【摘要】 本文简要介绍了天津地质调查中心海岸带与第四纪地质研究所(海岸带近现代地质环境变化研究小组)自1998年承担国土资源大调查任务以来,以滨海新区及渤海湾西岸海岸带为主要研究基地所取得的基本成果:(1)确立了泥质海岸带(沿海低地-潮间带-浅海区)地质环境变化(大致划分为(a)晚更新世以来-"小冰期"、(b")小冰期"结束-现代以及(c)未来50～100年3个时段)的主要研究方向。(2)根据在沿海地区和潮间带-浅海区的近30个揭穿全新统-晚更新统的全取心钻孔岩心(累计进尺1 600 m,其中海区约400 m)的多学科综合研究,探讨了晚更新世以来沿海地区和毗邻浅海区的地层结构、沉积间断、断块构造差异运动和层序地层学。(3)基于沿海低地-潮间带4 000余个Eijkelkamp全取心钻孔(总进尺逾20 000 m),将6～8 m以浅的中晚全新统划分为6～11层,并将它们归并为两个非正式地层单元"灰色单元"和"黄色单元"。前者为潮间带环境(向下可包括潮下带上部),后者为泻湖→盐沼→沼泽环境。通过1/5万区域地质调查(Eijkelkamp钻探、高程测量、综合研究、C-Tech软件对数据的处理),在临港工业区南西150 km2的泻湖-盐沼区进行了浅表地层(11层)的3D表达。进一步又将灰色单元划分为泥质的"马棚口湾式"和砂质的"驴驹河式"两类。(4)在滨海新区约3 000 km2的潮间带下部-浅海区首次开展了系统的测深仪-浅剖仪-全取心机械钻探-海底底质(和浅层)取样-旁侧声呐-单道地震公益性地质-地球物理-古生物-地球化学调查和包括地层学、地球物理学、生物学和年代学(包括年轻沉积物测年)在内的综合研究。将末次冰消期以来潮间带-浅海区沉积物划分为Ua-Uf六层,初步查明了海区沉积层序、底质物质组成、表层沉积速率、埋藏古河道和浅层气分布等。(5)通过不同时期地形图、航片及遥感影像对比,重建了近130年以来渤海湾西岸地表形态演化与海岸线变迁,发现阶段1"小冰期"结束后-20世纪前半叶以侵蚀为主,从曲折岸线向平直岸线转化和阶段2 20世纪后半叶-现代以淤进为主,人为活动占主导地位的基本特征。基于8条潮间带剖面的高程测量结果及仅有的天然岸段近年来强烈蚀退现象,提出了湾顶处滩面现代过程在近年来可能已转入阶段3新的自然蚀退过程的推测。(6)开创了滨海新区(和渤海湾西岸)210Pb和137Cs示踪与年轻沉积物测年研究。根据目前掌握的环渤海地区近百组210Pb或210Pb/137Cs数据(其中210Pb和137Cs同时测量的有近60组,笔者贡献了40组),初步划分出渤海湾西岸沿海低地沉积速率极低带(一般<1 mm/a)、潮间带高速沉积区(通常>5 mm/a、极端>30 mm/a)和浅海不稳定沉积区(通常>5mm/a),圈定了北塘水道口门等潮间带现代沉积中心区。该项研究成果,填补了渤海湾长期以来缺少现代沉积速率数值的空白。(7)通过表层(和浅孔)沉积物粒度分析,初步查明了潮间带-浅海区表层物质组成及分布特征。发现独流减河口-海河口岸段潮间带浅表层沉积物向北、向上变粗,分选性变好,推测是节制闸建成后半个世纪以来海河输送沉积物减少、近岸海洋影响增强的海河三角洲退化的结果。(8)开展了渤海湾现代有孔虫群(活体和死体)对比研究。根据现代有孔虫群与其所在的(经水准测量确定的)潮间带位置、(经潮位校正确定水深的)海底位置及盐度的关系,初步建立了从平均大潮高潮位到10 m不同水深的现代有孔虫群-水深转换函数,并据有孔虫代用指标尝试重建了全新世相对海面变化曲线。(9)开展了渤海湾硅藻群研究。初步划分出从潮间带至浅海区不同水深、盐度及泥质或粉细砂质不同底质环境的7个硅藻组合区,探讨了硅藻分布与环境因素(水深、盐度和底质)的关系。根据反映海洋影响强度-气候变化的硅藻代用指标,在岩心和牡蛎礁体中初步发现了距今约7 ka cal BP以来的8次海洋影响增强事件。(10)开展了渤海湾软体动物群研究。搜集并鉴定了双壳类和腹足类各100余种,划分出陆相、海相和海陆过渡相3类组合,初步研究了它们各自与水深、盐度的关系。(11)继续牡蛎礁(包括现代活牡蛎礁)时空分布、成因与环境演化研究。将牡蛎礁平原的47处礁体(近年来,在空港、滨海湖和浅海区新发现5处礁体)初步划分为10个礁群,确定了礁体与上覆泥层交替的10次第一等级(千年尺度)的旋回;礁体内部正常建礁与水平夹层交替的第二等级(百年-数十年(?))的旋回,则有数十次之多。(12)开创了渤海湾泥质海岸带贝类壳体生物碳酸钙18O,13C和87Sr同位素地质环境变化研究。根据对10余种常见贝壳13C组成的测量,发现了渤海湾全新世海相贝壳13C的平均值(-2.68‰PDB),并以此作为那些未经13C测量的14C直接测定值的同位素分馏效应校正的经验值,由此对600余个环渤海14C数据进行了统一的分馏效应校正,为后续的贮存库效应和全新世大气14C浓度变化校正打下了基础。通过对同一牡蛎个体的不同生长层(分别具有最重的、最轻的δ13C,代表开放海湾和受陆地径流/大气降水影响的两种亚环境的极端情况)的AMS 14C测年,提出了渤海湾全新世海岸带小而浅水体的14CO2迅速与大气达至平衡的假说,从而对该地区的14C数据统一校正提出了将陆地与海洋两种推荐程序相结合的方法,并得到了其他研究者近年来新发现的地区性贮存库年龄ΔR≈-170～-190 a的证实。经过13年的积累,初步建立了包括600余个数据在内的环渤海14C数据库,其中笔者贡献的(包括尚未获得结果的)达到250余个。(13)牡蛎壳体18O,13C和87Sr同位素组成的分辨率,已从20年前的季节级别提高到现在的半月级别,这是继发现牡蛎礁体记录的第一、二等级的环境变化之后,单个壳体记录的第三等级的变化(数十年际→年际→季节和月际变化)。壳体的个体形态学研究表明,位于河口、开放海湾不同微地貌环境的礁体中的牡蛎个体的高/宽比、重量和生长速率不同。大吴庄礁体近50个14C(其中AMS方法获得的数据30余个)和近20个OSL数据的研究,发现该处礁体历时的两种可能(>1 ka和<0.7 ka)。确定了牡蛎壳体分泌速率(1～1.7 cm/a)和休眠水温(6～11℃)等基本参数,并探讨了礁体发育与古气候(温度、降水等)的关系。(14)继续贝壳堤时空分布、成因与环境演化研究。提出了贝壳堤的水下线形沙坝→沿岸堤→风成沙丘多成因过程假说。近10处堤底板的水准测量表明,底板多向海倾斜。初步确定了各堤前缘、后缘底板及其高差平均值,堤顶部的高程,以及底板和顶部的年龄。根据新的发现,将III、II和I三堤分别划分为2道支堤。发现I堤叠加于歧口-马棚口NNW-SSE向的晚全新世线性埋藏凸起之上,为前人的渤海湾西部NNW-SSE向新构造形迹控制古海岸线的假说提供了证据。(15)继续全新世相对海面变化研究,初步建立了有孔虫、硅藻和软体动物、贝壳堤和牡蛎礁等代用指标,并与介形虫鉴定、岩石学(石膏与黄铁矿晶粒等)研究及AMS 14C和OSL测年(包括有孔虫壳体AMS 14C测年)相结合,揭示了地层记录的(大致分为两个阶段的)全新世9～11次海水影响增强事件。根据贝壳堤前、后缘底板的高度和沉积学特征,确定了底板作为海面变化标志点的自身误差经验值和对应平均大潮差范围的误差经验值;确定了牡蛎礁顶板起伏误差值并对应海平面位置,并被礁顶上覆潮间带泥层的平均厚度(对应海平面-平均高潮位之间的调适空间)所证实。(16)开展了泥质海岸带脆弱地质环境研究。初步发现了渤海湾西北部浅海区中全新世高能沉积事件、贝壳堤中的宋金、明末和"小冰期"风暴潮夹层或风力增强期。