西江―北江及珠江三角洲汇流区全新世泥炭腐木层时空分布与环境变化

西江和北江及珠江三角洲西北部汇流区广泛发育全新世的泥炭-淤泥腐木地层，结合剖面的沉积相特征和14C测年数据，对全新世沉积环境和含腐木地层的分布和环境变化进行探讨，获得以下认识：1）在西江和北江下游海侵北界以上的陆相沉积序列中，厚层泥炭主要形成于中晚全新世（7.5―1.5 cal. ka B.P.），集中堆积时间为5.0―1.5 cal. ka B.P.；2）珠江三角洲全新世海侵对三角洲边缘区陆相泥炭沼泽的形成起决定性作用，早全新世（约9―7 cal. ka B.P.）三角洲西北端的高速率河口相粉砂黏土沉积为后来的半咸水沼泽发育奠定了淤泥深厚的物质基础，而西江―北江下游陆相洪冲积或河漫滩沉积则在8 cal. ka B.P.左右开始发育，也为之后的水松泥炭沼泽繁盛奠定了基础；3）三水西南一带是中全新世西江―北江下游泛滥平原至古河口湾的过渡区，潮汐流与河流的双重作用是造成三角洲边缘区大面积泥炭沼泽湿地形成的主要原因；4）泥炭湿地生态环境大多在2.0―1.5 cal. ka B.P.前后在西江和北江被高位洪水平流沉积物埋藏，而在三角洲区域多被泛滥平原洪积物覆盖。多数剖面泥炭腐木迁移的原因与三角洲的快速加积作用导致的潮流与河流空间位置平衡被破坏和水文条件改变有关，晚全新世不断增强的人类农业活动和森林破坏与水土流失也是导致三角洲天然沼泽湿地消失的重要原因。

Environmental Changes Inferred from Spatial-temporal Distribution of Holocene Buried Peat Layers in Lower Reaches of the Xijiang and Beijiang and the River Confluence of Pearl River Delta

The buried peat and wood layers of Holocene are found widespread mainly in lower Xijiang and Beijiang Rivers, as well as in the confluence areas of northwestern part of Pearl River delta. In this paper, detailed studies of sedimentary facies, combined with radiocarbon dating, have enabled us to reconstruct the Holocene environment and evaluate the distribution of Holocene buried peat and wood layers in the study region. Four conclusions can be drawn as follows: 1) The terrestrial sedimentary sequences located in the northern boundary of Holocene Marine transgression and downstream areas of the Xijiang and Beijiang Rivers show the thick bedded peat which have the earliest age in the mid-late Holocene (7.5-1.5 cal. ka B.P.) and the main deposit period centered at 5.0-1.5 cal. ka B.P.; 2) In the marginal region of Pearl River Delta, terrestrial peat swamps emerged mainly due to the Holocene marine transgression, and the high sedimentation rate during the early Holocene (around 9-7 cal. ka B.P.) provided fertile mud for further development of brackish water swamp. In addition, the alluvial or flood deposits situated in downstream area of the Xijiang and Beijiang Rivers expanded after 8 cal. ka B.P., which also led to the prosperity of the Chinese cypress (Glyptostrobuspensilis) peat swamp; 3) The study area is considered to be a transitional region of ancient estuary and floodplain in the lower reaches of Xijiang and Beijiang Rivers during the mid-Holocene, that caused an emergence of peat swamp in a large scale, especially under its interaction between riverine and tidal currents; 4) The peatland was inundated by alluvial sediments at around 2-1.5 cal. ka B.P. under the process of aggradation in Pearl River Delta, that can be attributed to the destruction of tidal-fluvial balance, as well as the change in hydrological conditions. Moreover, the increasing human activity, deforestation and soil erosion should be also taken into consideration.