广东汕头南部近海晚第四纪埋藏古河曲的研究
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摘要
GEOPULSE甚高分辨率地震地层记录的研究表明 ,广东省汕头市南部近海埋藏有古河曲 ,曲率半径为 6— 7km ;发育有主河道和主、支汊道。主河道宽 2— 3km ,最深约 2 5m ;汊道宽 2 0 0— 1 5 0 0m ,深 4— 5m。在弯道处 ,主槽强烈东凸 ,侧向侵蚀显著。古河曲的形成在距今1 4kaB .P .之后 ,随着晚第四纪末次海面上升 ,在距今约 1 2 .3kaB .P .,古河曲的远岸部分开始淤浅 ,距今约 1 1kaB .P .时整个河曲被淤平而消失 ;尔后 ,古河曲的近岸部分被韩江现代水下三角洲所掩埋。古河曲为古练江的一部分 :从现在的练江口附近向东流去 ,在企望湾口转向南 ,再顺时针拐弯流向海洋。
The survey area covers the areas between 23°00′—23°30′N, 116°30′—117°00′E. It is near the Qiwang Bay, Shantou City, Guangdong, China. This area faces the Taiwan Shoal in the East, which is the southern part of the Taiwan Strait. The area extends from the coast to approximately 25 km offshore (35 m below sea level). The sea bed dips gently southeastwards at from 10 minute in shallow area (<20 m) to 5 minute in the areas beyond. Gravity core samples show that the near shore seabed is covered with fine sediments, such as clayey silt and silty clay. Form 25—30 m contour line, the deposit changes to coarse-grained sands. The Hanjiang River, the largest river in the study area, has a large number of tributaries and runs into the northern part of the area with an annual runoff of 296×10 8m 3 and sediments load of 11×10 6 t. The Lianjiang river with a smaller discharge is located in the west of the area. Most Hanjiang sediments deposited in the river mouth with part of them washed away by tides. From seismic profiles, four seismic sequences were identified in terms of seismic stratigraphy. The upper layer or Layer A, is characterized with high frequency, continuous, strong amplitude, parallel, and vertically uniform reflection waves. It is between 0—6 m in thickness, decreasing from the coast to the sea and wedged out at the area 16 km from the shoreline. Gravity cores S1 and S25 indicate that Layer A consists of mainly clayey silt which deposited in the late Holocene high sea level period around 6ka B.P.. It constitutes the forehead of modern Hanjiang subaqueous delta. Layer B has similar wave characteristics to Layer A, but with wavy surface with various dipping directions. Layer B, between 0—20 m thick, is comprised of channel deposits. In the near shore zone it was transgressed by Layer A but in the offshore zone it directly exposed without younger cover. The base of Layer B deeply incised into the underlying sediments. Layer C waves, observable mainly in the open sea with a thickness of 20m, are high frequency, medium amplitude, continuous to sub-continuous and generally parallel to the sea floor. The top of the layer mostly exposes on the sea floor and was locally cut and overlain by Layer B in the near shore zone. Sampling at S26 shows that Layer C consists of mainly coarse sands similar to the surface sediments in western Taiwan Shoal. Its 14 C dated age is (14107—13927)±(349—219)a B.P. or geologically Late Pleistocene. Layer D, the bottommost one, is a continental formation that has the greatest variation in wave characteristics. In this area, paleo-river channels and major and minor tributaries were identified from seismic profiles. The main channels were 2—3 km wide and 22 m deep, jointed by tributaries with various sizes. The base of the channel near shore is 44m below the present sea level, which cut into Layer D and underlies Layer A. The main channel offshore is 2.5 km wide and 25 m deep, 55 m below present sea level, which cut the Layer C. The age of the river is later than 14ka B.P.. Observations on two main channels showed that the past sea floor dipped to the south that is similar to the present sea floor. Strong asymmetry and clear curvature observed in this study indicated the existence of a meandering river system in this area. This system is a part of the Lianjiang river in the past. Based on the limited study on sea level changes since the Late Pleistocene in this area, the authors concluded that the paleo-meandering-river existed between 14—11ka B.P. or from Late Pleistocene to Early Holocene. Due to the sea level continues rising, at 6ka B.P., the Hanjing River underwater delta came into being. Therefore, the previous meandering river system was buried.
