【作者】 刘演；

【导师】 陈中原；

【作者基本信息】 华东师范大学 ， 自然地理， 2014， 博士

【摘要】 末次盛冰期全球气候寒冷,海平面位置在现今位置以下150米左右,河流下切侵蚀作用明显,形成巨大的古河谷.全新世早期,伴随着全球气候变暖,海平面快速上升,海水填充古河谷形成巨大的河口湾环境.全新世中期以来,海平面上升趋于平缓,河流携带的大量陆源碎屑物质在河口附近逐渐堆积,伴随着三角洲主体的形成,河口湿地也开始发育.在此背景下,新石器人类活动在世界主要大河三角洲地区开始出现,河流-三角洲成为孕育早期农业文明发展的重要摇篮之一.在我国长江三角洲地区,广阔的平原上现存着众多的新石器遗址,这些文化遗存忠实地反映了史前文明在该地区的演化过程,时间表现为马家浜文化、崧泽文化和良渚文化这一从老到新的演化序列.其中,良渚文化因其遗址数量最多,文化内涵最为丰富,被认为是早期文明发展的最高阶段.值得注意的是,虽然海平面在全新世中期以后总体上趋于稳定,并接近现代海平面,但感潮型的三角洲冲积平原对海平面的小幅波动仍然十分敏感,早期农业文明的发展仍然会受到海平面波动、风暴潮和大潮汐等环境变化的影响和制约.处于早期农业文明高级阶段的良渚古王国、即瓶窑-良渚古城和大坝(良渚古城体系,下同),三角洲环境对古文明提供了何种可依托的关系,古人又如何适应环境演变?古城体系的兴衰与三角洲环境变迁存在何种关联?这些将是论文着重探讨的内容.论文在杭州湾顶部瓶窑-良渚地区的良渚古城区域展开工作.在参考前人大量成果的基础上,在良渚古城附近获取了两支沉积物岩芯(LZ和XL钻孔),以及西北部塘山大坝白虎弄附近的三个沉积物剖面(BHN-A, BHN-B和BHN-C)通过对沉积物岩芯和剖面的年代学、代用气候和环境指标的分析,恢复了全新世中期以来杭州湾顶部地区的沉积地貌环境演变、气候和海平面波动过程.据此深入地探讨了环境演变与古城体系建造的相互关系,论文取得的主要进展和结论如下：1.建立了研究区全新世早期以来海平面波动的曲线,认为全新世中后期相对稳定的海平面变化促进了三角洲平原的发育.利用具有海平面指示意义的沉积相变化结合高精度加速质谱(AMS14C)测年以及遗址“最低居住面”高程信息首先重建了研究区全新世海平面波动曲线.海平面变化显示：研究区的海平面在约9,000到7,000cal yr BP期间快速上升到距现今海平面以下5m的高程；随后在7,000到6,000cal yr BP年期间逐渐接近现今海平面位置.最大海侵期,海岸线曾到达杭州湾西部天目山山脚,古城地区当时处在古杭州湾顶部的浅海环境中.沉积物粒度较细,且有孔虫数量较多,反映了河口湾-浅海相沉积环境特征.在全新世中期以来温暖的气候背景下,降水增多导致地表径流作用加强,大量泥沙被携带至此,同时钱塘江所带来的泥沙在此地汇合,一起在海湾堆积,共同建造三角洲平原.之前的浅海环境演变为河口-三角洲湿地环境,并逐渐成陆,形成广阔的冲积平原,这为良渚文明在此发展奠定了物质基础.2.建立了良渚古城区域古水系的分布,结合钻孔沉积相的分析,认为稳定的岸线和有利的古地形地貌特征吸引古人在聚居和筑城的主要因素.在最大海侵之后,三角洲岸线开始向海推进.古城以东密集、且平行分布的纵向水系反映了5,000cal yr BP之后海岸线快速向海推进的特点,也是长江三角洲广阔的冲积平原的共同特点.在距今7,000-5,000cal yr BP期间,长江三角洲平原主体广布潮滩和盐沼,当时的太湖盆地为一古泻湖,存有多处巨大的潮汐通道,与广海联通,环境仍十分脆弱,不适合古人长期居住,遑论修建古城.从成陆时间看,LZ孔揭示的成陆时间约为5,000cal yr BP,而位于东面、距离仅为5公里的XL钻孔成陆较晚,约4,300cal yr BP.成陆地层埋深在LZ仅为1.3米,XL成陆埋深在4米以下.这表明当时古海湾的地势坡度较大.但是,古城处在山体环绕的小山坳中,可有效减弱海侵、风暴潮和大潮汐等带来的海洋灾害的影响,同时也可依靠山体进行必要的躲避.因此,良渚古人在此容易获取资源并发展生产,进而在早期新石器文明的积淀上发展古城体系.3.建立了研究区气候、环境变化的代用指标序列,认为暖湿的气候和湿地淡水化过程促进了稻作农业在研究区的发展.全新世中期,研究区的气候延续了全新世大暖期的温暖湿润的特点.区内植被以常绿阔叶和落叶阔叶木本占优势,反映了温暖湿润的气候条件.在良渚文化期间(5,200-4,000cal yr BP),虽然松属含量增多,但青冈栎、胡桃和枫香等喜暖植被亦占据相当的比重,所反映的温和偏湿的气候条件十分适合早期稻作农业和人类活动.在5,200-5,000cal yr BP期间,LZ钻孔孢粉浓度值极高,而且耐盐的藜科含量较高,沉积物中发现少量有孔虫,表现为半咸水的潮滩相环境,不利于稻作农业的开展(禾本科(>40μm)含量极低).随后在5,000-4,000cal yr BP期间,藜科逐渐减少,一些陆生草本如麻黄和蒿属逐渐增多.淡水草本(香蒲和水蓼),以及水龙骨的出现,反映了湿地环境淡水化的过程.温和湿润的气候条件,以及逐渐淡水化的湿地环境为良渚古城地区稻作农业及人类文明发展提供了最基本的保障条件.根据LZ钻孔孢粉记录显示,约5,000cal yr BP之后,人工培育的水稻(禾本科>40μm)逐渐增加,并在约4,800cal yrBP以后开始快速增加,与炭屑(>125μm)良渚文化中后期的高值相吻合,代表了频繁的人类活动和稻作农业在良渚文化中后期达到顶峰.4.根据塘山大坝的年代学和磁学特征,提出其修建时间晚于古城,是古城重要的蓄水防洪工程,反映了古城发展的需求LZ钻孔的岩性在距今5,000年前后由灰色的有机质泥过渡为棕黄色粉砂质泥,反映了研究区成陆的过程.古城城墙基底的青灰色泥顶部的AMS-14C测年反映了可能建造古城的年代不早于4,800cal yr BP,这与考古学家报道的古城修建时间(约4,500-4,300cal yr BP)相近,处于良渚文化早中期.塘山大坝基底OSL测年结果表明大坝约修建于4.11kyr BP前后,属于良渚文化后期.坝体剖面BHN-A年代学数据排列无序,反映了塘山大坝在白虎弄段人为修建的特征.类似的,BHN-A剖面磁组构的测量结果也显示磁性矿物椭球体长轴磁偏角方向杂乱无章,与该剖面无序的年代学相似,反映了大坝人为修建的特征.修建大坝的工程用土来自于邻近地区,总土方量可能达到300万立方米以上.BHN-C的磁组构测量结果表明大坝基底以下的样品,长轴磁偏角的方向是较为统一的,主要指向南方和东南方,与北部山体河流入海流向是一致的,反映出河流冲积平原的特征.故本研究认为位于良渚古城西北部的塘山大坝在白虎弄段是人工修建而成,且大坝修建时间晚于古城.这反映了良渚古人对古城建造和社会发展的认知过程.在古城逐渐形成的过程中,当人们感受到来自季风暴雨、洪涝灾害的威胁时,修建大坝不仅可以直接抵御洪水,而且可以蓄水、灌溉,为古城人民的生活提供便利.5.讨论了良渚地区新石器文明与气候、海平面以及地貌环境演变的适应与响应关系,认为从全新世中期以来,良渚地区人类活动经历了由适应环境向改造环境的转变.LZ和XL钻孔和塘山大坝剖面的年代学以及代用环境和气候指标综合分析揭示：研究区约在6,000年前海平面稳定之后开始逐渐成陆,在5,000年左右环境由潮滩过渡到淡水沼泽.稳定的环境逐渐吸引了古人迁徙此地,在前期约2000年农业文明的基础上(马家浜和崧泽文化),发展了良渚古城体系,古文明达到顶峰.成陆之后的淡水湿地环境是良渚文明和稻作农业发展的基础,稻作农业的发展关系到文化的兴衰.炭屑数据及禾本科花粉的资料表明,稻作农业在良渚中后期发展到顶峰之后,随着良渚文明的衰弱也逐渐减弱.炭屑和禾本科的数据反映了古城衰败之后的一段时间内研究区鲜有人类活动,直到2,000cal yr BP前后的东汉时期才重新开始有人类活动迹象.在良渚文明后期塘山大坝的修建被认为是良渚人抵御洪水的努力,同时也为古城提供淡水储存和农田灌溉的服务.塘山大坝的修建,反映了古人在面对环境变化带来的问题时采取的主动措施,意味着古人由适应环境逐渐向改造环境的转变.良渚古城在距今约4000年后衰落了,解释有多种原因.本研究认为古城附近沉积物中出现大量的淡水藻类和蕨类反映了地表水体扩张,河网密布的环境特征,压缩了古城地区的人类活动空间.而太湖流域地区主要是由于太湖盆地当时正处在海水入侵、湖沼扩展的鼎盛期,当时的湖沼泥炭分布可以是现今的2倍之多,造成整个长江三角洲南部平原不易居住,文化衰落,这当然也不可避免地影响到良渚王国衰退.更多还原

