【作者】 王福；

【导师】 王宏；

【作者基本信息】 中国地质科学院 ， 第四纪地质学， 2009， 博士

【摘要】 本论文以渤海湾海岸带为研究区,通过对40组现代沉积物测年柱状样品的²¹⁰Pb、乃¹³⁷Cs活性-深度剖面的综合研究,发现了²¹⁰Pb、¹³⁷Cs活性-深度曲线的不同类型及其沉积环境;探讨了²¹⁰Pb、¹³⁷Cs活性与粘土含量之间的关系,以此为基础,进一步对其中的10组数据开展了初步的²¹⁰Pb_exc活性-深度剖面标准化研究;讨论了蓄积量与现代沉积速率之间的关系,定量地分析了研究区现代沉积过程及其环境意义。研究区的²¹⁰Pb活性-深度曲线主要表现为3种类型:（1）理想衰变型,（2）近等幅摆动型和（3）事件影响型。¹³⁷Cs活性一深度曲线也主要表现为3种类型:（A）不连续的¹³⁷Cs曲线,（B）无峰的连续¹³⁷Cs曲线,（C）至少有一个峰的连续¹³⁷Cs曲线。理论上至少存在9种²¹⁰pb_exc与¹³⁷Cs曲线组合类型。但是,在渤海湾海岸带地区实际上发现了其中的6种组合类型:即（1）1B、（2）2B、（3）2C、（4）3A、（5）3B和（6）3C组合类型。这些组合类型,分别反映了沉积过程和沉积环境的细微差别。其中,3B类型在潮间带地区最常见,即事件影响型的²¹⁰Pb活性-深度曲线与连续无峰¹³⁷Cs活性-深度曲线的组合。样品中的¹³⁷Cs活性与粘土含量变化无明显的相关性,但²¹⁰Pb_exc活性与粘土含量的变化存在明显的线性关系。通过线性回归,建立了海河北侧潮间带上部地区的²¹⁰Pb_exc活性与粘土含量之间的线性关系式（R²=0.87）,并以此为依据,对取自渤海湾潮间带及浅海区的10组现代沉积物测年柱状样的²¹⁰Pb_exc活性-深度剖面进行了标准化,结果显示,标准化前后,活性-深度曲线未见明显变化,曲线中的“活性低值区”为“事件”沉积所致。通过对研究区近50年来的风暴潮历史资料的分析、结合测年数据,发现²¹⁰Pb_exc活性-深度曲线中的“活性低值区”与风暴潮事件有很好的相关性,由此推断“活性低值区”为风暴潮事件所致。蓄积量与沉积速率之间存在正相关性,即蓄积量随着沉积速率的增加而增加。但是,目前还无法用具体的关系式来进行表达,还需要更多的数据积累,借鉴和引入新的数据处理、解释方法。渤海湾黄骅港南侧附近潮间带和浅海区沉积速率随着水深的增加而增加,黄骅港北侧沉积速率随着水深的增加呈高低高的趋势。（1）距岸线4km以内的区域,黄骅港北侧的沉积速率较高,为2～3cm/a,而南侧地区以侵蚀为主。（2）在离岸大于5km的浅海区,黄骅港南侧的沉积速率高于北侧,其中HHG6为一沉积中心区,沉积速率最高,说明该处沉积物补给充足,该处位于黄骅港2003年的防波堤的口门附近,因此,当风向与防波堤走向相同或相近时,易造成港口航道淤积。从南向北,渤海湾潮间带上部的沉积速率不尽相同。南侧的老狼坨子一带,沉积速率为2～3cm/a;t向北至D-L1站位沉积速率呈现降低的趋势,从该站位向北至DXP站位（大辛堡）沉积速率复又增加,向北至NPH（南排河）站位沉积速率继续增加,达到2.32～2.74cm/a,至马棚口沉积速率仍为2.32～2.74cm/a。结合取自马棚口附近的C4和Q1站位的结果,可以判断,马棚口及其南侧附近的潮间带地区是一个沉积速率非常活跃的区域,为一现代沉积中心。再向北,马棚口至大沽排污河岸段沉积速率呈现变低的趋势,且沉积速率均大于1cm/a,海河北侧蛏头沽至大神堂潮间带上部地区,沉积速率呈现变小的趋势,且沉积速率均小于0.84cm/a。有4条河流在研究区入海,除大口河外,均为高沉积速率。取自独流减河河口、大沽排污河河口和北塘水道入海口的3个柱样的沉积速率均大于1cm/a,而蓟运河口处最大超过3.17cm/a,为一现代沉积中心。为判明课题组新近发现的“蛏头沽活动断层”迹象而做的现代沉积速率调查表明,该断层两侧浅海区的现代沉积速率分别为0.30cm/a和0.34cm/a,并无明显差别,说明断层两侧近50年来未见明显的差异性运动。中国纬度最高的现代活牡蛎礁——汉沽区大神堂牡蛎礁——浅海区现代沉积速率为0.75～0.85cm/a,高于相邻潮间带上部和西侧蛏头沽附近浅海区（0.30～0.34cm/a,见上述）,推测与大神堂活牡蛎建礁的“促淤”作用有关。同时,所在研究小组其他同事的详细研究表明,生物建礁稍快于沉积物的机械沉积,因而礁体仍得以继续维持。本论文认真研究了前人成果,做了系统总结,并以此为基础,通过本文新增的28组²¹⁰Pb和¹³⁷Cs示踪与测年数据,首次系统地研究了渤海湾沿海低地→潮间带→浅海区的现代沉积速率,发现这一地区的现代沉积速率在0～4cm/a之间。这一数值的发现,弥补了影响（泥质）海岸带现代过程与趋势的6个基本要素——现有高程、现代垂直加积速率、防止环境恶化预案、地面下沉、海面上升与极端事件——中的“现代垂直加积速率”的空白。基于这些成果,开展了“天津市潮间带后备土地资源评价与选划”、“黄骅港区环境稳定性评价”、“海区活动断层的判断”与“牡蛎礁生态环境评价”等应用性研究。更多还原

【Abstract】 The study area was chosen on the west coast of Bohai Bay,40 short undisturbed cores（1～2m long） were used to study the modern sedimentation.The results show that different types of the ²¹⁰Pb and ¹³⁷Cs activity-depth profiles were identified,and the relationship between ²¹⁰Pb and ¹³⁷Cs activity and clay content was discussed,furthermore,the spatial distribution character of the modern sedimentation was analysised quantitatively.Three types of ²¹⁰Pb activity-depth profiles were identified,which were Ideal-decaying-type, 2) Wiggling with approximate equivalent amplitude,and 3) Episodic-event-influencing-type. Three types of the ¹³⁷Cs activity-depth