The survey area covers the areas between 23°00′—23°30′N, 116°30′—117°00′E. It is near the Qiwang Bay, Shantou City, Guangdong, China. This area faces the Taiwan Shoal in the East, which is the southern part of the Taiwan Strait. The area extends from the coast to approximately 25 km offshore (35 m below sea level). The sea bed dips gently southeastwards at from 10 minute in shallow area (<20 m) to 5 minute in the areas beyond. Gravity core samples show that the near shore seabed is covered with fine sediments, such as clayey silt and silty clay. Form 25—30 m contour line, the deposit changes to coarse-grained sands. The Hanjiang River, the largest river in the study area, has a large number of tributaries and runs into the northern part of the area with an annual runoff of 296×10 8m 3 and sediments load of 11×10 6 t. The Lianjiang river with a smaller discharge is located in the west of the area. Most Hanjiang sediments deposited in the river mouth with part of them washed away by tides. From seismic profiles, four seismic sequences were identified in terms of seismic stratigraphy. The upper layer or Layer A, is characterized with high frequency, continuous, strong amplitude, parallel, and vertically uniform reflection waves. It is between 0—6 m in thickness, decreasing from the coast to the sea and wedged out at the area 16 km from the shoreline. Gravity cores S1 and S25 indicate that Layer A consists of mainly clayey silt which deposited in the late Holocene high sea level period around 6ka B.P.. It constitutes the forehead of modern Hanjiang subaqueous delta. Layer B has similar wave characteristics to Layer A, but with wavy surface with various dipping directions. Layer B, between 0—20 m thick, is comprised of channel deposits. In the near shore zone it was transgressed by Layer A but in the offshore zone it directly exposed without younger cover. The base of Layer B deeply incised into the underlying sediments. Layer C waves, observable mainly in the open sea with a thickness of 20m, are high frequency, medium amplitude, continuous to sub-continuous and generally parallel to the sea floor. The top of the layer mostly exposes on the sea floor and was locally cut and overlain by Layer B in the near shore zone. Sampling at S26 shows that Layer C consists of mainly coarse sands similar to the surface sediments in western Taiwan Shoal. Its 14 C dated age is (14107—13927)±(349—219)a B.P. or geologically Late Pleistocene. Layer D, the bottommost one, is a continental formation that has the greatest variation in wave characteristics. In this area, paleo-river channels and major and minor tributaries were identified from seismic profiles. The main channels were 2—3 km wide and 22 m deep, jointed by tributaries with various sizes. The base of the channel near shore is 44m below the present sea level, which cut into Layer D and underlies Layer A. The main channel offshore is 2.5 km wide and 25 m deep, 55 m below present sea level, which cut the Layer C. The age of the river is later than 14ka B.P.. Observations on two main channels showed that the past sea floor dipped to the south that is similar to the present sea floor. Strong asymmetry and clear curvature observed in this study indicated the existence of a meandering river system in this area. This system is a part of the Lianjiang river in the past. Based on the limited study on sea level changes since the Late Pleistocene in this area, the authors concluded that the paleo-meandering-river existed between 14—11ka B.P. or from Late Pleistocene to Early Holocene. Due to the sea level continues rising, at 6ka B.P., the Hanjing River underwater delta came into being. Therefore, the previous meandering river system was buried.