【Abstract】 During the Last Glacial Maximum (LGM), global sea level was located at ca.150m below present position. The river valleys were strongly incised by ca.70-50m at large river mouth area. Sea level started to rise as climate turned warm after LGM, filling the incised valley into a large estuary. Rapid sea level rises occurred during the early Holocene till ca.7,000cal yr BP. Sea-level rise decelerated in the middle Holocene, and the marine invasion weakened as well. Therefore, this enhanced freshwater discharge carried a large amount of terrestrial materials to the river mouth to form a delta plain, including coastal wetlands. The Holocene delta formation had attracted our ancestors to move to the delta coast for agricultural activities, starting to settle down for sedentary livings. The Yangtze River delta of Eastern China coast had witnessed prosperous Neolithic cultures, represented by Majiabang, Songze and Liangzhu Cultures, among which the Liangzhu Culture was recognized as the most developed cultural stage, in terms of site numbers and culture connotations. Although the sea level stabilized and approached nearly to the present mean sea level in the middle Holocene, the delta plain was still very sensitive to subtle sea level fluctuations, storm surges and tidal currents, which affected and restrained the development of the agricultural-based cultures. As the Liangzhu culture progressed to a supreme level of civilization represented by the ancient Liangzhu city and an earth dyke (herein, the Liangzhu city complex) on the Southwest of the Yangtze delta plain, there are key questions to be paid attention to in this study:What was environmental changes on the Yangtze River delta that affected the Liangzhu city complex? How did the Neolithic people adapt to the environmental changes? How was the rise and fall of the Liangzhu city complex linked to these environmental changes?This study focuses on the Liangzhu city complex, which was located at the inner Hangzhou Bay. On the basis of previous study, two sediment cores, LZ and XL, were drilled near the ancient city, as well as three sediment profiles at the earth dyke, i.e. BHN-A, BHN-B and BHN-C. AMS14C dating, together with environmental and climate proxies was applied to sediment samples from both cores. The environment evolution processes of the inner Hangzhou Bay area since the middle Holocene was reconstructed, including sedimentary facies, climate and sea level fluctuations. Then, the human-environment interactions of the Liangzhu cultural stage were discussed, and conclusions were drawn as below:1. Sea level stabilization since the mid-Holocene triggers delta formationBased on our14C datings and the altitudes of the lowest habitant bases, the Holocene sea-level curve of the study area was reconstructed. The sea-level curve revealed a rapid rise from-25m to-5m during9,000-7,000cal yr BP, before approaching to the present sea-level at ca.7,000-6,000cal yr BP. The shoreline could have reached the foothill of Mt. Tianmu during the maximum marine invasion, making the study area a shallow bay environmental setting. This was featured by the fine grain sediment strata with abundant foraminifera. The increasing rainfall enhanced the river discharge to bring not only sediments from the Yangtze River to deposit at the study area, but also sediments from the Qiantang River, turning the former shallow bay into delta plain, as witnessed by transformation from grayish bay sediment to brownish coastal