北黄海BS24岩芯稀土元素地球化学与重矿物组成对北黄海晚全新世沉积演化过程的指示意义

The REE geochemistry and heavy mineral composition of BS24 core: implication to the Late Holocene sedimentary evolution in the North Yellow Sea

北黄海泥质区具有地理位置独特、陆源物质供应丰富、沉积环境复杂等特点,为了更好地理解全球变化背景下对北黄海“源-汇”过程的影响,对北黄海泥质区边缘BS24岩芯沉积物进行了AMS14C测年、粒度、黏土粒级稀土元素和重矿物组成特征分析,以判识沉积物的来源、沉积环境特征,并进一步探讨北黄海的沉积演化过程。研究表明,BS24岩芯轻重稀土元素具有明显分异,稀土元素的球粒陨石标准化配分曲线右倾,轻稀土元素富集,重稀土元素亏损,上陆壳标准化的δEu和δCe无明显异常。稀土元素的变化趋势较为一致,以170 cm为界,上段波动幅度较大,下段含量相对稳定。岩芯中共鉴定出30种重矿物,以黑云母(37.46%)和自生黄铁矿(22.39%)最为常见,辉石和氧化铁矿物及不稳定矿物含量低。黏土粒级及极细砂组分特征指示,BS24岩芯晚全新世以来主要接受黄河物质的沉积。BS24岩芯自生黄铁矿含量的变化可能指示了北黄海冷水团强度的变化。650 cal. a BP以来,北黄海冷水团强度增强,自生黄铁矿含量降低;650~1 560 cal. a BP期间,研究区处于还原环境,北黄海冷水团强度减弱,营造的缺乏对流性环境为自生黄铁矿的富集提供了有利条件。

The mud area of the North Yellow Sea is characterized by unique geographical location, abundant terrestrial sediment supply, and complex sedimentary environment. Therefore, revealing the sedimentary evolution of the mud area of the North Yellow Sea is of great significance for systematic understanding of “ source-sink”scheme in the North Yellow Sea under the impact of global change. In this paper, AMS14C dating, grain size, clay grain size, and REE(rare earth element) and heavy mineral composition of BS24 core sediments in the margin of the mud area of the North Yellow Sea were analyzed to identify the provenance and environment characteristics of the sediments. Furthermore, the sedimentary evolution process in the North Yellow Sea was discussed. Results show that the BS24 core has obvious differentiation of LREE and HREE, the chondrite normalized partition curve of REE inclines to the right, LREE is enriched, HREE is depleted, and had no obvious anomalies of δEu and δCe normalized in the overland crust. The variation trend of REEs is relatively consistent, a boundary at 170 cm, large fluctuation range in the upper segment, and a relatively stable content in the lower segment. A total of 30 heavy minerals were identified, of which biotite(37.46%) and authigenic pyrite(22.39%) are most common, and pyroxene, ferric oxide and unstable minerals were low in content. The clay grain size and very fine sand composition of the BS24 core indicate that the source was mainly from the Yellow River since the Late Holocene. The variation of authigenic pyrite content in BS24 core reflected the variation in cold water mass strength in the North Yellow Sea. Since 650 cal. a BP, the strength of the cold water mass in the North Yellow Sea increased and the authigenic pyrite content decreased. During 650-1 560 cal. a BP, the study area was in a reductive environment,and the strength of the cold water mass in the North Yellow Sea was weakened. The lack of convective environment was favorable for the formation of authigenic pyrite.