导致古森林沉没于海的福建深沪湾古地震研究
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摘要
福建深沪湾海底古森林是强古地震遗迹。研究结果表明 ,全新世早期该处海底古森林生长在由松散的晚更新世含砾砂粘土构成的低凹洼地内。距今 70 0 0a左右的强古地震导致古森林沉没于海并形成泻湖环境 ,约距今 2 0 0 0a的又一次强古地震使海底古森林沉没到更深的海底 ,推测这两次古地震的震级都超过 7级。
The submerged paleo forest in Shenhuwan Bay, Fujian Province, is accepted to be the vestige of strong paleo earthquake. The fossil trees were formerly growing in low lying land filled with late Pleistocene gravel bearing sandy clay during Holocene. A strong earthquake occurred 7000 years B.P. had caused the subsidence of the trees onto the seafloor and the development of lagoon environment, while another strong earthquake occurred 2,000 years B.P. had given rise to the further subsidence of the trees to a greater depth. The evidences of these two events are as follows: 1. Earthquake landform composed of loose sediments was buried by littoral facies deposits on the seafloor, and its remnants were left on the beach. This may indicate that the land was subsided rapidly below the sea level during the earthquake, while several island like highlands composed of red and yellow gravel bearing sandy clays of late Pleistocene age remained above the sea level after the earthquake. After long period erosion by sea water, red brown and yellow land spots were left on tidal zone or shoal, while isolated blocky highlands surrounded by marine and eolian deposits were remained on the coast. 2. Many paleo trees had killed simultaneously, some of which were collapsed and broken. Some broken trunks laid down on the sea floor, and some broken branches were still connected with the trunks. All these may indicate a sudden subsidence caused by strong earthquake, which had given rise to the rapid burying of the paleo trees. 3. Evidence from seismic facies sediments. The ZK 1 and ZK 2 drill holes on the shoal have revealed that the Holocene sediments contains a 20～30m thick bed of carbonized, half carbonized and un carbonized broken wood chips with a little amount of gravels. This bed has not been eroded and transported by the sea water, containing marine facies sands of fine to medium size and small yellow clay balls. The formation of this bed seems to closely related to the sudden subsidence caused by strong earthquake, which had given rise to the transgression of the sea and the transportation of fine to medium grained sands into the pre existing slope wash and alluvium. 4. Evidence from the rate of crustal movement. The Shenhuwan paleo earthquake occurred 7,000 years ago. According to estimation, the rate of sedimentation during the period of 7,000～6,000a B.P. was 11 times as high as that during the period of 6,800～2,000a B.P. The rate of crustal movement during the former period was 25 times as high as that during the latter period. 5. Four sag ponds possibly produced by earthquake are distributed along the fault in the coastal area on the southwest margin of the Shenhuwan graben. The earthquake of late Holocene occurred about 2,000 years ago. This event can be confirmed by the facts that the elevation of littoral deposits at Shenhuwan Bay at that time differed from the sea level for about 4m, and that elovian sand deposits of continental facies were remained in the marine strata on the seafloor. According to the estimation, the subsidence of Shenhuwan Bay caused by these two earthquakes reached up to 3m, and the magnitudes of the two events are postulated to be above 7.
