南海西北部珊瑚礁记录所反映的新构造运动
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摘要
珊瑚礁是发育于热带海洋环境中由生物作用和地质作用共同形成的地质体,具有独特的新构造运动意义。南海西北部珊瑚礁记录所反映的新构造运动主要有火山活动、地壳升降运动和地震活动等。珊瑚礁区第四纪火山活跃,到现代已停止活动,部分火山构成珊瑚礁的基座,个别出露海面为火山岛;地壳升降运动差异较大,雷州半岛西南部珊瑚礁呈上升趋势,上升率为0.02~0.05mm/a;西沙群岛等岛礁地壳运动则呈下降趋势,下降率为-0.07~-0.10mm/a,岛礁中的造礁石珊瑚生长率、礁顶和灰沙岛的堆积率均相当于或大于地壳下降率与现代海平面上升率的总和;南海西北部珊瑚礁区内地震活动较强,尤其是1994年12月31日和1995年1月10日在雷州半岛西南部海域发生了6.1级和6.2级地震,这两次地震对该区珊瑚礁的发育有较大的影响。
The coral reef in northwest of the South China Sea is one of the typical coral reef areas since Holocene,thus is ideal to study the neotectonic movement and environmental changes recorded in coral reef.Through field investigation and sampling in this area as well as laboratory analysis,and based on former researches,the detailed neotectonic movements,evolvement process of coral reef,and the relative sea level change during Holocene and the modern earthquake recorded in coral reef are discussed in this paper.Coral reefs,formed in the process of biological-geological interaction in tropic oceanic environment,have recorded particular characteristics of neotectonic movement.The types and characteristics of neotectonic movement in this area are as follows: Most of the rifts were normal faults,forming small-sized grabens, fault basins and buried coral reefs.Marine volcanoes were active in Quaternary,although are extinct now.Some of them formed substrates of coral reefs,with only one forming a volcanic island above the sea.Earthquake activities in special areas are intense.Crust has been subsiding since Late Oligocene,but the rate is very low,only at about 0.1mm/a on an average.All growing rates of reef-building corals and the deposition rates of reef flats and limesand islets are equal to or exceed the sum total of crustal subsident rate and modern sea level rise rate in this area.Consequently,the numbers of dried reefs and limesand islets increase on South China Sea islands.The neotectonic movement of this area is feeble and it is favorable for the engineering construction on the islets and reefs.Because of a similar growth environment in Southwestern Leizhou Peninsula,assuming that the 1.88m thickness of the Goniopora reef reflects the magnitude of crustal subsidence,the subsidence rate was calculated as 9.4mm/a.During this subsidence period(6460aB.P.to 6670aB.P.),four rapid cooling events occurred,leading to growth discontinuities.The fifth layer was raised above the low spring tidal level,and its surface was eroded.An apparent crustal subsidence rate of 3.8mm/a was implied during 6310aB.P.to 6460aB.P.Considering the eroded surfaces,the subsidence rate might be even higher.During this period,two rapid cooling and sea-level dropping events occurred,resulting in the formation of eroded growth discontinuities.During the last 150a,a mean apparent subsidence rate is 5.9mm/a.Since 6200aB.P.,the crust has been raised and seal level dropped,and the Goniopora reef surface emerged 30cm above the low spring tidal.This corresponds to a mean apparent crustal uplift rate of 0.05mm/a.In Northwestern South China Sea,neotectonic movement recorded in coral reefs mainly includes volcanic activity,vertical movement and earthquake activity.In reef region,volcanism was active in Quaternary,but has ceased now.Some volcanoes became the reef substrates,and few emerged to become volcanic islands.The discrepancy between uplift and subsidence is conspicuous: coral reefs in Southwestern Leizhou Peninsula tend to uplift,at rates of 0.02～0.05mm/a;and coral reefs in Xisha Islands tend to subside,at rates of-0.07～(-0.10mm/a,) where the growth rate of reef building corals and the deposition rate of reef flats and sand cays are equal to or exceed the sum total of crustal subsiding rate and sea-level rising rate.Earthquakes in reef region of Northwestern South China Sea are intense,especially these two taking place on December 13 in 1994 and October 1 in 1995 in sea area of Southwestern Leizhou Peninsula,with magnitudes of 6.1 and 6.2 respectively,which have influenced the growth of coral reef greatly.Therefore,the various types of neotectonic movement recorded in coral reefs in Northwestern South China Sea are controlled by geological tectonic actions.
