【作者】 商志文；

【导师】 王宏；

【作者基本信息】 中国地质科学院 ， 第四纪地质学， 2011， 博士

【摘要】 本论文以渤海湾西部(大津岸段)潮间带-浅海区及相邻沿海平原为研究区,主要进行了以下两个方面的研究。第一,通过对潮间带-浅海区表层沉积物95个站位样品的硅藻分析,查明了表层沉积硅藻组成、优势种及组合的分布特征,探讨了它们与水深、盐度和底质沉积物粒径等环境因素的关系,建立了硅藻优势种及组合与环境因素的转换关系。第二,在表层沉积硅藻研究的基础上,开展了钻孔岩心和牡蛎礁地层的实例研究,探讨了渤海湾西北部浅海区-沿海平原全新世古水深、盐度及海洋影响等地质环境的演变,建立了研究区硅藻-海洋影响曲线及硅藻环境代用指标。天津海域表层沉积硅藻主要优势种为Cyclotella striata/stylorum, Paralia sulcata, Actinoptychus undulatus, Coscinodiscus argus, Coscinodiscus perforatus, Coscinodiscus radiatus, Coscinodiscus decrescens, Coscinodiscus subconcavus, Surirella armoricana, Amphora ovalis, Thalassiosira excentrica, Achnanthes delicatula, Nitzschia lanceolata及Thalassionema nitzschioides等。常见种类有Coscinodiscus oculatus, Diploneis bombus, Deploneis smithii, Grammatophora oceanica, Tryblioptychus cocconeiformis和Actinocyclus ehrenbergii等。通过对研究区表层沉积硅藻优势种的聚类分析,将天津海域表层沉积硅藻划分为7个组合区(A-G),分别对应于潮间带-浅海区不同的亚环境,除受河口影响的E区外,各组合区几乎平行于现代岸线分布。研究区硅藻组合与筛选出的7个非浮游硅藻优势种随水深变化的垂直分布特征表明,水深是控制研究区表层沉积硅藻分布的主要因素之一,并建立了硅藻优势种、垂直组合带与地质环境及水深的转换关系。结果表明,Coscinodiscus decrescens, C. perforatus和C. subconcavus及组合Ia、Ib和IIa对水深变化的指示精度相对较高。天津海域表层沉积硅藻优势种与硅藻组合分布特征与盐度关系的研究表明,盐度是影响研究区表层沉积硅藻分布的另一环境因素,并以此为丛础,讨论了硅藻优势种富集区及不同硅藻组合区分布的盐度范围。讨论了潮间带及水深<-10m海区底质沉积物粒径对表层沉积硅藻优势种及硅藻组合区分布的影响。结果表明,除Amphora ovalis和Achnanthes delicatula外,底质沉积物粒径对大津海域表层沉积硅藻优势种及组合的分布特征不构成显著影响。以天津海域表层沉积硅藻研究为基础,通过渤海湾西北部海区及陆域4个钻孔及牡蛎礁,对全新统的沉积硅藻进行了详细的分析,探讨了渤海湾西北部现代海区及毗邻沿海平原在全新世经历的不同地质环境演变过程。山硅藻代用指标初步建立的海洋影响曲线显示,7000calBP以来共记录了8次海洋影响增强时期,且各次峰值期多与气候温暖期对应,表明硅藻-海洋影响增强期的峰值多表征气候温暖期。海洋影响曲线与渤海湾代表岸线停顿的贝壳堤发育年代对比显示,在时间上,海洋影响增强时贝壳堤开始发育。之后,随着暖期结束、海洋影响减弱,贝壳堤也逐渐停止发育。表明气候变化引起的海洋影响波动变化,控制着研究区岸线变迁与贝壳堤的发育。更多还原

【Abstract】 Taking the intertidal zone, shallow sea and the contiguous coastal lowland, Tianjin section of west Bohai Bay, as the studying area, two major works have been done in this thesis. Firstly, diatom identification, statistics and analysis of 95 surfacial sediment smaples have been systematically carried out. Diatom assemblages, dominant species, their distribution characteristics and relationship with the environmental factors were found out. Transforamtion between dominant species, assemblages and environmental factors were established. Sceondly, based on the abovementioned results, 2 boreholes, drilled in the shallow sea, and 2 oyster reefs, burried in the coastal lowland, have been selected for the case studied in order to reveal the palaeo water depth, salinity and marine influences by using diatom analysis in this thesis. As a result, marine influence curve and diatom proxy were also preliminarily established in the study area.The dominant species in surfacial sediments of the study area consist of Cyclotella striatalstylorum, Paralia sulcata, Actinoptychus undulatus, Coscinodiscus argus, Coscinodiscus perforatus, Coscinodiscus radiatus, Coscinodiscus decrescens, Coscinodiscus subconcavus, Surirella armoricana, Amphora ovalis, Thalassiosira excentrica, Achnanthes delicatula, Nitzschia lanceolata, Thalassionema nitzschioides and so on. The common species are composed of Coscinodiscus oculatus, Diploneis bombus, Deploneis smithii, Grammatophora oceanica, Tryblioptychus cocconeiformis, Actinocyclus ehrenbergii and so on.By using the cluster-analysis for the dominant species, the diatom assemblages of the surfacial sediments have beeen separated into 7 groups (from A to G), which correspond to the various subenvironments from the intertidal zone to shallow sea, respectively. Obviously, the distribution of each group almost parallels to the morden shoreline expect the Group E, which protrudes seawards, influenced by the river discharge.Diatom assemblages and 7 selected non-planktonic dominant species all indicate that water depth is a major factor controlling the diatom vertical distribution. Quantitative relationship of the vetical distributions of different diatom species, assemblages with geoenvironments and water depth were thoroughly discussed. The results indicate that Coscinodiscus decrescens, C. perforatus, C. subconcavus and assemblagesⅠa,Ⅰb,Ⅱa are much more sensitively for water depth change.The relationship between the dominant species, assemblages and salinity indicate that salinity is another factor controlling the diatom distribution of the surfacial sediments. Appropriate range of salinity, in which different species and their assemblages lived were also scrutinized.Also, the other environmental factors influencing diatom composition have been studied in this thesis. Comprehansive analyses on different species and assemblages indicate that, except Amphora ovalis and Achnanthes delicatula, grain sizes of the surfacial sediments in the intertidal zone and shallow sea, with water depth <-10m, do not give obvious influences on the diatom distribution.As the second portion of this thesis,4 case-studies, located on the shallow water, northwest Bohai Bay, and the contiguous coastal lowland, were carried out for their diatom compositions in the Holocene strata in order to reconstruct the local palaeoenvironmental changes during the Holocene period.Marine influence curve, established by diatom proxy, indicate that 8 periods of enhanced marine influence were recorded since 7000 cal BP in the study area. And the peak of each diatom-determined period almost corresponds to those warm periods, estimated from the Bond et al. (1997) and Hong et al. (2009) and many others, indicating the peaks of the marine influence curve usually reveal warm climate in the study area. Futhermore, comparision between the diatom-based marine influence curve and the cheniers show that the onset of cheniers was usually synchronous with the increase of marine influence and then gradually ended when the warm period and marine influence diminished. Marine influence fluctuation which was forced by climate changes, controlled shoreline change and cheneir formation in the study area.更多还原