引文
王文介,1985.粤东锯齿状海岸弧形砂质湾滩的发育.热带海洋,4(2):15—21[WangWJ ,1985.Developmentofarc shapedbeachofsawtoothedcoastsintheeasternGuangdongProvince,China.TropicalOcean,4(2):15—21]
王文介,欧兴进,林怀兆,1986.韩江河口发育的现代过程和演变.热带海洋,5(1):37—45[WangWJ ,OuXJ ,LinHZ ,1986.Moderndevelopmentprocessesandevolu tionofHanjiangRiverestuary.TropicalOcean,5(1):37—45]
中国科学院南海海洋研究所海洋地质研究室,1978.华南沿海第四纪地质.北京:科学出版社,21—22[MarineGeologicalDepartmentofSouthChinaSeaInstituteofChi neseSciencesAcademy,1978.QuaternaryGeologyofcoastareainSouthChina.Beijing:SciencePress,21—22]
李 凡,董太禄,姜秀珩等,1990.莺歌海附近陆架区埋葬古河道及海平面变化.海洋与湖沼,21(4):347—356[LiF ,DongTL ,JiangXH ,1990.Buriedpaleo riverchannelsandsealevelchangesincontinentalshelfnearYinggeHai.OceanologiaetLimnologiaSinica,21(4):347—356]
李 凡,于建军,姜秀珩等,1991.南黄海埋葬古河系研究.海洋与湖沼,22(6):501—508[LiF ,YuJJ,JiangXH ,1991.Studyonburiedpaleo riversysteminsouthernYellowSea.OceanologiaetLimnologiaSinica,22(6):501—508]
李平日,黄镇国,张仲英等,1987.广东东部晚更新世以来的海平面变化.海洋学报,19(2):216—222[LiPR ,HuangZG ,ZhangZY ,1987.SealevelchangesintheeasternGuangdongsinceLatePleistocene.ActaOceanolog icaSinica,19(2):216—222]
许志峰,王明亮,洪阿实等,1989.台湾海峡西部海域晚更新世以来沉积物年代与沉积速率.台湾海峡,8(2):114—121[XuZF ,WangML ,HongAS ,1989.AgesanddepositratioofsedimentsinthewesternTaiwanStraitsincetheLatePleistocene.TaiwanStrait,8(2):114—121]
邱传珠、陈俊仁,1986.台湾浅滩沉积物和沉溺海滩岩的研究.热带海洋,5(1):46—52[QiuCZ ,ChenJR ,1986.StudyondrownedbeachrocksandsedimentsinTai wanShoal.TropicOceanology,5(1):46—52]
杨怀仁,谢志仁,1984.中国东部近20000年来的气候波动与海面升降运动.海洋与湖沼,15(1):1—13[YangHR ,XieZR ,1984.Climatefluctuationandsealevelchangesinthelast2000yearsinEastChina.OceanologiaetLimnologiaSinica,15(1):1—13]
罗又郎,劳焕年,王渌漪,1985.南海东北部表层沉积物类型与粒度特征的初步研究.热带海洋,4(1):33—41[LuoYL ,LaoHN ,WangLY ,1985.Apreliminarystudyonpatternsandgranularcharacteristicsofsurfacesed imentsinthenortheasternSouthChinaSea.TropicO ceanology,4(1):33—41]
郑铁民,张君元,1982.台湾浅滩及其邻近大陆架的地形和沉积特征的初步研究.黄东海地质,北京:科学出版社,52—66[ZhengTM ,ZhangJY ,1982.Aprelimi narystudyontopographyandsedimentsinTaiwanShoalanditsadjacentcontinentalshelf.GeologyoftheEastChinaSeaandYellowSea,Beijing:SciencePress,52—66]
倪仁晋,马蔼乃,1998.河流动力地貌学.北京:北京大学出版社,38-40[NiRJ ,MaAN ,1998.Dynamicalgeo morphologyofrivers.Beijing:PressofBeijingUniversity(inChinese),38—40]
梁国雄,1986.汕头南部企望湾海岸地貌发育.热带海洋,5(3):33—41[LiangGX ,1986.Geomorphologicdevel opmentsoftheQiwangBaycoastinsouthShantou.TropicOceanology,5(3):33—41]
谢以萱,1983.南海东北部的海底地貌.热带海洋,2(3):182—190[XieYX ,1983.GeomorphologyofseafloorofthenortheasternSouthChinaSea.TropicOceanology,2(3):182—190]