The submerged paleo forest in Shenhuwan Bay, Fujian Province, is accepted to be the vestige of strong paleo earthquake. The fossil trees were formerly growing in low lying land filled with late Pleistocene gravel bearing sandy clay during Holocene. A strong earthquake occurred 7000 years B.P. had caused the subsidence of the trees onto the seafloor and the development of lagoon environment, while another strong earthquake occurred 2,000 years B.P. had given rise to the further subsidence of the trees to a greater depth. The evidences of these two events are as follows: 1. Earthquake landform composed of loose sediments was buried by littoral facies deposits on the seafloor, and its remnants were left on the beach. This may indicate that the land was subsided rapidly below the sea level during the earthquake, while several island like highlands composed of red and yellow gravel bearing sandy clays of late Pleistocene age remained above the sea level after the earthquake. After long period erosion by sea water, red brown and yellow land spots were left on tidal zone or shoal, while isolated blocky highlands surrounded by marine and eolian deposits were remained on the coast. 2. Many paleo trees had killed simultaneously, some of which were collapsed and broken. Some broken trunks laid down on the sea floor, and some broken branches were still connected with the trunks. All these may indicate a sudden subsidence caused by strong earthquake, which had given rise to the rapid burying of the paleo trees. 3. Evidence from seismic facies sediments. The ZK 1 and ZK 2 drill holes on the shoal have revealed that the Holocene sediments contains a 20～30m thick bed of carbonized, half carbonized and un carbonized broken wood chips with a little amount of gravels. This bed has not been eroded and transported by the sea water, containing marine facies sands of fine to medium size and small yellow clay balls. The formation of this bed seems to closely related to the sudden subsidence caused by strong earthquake, which had given rise to the transgression of the sea and the transportation of fine to medium grained sands into the pre existing slope wash and alluvium. 4. Evidence from the rate of crustal movement. The Shenhuwan paleo earthquake occurred 7,000 years ago. According to estimation, the rate of sedimentation during the period of 7,000～6,000a B.P. was 11 times as high as that during the period of 6,800～2,000a B.P. The rate of crustal movement during the former period was 25 times as high as that during the latter period. 5. Four sag ponds possibly produced by earthquake are distributed along the fault in the coastal area on the southwest margin of the Shenhuwan graben. The earthquake of late Holocene occurred about 2,000 years ago. This event can be confirmed by the facts that the elevation of littoral deposits at Shenhuwan Bay at that time differed from the sea level for about 4m, and that elovian sand deposits of continental facies were remained in the marine strata on the seafloor. According to the estimation, the subsidence of Shenhuwan Bay caused by these two earthquakes reached up to 3m, and the magnitudes of the two events are postulated to be above 7.
引文
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李平日,黄镇国,宗永强.1987.韩江三角洲.北京:海洋出版社.LiPingri,HuangZhenguo,ZongYongqiang,etal.1987HanjangRiverDelta.Beijing:MarinePublishingHouse(inChiense)
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徐起浩.2001.深沪湾新发现的海底古森林遗迹的分布及植物学、年代学特征.海洋科学,25(2):46～49.
XuQihao.2001.Theplantkingdomandagepropertyofthepalaeo forestvestigewhicharediscoveredrecentlyonShenhuwanGulf.MarineSciences,25(2):46～49.
徐起浩,冯炎基.2000.深沪湾古森林沉没海底前生长的古凹陷环境.南京师范大学学报(应用第四纪专集),23(4):164～169.
XuQihao,FengYanji.2000.Thepalaeo hollow,troughenvironmentonwhichthepalaeo forestweregrowinginShenhuwanbeforetheyweresunkinbottomofthesea.JoumalofNanjingNormalUniversity(Naturalscience)(SpecialcollectedworksofappliedQuaternaryScience),23(4):164～169(inChinese).
王绍鸿,唐丽玉,赵希涛.1999.福建深沪湾海底林的测量与新发现.第四纪研究.19(5):477.
WangShaohong,TangLiyu,ZhaoXitao.1999.SurveyingandnewdiscoverofsubmergedforestsinShenhuwanBay,FujianProvine.QuaternarySciences,19(5):477(inChinese).
吴正,黄山,胡守真,等.1995.华南海岸风成砂地貌研究.北京:科学出版社.WuZheng,HuangShan,HuShouzhen.1995.ResearchontheLandformsoftheWind driftSandinSouthChinaCoast.Bei jing:SciencePress.
朱海之.1983.第四纪研究中有关地震灾害与古地震研究的若干问题.国际地震动态,6:11～14.
