辽河三角洲海岸带全新世沉积演化时空差异的研究

Sea level changes and depocenter shifting were widely considered to be highly related with the sedimentary evolution in the estuarine deltas. However, recent study revealed that the above two can’t well explain all of the sedimentary evolution in the Liaohe Delta. The Liaohe Delta initiated at ~7000 cal a BP in the whole, but evolved into a 2000 yr time lag of the sedimentary evolution between the east side and west side of the modern coastal area. We plan to accomplish on studies of the provenance analysis, paleoclimate changes and ancient human impacts，and also half-quantify the strength of weathering erosion in the catchments and sediment influx changes since the Holocene in the Liaohe Delta. It is expected to obtain a comprehensive assessment of the paleoclimate change, ancient human activities and paleochannel shifting on the deltaic sedimentary evolution. It will be also expected to reveal the main controlling factor of different evolution between the east side and west side of the modern coastal area. Our results will deepen the understandings on delta evolutionary process and mechanism, and the interaction mechanism between land and ocean in the coastal zone and also partly provide scientific insight to protect the geological and ecological environments of modern deltas nowadays.

河口三角洲地区的沉积演化一直被认为与海平面变化和沉积中心迁移息息相关，然而近年来辽河三角洲的研究表明海平面变化和沉积中心迁移并不能完全解释该地区的沉积演化。辽河三角洲整体于7000 cal a BP左右开始形成，然而现今海岸带附近东西两侧在沉积演化上存在约2000年左右的时间差异。本项目拟对辽河三角洲地区ZK1、ZK3钻孔进行物源分析、古气候演化和古人类活动影响研究，并半定量流域风化剥蚀强度和全新世以来入海泥沙量变化，以此综合评估古气候变化、古人类活动以及古河道变迁对三角洲地区沉积演化的影响，揭示控制辽河三角洲地区海岸带附近东西两侧沉积系统在时间上差异演化的主要原因。这将加深现代三角洲地区沉积演化过程和机制的理解，并对探索海陆相互作用机制具有较重要的科学意义，同时也能对当下现代三角洲地区地质和生态环境保护提供一定的科学参考价值。

本项目研究了辽河三角洲全新世以来地层框架、沉积演化历史、沉积物源、古气候演变和化学风化特征等情况，其主要成果包括：辽河三角洲是多河流-潮控三角洲，大致以辽河口为界，东至营口的海岸带附近5000 cal a BP左右开始接收三角洲沉积，7000 a以来的东侧古海岸线向海推进平均速率约8.6 m/a；西至小凌河河口的海岸带附近约3000 cal a BP才开始接收三角洲沉积，7000 a 以来的西侧古海岸线向海推进平均速率约2.8m/a。对西侧大凌河口钻孔的碎屑矿物和粘土矿物鉴定分析结果显示：西侧三角洲沉积物物源主要来自辽河和大辽河，因此西侧海岸带沉积滞后主要原因是辽河口沉积中心向西海岸迁移晚有关。另外，孢粉、黏土矿物和常量元素揭示了辽河三角洲地区全新世以来化学风化特征与气候演变历史:全新世早期化学风化程度逐渐增强, 气候逐步向温湿方向发展; 全新世早中期化学风化程度最强, 气候暖湿; 全新世中期风化强度较强, 但有减弱的趋势,气候温湿;全新世中晚期化学风化程度在该时期属于最弱阶段, 气候冷干; 全新世晚期气候温干, 风化程度有所增强。