曾从盛,1991.福建沿海全新世海平面变化.台湾海峡,10(1):77—84[CengCS ,1991.SealevelchangesincoastalareaofFujianProvinceduringHolocene.TaiwanStrait,10(1):77—84]
曾成开,朱永其,王秀昌,1982.台湾海峡的底质类型与沉积分区.台湾海峡,1(1):54—61[CengCK ,ZhuYQ ,WangXC ,1982.Bottomsedimentpatternsanddepositre gionsinTaiwanStrait.TaiwanStrait,1(1):54—61]
蓝东兆,张维林,陈承惠等,1991.台湾浅滩中粗砂的时代与成因.台湾海峡,10(2):156—161[LanDZ ,ZhangWL ,ChenCH ,1991.AgeandoriginofmediumcoarsesandinTaiwanShoal.TaiwanStrait(inChinese),10(2):156—161]
蓝东兆,1989.台湾海峡西部海域表层沉积物中硅藻和硅鞭毛藻的分布.台湾海峡,8(4):322—328[LanDZ ,1989.DistributionsofdiatomandsilicoflagellateofsurfacesedimentsinthewesternTaiwanStrait.TaiwanStrait,8(4):322—328]
LiuAC ,MissiaenT ,HenrietJP ,1992.ThemorphologyoftopTertiaryerosionsurfaceintheBelgiansectoroftheNorthSea.MarineGeology,105:275—284
LiuAC ,DeBatistM ,HenrietJPetal,1993.PlioPleistocenescourhollowsintheBelgiansectoroftheNorthSea.Geolo gieenMijnbouw,71:195—204
MitchumRMJR ,VailPR ,SangreeJB ,1977.Stratigraphicinterpretationofseismicreflectionpatternsindepositionalsequences.BulletinofAmericanAssociationofPetroleumGeologists,Memoir,26:117—133
SheriffRE ,1976.Inferringstratigraphyfromseismicdata.Bul letinofAmericanAssociationofPetroleumGeologists,60(4):528—542
VailPR ,MitchumRMJR ,ThompsonS ,1977.Relativechangesofsealevelsfromcoastalonlap.BulletinofAmeri canAssociationofPetroleumGeologists,Memoir,26:63—82
王文介,欧兴进,林怀兆,1986.韩江河口发育的现代过程和演变.热带海洋,5(1):37—45[WangWJ ,OuXJ ,LinHZ ,1986.Moderndevelopmentprocessesandevolu tionofHanjiangRiverestuary.TropicalOcean,5(1):37—45]
中国科学院南海海洋研究所海洋地质研究室,1978.华南沿海第四纪地质.北京:科学出版社,21—22[MarineGeologicalDepartmentofSouthChinaSeaInstituteofChi neseSciencesAcademy,1978.QuaternaryGeologyofcoastareainSouthChina.Beijing:SciencePress,21—22]
李 凡,董太禄,姜秀珩等,1990.莺歌海附近陆架区埋葬古河道及海平面变化.海洋与湖沼,21(4):347—356[LiF ,DongTL ,JiangXH ,1990.Buriedpaleo riverchannelsandsealevelchangesincontinentalshelfnearYinggeHai.OceanologiaetLimnologiaSinica,21(4):347—356]
李 凡,于建军,姜秀珩等,1991.南黄海埋葬古河系研究.海洋与湖沼,22(6):501—508[LiF ,YuJJ,JiangXH ,1991.Studyonburiedpaleo riversysteminsouthernYellowSea.OceanologiaetLimnologiaSinica,22(6):501—508]
李平日,黄镇国,张仲英等,1987.广东东部晚更新世以来的海平面变化.海洋学报,19(2):216—222[LiPR ,HuangZG ,ZhangZY ,1987.SealevelchangesintheeasternGuangdongsinceLatePleistocene.ActaOceanolog icaSinica,19(2):216—222]
许志峰,王明亮,洪阿实等,1989.台湾海峡西部海域晚更新世以来沉积物年代与沉积速率.台湾海峡,8(2):114—121[XuZF ,WangML ,HongAS ,1989.AgesanddepositratioofsedimentsinthewesternTaiwanStraitsincetheLatePleistocene.TaiwanStrait,8(2):114—121]
邱传珠、陈俊仁,1986.台湾浅滩沉积物和沉溺海滩岩的研究.热带海洋,5(1):46—52[QiuCZ ,ChenJR ,1986.StudyondrownedbeachrocksandsedimentsinTai wanShoal.TropicOceanology,5(1):46—52]