统计了19世纪末期以来10次重大风暴潮的淹浸范围、并将百余年来的极端高水位(在进行了地面下沉校正后)统一折算为黄海85高程,根据海洋气象部门的渤海湾西岸不同重现期风暴潮水位高度,确定了上述10次风暴潮水位的重现期。提出了叠加地学因素(地面下沉、海面上升、海面上升的净增水效应及河口增水效应等)的渤海湾西岸2010～2050年从50年到10 000年的5个不同重现期的风暴潮水位预测方案。通过海(河)堤及沿海低地的RTK测量,初步查明了滨海新区和海(河)堤地表高程现状。通过对地下潜水位高程测量,初步发现了潜水位面向陆反向倾斜的特征。(17)建立了包括5个地学参数共计11项指标的泥质海岸带环境地学评价体系。向地方政府提交了南港工业区围海造陆区地质环境评价、天津港风暴潮预测、天津浅海区软土分布、贝壳堤与牡蛎礁重新划界、海区人工鱼礁选址、海区活牡蛎礁勘查、海岛地名普查和黄骅港及周边地区地质环境评价等研究报告。此外,在风暴潮预警、海堤加高等方面,积极向有关部门提出建议。在完成地质调查任务的同时,力争以扎实的地学研究成果服务地方经济社会发展。更多还原

【Abstract】 As a part of the 13-year long,nationwide Land and Resource Investigations,multidisciplinary studies,concentrated on the coastal Quaternary geology,have been carrying out on the muddy coast of Binhai New Area,Tianjin and adjacent muddy coast along the west Bohai Bay.This paper,as a brief summary,introduces,most conscientiously,the results obtained in the past 13 years as follows. (1) The geoenvironmental changes on the muddy coast(coastal lowland-intertidal zone-shallow sea) have been defined as the main direction and major task. (2) Stratigraphical framework,depositional discontinuities,differential tectonic movements and sequence stratigraphy since the late Pleistocene,ca.140 ka BP,have been discussed based on nearly 30 boreholes of total footage 1 600 m,and,of them 400 m were drilled on the shallow sea. (3) Two informal stratigraphical units,the Gray Unit and the Yellow Unit,occurred in the mid-to late Holocene,as the upper portion of the Marine Bed I,have been set up based on more than 4 000 Eijelkamp cores.The Gray Unit is intertidal while the Yellow Unit is supratidal,including lagoonal-salt marshy-swampy environments.Geological mapping,1/50 000,is able to give further computer-processing pseudo-3D representation. (4) A first non-profitable investigation,including bathymetry-subbottom profiling-fully-coring drilling-subbottom sampling-side sonar-single channel seismology-210Pb and 137Cs dating of the surficial sediments,has been pursued systematically in the sallow sea area,3 000km2,west Bohai Bay.The sediments after Deglaciation has been subdivided into 6 units from Ua to Uf. (5) Shoreline migrations of the past 130 years have been reconstructed correlating the historical maps with air photos and satellite images at different years.It can be separated into two stages.The Stage 1,between the end of LIA(Little Ice Age) and the 1950’s,shoreline changed from tortuous to straightforward with erosion,and the Stage 2,from the 1950’s up to now,human-influenced accumulation and reclamation push the shoreline extending seaward.However,annual monitoring on tidal flat morphology has revealed that the tidal flat seems to entering a new Stage 3,in which a new recession seems to be over its threshold. (6) 210Pb and 137Cs dating for young sediments has been firstly created in Bohai Bay coast.Based on nearly a hundred sets of the 210Pb and 137Cs data,of which both 210Pb and 137Cs simultaneously dated are near 60 sets that we contributed 40,a preliminary zonation of the modern sedimentation rates in Bohai Bay coastline has been delineated showing the lowest rate zone of <1 mm/a,high rate zone of >5 mm/year with maximum of >30 mm/a and unstable