Relationship between shelf sedimentation and climate changes in the upper Pliocene Dainenji Formation in Fukushima, northeastern Japan

Abstract

Pliocene Dainenji Formation is distributed in the Pacific Ocean side of the Fukushima Prefecture. The depositional age is from 4.18 to 2.6 Ma. We carried out facies analysis and geochemical analysis, such as total organic carbon (TOC), total sulfur (TS), and stable carbon isotope ratio of organic matter (δ¹³C_org). Our results are as follows : (1) Abundant land-derived organic matter was transported to the shelf and was preserved in the sediment in warm period (3.75-3.5 Ma), (2) Productivity of marine organism increased in the early cooling period (3.5-3.35 Ma), (3) The considerable variations in TS, TOC and δ¹³C_org are seen in cooling stage after 3 Ma, which succeeded to the Quaternary ice age. Theses considerable variation are shown in δ¹⁸O curve of the same age.