青岛崔家潞海湾弱能海滩地貌、沉积年代与潮下带泥质沉积速率

MUDDY SEDIMENTS AND COASTAL CHANGES IN AN ENCLOSED BAY IN QINGDAO,CHINA

崔家潞海湾是典型的圆形海湾,海湾西侧的连续沉积了泥质潮坪和沙滩,形成独特的海岸地貌。为进一步了解这类地貌剖面特征、沉积特征、沉积速率及导致海岸变化的因素,对海滩/潮滩剖面进行测量、取样;对比了历年来的历史地图,以了解海湾湾口、入海河流、低潮线等的变化。地貌上,由陆向海的剖面揭示了小型河流、沙坝、砂质海滩和低潮带的泥质沉积。这段海岸后滨向岸有小型河流,河流输沙形成沙坝,坝后形成小型滨海湿地。光释光年代和14C显示沙坝形成于6.1ka。利用210 Pb和137 Cs测年分析了泥质潮坪的沉积速率及沉积对口门变化的响应。海滩上部为中粗砂海滩,显示为低能的反射型海滩;下部则为低平的宽阔潮坪,有厚达1m的泥质沉积,而且潮坪上没有潮沟发育,坡度小。泥质沉积在近岸处和低潮处较薄,而在中间位最厚。潮平泥质在平面上的分布也不均匀。测年和历史地图都显示,泥质沉积主要出现在1950年之后。根据137 Cs,1954年至2009年,沉积了厚达1m的泥质,平均沉积速率在15mm/a。测试结果还显示上部70cm为沉积速率19.7mm/a,大于下部20cm沉积速率的9.0mm/a。湾口大坝的修建可能导致淤积加快。

Cuijialu Bay is a unique circular bay in Qingdao,China.Beach profiles,historical maps,and^210 Pb/^137 Cs dating of sediment cores from the beaches and muddy tidal flats located along the western coast of the bay were used to study the changes that have occurred to the bay and the relationship of those changes to the construction of a harbor.The landward beach is composed of a narrow swath of coarse sand with a steep gradient.The muddy tidal flats are relatively wide with a gentle gradient and consist of muddy silts.These muddy tidal flats occur only in the middle of the western coast and are characterized by fine sediments with a depth of as much as one meter.^210 Pb/^137 Cs data show that these muddy sediments have been present since the 1950 sand have accumulated at an average rate of 15 mm/a.In a core of 1.0 meters,the upper 0.7 mof muddy sediments is deposited under a sedimentation rate greater than that of the lower 0.2 m.It suggests that muddy sediments have accumulated more rapidly during the last 35 years since 1975.That date corresponds to the construction of a dyke,which reduced the width of the bay′s mouth by 30% and has very likely increased the siltation rate in the bay.OSL ages and 14 C ages show that the river mouth bar was at least formed since 6.1 ka.