profiles were identified,which were:A) Discontinuous ¹³⁷Cs curves,B) No peak can be identified continuous curves,and C) at least one peak can be identified relative ideal continuous ¹³⁷Cs curves.Theoretically,nine types of ²¹⁰Pb and ¹³⁷Cs activity-depth profiles（1A-1C,2A-2C and 3A-3C） were existed.However,six types of ²¹⁰Pb and ¹³⁷Cs curves from the nine types were discovered on Bohai Bay,which were（1） 1B,（2） 2B,（3） 2C, （4） 3A,（5） 3B,and（6） 3C.Moreover 3B was most commonly in the study area,which represented that intertidal zone were episodic events（storm surge） influencing environments with tidal currents,waves,and mixing activities;Moreover,the records of the storm surge during the last 50 years and ²¹⁰Pb activity-depth profiles supported this results.The relationship between the activity and clay content was studied,and the results showed that 1) no obvious relationship between the clay content and ¹³⁷Cs activity,2) linear relationship between the clay content and ²¹⁰Pb_exc activity was obvious.Furthermore,the liner equation between the clay content and ²¹⁰Pb_exc activity was constructed（R²=0.87）,which provided the basic data for standardizing the ²¹⁰Pb_exc activity-depth profiles.Based on this equation,the ²¹⁰Pb_exc activity-depth profiles of 10 cores were standardized,which showed that the "low activity of ²¹⁰Pb_exc" was not caused by the change of clay content.At mean time,the inventory and sedimentation rates were discussed,and the results showed that the sedimentation rates increased with the inventory,but no obvious equation between them.The intertidal zone and parts shallow sea area from Huanghua Harbor to Dashentang on Baohai Bay,modern sedimentation rates showed different spatial distribution characteristics.The littoral currents from NW to SE was cut off by the seawall of Huanghua Harbor,which led to the sedimentation rates in less than～4km away from shoreline in the north of the Harbor were obviously higher than the southern area of the Harbor.5km far away from the shoreline,the sedimentation rates were higher in southern area of the harbor.Moreover,the site of HHG6 was a sedimentation center,the sedimentation rate was 1.36cm/a,which mean that sediments supplying were enough.Moreover,HHG6 was near the mouth of the two breakwater of the Harb in 2003,so port channel siltation will happen when the wind direction was similar with the breakwater direction.The sedimentation rates of the supratidal zone of Laolangtuozi in the north Huanghua Harbor was 2～3cm/a.The sedimentation rates decreased from Laolangtuozi to D-L1,and increased from D-L1 to Daxinpu village,till to Nanpaihe Count,where the sedimentation rate was 2.32～2.74cm/a.The sedimentation rate of Mapengkou was also 2.32～2.74cm/a.Considering the C4 and Q1 taken near Mapengkou,the sedimentation