The Magadan Shelf is a sector of the shelf of the northern part of the Sea of Okhotsk. It corresponds with the Magadan basin to the south of Magadan, the Gizhigin basin to the northeast, and part of TINRO basin farther to the south. It is within the North Okhotsk rift zone, which extends along the south margin of the Okhotsk-Chukot volcanic belt. Rifting was during Paleogene-early Miocene time. Four offshore wells have been drilled in Magadan basin.
The sedimentary section of the Magadan basin is subdivided into six structural-stratigraphic complexes: Upper Cretaceous, Paleocene-Eocene, Oligocene-lower Miocene, middle-upper Miocene, upper Miocene-Pliocene, and Pliocene-Quaternary.
The Upper Cretaceous has been identified on Magadan high from seismic surveys and drilling. Thickness and distribution have not been determined.
The Paleocene-Eocene complex collected during the early rift stage of the downwarp and is 0.1-6.0 km thick. The section consists of continental and near-shore marine clastics. Continental deposits probably predominate in Gizhigin basin. On the outer shelf is the TINRO depression, where relatively deep-water clays are present.
The Oligocene-lower Miocene complex was deposited during the late rift stage and is 200-3000 m thick. Present over a large part of the shelf are shallow- and deep-water sand-silt-clay and siliceous deposits. To the south toward the TINRO depression the clastic component is reduced and acoustically transparent siliceous material is prominent.
The middle-upper Miocene complex was deposited at the beginning of the post-rift stage and is 400 to 3000 m thick. Deformation is mild. Lithology is the same as in the underlying complex except for presence of more siliceous material here.
The upper Miocene-Pliocene complex is 400-1000 m thick and consists of silt-clay-siliceous deposits.
The Pliocene-Quaternary complex is 500-1000 m thick.
Reservoir rocks are present in the Paleocene-Eocene, Oligocene-lower Miocene, and middle-upper Miocene complexes. The Paleocene-Eocene complex consists of argillites in its upper part and largely coarse clastics in it lower. Maximum total thickness of reservoir rock is 3000-4000 m. The Oligocene-lower Miocene complex consists of three parts: upper, which has good reservoir properties; middle, which is favorable for fracture reservoirs; and lower, where reservoir properties are poor. The middle-upper Miocene complex corresponds with a large transgressive- regressive cycle and consists of clay-siliceous rocks with some coal. Total thickness of the middle-upper Miocene reservoir rocks is 250-750 m.
Source beds are present in the same three complexes as are the reservoir rocks. The greatest thickness of source beds in the Paleocene-Eocene complex is found in the TINRO depression at 3000-4000 m. In the Oligocene-lower Miocene complex source beds are 2000-3000 m thick in TINRO depression, and in the middle-upper Miocene complex - up to 2800 m in the Magadan sector of the shelf.
The scale of expulsion of hydrocarbons from the source beds was estimated according to thickness and their maturation. The Paleocene-Eocene complex has the greatest expulsion potential at 5-10 million tons per sq km for the Magadan sector. For the Oligocene-lower Miocene complex the estimates are 5-7.5 million tons per sq km for the Magadan sector and 13.7 million tons per sq km for TINRO depression. Estimated values for the middle-upper Miocene are 2.5 million tons per sq km. (Taken from Koblov and Kharakhinov (1997); digested in Petroleum Geology, vol. 34, no. 4, p. 391-400, one map)
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