rate zone in adjacent shallow sea area of >5 mm/a usually. (7) Surficial sediments of the intertidal flat and shallow sea area have been granulometrically analyzed indicating zonal characteristics both horizontally and vertically.At the intertidal flat of the sector between Duliujianhe mouth and Haihe mouth,surficial sediments are both coursing-up/coursing northward and sorting better upward/northward as well.This is estimated as a result of water sluice building-up half a century ago,which damped water and sediment discharges.Consequently,the Haihe Delta waned gradually due to prevailed sea water influences. (8) Modern(both living and dead) foraminifera assemblages are precisely positioned with micromorphology,by Geodimeter on intertidal flat,and sea bottom locations by bathymetry.Thus,the transfer function of modern foraminifera assemblages and water depth(1~10 m) has been preliminarily established.Tentatively,a Holocene relative sea level curve has been set up. (9) Seven diatom assemblages have been distinguished based on various sampling stations with water depths from intertidal to shallow water,different muddy and sandy subbottoms and various salinities.Thus,relationship between diatom distribution and environmental factors,including water depth,salinity and substrata,has pursued.Furthermore,8 events of enhanced marine-influence have been revealed since ca.7 ka cal BP,based on the diatom-based proxy indicating marine influence and climate changes. (10) More than 100 species of bivalve and gastropoda shells,collected and identified in the past decade,have been divided into three major groups as land,marine and transitional facies,and relationships between shells and water depth and salinity have been preliminarily studied and has been used for relative sea level reconstruction. (11) Adding newly discovered five sites,now total 47 sites of oyster reefs have been found,among which 10 reefs are with our intensive observations.Based on their locations and ages ten major reef-groups have been divided indicating the ten cyclicities between reef and overlying mud as the first order category;while the second order cyclicity,consisting of alternation between vertical building-up and intercalated horizontal layers inside the reef bodies,amount to several ten times. (12) Biocarbonate isotope compositions of 18O,13C and 87Sr have been analyzed for numerous shells.A local average δ13C(-2.68 ‰ PDB),obtained by measuring a dozen various shells,has been used for systematic calibration of isotope fractionation in order to get approximate conventional ages for more than 500 non-conventional dates.Rapid-balance hypothesis,by measuring different microgrowth increments of oyster shell,gives a way for further accurate calibration which has been proved by advanced local reservoir values(ΔR=-170～-180a),cited from CALIB.After a decade-long effort,a databank of more than 600 14C ages has been set up. (13) Solution of 18O,13C(and 87Sr) of the oyster shells has been improved from season to a half month level.By measuring the height/width ratio and weight/growth ratio,it is able to distinguish various subenvironments such as estuary and