硅藻Auliscus caelatus对渤海湾西北岸大吴庄埋藏牡蛎礁形成环境的复原
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摘要
通过对渤海湾西北岸大吴庄牡蛎礁18个层位牡蛎壳内泥质填充物样品的硅藻分析,首次发现在渤海湾埋藏牡蛎礁中富含代表潮间带环境的Auliscus caelatus种硅藻化石,体积分数高达15%～40%,显示整个牡蛎礁形成于潮间带环境。根据潮间带标志种Auliscus caelatus,结合生活在海湾内侧河口处环境的Cyclotella stylorum和沿岸分布的内湾指标群种Thalassionema nitzschioides 3种硅藻比例在垂向上的变化,将牡蛎礁分为潮间带下部(Ⅰ带)、潮间带中上部(Ⅱ带)、潮间带中下部(Ⅲ带)和潮间带中上部(Ⅳ带)4个硅藻带。牡蛎礁上半部(Ⅱ带和Ⅲ带)中的4条水平夹层中的硅藻,与其下伏相邻正常建礁层的硅藻对比,均显示出Auliscus caelatus体积分数显著偏低、咸水种硅藻的比例偏高以及硅藻种属类型偏多等特征,推测出各水平层的海相性和开放性均有强于下伏相邻正常层的倾向。水平夹层的形成原因:一是牡蛎礁发育后期,礁体所处环境发生显著变化,从距河口相对较远的潮间带下部(不含水平层的Ⅰ带)环境转为距河口相对较近的潮间带中上部(Ⅱ带—Ⅳ带)环境,较浅的海水环境使得牡蛎礁易受外界环境的影响;二是来自海洋方向的风暴潮或较强的波浪,将牡蛎礁向海一侧的潮间带泥沙冲到礁顶,导致牡蛎倒伏死亡后被泥沙掩埋。
Diatom analysis has been carried out on the muddy sediments filling in oyster shells collected from 18 layers in Dawuzhuang oyster reef on northwest coast of Bohai Bay.Diatom Auliscus caelatus,which could serve as an indicator for intertidal zone environment,is found,for the first time and it could make up to 15%-40% of the buried oyster reef in volume.It seems that the oyster reef under study was formed in an intertidal zone environment. Four diatom zones,namely,the lower part of the intertidal zone(Zone I),the middle and upper part of intertidal zone(Zone II),the middle and lower part of intertidal zone(Zone III) and the middle and upper part of intertidal zone(Zone IV),have been recognized in the oyster reef by the vertical change in three kind of diatoms proportion-Auliscus caelatus,Cyclotella stylorum and Thalassionema nitzschioides.The 4 horizontal interlayers in the upper part of the oyster reef(Zone II and Zone III),when compared with the adjacent underlying normal layers,contain less Auliscus caelatus,more brackish diatoms and more diatom species.So we believe that these four horizontal interlayers were affected by more marine and more open environment than the underlying normal layers.Based on the above studies,two reasons for the formation of the four horizontal interlayers are suggested.First,the living environment of the oyster reef changed from the lower part of the intertidal zone(Zone I),which is relative far from the estuary,to the middle and upper part of intertidal zone(Zone II-Zone IV),which is relatively near to the estuary during the late development of the oyster reef.Shallow water environment made the oyster reef easily be influenced by external environment.Second,the muddy-sandy sediments from the interti-dal zone were carried by the storm surges and ocean waves and were laid over on the top of the oyster reef,then caused the death of the diatoms in the reef.
