末次盛冰期黄海陆架气候变化的钙质结核硼－碳－氧同位素记录

The continental shelf, which preserves plenty of geological records, be called as archives. During the ice age, sea level had decreased and kept the water from the shelf. Weathering demolished geological record on the shelf and led study of paleoclimatic changes during the glaciation weaker than that during the deglaciation. The Yellow Sea shelf almost changed from marine to continental facies at all in the Last Glacial Maximum. On the Yellow Sea shelf, special secondary carbonate, called as calcareous concretion, formed in the relict sediment. In this program, forming ages of calcareous concretions would be analyzed in detail to understand the spatial pattern of these ages on the shelf. According to the order of forming ages, the samples would be selected, included some concretions , their "parent" sediment and shell. Element contents and boron, carbon and oxygen isotopic compositions would be analyzed for those sediments and shells, and associated with previous study works to build the index system of depositional environment and material sources. Selected concretions would be stratified sampling. To know the life-span and growth rate of concretions, mineral assemblages, element contents, U-series dating and isotopic compositions of boron, carbon and oxygen be analyzed. Then, the changes of sources, depositional environment, ratio of sea water and pH during the life span be argued according to the index system. Based on the above, abrupt paleoclimatic events would be revealed in last glacial maximum based on isotopic records of boron, carbon, and oxygen. Further, the history of paleoclimatic change be reconstructed and the geological importance of calcareous concretion should be recognized for paleoclimatic changes on the shelf region, during glaciation.

陆架是保存详细地质信息的"档案馆"。冰期陆架环境由海相转为陆相，风化作用破坏了地质记录，导致冰期研究程度相对较低。末次盛冰期黄海陆架几乎完全暴露，但沉积物中形成一种次生碳酸盐沉积－钙质结核，为冰期气候研究提供了信息载体。课题对黄海钙质结核开展系统测年，获得结核年龄的空间分布规律。按形成顺序选择典型结核及赋存结核的"母体"沉积物和生物壳体；沉积物和壳体分析元素和硼、碳、氧同位素组成，建立结核环境与物源指标体系；结核分层取样，测定矿物、元素、U系年龄和硼、碳、氧同位素组成，确定结核"寿命"、生长速率；在环境与物源指标体系内讨论成核过程中物源、成核环境类型、海水组分比例、溶液酸碱度等方面的变化情况，揭示气候变化对结核生长的影响。综合上述研究，识别结核中末次盛冰期气候突变事件的碳、氧、硼同位素信号，重塑末次盛冰期详细的气候变化史，阐明钙质结核对于冰期气候与环境变化的研究意义。

冰期陆架暴露，风化作用破坏了陆架上保存的丰富沉积物及其中蕴含的地质信息，导致冰期研究程度相对较低。末次盛冰期黄海陆架几乎完全暴露，但沉积物中形成一种次生碳酸盐沉积－钙质结核，为冰期气候研究提供了信息载体。课题对黄海钙质结核开展矿物、地球化学分析，获得结核形成矿物组合、年代、元素（包括稀土）及碳-氧-硼同位素组成数据，结合前人研究成果，获得以下认识。首先，黄海结核形成于15000-30000a B.P.，与中国黄土形成时间相近，结核年龄具有由岸向海逐渐变年轻的分布特点。其次，黄河与赋存结核的残留沉积矿物组合指示，含结核沉积物物为经改造的古黄河三角洲沉积。再次，相对于形成时代相似的松散沉积物，结核具高方解石、长石、石英、伊利石、Ca、Cd、Sr、Ni、Pb、U，低云母、高岭石、Nb、Ta、Rb、Th的特征。最后，结核碳-氧-硼同位素特征指示，钙质结核的成核物质主要有两个来源，区内结核形成过程中有一次明显的变暖事件（即MWP-1A快速海侵事件）。上述研究，对于重塑末次盛冰期详细的气候变化史，阐明冰期气候与环境变化具有重要意义。