摘要
通过对台湾东北部古海湾及周边356个海底表层沉积样品的粒度分析及碎屑矿物分析,揭示了古海湾及周边陆架自末次盛冰期以来的沉积环境演变特征,并分析了古海湾的成因。结果表明,该古海湾及周边海域沉积环境的演变可划分为3个阶段:(1)末次盛冰期,浊流、滑坡事件在海湾边缘及陆架边缘频繁发生,可携带大量的陆源碎屑物质输运至古海湾内(B-3),下蚀其海床及下伏地层,并塑造了作为浊流通道的两个砾石条带,在B-3内部保留分选差、改造弱的沉积物。在此期间,潮流、波浪和跨陆架流在东亚冬季风的影响下严重侵蚀B-3的湾口及湾缘,并沉积大量的砂、石英及低含量的生物碎屑物质,石英/长石比值也较高;(2)末次冰消期,随着海平面的阶段性上升,古海岸线向陆大幅迁移,导致浊流强度减弱,潮流逐渐成为陆架区主要的作用营力,相关的潮流底应力可改造陆架沉积物,此时期,西部陆架含砾砂-砾质砂区(B-1)和北部陆架含砾砂-含砾泥质砂区(B-2)的地势差异及其所影响的水平海侵速度和潮波强度的差异是造就两者沉积组分、类型、石英、长石、岩屑和生物碎屑的含量及石英/长石比值差异的主因;(3)高水位时期,黑潮强度在本区增强,除侵蚀B-1底床,黑潮底层流也对B区的浅水地带进行冲刷,加之台湾暖流及沿岸流、长江冲淡水对该区的影响较小,使得B区细粒沉积物质含量较低,A区(北部陆架含砾泥质砂沉积区)细粒沉积广布,除与弱潮流作用相关外,弱的底层流的影响也是原因之一,同时来自台湾暖流可能携带部分细粒沉积物在此卸载。对于古海湾的成因而言,末次盛冰期频繁的浊流是将前更新世时期受湾内断裂作用而形成的半地堑地貌的海湾雏形进一步塑造成深凹地貌的主因,它进一步加剧了其深凹的地貌,在后期的冰消期和高水位时期,潮波系统及黑潮逐渐强盛,阻止了细粒沉积物的输入,保留了古海湾的深凹地貌。
Sediment types,grain size parameters and fragmental minerals of the 356 surface sediment samples from the paleogulf located off the northeastern Taiwan and surrounding shelves are studied for dynamic environments and origins.The evolution of the Holocene sedimentary dynamic environments of the gulf could be clearly divided into three phases.During the last glacial maximum(LGM),turbidity currents and landslides dominated the edge of the paleo-gulf(B-3).A great amount of terrigenous sediments rapidly poured into the Gulf.Seabed and underlying strata were eroded and two gravel belts formed as turbidity channels,and left behind poorly-sorted and inadequately reworked sediments.Tides,waves and cross-shelf currents,especially strengthened by the East Asian Winter Monsoon(EAWM),severely washed and eroded the edge and mouthof the B-3,where formed the sediments with high contents of sand and quartz,quartz/feldspar ratios,and little bio-detritus;During the last deglaciation,owing to the periodic sea-level rises and significant coast retreat,turbidity currents weakened,and tidal currents became the major dynamic force on the shelf.Tidal bottom stress reworked the shelf sediments.Differences in sediment compositions,types,contents of quartz,feldspar,lithic fragments and biodetritus,quartz/feldspar ratios between(B-2)the western shelf pebbly-gravelly sand area(B-1)and the northern shelf pebbly sand-pebbly muddy sand area(B-2)reflect the difference in sea bottom topography which control the strength of tides and waves in addition to the speed of horizontal transgression;In the subsequent highstand period,the influence of Kurosio Current(KC)in the study area was increased.In addition to seafloor erosion,its bottom current also hindered the deposition of modern terrestrial sediments,and thus left behind coarse sediments in B.The deposition of fine-grained sediments was partly attributed to the weakening of the bottom current in A as well as local tides and waves.For the origin of the paleo-gulf,turbidity currents of the LGM certainly played an important role.They eroded the bottom deposits and strata,deepened the depressed geomorphology under the influence of the previous NW-trending fault activity;Moreover,strong hydrodynamics such as tide-wave system,the KC of subsequent periods prevented fine-grained sediments deposition in the B-3,and finally retained its depressed geomorphology.
作者
安振振
李广雪
丁咚
徐继尚
马妍妍
闵建雄
王丽艳
张剑
AN Zhenzhen;LI Guangxue;DING Dong;XU Jishang;MA Yanyan;MIN Jianxiong;WANG Liyan;ZHANG Jian(College of Marine Geosciences, Key Laboratory of Submarine Science and Prospecting Techniques, Ministry of Education, Ocean University of China, Qingdao 266100, China;Fisheries College, Ocean University of China, Qingdao 266100, China;Key Laboratory of Marine Hydrocarbon Resources and Environmental Geology, Ministry of Land and Resources, Qingdao Institute of Marine geology, China Geological Survey, Qingdao 266071, China;Qingdao National Laboratory for Marine Science and Technology, Qingdao 266071 , China)
出处
《海洋地质与第四纪地质》
CAS
CSCD
北大核心
2018年第2期38-51,共14页
Marine Geology & Quaternary Geology
基金
国家重点基础研究发展规划(973)项目(2005CB422304)"中国东部陆架边缘海海洋物理环境演变及其环境效应"项目
关键词
古海湾
末次盛冰期
沉积物分布
碎屑矿物
沉积环境
东海陆架边缘
paleo-gulf
last glacial maximum
sediment distribution
fragmental minerals
sedimentary environment
East China Sea continental shelf margin