A Characteristic Form of Diatom Melosira as an Indicator of Marine Limit during the Holocene in Japan

Abstract

A diatom form, tentatively named Melosira sp. 1, with strongly silicified hemispherical valves or sub-spherical frustules, occurs in the sedimentary sequences recording Holocene sea-level changes in Japan. It reaches maximum abundance in the uppermost part of marine facies formed as a result of Holocene transgression, and disappears in overlying freshwater sediments at several sites along the coastal areas in Japan. Its distinctive morphology, corrosion resistant thick valves, common occurrence with abundance peaks near the upper limit of marine facies described in this paper and occurrence in the present-day tidal flat reported by Kosugi (1986, 1988), should make this diatom form one of the useful indicators for identifying marine limit. The abundance peaks of the form indicating former sea-level stand during the Holocene would be helpful to reconstruct local histories of Holocene sea-level changes in Japan.