Reconstruction of Sedimentary Environments for Late Pleistocene to Holocene Coastal Deposits of Lake Kamo, Sado Island, Central Japan

Abstract

Multiproxy analyses including grain size, total organic carbon (TOC), total sulfur (TS), total nitrogen (TN), calcium carbonate (CaCO₃) contents, diatom as well as sedimentary properties of the boring core KM-11 (54m in length) collected from a brackish lake, Lake Kamo, are used to reconstruct paleoenvironment and coastal evolution of northeast coast of Sado Island in central Japan. Anoxic and normal marine sediments can be detected by TOC-TS relationship, and the origin of organic matter is inferred from the TOC/TN ratio. Geochemical characteristics of the sediments respond striking to sea-level change. In the Late Pleistocene, fluvial sediments are characterized by high TOC, very low TS and terrigenous organic matter. The overlying coastal marsh sediments are characterized by high TOC and abruptly increasing trend of TS suggesting sea water spilled into the site, and are overlain by estuarine sediments which obviously indicates the beginning of the Holocene transgression. Embayment sediments are characterized by low TOC, marine organic matter and low productivity condition indicating the rapid relative sea-level rise. The maximum Holocene transgression could be inferred between 6, 500 and 5, 000yrs BP. After that fluctuations of relative sea-level are characterized by high TOC, high TS, a mixed type of marine/terrigenous organic matter and high productivity condition to be inferred marine/brackish lagoonal sediments. Diatom floral changes of the core KM-11 also support the geochemical data to interpret the paleoenvironment and evolution of the coastal deposits.