In the Sanriku coastal area,discrepancies have been suggested in crustal movements between long (104-105 years) and short (101-102 years) time scales. To clarify the cause of these discrepancies and reconstruct the tectonic history of this area, knowledge of incised valley fills with many radiocarbon ages provides basic and important data. Although the southern Sanriku coast has some small alluvial plains in the environments of ria coasts, the formation process of valley fills has not been discussed on the basis of a number of radiocarbon ages. In this study, a sediment core,TY1, is acquired from the lower reaches of the Tsuya Plain, southern Sanriku coast. Core sediments show a shallow marine succession influenced by Holocene sea-level change. Based on twelve radiocarbon ages, the accumulation rate is high-( > 5 mm/yr) at 9,000 to 7,100 cal BP, low (ca.1 mm/yr) at 4,080 to 2,800 cal BP, and high (3-5 mm/yr) after 2,800 cal BP. High accumulation rates in bay mouth deposits during the middle Holocene, when relative sea-level rise decelerated, indicates sedimentation from the seaward area during the period of marine transgression. This marine transgression can be explained by the deposition of terrestrial sediments in small basins upstream from the Tsuya Plain and setback in the deceleration of relative sea-level rises by the Holocene subsidence trend. In the regressive phase since the middle Holocene, a low accumulation rate in deltafront deposits and a high accumulation rate in delta plain deposits coincide with changes of accumulation rate in the coastal area where relative sea-level has risen in a millennium scale. This also implies that the Tsuya plain subsided during the Holocene.
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机译：在三陆沿岸地区，地壳运动在长（104-105年）和短（101-102年）之间存在差异。为了弄清这些差异的原因并重建该地区的构造历史，了解许多放射性碳年代的切谷填充物提供了基础和重要数据。尽管三里库南部海岸在里亚海岸沿岸有一些小型冲积平原，但尚未根据许多放射性碳年龄讨论山谷填充物的形成过程。在这项研究中，沉积岩心TY1是从三陆南部海岸的Tsuya平原的下游获取的。核心沉积物显示出受全新世海平面变化影响的浅海演替。基于十二个放射性碳年龄，在9,000至7,100 cal BP时，成藏率高（> 5 mm / yr），在4,080至2,800 cal BP时成藏率低（约1 mm / yr），而高（3-5 mm / yr）在2,800 cal BP之后。在全新世中期，当相对海平面上升减速时，海湾口沉积物的高积累率表明，在海侵期间，来自沿海地区的沉积物。这种海侵现象可以解释为：津谷平原上游小盆地中的陆相沉积物的沉积，以及由于全新世沉陷趋势而导致的相对海平面上升速度的减缓。在自中全新世以来的退相期，三角洲前缘沉积物的低积累率和三角洲平原沉积物的高积累率与沿海地区相对海平面在千年规模内上升的积累率变化相吻合。这也意味着在全新世期间，津屋平原平息了。
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