The coral reef in northwest of the South China Sea is one of the typical coral reef areas since Holocene,thus is ideal to study the neotectonic movement and environmental changes recorded in coral reef.Through field investigation and sampling in this area as well as laboratory analysis,and based on former researches,the detailed neotectonic movements,evolvement process of coral reef,and the relative sea level change during Holocene and the modern earthquake recorded in coral reef are discussed in this paper.Coral reefs,formed in the process of biological-geological interaction in tropic oceanic environment,have recorded particular characteristics of neotectonic movement.The types and characteristics of neotectonic movement in this area are as follows: Most of the rifts were normal faults,forming small-sized grabens, fault basins and buried coral reefs.Marine volcanoes were active in Quaternary,although are extinct now.Some of them formed substrates of coral reefs,with only one forming a volcanic island above the sea.Earthquake activities in special areas are intense.Crust has been subsiding since Late Oligocene,but the rate is very low,only at about 0.1mm/a on an average.All growing rates of reef-building corals and the deposition rates of reef flats and limesand islets are equal to or exceed the sum total of crustal subsident rate and modern sea level rise rate in this area.Consequently,the numbers of dried reefs and limesand islets increase on South China Sea islands.The neotectonic movement of this area is feeble and it is favorable for the engineering construction on the islets and reefs.Because of a similar growth environment in Southwestern Leizhou Peninsula,assuming that the 1.88m thickness of the Goniopora reef reflects the magnitude of crustal subsidence,the subsidence rate was calculated as 9.4mm/a.During this subsidence period(6460aB.P.to 6670aB.P.),four rapid cooling events occurred,leading to growth discontinuities.The fifth layer was raised above the low spring tidal level,and its surface was eroded.An apparent crustal subsidence rate of 3.8mm/a was implied during 6310aB.P.to 6460aB.P.Considering the eroded surfaces,the subsidence rate might be even higher.During this period,two rapid cooling and sea-level dropping events occurred,resulting in the formation of eroded growth discontinuities.During the last 150a,a mean apparent subsidence rate is 5.9mm/a.Since 6200aB.P.,the crust has been raised and seal level dropped,and the Goniopora reef surface emerged 30cm above the low spring tidal.This corresponds to a mean apparent crustal uplift rate of 0.05mm/a.In Northwestern South China Sea,neotectonic movement recorded in coral reefs mainly includes volcanic activity,vertical movement and earthquake activity.In reef region,volcanism was active in Quaternary,but has ceased now.Some volcanoes became the reef substrates,and few emerged to become volcanic islands.The discrepancy between uplift and subsidence is conspicuous: coral reefs in Southwestern Leizhou Peninsula tend to uplift,at rates of 0.02～0.05mm/a;and coral reefs in Xisha Islands tend to subside,at rates of-0.07～(-0.10mm/a,) where the growth rate of reef building corals and the deposition rate of reef flats and sand cays are equal to or exceed the sum total of crustal subsiding rate and sea-level rising rate.Earthquakes in reef region of Northwestern South China Sea are intense,especially these two taking place on December 13 in 1994 and October 1 in 1995 in sea area of Southwestern Leizhou Peninsula,with magnitudes of 6.1 and 6.2 respectively,which have influenced the growth of coral reef greatly.Therefore,the various types of neotectonic movement recorded in coral reefs in Northwestern South China Sea are controlled by geological tectonic actions.
引文
