中晚全新世以来闽江口水下三角洲物质来源及古环境演变

Provenance and paleoenvironmental evolutionof Minjiang subaqueous delta since the middle-late Holocene

通过对闽江口南侧柱状样沉积物开展高分辨率的粒度、粘土矿物分析及AMS14C测年,揭示了中晚全新世以来闽江口水下三角洲物质来源及古环境演变。中全新世(7 ka BP—4 ka BP)高海平面时期,梅花水道可能是闽江口南侧陆源物质输运的主要通道,沉积了以砂为主[(58.6±8.7)%]的沉积物,平均粒径为(3.76±0.49)φ,为较高能的沉积环境。期间,增强的浙闽沿岸流携带更多的长江物质沉积到闽江口,导致沉积物中蒙脱石含量增多。然而,到晚全新世(3 ka BP)海平面略有下降,梅花水道衰退,闽江口南侧的水动力条件减弱,形成以粉砂为主[(58.1±4.4)%]的沉积物,平均粒径为(6.30±0.32)φ。晚全新世浙闽沿岸流有所减弱,闽江口沉积物中的蒙脱石含量明显减少,而来自闽江的高岭石含量增加。

Based on a high resolution grain size,clay minerals and AMS 14 C dating analysis of core MJK16 from the south of Minjiang Estuary,we attempt to reveal the provenance and paleo-environmental evolution of Minjiang subaqueous delta since the middle-late Holocene.During the high sea level period of the middle Holocene(7—4 ka BP),Meihua Branch may be the main channel for the transportation of terrigenous materials to the south of Minjiang Estuary.The sediment dominated by sand[(58.6±8.7)%]with a mean grain size of(3.76±0.49)φ.In addition,more Yangtze River terrigenous materials were transported to the Minjiang Estuary by enhancement of Zhejiang-Fujian coastal current,resulting in the increase of smectite content in sediments.However,the sea level decreased slightly and Meihua Branch degraded during the late Holocene(3 ka BP).The sediment in the southern of Minjiang Estuary was mainly silt[(58.1±4.4)%],and the mean grain size was(6.30±0.32)φ,which was similar to fore-delta sedimentary environment.In the late Holocene,the content of smectite in the sediments of Minjiang Estuary decreased significantly caused by the weakening of Zhejiang-Fujian coastal current meanwhile the content of kaolinite from Minjiang increased.