rates result showed that it was a modern deposition center on the intertidal zone from Nanpaihe Count to Mapengkou.The sedimentation rates of the supratidal zone on the south Haihe River were higher than northern.The sedimentation rates on the supratidal zone from Mapengkou to Dagu Pollution River showed decreased trend, and the sedimentation rates were all higher than lcm/a;the sedimentation rates of supratidal zone from Chengtougu to Dashentang showed decreased trend,and the sedimentation rates were all less than 0.84cm/a.There are four rivers in the study area into the sea,and high sedimentation rates happened to estuary except Dakouhe estuary on Bohai Bay.The cores taken from the estuary of Duliujianhe River,Dagu Plution River and Beitang Channel show that the sedimentation rates were all higher than lcm/a.The sedimentation rate of Beitang Channel was higher than 3.17cm/a, where was a sedimentation center.The sedimentation rates of Chengtougu fault in the north Haihe River were 0.30～0.34cm/a, which were lower than the supratidal zone next to it.The close sedimentation rates on both side of the fault meaned that no obvious sign to judge the fault active during the last fifty years.The highest latitude of modern living oyster reef——Dashentang living oyster reef——the shallow sea area next to Dashentang Village,the sedimentation rates near Dashentang live oyster reef were 0.75～0.85cm/a,which were higher than the supratidal zone next to it.Maybe,this sedimentation rates was caused by the construction of the living oyster reef.Compared with the growth rate of the oyster reef calculated by a colleague of our research group,the sedimentation rates were lower, which means that the Dashentang living oyster reef was still in the construction period.Finally,the use of modern sedimentation on geo-environmental changes of Bohai Bay was introduced and sumarized.In this paper,the results of the past were carefully studied,and a systematic summary had been done.Based on it,through the addition of 28 ²¹⁰Pb and ¹³⁷Cs data,a systematic study of modern sedimentation rate of intertidal zone and shallow sea of Bohai Bay were done for the first time,and gained the sedimentation rates（0～4cm/a）.The discovery of this value,make up for the impact of（muddy） coastal processes and trends of the modern six basic elements——existing land surface elevation,modern sedimentation rates,plans to prevent environmental degradation,land subsidence,sea-level rise and extreme events——modern sedimentation rates.Based on these results,many programs have been done,such as "Tianjin intertidal zone land resources evaluation and selection","environmental stability evaluation of Huanghua Harbor","evaluation of fault activity","evaluation of the ecosystem of the living oyster reef",and so on.更多还原