AGE OF TERRIGENOUS ROCKS OF NORTHEASTERN KARAGINSKIǐ ISLAND (EASTERN KAMCHATKA)

Abstract

Terrigenous complexes of the Cenozoic accretionary prism are exposed in the northeast of Karagin- ski œ Island (eastern Kamchatka). Their age is debatable to the present day. The studied nannoplankton from mudstone and the fission-track dating of detrital zircon from sandstone elucidate age of terrigenous rocks. Aleu- ropelites yield two nannoplankton assemblages. One ranging in age from the Ypresian-Lutetian (Supra- Khynkhlonai sequence) to Bartonian-Oligocene (sedimentary melange) is considered as an in situ assemblage characterizing age of sediments. The other one consisting of Upper Cretaceous-Paleocene taxa is regarded as redeposited from older sediments of unknown provenance. According to fission-track dating, the youngest pop- ulation of detrital zircons is close in age to the deposition time of the most rocks studied. Terrigenous rocks of the Karaginski œ Island tend to be younger southeastward off the axial zone. The flysch complex is dated back to the Bartonian-early Oligocene, whereas rocks of sedimentary melange range in age from the Oligocene to early Miocene according to the fission-track dating of detrital zircon. Younger ages of rock located closer to the trench are typical of accretionary prisms.