open bay,in which the animal lived.Some essential information,including the growth rate of shell(1～1.7 cm/a) and winter-dormancy temperature(6～11°C),have been acquired based on isotopic results. (14) A hypothesis of polygenetic processes of subaqueous linear bar→barrier island→beach ridge→windblown dune has been raised for the local shelly cheniers.Levelling at many sites indicates that the bottom of chenier often seaward inclines with average of 1 m between the front-foot and rear-base.Based on our new observation and reexamination of previous material,Cheniers III,II and I can be bifurcated in to two branches,respectively.Chenier I,overlying on the buried,protruding-up liner mound,seems to be a causal continuation of the NNW-SSE oriented neotectonic lineation along the shoreline of west Bohai Bay. (15) Multi proxies,including foraminifera,ostrocoda,diatom,mollusks,nodules of gypsum and pyrite,with AMS 14C and OSL dating,have revealed 9～11 times of enhanced sea water influences belonging to two stages separated by a remarkable waning of sea water during the mid-Holocene.The bottom of chenier and the top of oyster reef have been recognized as tow sea level indicators.The former represents a contemporaneous vertical range of MHW and MLW,with an error value of ±1.5 m.The latter lies on a contemporaneous msl with an error of ±0.7 m,which has been also evidenced by a maximum accommodation space providing for the overlying tidal sediments,of which average thickness is practically measured as 1.6 m,ie.is approximately equal to the range between msl and MHW. (16) Coastal geoenvironmental study has revealed a number of interesting phenomena including the mid-Holocene high dynamic event,6.8～3.5 ka cal BP,in shallow sea area;intercalated storm dumping layers,occurred during Song-Jin Dynasty,late Ming Dynasty and LIA,in cheniers;maximum flooding areas of top ten storms since the late 19th century.The extreme water levels of such top ten have been systematically re-corrected against to the present national datum considering the land subsidence changeable during the past 120 years.As a result,a scenario,named "Adding Geological Factors",for storm prediction till 2050,with various reappearances from 1 in 50 to 1 in 10 000 years,has been raised with land subsidence,sea level rise,enhanced storm water exerted by sea level rise and estuary channel effect,etc. (17) A muddy coastal geoenvironmental assessing system,including 11 parameters of which 5 are geological parameters,has been preliminarily created.We have submitted a number of reports,dealing with assessments of the in Nangang land reclamation area and coast of Huanghua Harbour,Storm-surge prediction for Tianjin Harbour,Soft mud distribution in the shallow sea area of Tianjin,Site-choosing for artificial fishery reefs,Investigation of the living oyster reefs in the shallow sea,Island survey and so on.Also,various suggestions have been conveyed to the local governments from storm forecasting to increasing the height of seadyke.While fulfilling the geological investigations,we perform services for the local eco-and societal development with our solid geo-scientific results.更多还原