ZhuHaizhi.1983.Somequestionsaboutresearchofseismiccalamityandpalaeo earthquakeinQuaternaryresearch.RecentDevelopmentinWorldSeismology,6:11～14(inChinese).
SugimuraA ,Naruse.1954.Changesinsealevel,seismicupheavals,andcoastalterracesinthesouthernKantoregionJapan,I.JapanJGeolGeogr,24:101～113.
SugimuraA ,Naruse.1955.Changesinsealevel,seismicupheavalsandcoastalterracesinthesouthernKantoregion,Japan2.JapanJGeolGeogr,25:165～176.
SimsJD .1973.EarthquakeinducedstructuresofVanNormanLake,SanFernandoCalifornia.Science(183),4:108.SimsJD .1979.Recordsofprehistoricearthquakesinsedimentarydepositsinlakes.EarthquakeInformationBulletin,(11):6.Хромовеких.ВС.1979.ПалеосейсмогеологияБольшогоКавкза.Издательство《Наука》,Москва.ХоджаевА.1985.Палеосейсмогеология.ЧаткалоКураминскогоРегиона,Издательство“Фан”УзбекскойССР.АбдрахматовКЕ,ННЛемзцн.1989.ПалеосейсмнчностьЦентральногоТяньшаня,ИнститутСейсмологииАНКиреССР.,Посттипла.Удк550,34(21).
ChenEnmin,HuangYongyin.1979.Preliminarydiscussiononthe1605Qiongzhoustrongearthquakeanditsseismogeneticstructure.SeismologyandGeology,1(4):34～44(inChinese).
丁国瑜.古地震研究情况.1982.见:史前地震与第四纪地质文集.西安:陕西科学技术出版社.3～7.
DingGuoyu.1982.Researchsituationofpalaeo earthquakes.In:CollectedworksofprehistoricearthquakesandQuaternarygeology.Xi’an:ScienceandTechnologyPublishingHouseofShanxiProvince.3～7(inChinese).
丁祥焕,王耀东,叶盛基.1988.福建东南沿海活动断裂与地震.福州:福建科学技术出版.
DingXianghuan,WangYaodong,YeShengji.1988.TheactivefaultsandearthquakesinSoutheastcoastalareasofFujianProvince.Fuzhou:ScienceandTechnologyPublishingHouse(inChinese).
邓起东,冯先岳,尤惠川,等.1991.新疆独山子-安集海活动逆断裂晚第四纪特征及古地震.见:国家地震局地质研究所编.活动断裂研究(1).北京:地震出版社.37～56.
DengQidong,FengXianyue,YouHuichuan,etal.1991.PaleoseismologyandlateQuaternaryactivityoftheDushanzi-Anjihaireversefaultzone,Xinjiang.In:InstituteofGeology,CSB ,ed.Researchonactivefault(1).Beijing:Seismo logicalPress.37～56(inChinese).
冯先岳著.1997.新疆古地震.乌鲁木齐:新疆科技卫生出版社.FengXianyue.1997.Palaeo earthquakesofXinjiang.Wulumuqi:Science,TechnologyandHealthPublishingHouse(inChinese).
李平日,黄镇国,宗永强.1987.韩江三角洲.北京:海洋出版社.LiPingri,HuangZhenguo,ZongYongqiang,etal.1987HanjangRiverDelta.Beijing:MarinePublishingHouse(inChiense)
.徐起浩.1986.琼北东寨港的近期下沉.海洋科学,10(1):24～28.
XuQihao.1986.RecentsubsidenceoftheDongzhaigangBayarea,NorthernHainan.MarineSciences,10(1):24～28(inChinese).
徐起浩,冯炎基.1990.深沪湾晚更新世以来的古气候、古海平面与地壳升降运动.台湾海峡,9(3):231～238.
XuQihao,FengYanji.1990.Palaeo climate,palaeo sealevelandcrustalmovementofShenhuwanBayofFujianProvincesincelatePleistocene.JournalofOceanographyinTaiwanStrait,9(3):231～238(inChinese).
