Benthic foraminifers and depositional environments of the Lower Cretaceous Miyako Group on Hideshima Island, Miyako area, Iwate Prefecture, northeast Japan

Abstract

On Hideshima Island (Miyako area, Iwate Prefecture, northeast Japan), the Albian Hideshima Formation of the Lower Cretaceous (Aptian to Albian) Miyako Group consists mainly of alternations of turbidite sandstone and mudstone, thick sandstone, and conglomerate. It is also characterized by slump beds and debris flow deposits containing poorly preserved shallow-marine bivalves such as Glycymeris, Eriphyla, Nipponitrigonia, and rudists, representing typical allochthonous occurrences. Eleven genera of the benthic foraminifera have recently been identified in the mudstone of the middle part of the Hideshima Formation. The benthic foraminiferal assemblage is dominated by Bathysiphon spp., Recurvoides spp., and Haplophragmoides spp. Facies analysis and the composition of the benthic foraminifera indicate that the Hideshima Formation accumulated in a slope environment.