1 Taylor F W,Isacks B L,Jouann ic Cet al.Coseism ic andQuaternary vertical tecton ic movem ents,Santo and Maleku laIslands,New Hebrides Island Arc.Journal ofGeophysicalResearch,1980,85:5367~5381
2 Taylor F W,Jouann ic C,B loom A L.Quaternary uplift of theTorres Islands,Northern New Hebrides Frontal Arc:Comparisonw ith Santo and Maleku la Islands,Central New Hebrides FrontalArc.Journal ofGeology,1985,93:419~438
3 Taylor F W,Frohlich C,Lecolle Jet al.Analysis of partiallyem erged corals and reef terraces in the central Vanuatu Arc:Comparison of contemporary coseism ic and nonseism ic w ithQuaternary vertical movem ents.Journal of Geophysical Research,1987,92:4905~4933
4曾昭璇,梁景芬,丘世钧著.中国珊瑚礁地貌研究.广州:广东人民出版社,1997.121~124Zeng Zhaoxuan,L iang Jingfeng,Q iu Sh ijun.Geomorphology ofCh ina Coral Reefs.Guangzhou:Guangdong People Press,1997.121~124
5 Sm ith S V.Coral-reef area and contributions of reefs to processesand resources of the world s ocean.Nature,1978,273:225~226
6聂宝符,陈特固,梁美桃等著.南沙群岛及其邻近礁区造礁珊瑚与环境变化的关系.北京:科学出版社,1997.1~101N ie Baofu,Chen Tegu,L iang M eitaoet al.The Relationsh ipbetween Reef Coral and Environm ental Changes of Nansha Islandsand Ad jacent Regions.Beijing:Science Press,1997.1~101
7聂宝符,陈特固,梁美桃等.雷州半岛珊瑚礁与全新世高海面.科学通报,1997,42(5):511~514N ie Baofu,Chen Tegu,L iangM eitaoet a.l Coral reefs from LeizhouPen insu la and Holocene sea level h ighstands.Chinese ScienceBulletin,1997,42(5):511~514
8赵希涛著.中国海岸演变研究.福州:福建科学技术出版社,1984.132~145Zhao X itao.Ch inese Coast Evolution.Fuzhou:Fu jian Science andTechology Press,1984.132~145
9赵焕庭.南海诸岛珊瑚礁新构造运动的特征.海洋地质与第四纪地质,1998,18(1):37~45Zhao Huanting.Characteristics of neotecton ic movem ent of coral reefarea of the South Ch ina Sea Islands.Marine Geology&QuaternaryGeolog,y 1998,18(1):37~45
10赵焕庭,张乔民,宋朝景.华南海岸和南海诸岛地貌与环境.北京:科学出版社,1999.370~447Zhao Huanting,Zhang Q iaom in,Song Chaojing.Geomorphologyand Environm ental of the South Ch ina Coast and the South Ch inaSea Islands.Beijing:Science Press,1999.370~447
11 Zhang Q iaom in.On the b iogeomorphology of coral reefs:A casestudy on reef flat of Sanya fringing reefs,Hainan Island.In:W angY ing,Zhu X iaodong eds.Schedu le and Abstracts,InternationalAssociation of Geomorphologists,IGA 2000 Thematic Conference.Nan jing:Nan jing Un iversity,2000.144~145
12黄镇国,蔡福祥,韩中元等著.雷琼第四纪火山.北京:科学出版社,1993.1~7Huang Zhengguo,Cai Fuxiang,Han Zhongyuanet a.l TheQuaternary Volcano of Leizhou Pen insu la and Hainan Island.Beijing:Science Press,1993.1~7
13王国忠著.南海珊瑚礁区沉积学.北京:海洋出版社,2001.48~73W ang Guozhong.Coral Reef Sed im ent in the South Ch ina Sea.Beijing:Ch ina Ocean Press,2001.48~73
14余克服,刘东生,沈承德等.雷州半岛全新世高温期珊瑚生长所揭示的环境突变事件.中国科学(D辑),2002,32(2):149~157Yu Kefu,L iu Tungsheng,Shen Chengdeet a.l H igh-frequencyclimatic oscillations recorded in a Holocene coral reef at LeizhouPen insu la,South Ch ina Sea.Science in China(Series D),2002,45(12):1057~1068
15丘世均.礁坪发育与海平面变化.热带地貌,1996,17(1):80~87Q iu Sh ijun.Coral reefs and sea leve changes.Tropic Geography,1996,17(1):80~87
16詹文欢,钟建强.雷西南部地洼盆地构造沉降及其演化.大地构造与成矿学,1992,16(4):337~342Zhan W enhuan,Zhong Jianq iang.Tecton ic subsidence andevolution in the D iwa basin of Southwestern Leizhou Pen insu la.Geotectonica etM etallogenia,1992,16(4):337~342
17詹文欢.南海西北部现代活动构造及其生态环境灾害.北京:科学出版社,2004.1~133Zhan W enhuan.Modern Active Tecton ics and Environm entalD isaster in Northwestern South Ch ina Sea.Beijing:Science Press,2004.1~133
18 Shen G T.Paleochem istry of manganese in corals from theGalapagos Islands.Coral Reefs,1991,10(2):91~100
19 Stem B.A lgorithm s for porosity and subsidence h istory.Computerand Geosciences,1987,13:317~349
20 Calmant S,Gab iocha G,Regn ier Met a.l Coseism ic uplifts andinterseism ic subsidence recorded in corals at Maleku la(Vanuatu,Southwest Pacific).Earth and Planetary Science,1999,328(10):711~716
21 Edwards R L,Taylor F W,W asserburg G J.Dating earthquakesw ith h igh-precision thorium-230 ages of very young corals.Earthand Planetary Science Letters,1988,90(4):371~381