徐起浩,冯炎基.1997.广东中山晚更新世最早海浸层与水动型海平面变化.地震地质,19(1):91～95.
XuQihao,FengYanji.1997.TheearliesttransgressionlayersincelatePleistoceneinZhongshancityofGuangdongProvinceand“Eustatic”sealevelchanges.SeismologyandGeology,19(1):91～95(inChinese).
徐起浩.1998.福建深沪湾又新发现两大片海底古森林遗迹.见:中国地震学会第7次学术会议论文摘要集.北京:地震出版社.74.
XuQihao.1998.Thepalaeo forestvestigesoftwobigsiteontheseafloorareagaindiscoveredrecentlyinShenhuwanBayofFujianProvince.In:Collectedabstractsofworksof7thacademicplenarysessionofChineseSeismologicalSociety.Bei jing:SeismologicalPress.74(inChinese).
徐起浩.2001.深沪湾新发现的海底古森林遗迹的分布及植物学、年代学特征.海洋科学,25(2):46～49.
XuQihao.2001.Theplantkingdomandagepropertyofthepalaeo forestvestigewhicharediscoveredrecentlyonShenhuwanGulf.MarineSciences,25(2):46～49.
徐起浩,冯炎基.2000.深沪湾古森林沉没海底前生长的古凹陷环境.南京师范大学学报(应用第四纪专集),23(4):164～169.
XuQihao,FengYanji.2000.Thepalaeo hollow,troughenvironmentonwhichthepalaeo forestweregrowinginShenhuwanbeforetheyweresunkinbottomofthesea.JoumalofNanjingNormalUniversity(Naturalscience)(SpecialcollectedworksofappliedQuaternaryScience),23(4):164～169(inChinese).
王绍鸿,唐丽玉,赵希涛.1999.福建深沪湾海底林的测量与新发现.第四纪研究.19(5):477.
WangShaohong,TangLiyu,ZhaoXitao.1999.SurveyingandnewdiscoverofsubmergedforestsinShenhuwanBay,FujianProvine.QuaternarySciences,19(5):477(inChinese).
吴正,黄山,胡守真,等.1995.华南海岸风成砂地貌研究.北京:科学出版社.WuZheng,HuangShan,HuShouzhen.1995.ResearchontheLandformsoftheWind driftSandinSouthChinaCoast.Bei jing:SciencePress.
朱海之.1983.第四纪研究中有关地震灾害与古地震研究的若干问题.国际地震动态,6:11～14.
ZhuHaizhi.1983.Somequestionsaboutresearchofseismiccalamityandpalaeo earthquakeinQuaternaryresearch.RecentDevelopmentinWorldSeismology,6:11～14(inChinese).
SugimuraA ,Naruse.1954.Changesinsealevel,seismicupheavals,andcoastalterracesinthesouthernKantoregionJapan,I.JapanJGeolGeogr,24:101～113.
SugimuraA ,Naruse.1955.Changesinsealevel,seismicupheavalsandcoastalterracesinthesouthernKantoregion,Japan2.JapanJGeolGeogr,25:165～176.
SimsJD .1973.EarthquakeinducedstructuresofVanNormanLake,SanFernandoCalifornia.Science(183),4:108.SimsJD .1979.Recordsofprehistoricearthquakesinsedimentarydepositsinlakes.EarthquakeInformationBulletin,(11):6.Хромовеких.ВС.1979.ПалеосейсмогеологияБольшогоКавкза.Издательство《Наука》,Москва.ХоджаевА.1985.Палеосейсмогеология.ЧаткалоКураминскогоРегиона,Издательство“Фан”УзбекскойССР.АбдрахматовКЕ,ННЛемзцн.1989.ПалеосейсмнчностьЦентральногоТяньшаня,ИнститутСейсмологииАНКиреССР.,Посттипла.Удк550,34(21).
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