MIDDLE JURASSIC TO EARLY CRETACEOUS RADIOLARIA FROM THE OMGON RANGE, WESTERN KAMCHATKA

Abstract

The Omgon Range (Western Kamchatka) includes intensely deformed tectonic units, some of which consist of volcanogenic rocks and siliceous sediments, whereas others are represented by siliceous sediments and terrigeneous turbidites. All these rocks were considered so far to be not older than Early Cretaceous. Radiolarian assemblages ranging in age from Middle Jurassic to late Early Cretaceous are here reported from siliceous sedimentary rocks in three distinct unit. In particular, Middle Jurassic (Bajocian-Bathonian) radiolarians were collected from red cherts of the lowermost of these units. This is the first finding of Jurassic radiolaria in Kamchatka. A late Tithonian to late Barremian-early Aptian radiolarian assemblage has been yielded by siliceous levels in an overlying unit. An Early Cretaceous radiolarian assemblage has been found in siliceous rocks associated with pillow basalts in a unit lying in a higher tectonic position. The Middle Jurassic radiolarian assemblage shows Boreal affinity; whereas the Late Jurassic-Early Cretaceous (Tithonian-Berriasian) radiolarian assemblages can be related to both Tethyan and Boreal Provinces. The following new species are described: Archaeodictyomitra curta n. sp., Archaeodictyomitra elliptica n. sp., Stichocapsa globosa n. sp., Parvicingula omgonensis n. sp. and Xitus? primitivus n. sp.