene-lower Oligocene sedimentary pile reaches 4-6 km.
The next complexes upward in the section are in the post-rift part of the sedimentary fill of Magadan basin.
The lower part of the upper Oligocene-middle Miocene complex seals the underlying graben-like downwarps. In the eastern part of the basin this complex passes into relatively deep-water facies with a deficit of sand-silt components - biogenic-siliceous. This was a time of sharp rise in sea level. High rates of sedimentation continued with addition of 2.0-2.5 km to the section. The newly-formed TINRO deep-water depression was part of all this.
Deposition of the middle-upper Miocene complex was marked by increased production of algal siliceous plankton. Upwelling was a definite factor here. Opoka and opoka-like clays up to 2.5 km in thickness collected in the basin.
The upper Miocene-Quaternary sedimentary complex was deposited
everywhere on an open shallow-water shelf with predominance of biogenic
material in the lower part and siliceous-clastic in the upper. Maximum
thickness of this complex is 1.6 km.
Continued in next News Letter
Taken from O. A. Krovushkina, 2001; digested in Petroleum Geology,
Vol. 37, No. 1, 2003, in preparation, two maps, one seismic section,
one chart showing range in petroleum generation and expulsion.
Copyright 2002, James Clarke. You are encouraged to print out
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ERRATA: Heading of the last News Letter should read No. 163, not 165.
If thou art pained by any external thing, it is not this that disturbs you,
but thy own judgement about. - Marcus Aurelius, Meditations, VIII, No. 47.