Cyclic changes of sediments and molluscan fossil associations caused by glacio-eustatic sea-level changes during the early Pleistocene. A case study of the middle part of the Omma Formation at the type locality.

Abstract

Early Pleistocene sea-level changes assignable to be glacio-eustatic origin are detected from the shallow marine sedimentary sequences in the middle part of the Omma Formation, Kanazawa, Japan. The sea-level changes are demonstrated by at least ten cyclic changes of sedimentary facies and of autochthonous molluscan fossil associations. This change within the cycle is attributed to not only the water regime changing from cold to warm current but also relative sea-level changes with an amplitude up to 50m. The periodicity of the cyclic changes is estimated to be in the order of few tens thousand years on the average, based on biostratigraphic as well as paleomagnetic data. -from Engligh summary