The tectonic framework of the NW. quadrant of the circum-Pacific orogenic belt is explained as the result of the process postulated in the theory of growing continental masses. The festoons of island arcs marked by the Nampo Shoto, Northern Japan, the Kuriles, Kamchatka, and the Aleutian Islands are the most recent additions to the northeastern part of the Asian continent and have resulted from late Mesozoic and Tertiary orogenies. Japan and Kamchatka are polycyclic orogenic mountain arcs and were part of older festoons of island and mountain arcs extending from Kamchatka through Formosa and the Philippines. Early orogenic movements can be traced in Japan in the late Devonian, Carboniferous, and middle Permian. The present forms and positions of the Japanese islands were probably defined during early Mesozoic orogenies. In narrow, coastal areas of NW. Honshu, western Hokkaido, and SW. Sakhalin, small production of oil and gas is obtained from Upper Tertiary formations on folded and faulted structures fringing the mobile side of the Japan Sea sedimentary basin. In northeastern Sakhalin, more substantial oil production is obtained from Tertiary beds where structural and stratigraphic conditions suggest that the accumulations occur on the present, more or less stable side of the Okhotsk Sea idiogeosynclinal basin. New, and perhaps important, oil discoveries can be expected from structural folds located off the NW. coasts of Honshu and Hokkaido, and perhaps off the SW, coast of Sakhalin. Some oil may be found in small intramontane type basins in central and NW. Hokkaido. Additional production should be found in structural or stratigraphic traps off the NE. coast of Sakhalin.

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