silt of delta plain origin. This provided a habitable base for building the ancient Liangzhu city complex.2. Shoreline and paleo-topography in favor of the Liangzhu city constructionAfter the maximum marine invasion, the shoreline of the study area prograded seawards. The densely distributed river networks of the delta plain to the east of the ancient city recorded a fast progradation of the shoreline after ca.5,000cal yr BP. The extensive tidal flat and salt marsh prevailed during7,000-5,000cal yr BP in the delta plain proper. Several huge tidal openings were linked to the open sea, allowing tidal currents free to invade, making the delta plain extremely vulnerable for the long-term occupation and impossible for large constructions like the ancient Liangzhu city complex. The coastal setting formed at ca.5,000cal yr BP at the LZ core site was earlier than that of XL core, ca.4,300cal yr BP, only5km in distance. The burial depth of coastal sediment between the two cores is>3m (1.1m vs4.3m below the ground surface), showing the LZ site was much suitable for the ancient city construction, in stead of a steep gradient of paleo-topography in the former bay area (Core XL). Moreover, the Liangzhu area located at inner Hangzhou Bay was protected by surrounding mountains and hills from storm surges and spring tides. These together would have given an easy access to freshwater, forests, hunting, fishing, plant gathering, and for defensive protection.3. Warm and humid climate and desalinization of salt marsh catalyzed rice cultivationDuring the mid-Holocene, the climate stayed warm as the Holocene Mega-thermal continued. The vegetation of the study area was dominated by evergreen and deciduous broad-leaved arboreal, reflecting a warm climate condition. Pinus became dominant during the Liangzhu cultural period (5,200-4,000cal yr BP), followed by Quercus, Juglans and Liquidambar in great portions, reflecting a moderate and humid climate condition, which was favorable for rice cultivation and human activities. At5,200-5,000cal yr BP, the extremely high pollen concentration in core LZ, the occurrence of salt-tolerant Chenopodiaceae and foraminifera illustrated a tidal flat environment, which was not the best environment for rice cultivation (as the Poaceae (>40μm) was low). Later, during5,000-4,000cal yr BP, Chenopodiaceae was replaced by Ephedra and Artemisia, freshwater herbs (Typha and Polygonum hydropiper) and Polypodiaceae, as the salt marsh turned into freshwater wetland, making rice cultivation and human activities possible. The pollen record of core LZ showed Poaceae (>40μm) has started to rise since5,000cal yr BP and then roared up after4,800cal yr BP, which fit the growing trend of macro charcoal (>125μm), and peaked at mid-late Liangzhu cultural period, implying the highlight of rice cultivation and human activities at and near the Liangzhu city complex. The content of Poaceae and macro charcoal dropped dramatically in the late Liangzhu cultural period, showing a weakened human occupation which would be linked to the fall of the city complex.4. The belated construction of earth dyke reflected the need for further developmentThe transformation of sediment in core LZ from greyish clay to brownish silt at ca.5,000-4,800cal yr BP shows the coastal formation in the study area. The gray sediment at the base of the Liangzhu city wall was dated at4,800cal yr BP, suggesting the city was built no earlier than4,800cal yr BP, which was close to the age of the city reported by the archaeologists (4,500-4,300cal yr BP). The Optically Stimulated Luminescence (OSL) results of sediment profile BHN-C, which was obtained under the dyke construction, showed the age of the dyke construction at ca.4.11kyr BP, late Liangzhu cultural period. The OSL dating results from profile BHN-A were vertically disordered, showing the feature of artificial dyke construction at this section. Similarly, the anisotropy magnetic susceptibility of profile BHN-A was showing chaotic directions of magnetic declination, reflecting the man-made nature of the dyke. In our study, we suspected the soil used for dyke construction was taken from the adjacent flood plain, which would be over3million m3at least. The results from profile BHN-C was showing a main direction, S-SE, paralleled to the river flow direction from the north, reflecting the characteristics of fluvial plain.On the basis of the OSL dating and the anisotropy magnetic susceptibility measurement at the BHN profiles, we deducted that this part of dyke was constructed by human during the late Liangzhu cultural period, which was later than the city construction. We consider this time difference to be the process of learning from the nature. The study area was warm and humid, and the annual rainfall was concentrated during monsoon season, which was easy to trigger debris flood hazard to threat the city and rice field nearby. After hundreds of years living in that area, the ancient people came to realize the importance of building an earth dyke:not only to defend the flood hazard, but also to impound freshwater for irrigation and city needs.5. The rise and fall of the city complex and the adaptation to environmental changeOur study revealed that the coastal formation started at ca.6,000cal yr BP as the sea level stabilized in the study area. The former tidal flat transformed into freshwater marshland after5,000cal yr BP, which attracted ancient foragers to settle down to develop the Liangzhu city complex, on the basis of the previous2,000years of agriculture-based civilization. The freshwater marshland was fundamental to rice cultivation, which was also crucial to the development of Liangzhu culture. Both macro charcoal and Poaceae data showed the human activity around the city complex peaked at mid-late Liangzhu cultural period before its deterioration. Human activity did not occurred in the study area until East Han Dynasty, as evidenced by macro charcoal and Poaceae data.The earth dyke, built in the late Liangzhu cultural period, was considered as a multi-functional system. It was not only a great effort in fighting against floods, but also used for water restore and irrigation. To build the earth dyke was a positive move in dealing with natural hazard, showing an important leap from adaptation toward modification to the environment. The city complex was abandoned mysteriously at ca.4,000cal yr BP, and the reason was still debatable. In view of the present study, the flourish of ferns and algae after ca.4,000cal yr BP were indicative of expanded water body around the city area, depressing human activities severely. Also, it seems that the cultural abandonment is linked to the expansion of brackish wetlands following marine invasion in the mid-late Holocene. The salt marsh area was twice as large as it is today, making significant habitation impossible on the entire southern flank of Yangtze River delta. This would have limited population growth and decreased human demands, thus implying that environmental drivers were responsible for the demise of the city.更多还原