The Late Cenozoic basins of the Kurile-Kamchatka region have been outlined by seismic and gravity surveys. Most of these basins are continuing their development at the present time. They have not been exposed to erosion, and they are masked by Pleistocene deposits. There are few surface signs of hydrocarbons. Particularly unclear are prospects for the offshore depressions, one part of which is on the shelf and the other in deep water. Nevertheless, similar tectonic features in the other part of the world are host to numerous oil and gas fields including giants.
Geologic development of the Kurile-Kamchatka region in Pliocene and Pleistocene time was under the strong influence of rifting. The modern structure was governed by superposition of a rift system onto Mesozoid orogenic structures. Rifting began at least in the Eocene and was dispersed. Intensity of this rifting increased sharply in the middle Pliocene, when deep-water trenches began to form.
Several depressions formed in Pliocene and Pleistocene time in the study area. They are disposed largely in two groups. One extends from southwestern Kamchatka southward on the west of the Kurile Islands, and the other is offshore to the east of southern Kamchatka, extending southward on the east of the Kuriles. Dimensions of these depressions range from 15 by 30 km to 40 by 70 km and more. Area of the small depressions is from 500 to 3000 sq km, and that for the large ones is up to 40,000 sq km.
Litken depression in the central part of southern Kamchatka has been well studied. This feature formed under conditions of transition from land to sea during late Paleogene-Miocene time. This was never a deep-water feature; deposition was on a shallow-water shelf or on coastal plain. The Golygin depression is a similar structure; it extends southward from the southern tip of Kamchatka and is filled with Neogene and Quaternary marine deposits with a large volcanic component. Sedimentary thickness in its marine portion is up to 6 km. Kolpakov depression in the southwest part of Kamchatka extends offshore. Gas-condensate fields are present in the onshore part.
In Miocene time all the depressions of the study area were epi-continental compensated features and have been very favorable for accumulation of oil and gas. Morphology of the basins of sedimentation is very favorable; there has been a minimum of inversion. Great thickness of the Upper Cenozoic indicates high rate of sedimentation. Lithology is favorable, and a variety of traps are present. The high seismicity, heat flow, and volcanism are important to rapid generation of hydrocarbons. Favorable conditions obtain in Central and Eastern Kamchatka in contrast to Western Kamchatka where the source rocks are close to the surface and eroded. The gas-condensate fields of Western Kamchatka are not in these latter areas but rather in Kolpakov depression, where molasse is up to 6 km thick. Kolpakov depression is favorable for large discoveries, particularly offshore. Favorability for the Kurile region is not great. (Taken from Yermakov and Shteynberg (2000); digested in Petroleum Geology, vol. 35, no. 1, p. 1-9, 2001, three maps, in preparation)
Copyright 2000 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/
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