杨怀仁,谢志仁,1984.中国东部近20000年来的气候波动与海面升降运动.海洋与湖沼,15(1):1—13[YangHR ,XieZR ,1984.Climatefluctuationandsealevelchangesinthelast2000yearsinEastChina.OceanologiaetLimnologiaSinica,15(1):1—13]
罗又郎,劳焕年,王渌漪,1985.南海东北部表层沉积物类型与粒度特征的初步研究.热带海洋,4(1):33—41[LuoYL ,LaoHN ,WangLY ,1985.Apreliminarystudyonpatternsandgranularcharacteristicsofsurfacesed imentsinthenortheasternSouthChinaSea.TropicO ceanology,4(1):33—41]
郑铁民,张君元,1982.台湾浅滩及其邻近大陆架的地形和沉积特征的初步研究.黄东海地质,北京:科学出版社,52—66[ZhengTM ,ZhangJY ,1982.Aprelimi narystudyontopographyandsedimentsinTaiwanShoalanditsadjacentcontinentalshelf.GeologyoftheEastChinaSeaandYellowSea,Beijing:SciencePress,52—66]
倪仁晋,马蔼乃,1998.河流动力地貌学.北京:北京大学出版社,38-40[NiRJ ,MaAN ,1998.Dynamicalgeo morphologyofrivers.Beijing:PressofBeijingUniversity(inChinese),38—40]
梁国雄,1986.汕头南部企望湾海岸地貌发育.热带海洋,5(3):33—41[LiangGX ,1986.Geomorphologicdevel opmentsoftheQiwangBaycoastinsouthShantou.TropicOceanology,5(3):33—41]
谢以萱,1983.南海东北部的海底地貌.热带海洋,2(3):182—190[XieYX ,1983.GeomorphologyofseafloorofthenortheasternSouthChinaSea.TropicOceanology,2(3):182—190]
曾从盛,1991.福建沿海全新世海平面变化.台湾海峡,10(1):77—84[CengCS ,1991.SealevelchangesincoastalareaofFujianProvinceduringHolocene.TaiwanStrait,10(1):77—84]
曾成开,朱永其,王秀昌,1982.台湾海峡的底质类型与沉积分区.台湾海峡,1(1):54—61[CengCK ,ZhuYQ ,WangXC ,1982.Bottomsedimentpatternsanddepositre gionsinTaiwanStrait.TaiwanStrait,1(1):54—61]
蓝东兆,张维林,陈承惠等,1991.台湾浅滩中粗砂的时代与成因.台湾海峡,10(2):156—161[LanDZ ,ZhangWL ,ChenCH ,1991.AgeandoriginofmediumcoarsesandinTaiwanShoal.TaiwanStrait(inChinese),10(2):156—161]
蓝东兆,1989.台湾海峡西部海域表层沉积物中硅藻和硅鞭毛藻的分布.台湾海峡,8(4):322—328[LanDZ ,1989.DistributionsofdiatomandsilicoflagellateofsurfacesedimentsinthewesternTaiwanStrait.TaiwanStrait,8(4):322—328]
LiuAC ,MissiaenT ,HenrietJP ,1992.ThemorphologyoftopTertiaryerosionsurfaceintheBelgiansectoroftheNorthSea.MarineGeology,105:275—284
LiuAC ,DeBatistM ,HenrietJPetal,1993.PlioPleistocenescourhollowsintheBelgiansectoroftheNorthSea.Geolo gieenMijnbouw,71:195—204
MitchumRMJR ,VailPR ,SangreeJB ,1977.Stratigraphicinterpretationofseismicreflectionpatternsindepositionalsequences.BulletinofAmericanAssociationofPetroleumGeologists,Memoir,26:117—133
SheriffRE ,1976.Inferringstratigraphyfromseismicdata.Bul letinofAmericanAssociationofPetroleumGeologists,60(4):528—542
VailPR ,MitchumRMJR ,ThompsonS ,1977.Relativechangesofsealevelsfromcoastalonlap.BulletinofAmeri canAssociationofPetroleumGeologists,Memoir,26:63—82
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