Diatom analysis has been carried out on the muddy sediments filling in oyster shells collected from 18 layers in Dawuzhuang oyster reef on northwest coast of Bohai Bay.Diatom Auliscus caelatus,which could serve as an indicator for intertidal zone environment,is found,for the first time and it could make up to 15%-40% of the buried oyster reef in volume.It seems that the oyster reef under study was formed in an intertidal zone environment. Four diatom zones,namely,the lower part of the intertidal zone(Zone I),the middle and upper part of intertidal zone(Zone II),the middle and lower part of intertidal zone(Zone III) and the middle and upper part of intertidal zone(Zone IV),have been recognized in the oyster reef by the vertical change in three kind of diatoms proportion-Auliscus caelatus,Cyclotella stylorum and Thalassionema nitzschioides.The 4 horizontal interlayers in the upper part of the oyster reef(Zone II and Zone III),when compared with the adjacent underlying normal layers,contain less Auliscus caelatus,more brackish diatoms and more diatom species.So we believe that these four horizontal interlayers were affected by more marine and more open environment than the underlying normal layers.Based on the above studies,two reasons for the formation of the four horizontal interlayers are suggested.First,the living environment of the oyster reef changed from the lower part of the intertidal zone(Zone I),which is relative far from the estuary,to the middle and upper part of intertidal zone(Zone II-Zone IV),which is relatively near to the estuary during the late development of the oyster reef.Shallow water environment made the oyster reef easily be influenced by external environment.Second,the muddy-sandy sediments from the interti-dal zone were carried by the storm surges and ocean waves and were laid over on the top of the oyster reef,then caused the death of the diatoms in the reef.
引文
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[7]方晶,范昌福,王海峰,等.黏土混浊水电导率对牡蛎礁水平夹层成因的解释:以渤海湾西北岸大吴庄牡蛎礁为例[J].第四纪研究,2011,31(4):746-748.Fang Jing,Fang Chang-fu,Wang Hai-feng,et al.Appli-cation of Clayey Water Electric Conductivity Recoveredfrom Origins of Horizontal Interlayers in the Buried OysterReef:A Case Study of the Dawuzhuang Oyster Reef in theNorthwest of Bohai Bay[J].Quaternary Sciences,2011,31(4):746-748.
[8]Kosugi Masato.Classification of Living Diatom Assembla-ges as the Indicator of Environments,and Its Applicationto Reconstruction of Paleoenvironments[J].The Quater-nary Research,1988,27(1):1-20(in Japanese).
[9]Kashima Kaoru.Holocene Successions of Diatom FossilAssemblages in Alluvium,and Those Relations to Paleo-Geographical Changes[J].Geographical Review of Ja-pan,1986,59(7):383-403(in Japanese).
[10]Ando Kazuo,Fujimoto Kiyoshi.Paleo-Environmental His-tory and Sea-Level Records Based on the Diatom Assem-blages in the Middle Part of the Arakawa Lowland,Cen-tral Japan[J].The Quaternary Research,1990,29(5):427-437(in Japanese).
[11]Stuiver M,Reimer P J,Reimer R.CALIB6.0.1Manuals[EB/OL].2010,http://calib.qub.ac.uk/calib.
[12]Chinzei Kiyotaka.Paleoecolgy of Oysters(1)[J].Fos-sifs,1982,31:27-34(in Japanese).
[13]商志文,王宏,车继英,等.渤海湾表层沉积硅藻组合[J].海洋地质与第四纪地质,2006,26(5):21-26.Shang Zhi-wen,Wang Hong,Che Ji-ying,et al.DiatomAssemblages in the Surface Sediments of Bohai Bay[J].Marine Geology&Quaternary Geology,2006,26(5):21-26.
[2]范昌福,裴艳东,王宏,等.渤海湾西北岸埋藏牡蛎礁体中的壳体形态与沉积环境[J].第四纪研究,2007,27(5):806-813.Fan Chang-fu,Pei Yan-dong,Wang Hong,et al.Corre-lation of Oyster Shell Form and Sediment Environmentfrom two Buried Oyster Reefs on the Northwest Coast ofBohai Bay[J].Quaternary Sciences,2007,27(5):806-813.
