9:15 AM - 9:30 AM
[HQR04-02] Last 2000-year coastal environmental changes in the Kii Peninsula, central Japan
★Invited Papers
Keywords:Yukashi-gata Lagoon, Lake sediments, Pollen analysis, Diatom analysis, human impacts, Wakayama Prefecture
In this research, 292-cm-length lake sediment core were collected from center part (water depth : 3.6 m) at the Yukashi-gata Lagoon located in Nachikatsuura Town, Wakayama Prefecture, central Japan.
The Kii Peninsula consists mostly of steep mountainous terrain with a few lowlands and almost no lakes or marshes, even in the coastal areas. This topographical feature has left unreported area for paleoenvironmental researches. we have an lake drilling scientific research at the Yukashi-gata Lagoon, a remnant marine lake in the southeastern part of the peninsula. The objectives of this study are to detect climatic changes in historical times, to examine the frequency of floods and tsunami intrusion by event strata, and to reconstruct the history of human impacts related to the Kumano faith through comprehensive paleoenvironmental analysis of the collected sediments.
The lithology of the core consists of massive fine sand to silt layers with some bioturbation, including many blue-gray plants and shell fragments, except for a dark gray silt layer of topmost 30 cm. There are no interbeded coarse-grained thin layers that would qualify as event strata. Four radiocarbon dating of plant remains indicates that the lowest part of the core was deposited approximately 1,500 years ago (500 A.D.), suggesting that a stable sedimentation with a rate of approximately 3 mm per year has continued until the present.
According to the sequential results of geochemical, diatom and pollen analyses for the sediment samples, the results of this study revealed the following three points: (1) the lagoon environment has continued for the past 1500 years, (2) anthropogenic modification of the environment was recognized in the 7th century and later periods, synchronizing with the start of the Kumano mountain worship, and (3) the tsunami deposits caused by the Nankai Trough in the historical period were not found at various sites along the Pacific coast.
The Kii Peninsula consists mostly of steep mountainous terrain with a few lowlands and almost no lakes or marshes, even in the coastal areas. This topographical feature has left unreported area for paleoenvironmental researches. we have an lake drilling scientific research at the Yukashi-gata Lagoon, a remnant marine lake in the southeastern part of the peninsula. The objectives of this study are to detect climatic changes in historical times, to examine the frequency of floods and tsunami intrusion by event strata, and to reconstruct the history of human impacts related to the Kumano faith through comprehensive paleoenvironmental analysis of the collected sediments.
The lithology of the core consists of massive fine sand to silt layers with some bioturbation, including many blue-gray plants and shell fragments, except for a dark gray silt layer of topmost 30 cm. There are no interbeded coarse-grained thin layers that would qualify as event strata. Four radiocarbon dating of plant remains indicates that the lowest part of the core was deposited approximately 1,500 years ago (500 A.D.), suggesting that a stable sedimentation with a rate of approximately 3 mm per year has continued until the present.
According to the sequential results of geochemical, diatom and pollen analyses for the sediment samples, the results of this study revealed the following three points: (1) the lagoon environment has continued for the past 1500 years, (2) anthropogenic modification of the environment was recognized in the 7th century and later periods, synchronizing with the start of the Kumano mountain worship, and (3) the tsunami deposits caused by the Nankai Trough in the historical period were not found at various sites along the Pacific coast.