紀要論文 四国東部における灌漑水田農耕の受容期の年代について ―炭素14年代法を用いた地域事例―

近藤, 玲  ,  Ryo , KONDO  ,  コンドウ, リョウ

(13)  , pp.149 - 193 , 2017-03-31 , 総合研究大学院大学文化科学研究科
ISSN:1883-096x
内容記述
灌漑水田農耕の受容期の年代について、炭素14年代法を用いた分析を、四国東部の徳島における集落遺跡を対象として行った。炭素14年代法を用いて、徳島市三谷遺跡、庄~南蔵本遺跡のシカ骨、オキシジミ貝殻、土器付着炭化物、杭等の木製品の年代測定を行い、発掘調査から得られた考古学的な所見を加味し、徳島における弥生時代前期の暦年較正年代を求めた。前期前葉の徳島凸帯文土器Ⅳ-2期(板付Ⅱa併行期)は、700–600cal BCのうちの40~50年間、徳島Ⅰ-1期(板付Ⅱa併行期)は、700–600cal BCのうちの徳島凸帯文Ⅳ-2期に後続する50年間、徳島Ⅰ-2期(板付Ⅱb併行期)は、600–500cal BCの100年間、徳島Ⅰ-3(前半)期(板付Ⅱb併行期)は、500–400cal BCの100年間、徳島Ⅰ-3(後半)期(板付Ⅱc併行期)は、400–350cal BCの50年間となる可能性を指摘した。この時間幅で、徳島における稲作受容期の集落景観を復元した。暦年較正年代を基準にした時期ごとに見てくると、稲作が伝わった当初、すぐに稲作だけに切り替わったのではなく、40~50年ほどは、狩猟、漁労、採集に雑穀とマメ類を栽培していた従来からの生業に、新たにコメ栽培を加えて試行錯誤を繰り返している様子が窺われる。その後、灌漑水田の適地を探すように集落を移動させて、河川の状況を見ながら水田を徐々に開田し、前時期よりは、少し集落の人口を増やしつつ、また、約50年この状態が続いていった。この段階を経て、600cal BC頃から、大規模地形改変を試み、本格的に灌漑水田を造成し、2~3棟の竪穴住居で構成される集落を営んでいた。この時期、人々が、灌漑水田を志向する傾向を読み取ることができるものの、畑も作り、多様な農耕を行っていたことが看取される。こうした状態が約200年、400cal BC頃まで続いていくので、当地にあっては、灌漑水田の本格的な施工によって、ただちに集落の構造に変化は認められず、稲作農耕による社会変化は、非常に緩慢であったと考えられる。そして、集落の様相が大きく変化するのが、次の段階の350cal BCまでのおよそ50年間である。複数ある居住域のそれぞれには、絶えず竪穴住居が2棟以上存在し、集落全体では10棟前後となり、以前よりは格段に集落規模は大きくなって、前時期の2倍以上、人口が増加していると推定される。We conducted a carbon-14 dating-based survey on settlement sites in Tokushima, the eastern part of Shikoku, to determine the date of introduction of paddy farming in the area.We used the carbon-14 dating method to date materials, including deer bones, mollusk shells, carbonized material adhering to pottery, and products made of wood, such as piles, from the Mitani and Sho-Minami Kuramoto sites in Tokushima City. Consulting archaeological findings obtained from excavations and surveys, we ascertained calibrated dates for the items from the early Yayoi period as it occurred in Tokushima.We dated the Tokushima convex rimmed pottery IV-2 back to a period in the first part of early Yayoi (concurrent with the Itazuke IIa phase), a 40–50-year period in 700–600cal BC; the Tokushima I-1 (concurrent with the Itazuke IIa phase) to a 50-year period following IV-2; the Tokushima I-2 (concurrent with the Itazuke IIb phase) to a 100-year period in 600–500cal BC; the Tokushima I-3 (first half) (concurrent with Itazuke IIb phase) to a 100-year period in 500–400cal BC; and the Tokushima I-3 (latter half) (concurrent with Itazuke IIc phase) to a 50-year period in 400–350cal BC.Based on this timeframe, we reproduced the scenery of the village sites during the introduction of wet rice agriculture in Tokushima. Looking at each stage with the calibrated chronology as a frame of reference, it is clear that the population did not switch to practicing rice farming exclusively soon after the introduction of rice agriculture; instead, they experimented for around 40 to 50 years with rice farming alongside their traditional means of subsistence like hunting, fishing, and stockpiling grains and beans. Thereafter, they relocated their settlements in search of land suitable for creating irrigated paddies, and gradually developed these while monitoring the state of the rivers. This situation continued for approximately 50 years, as their population increased to considerably more than before. Around 600cal BC, they started to attempt major reshaping of the land, began the full-fledged creation of irrigated paddies, and started to reside in settlements consisting of two to three pit dwellings. While evidence suggests that the people were oriented toward irrigated paddy-field farming at this time, there is evidence to show that they also made dry fields and engaged in a variety of different kinds of agriculture. Given that this trend continued for around 200 years until 400cal BC, it is apparent that the full-fledged effort to implement irrigated paddy field agriculture did not result in an immediate change in the structure of settlements; rather, the social changes accompanying rice farming must have been rather slow to take effect. A major change in the settlements occurred during the 50-year period before 350cal BC in the following stage. The scale of the settlements expanded markedly, with each living area invariably having at least two pit dwellings, and the settlement as a whole having around ten. From this, we surmised that the size of the population had reached more than double that of the previous period.
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