第四紀の浅海環境変遷史の解明(貝類化石による第四紀海成層の高分解能層序学)

阐明第四纪浅海环境变迁的历史（利用贝类化石进行第四纪海相地层高分辨率地层学）

• 批准号: 06740404
• 负责人: 北村 晃寿
• 金额: $ 0.58万
• 依托单位: Shizuoka University
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Encouragement of Young Scientists (A)
• 财政年份: 1994
• 资助国家: 日本
• 起止时间: 1994 至 无数据
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-06740404/
• 关键词: 第四紀; 浅海環境; 貝類; 氷河性海水準変動; 対馬海流

本研究の課題は,第四紀の汎世界的な気候変動(氷期・間氷期サイクル)とそれに伴う氷河性海水準変動が,浅海の環境と生物にどのような影響を与えたかを解明することである.筆者のこれまでの研究により,大桑層の模式露頭(石川県金沢市犀川河床)において,140万年前から80万年前までの間に起きた氷河性海水準変動による堆積シーケンスと貝化石群集の周期的変遷が明らかにされている.だが,これらの記録からは,1地点における環境・生物の時間的変化しか解読できない.そこで,本研究では大桑層の模式露頭の沖合いとより沿岸に堆積した大桑層の岩相・貝化石の層位分布を精査した.その結果,氷期については水深20-30mから50-60m,間氷期については水深20-30mから100-120mまでの堆積物と貝化石の深度分布を解明できた。氷期には,水深の増加とともに堆積物は細粒化し,貝化石群集はPeronidia群集,Felniella群集,Clinocardium-Turritella群集(これらはいずれも寒流系上部浅海帯群集に分類される)の順に変化する.一方,間氷期の堆積物は,沖合いに向かって水深50-60mまでは細粒化するがそれを超えると粗粒化し,そして水深100-120mを超すと再び細粒化傾向に転じる.また,貝化石群集は,暖流系上部浅海帯群集,暖流系下部浅海帯群集,寒暖混合群集の生息深度は約100m以深と推定される.現在の日本海では,寒暖混合群集は対馬海流と日本海固有水に挟まれた中間水に生息し,その深さは140m以深である.よって,寒暖混合群集の生息深度の差は,100万年前の間氷期の対馬海流の厚さが現在のそれの約2/3であったことを示唆する.以上が本研究で得た新知見であるが,特に対馬海流の流入量が現在と過去では異なるという知見は重要である.

This research topic is about the seasonal fluctuation of Quaternary in the world, and the influence of the seasonal fluctuation of river seawater on the environment and biology of shallow sea. The model outcrop of the Okamura Formation (Ishikawa River Bed, Kanazawa City, Ishikawa Prefecture) was discovered 1.4 million years ago, and the period from 1.8 million years ago to 800 million years ago was characterized by the quasi-fluctuation of fluvial seawater and the accumulation of fossil conch assemblages. The change of environment and biological time in 1 place. This study is aimed to investigate the impact of model outcrops of the large mulberry beds and the stratigraphic distribution of lithofacies and shellfish fossils in the large mulberry beds accumulated along the coast. The results show that the depth distribution of the sediments and shellfish fossils in the middle stage is 20-30m to 50-60m, and in the middle stage is 20-30m to 100-120m. During this period, the sediments became finer as the water depth increased, and the fossil constellations became Peronidia constellations,Felniella constellations,Clinocardium-Turritella constellations. On the other hand, the interphase deposits tend to be fine grained at water depths of 50-60m, and coarse grained at water depths of 100-120m. It is inferred that the fossil constellations are clustered in shallow sea zone in the upper part of warm current system, in shallow sea zone in the lower part of warm current system, and in mixed cold-warm system at a depth of about 100m. At present, the Japan Sea is full of cold and warm mixed clusters, which live in the middle water of the Japan Sea, and the depth is more than 140m. The difference between the living depths of the cold-warm mixed clusters is about 2/3 of the thickness of the equine current in the interval of 1 million years ago. The above new insights are gained in this research, but in particular, the inflow of the Ma Hai current is different from the present and the past. These insights are important.