Stratigraphic variations in lacustrine sediment gravity-flow deposits intercalated in varved diatomite: An example from the Hiruzenbara Formation, Okayama Prefecture, southwest Japan

摘要

The Hiruzenbara Formation, which is distributed within the Hiruzenbara Basin of southwest Japan, includes a section of varved diatomite, representing ca. 8000 y of deposition in a dammed lake formed during the Middle Pleistocene. The varve, on average, ca. 1.5 mm thick, consists of light-and dark-green laminae sets, and is predominately composed of planktonic diatoms. Several facies types of sediment gravity-flow deposits are intercalated in the varved diatomite. In this study, we examined the sedimentary facies, lateral changes, and stratigraphic variations of these sediment gravity-flow deposits. In addition, we also analyzed a time series of varve thickness fluctuations.