In Hokkaido, two asynchronous pairs of Jurassic to earliest Tertiary arc-trench systems are recognized. Tlie trench belt of the older pair occupies a part of the Jurassic to Cretaceous Yezo Geosyncline, where the Kamuikotan metamorphic rock belt may represent a west-dipping subduction zone. The trench belt of the younger pair is represented by the latest Cretaceous to earliest Tertiary Small Kuril Geosyncline (new name). In both geosynclines, the trench sediments are characterized by the following fourfold succession, in ascending order: (1) radiolarian chert or siliceous shale and pillow lavas, (2) flysch, (3) shallow-marine muddy sediment, and (4) molasselike sequences. Farther to the south of the Small Kuril Geosyncline, the modern Kuril Trench has been developed. These consecutive developments of arc-trench systems present a good example of oceanward migration patterns of the systems.
Figures & Tables
The Kay Conference was held in Madison, Wisconsin, November 1972. This symposium volume contains the texts of papers presented at Madison. It is organized in a topical manner, and in most areas of discussion, modern analogues and ancient examples together provide a comparative basis for evaluating sedimentary models for geosynclines. In the 1970s students of both modern and ancient sediments have compiled an immense body of knowledge relevant to the geosynclinals concept. Moreover, the new theory of plate tectonics has required a complete reassessment of the geosynclines as well as orogenesis. The purpose of this volume is to evaluate by comparison of modern and ancient sediments a number of depositional models applicable to the great variety of strata seen in orogenic belts also called geosynclinal.