重庆阿蓬江涪碛口遗址近3000年来环境变化研究

EVIRONMENTAL RESEARCH OF A 3000 YEAR RECORD FROM FUQIKOU ARCHAEOLOGICAL SITES IN APENG RIVER, CHONGQING

涪碛口遗址位于黔江区两河镇高碛村,地理坐标为29°12′25″N,108°45′26″E,海拔高程399m。遗址探方共约3m,发现了东周以来的文化堆积,文化层底部测得AMS^(14)C年龄为4807±31aB.P.。对该遗址剖面进行了沉积物粒度、孢粉、炭屑等古环境指标的综合研究。粒度分析结果显示,遗址地层的沉积物粒度变化较小,均以粉砂为主,粘土次之。通过与1982年特大洪水沉积特征的对比,发现两者的沉积物概率累积曲线特征基本一致,而与研究区现代河漫滩的粒度特征存在较大差别,河漫滩较粗粒的滚动组分较高,比遗址点的疑似洪水层和1982年洪水粒度偏粗。该遗址剖面共鉴定出孢子花粉34个属/科,其中木本或灌木花粉共11个科/属,结果显示,整个剖面蕨类孢子含量较高,而花粉中的草本类型较为丰富,尤其以禾本科(Poaceae)、十字花科(Cruciferae)、莎草科(Cyperaceae)、蒿属(Artemisia)为主,并且由下往上逐渐增加。乔木花粉在整个剖面中均含量较低,较常见的是栎(Quercus)、栲(Castanopsis)、松(Pinus)等。此外,根据禾本科花粉含量判断,该地水稻种植可能始于唐宋时期,而该地成为耕地应在明清以后,同时伴有十字花科等农作物花粉迅速增加。遗址剖面从老到新孢粉结果表明了森林类型的乔木植物花粉逐渐减少,而次生蕨类芒箕孢子、草本植物花粉和伴人植物花粉增多,显示出人类农业活动对森林生态系统的破坏逐渐加强的过程。同时炭屑的分析结果表明,先秦的商周时期地层中炭屑极少,反映了这一阶段可能仍属于高位河漫滩,雨季洪水淹没频繁,不利于农业生产,而唐宋时期与人类活动有关的粗颗粒炭屑开始增加,进入明清时期炭屑总量剧增,反映了人类活动加剧的过程。记录人类活动的各文化层是在多次洪水堆积的沉积面上发生,明清以后阶地面上明显存在人类聚落和耕作的痕迹。沉积地层在人类农业等活动的改造下使沉积物的粒度组分发生部分变化,从而形成所谓的文化层和间歇层。本研究为阿蓬江流域自然环境变迁和人类活动历史的深入探讨提供了新的论据。

Fuqikou archaeological site （29°12′25″N,108°45′26″E ） is located in Gaoqi village, Lianghe Town, Qianjiang District, Chongqing, at an elevation of 399m. The whole profile with a depth of 3 meters, consists of cultural layers deposited since the Eastern Zhou Dynasties, and the radiocarbon age of the sample from the bottom is 4807±31 aB. P. In this paper,we have made a comprehensive study with methods of multi-proxies （ grain size, pollen and charcoal） on the sediments. The grain-size results show the predominance of silt and clay for all samples,with small extent variations along the profile. By comparing with grain-size characteristics of the catastrophic flood layer of 1982, the possibility cumulative curves of the archaeological site are consistent with the modern flood layer, and different greatly from floodplain sediments, which contain more rolling components than the former two. Pollen analysis identified a total of 34 families and genera,including trees and shrubs of 11 families and genera. The results present a relatively high percentages of the spores and abundant herb pollens dominated by Poaceae, Cruciferae, Cyperaceae and Artemisia, and the herbs gradually increased from bottom to top. While tree pollens show lower percentages throughout the profile, in which tree species such present. At the same time, the pollen abundance of Poaccae as Quercus, Castanopsis and Pinus were more common indicates that rice cultivation in this region probably began in Tang and Song dynasties,while it was supposed that the in-situ land turned into cultivated land since the Ming and Qing Dynasties, simultaneously accompanied by rapid increase of the crops pollen such as Cruciferae. In the whole section upwards, the natural arboreal trees reduced, but the percentages of Dicranopteris spores, herbs and anthropogenic plants increased, which demonstrated the strengthening process of forest ecosystem deterioration caused by human agricultural activities. The analysis of charcoal further confirmed the growing process of human activities. Charcoal with low content in Shang and Zhou Dynasties strata reflects the site might still belong to high floodplain, frequently emerged during the rainy seasons and not suitable for agricultural development. During Tang and Song Dynasties, the abundance of large charcoal began to increase, and the total concentration sharply increased since Ming and Qing Dynasties,implying the strengthening of human activities. Our study also proved that cultural layers with human activities occurred on the surface of a number of flooding sediments, especially since the Ming and Qing,which suggests the existence of human settlement and farming on the terrace. Agricultural cultivation and other human activities changed the composition of grain size of the flood deposits underneath to some extent, resulting in the division of cultural layer and cultural interruption. This research provides the new arguments for deeply understanding the natural environmental changes and the process of past human activities in Apeng Valley.