2 Taylor F W,Jouann ic C,B loom A L.Quaternary uplift of theTorres Islands,Northern New Hebrides Frontal Arc:Comparisonw ith Santo and Maleku la Islands,Central New Hebrides FrontalArc.Journal ofGeology,1985,93:419~438
3 Taylor F W,Frohlich C,Lecolle Jet al.Analysis of partiallyem erged corals and reef terraces in the central Vanuatu Arc:Comparison of contemporary coseism ic and nonseism ic w ithQuaternary vertical movem ents.Journal of Geophysical Research,1987,92:4905~4933
4曾昭璇,梁景芬,丘世钧著.中国珊瑚礁地貌研究.广州:广东人民出版社,1997.121~124Zeng Zhaoxuan,L iang Jingfeng,Q iu Sh ijun.Geomorphology ofCh ina Coral Reefs.Guangzhou:Guangdong People Press,1997.121~124
5 Sm ith S V.Coral-reef area and contributions of reefs to processesand resources of the world s ocean.Nature,1978,273:225~226
6聂宝符,陈特固,梁美桃等著.南沙群岛及其邻近礁区造礁珊瑚与环境变化的关系.北京:科学出版社,1997.1~101N ie Baofu,Chen Tegu,L iang M eitaoet al.The Relationsh ipbetween Reef Coral and Environm ental Changes of Nansha Islandsand Ad jacent Regions.Beijing:Science Press,1997.1~101
7聂宝符,陈特固,梁美桃等.雷州半岛珊瑚礁与全新世高海面.科学通报,1997,42(5):511~514N ie Baofu,Chen Tegu,L iangM eitaoet a.l Coral reefs from LeizhouPen insu la and Holocene sea level h ighstands.Chinese ScienceBulletin,1997,42(5):511~514
8赵希涛著.中国海岸演变研究.福州:福建科学技术出版社,1984.132~145Zhao X itao.Ch inese Coast Evolution.Fuzhou:Fu jian Science andTechology Press,1984.132~145
9赵焕庭.南海诸岛珊瑚礁新构造运动的特征.海洋地质与第四纪地质,1998,18(1):37~45Zhao Huanting.Characteristics of neotecton ic movem ent of coral reefarea of the South Ch ina Sea Islands.Marine Geology&QuaternaryGeolog,y 1998,18(1):37~45
10赵焕庭,张乔民,宋朝景.华南海岸和南海诸岛地貌与环境.北京:科学出版社,1999.370~447Zhao Huanting,Zhang Q iaom in,Song Chaojing.Geomorphologyand Environm ental of the South Ch ina Coast and the South Ch inaSea Islands.Beijing:Science Press,1999.370~447
11 Zhang Q iaom in.On the b iogeomorphology of coral reefs:A casestudy on reef flat of Sanya fringing reefs,Hainan Island.In:W angY ing,Zhu X iaodong eds.Schedu le and Abstracts,InternationalAssociation of Geomorphologists,IGA 2000 Thematic Conference.Nan jing:Nan jing Un iversity,2000.144~145
12黄镇国,蔡福祥,韩中元等著.雷琼第四纪火山.北京:科学出版社,1993.1~7Huang Zhengguo,Cai Fuxiang,Han Zhongyuanet a.l TheQuaternary Volcano of Leizhou Pen insu la and Hainan Island.Beijing:Science Press,1993.1~7
13王国忠著.南海珊瑚礁区沉积学.北京:海洋出版社,2001.48~73W ang Guozhong.Coral Reef Sed im ent in the South Ch ina Sea.Beijing:Ch ina Ocean Press,2001.48~73
14余克服,刘东生,沈承德等.雷州半岛全新世高温期珊瑚生长所揭示的环境突变事件.中国科学(D辑),2002,32(2):149~157Yu Kefu,L iu Tungsheng,Shen Chengdeet a.l H igh-frequencyclimatic oscillations recorded in a Holocene coral reef at LeizhouPen insu la,South Ch ina Sea.Science in China(Series D),2002,45(12):1057~1068
15丘世均.礁坪发育与海平面变化.热带地貌,1996,17(1):80~87Q iu Sh ijun.Coral reefs and sea leve changes.Tropic Geography,1996,17(1):80~87
16詹文欢,钟建强.雷西南部地洼盆地构造沉降及其演化.大地构造与成矿学,1992,16(4):337~342Zhan W enhuan,Zhong Jianq iang.Tecton ic subsidence andevolution in the D iwa basin of Southwestern Leizhou Pen insu la.Geotectonica etM etallogenia,1992,16(4):337~342
17詹文欢.南海西北部现代活动构造及其生态环境灾害.北京:科学出版社,2004.1~133Zhan W enhuan.Modern Active Tecton ics and Environm entalD isaster in Northwestern South Ch ina Sea.Beijing:Science Press,2004.1~133
18 Shen G T.Paleochem istry of manganese in corals from theGalapagos Islands.Coral Reefs,1991,10(2):91~100
19 Stem B.A lgorithm s for porosity and subsidence h istory.Computerand Geosciences,1987,13:317~349
20 Calmant S,Gab iocha G,Regn ier Met a.l Coseism ic uplifts andinterseism ic subsidence recorded in corals at Maleku la(Vanuatu,Southwest Pacific).Earth and Planetary Science,1999,328(10):711~716
21 Edwards R L,Taylor F W,W asserburg G J.Dating earthquakesw ith h igh-precision thorium-230 ages of very young corals.Earthand Planetary Science Letters,1988,90(4):371~381
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