珠江三角洲三水盆地早全新世以来孢粉分析与古环境重建

为了深入探讨珠江三角洲的沉积古环境和古气候历史，在三水市区获取了2个高取芯率的钻孔岩芯，进行了12个AMS 14C测年，并结合孢粉、硅藻等分析结果探讨三水地区全新世的海平面与河流水动力变化，以及古植被演替过程。结果表明：钻孔所在区域全新世沉积总体从9 000 cal. a B.P.左右开始，呈现河流相―河湾相―河口湾相―潮坪相―河口湾相―河漫滩相的演变过程。三水区的早全新世沉积阶段年代最早为9 000 cal. a B.P.左右，表现为河口湾相的淤泥质粉砂沉积，硅藻以淡水种类为主，最高沉积速率为1.6 cm/a。海侵初始时间为8 700 cal. a B.P.左右，最高海平面时间为7 600 cal. a B.P.左右，此时海岸带发育红树林，丘陵山地发育较茂盛的亚常绿热带常绿阔叶林；中―晚全新世阶段（6 500―2 200 cal. a B.P.），以泥炭粉砂沉积为主，沉积速率为0.2~0.5 cm/a，河口区高潮线附近及河流弯道低洼滩地在5 000 cal. a B.P.前后形成淡水沼泽、河口三角洲边缘区洼地水松林发育。在晚全新世（2 200 cal. a B.P.左右）以来，陆相黏土质沉积指示河口泥沙快速堆积，三角洲平原迅速扩大，沉积速率高达1.7 cm/a。孢粉结果显示次生的芒箕孢子剧增，陆地植被稀疏，人类活动显著增强。

Holocene Paleoenvironment Reconstruction Based on Pollen Data in the Sanshui Basin,Northern Pearl River Delta

Sanshui basin is located on the convergence of Xijiang and Beijiang Rivers of the northern Pearl River delta, where the sediment recorded the sea level changes during Holocene. Based on 12 AMS 14C dating results, pollen and diatom analyses were used to reconstruct paleoenvironment and seal level change during early Holocene. The results showed that because of the rapid sea-level rise Sanshui basin was inundated and the onset of rapid deltaic accumulation was at ~9 000 cal. a B.P. and 3 000 cal. a B.P. respectively. The environment varied as an evolution process of fluvial - river bay - estuarine - tidal-flat - estuarine- alluvial flat facieses. The sediment rate was at 1.6 cm/a in early Holocene, the sediment was mainly composed of fine silt. The marine transgression occurred at ~8 700 cal. a B.P., and reached the highest sea level stand at ~7 600 cal. a B.P. The mangrove forest was distributed around the seacoast, but the regional vegetations were characterized by subtropical evergreen forest which was dominated by Castanopsis and Quercus-evergreen type. The sediment consisted of silty peat at mid- and late Holocene (6 500-2 200 cal. a B.P.), with the sediment rate of 0.2-0.5 cm/a. The mangrove forest disappeared and the swamp developed, which was composed of Cyperaceae, Poaceae and spores. Since the age of ~2 200 cal. a B.P., the sediment rate has reached the highest value (1.7 cm/a) and the delta plain expended rapidly. Pollen evidence showed that the natural forest was likely disturbed by agricultural development during the late Holocene.