[3]李冬玲,范昌福,黄玥,等.渤海湾西北岸中全新世埋藏牡蛎礁的硅藻记录及古环境意义[J].海洋通报,2009,28(3):22-28.Li Dong-ling,Fan Chang-fu,Huang Yue,et al.Paleo-Environmental Reconstruction with Diatom Assemblagesin the Buried Oyster Reef on the Northwest Coast of theBohai Bay During the Middle Holocene[J].Marine Sci-ence Bulletin,2009,28(3):22-28.
[4]商志文,范昌福,李冬玲,等.硅藻组合指示的渤海湾西北岸两个牡蛎礁体生长环境的差异[J].海洋地质与第四纪地质,2010,30(5)33-39.Shang Zhi-wen,Fan Chang-fu,Li Dong-ling,et al.Re-vealing Paleo-Environment Difference of Two Oyster Reefsby Diatom Assemblages in the Northwest Coast of BohaiBay[J].Marine Geology&Quaternary Geology,2010,30(5):33-39.
[5]范昌福,高抒,王宏,等.渤海湾西北岸全新世埋藏牡蛎礁建造记录中的间断及其解释[J].海洋地质与第四纪地质,2006,26(5):27-35.Fan Chang-fu,Gao Shu,Wang Hong,et al.Interpretingthe Hlatus in Holocene Oyster Reefs on the NorthwestCoast of Bohai Bay[J].Marine Geology&QuaternaryGeology,2006,26(5):27-35.
[6]范昌福,王宏,裴艳东,等.稳定同位素贝壳年轮指示的牡蛎礁体水平夹层的成因[J].第四纪研究,2010,30(5):995-1002.Fan Chang-fu,Wang Hong,Pei Yan-dong,et al.Summa-ry of the Studies on Holocene Oyster Reefs in the North-west Coast of Bohai Bay[J].Quaternary Sciences,2010,30(5):995-1002.
[7]方晶,范昌福,王海峰,等.黏土混浊水电导率对牡蛎礁水平夹层成因的解释:以渤海湾西北岸大吴庄牡蛎礁为例[J].第四纪研究,2011,31(4):746-748.Fang Jing,Fang Chang-fu,Wang Hai-feng,et al.Appli-cation of Clayey Water Electric Conductivity Recoveredfrom Origins of Horizontal Interlayers in the Buried OysterReef:A Case Study of the Dawuzhuang Oyster Reef in theNorthwest of Bohai Bay[J].Quaternary Sciences,2011,31(4):746-748.
[8]Kosugi Masato.Classification of Living Diatom Assembla-ges as the Indicator of Environments,and Its Applicationto Reconstruction of Paleoenvironments[J].The Quater-nary Research,1988,27(1):1-20(in Japanese).
[9]Kashima Kaoru.Holocene Successions of Diatom FossilAssemblages in Alluvium,and Those Relations to Paleo-Geographical Changes[J].Geographical Review of Ja-pan,1986,59(7):383-403(in Japanese).
[10]Ando Kazuo,Fujimoto Kiyoshi.Paleo-Environmental His-tory and Sea-Level Records Based on the Diatom Assem-blages in the Middle Part of the Arakawa Lowland,Cen-tral Japan[J].The Quaternary Research,1990,29(5):427-437(in Japanese).
[11]Stuiver M,Reimer P J,Reimer R.CALIB6.0.1Manuals[EB/OL].2010,http://calib.qub.ac.uk/calib.
[12]Chinzei Kiyotaka.Paleoecolgy of Oysters(1)[J].Fos-sifs,1982,31:27-34(in Japanese).
[13]商志文,王宏,车继英,等.渤海湾表层沉积硅藻组合[J].海洋地质与第四纪地质,2006,26(5):21-26.Shang Zhi-wen,Wang Hong,Che Ji-ying,et al.DiatomAssemblages in the Surface Sediments of Bohai Bay[J].Marine Geology&Quaternary Geology,2006,26(5):21-26.