天竜川扇状地で得られたコア堆積物の堆積相と堆積速度(地域研究)

概要

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A 50-m-long core (TR1 core) was collected from an alluvial fan at the lower reaches of Tenryu River, central Japan. TR1 core was divided into three units on the basis of sedimentary facies and physical properties. Unit 1, consisting of the alternation of pebble and pebbly sand, was considered to be fluvial sediment deposited before 9600 cal BP. Unit 2 (9600 to 7100 cal BP) consists of the alternation of sand and mud with rich organic matter. Electric conductivity and diatom species suggest that the deposition of the Unit 2 was occurred under the marine and estuarine environments. Unit 3, consisting of clast-supported gravel and organic-rich mud was formed under the fluvial environment after 7100 cal BP. Larger accumulation rate, approximately 12.4m/kyr, occurred in Unit 1 and Unit 2. After about 8000 cal BP, it decreases considerably by 2.5m/kyr. They should be related to the deceleration of the post-glacial eustatic sea-level rise.
2009-10-25