| 地震岩问题 |
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| 引用本文： | 山穆玕著,冯增昭,刘敏译.地震岩问题[J].古地理学报,2017,19(1):19-46. |
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| 作者姓名： | 山穆玕著 冯增昭 刘敏译 |
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| 作者单位： | 1.地球与环境科学系,得克萨斯大学阿灵顿分校,阿灵顿TX76019,美国;2.中国石油大学(北京),北京 100083; |
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| 摘 要： | 在过去的82年(1931—2013)中,共出现了39个成因术语。在这39个术语中,只有10个是真正沉积成因的(例如浊积岩),其他29个术语都是比较草率地提出的(just jargons;例如地震岩、海啸岩等)。“地震岩”(seismites)这一成因术语是赛拉赫(Seilacher,1969)提出的,它指沉积记录中的古地震。这是一个误用的(misnomer)术语。赛拉赫仅仅根据美国加利福尼亚州的中新统蒙特雷组(Miocene Montery Formation)10,m厚的露头观察,就匆忙地提出这个术语。他并未对这个露头进行认真的科学研究。最根本的问题是,地震是一个触动因素①,并不是一个沉积作用。在古代的沉积记录中,鉴别不出各种触动因素(trigger)②,因为自然界不能保留触动因素曾经存在过的证据。“软沉积物变形构造”(soft-sediment deformation structures,可简称为SSDS),通常被人们用来作为地震岩的鉴别标志,其实它是“液化作用”(liquefacation)的结果。液化作用可以由21种触动因素中的任何一种引起,其中包括地震(earthquake)、陨石冲击(meteorite impact)、海啸(tsunami)、沉积负载(sediment loading)等。在死海盆地中的角砾碎屑,所谓典型的由地震引起的沉积,实际上是常见的同沉积作用的碎屑流的产物,与地震没有关系。其他类型的SSDS,例如 “双向叠层构造”(duplex-like structures)和碎屑注入体(clastic injections),也可以说是同沉积作用的产物,与地震没有关系。世界上广泛分布的砂岩储油层,包括墨西哥湾、北海、挪威海、尼日利亚、赤道几内亚、加逢、孟加拉湾,都表明这些地区的SSDS的第一起因(primary cause)是沉积负载,其证据是可以观察到的和令人信服的。海啸及陨石冲击,都可以形成大量的沉积,例如SSDS的侧向延伸(lateral extent of SSDS),但这些沉积都不能当作地震的鉴别标志。位于印度东部大陆边缘的Krishna-Godavari(KG)盆地中的SSDS,是多种触动因素①引起的沉积物的失控和液化作用的结果,即多成因的SSDS。由于这些原因,“地震岩”这个成因术语确实没有什么科学价值,应当废弃。
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| 关 键 词： | 软沉积物变形构造(SSDS) 地震岩 地震 陨石冲击 液化作用 碎屑注入体 |
| 收稿时间： | 10 October 2016 |
The seismite problem |
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| G. Shanmugam,Feng Zengzhao,Liu Min.The seismite problem[J].Journal of Palaeogeography,2017,19(1):19-46. |
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| Authors: | G Shanmugam Feng Zengzhao Liu Min |
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| Institution: | 1.Department of Earth and Environmental Sciences,The University of Texas at Arlington,Arlington,TX 76019,USA;2.China University of Petroleum(Beijing), Beijing 100083; |
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| Abstract: | During a period of 82 years(1931-2013),39 genetic terms were introduced for various deposits. Of the 39 terms,only 10 are meaningful in understanding the true depositional origin(e.g.,turbidites),the remaining 29 are just jargons(e.g., seismites,tsunamites, etc.). The genetic term “seismites”,introduced by Seilacher(1969)for recognizing palaeoearthquakes in the sedimentary record,is a misnomer. The term was introduced in haste,based on an examination of a single exposure of the Miocene Monterey Formation(10,m)in California,without a rigorous scientific analysis. The fundamental problem is that earthquake is a triggering mechanism,not a depositional process. Type of triggers cannot be recognized in the ancient sedimentary record because evidence for triggers is not preserved by nature. Soft-sediment deformation structures(SSDS),commonly used as the criteria for interpreting seismites,are a product of liquefaction. However,liquefaction can be induced by any one of 21 triggers,which include earthquakes,meteorite impacts,tsunamis,sediment loading,among others. Brecciated clasts,typically associated with earthquake-induced deposits in the Dead Sea Basin,are also common depositional products of debris flows(i.e.,synsedimentary product unrelated to earthquakes). Also,various types of SSDS,such as duplex-like structures and clastic injections,can be explained by synsedimentary processes unrelated to earthquakes. Case studies of sandstone petroleum reservoirs worldwide,which include Gulf of Mexico,North Sea,Norwegian Sea,Nigeria,Equatorial Guinea,Gabon,and Bay of Bengal,reveal that there is compelling empirical evidence for sediment loading being the primary cause of SSDS. The Krishna-Godavari Basin,located on the eastern continental margin of India,is ideal for sediment failures by multiple triggering mechanisms where overpressure and liquefaction have led to multi-origin SSDS. Because tsunamis and meteorite impacts are important phenomena in developing extensive deposits,lateral extent of SSDS cannot be used as a unique distinguishing attribute of earthquakes. For these reasons,the genetic term “seismites”,which has no redeemable scientific value,is obsolete. |
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| Keywords: | soft-sediment deformation structures(SSDS) seismites earthquakes meteorite impacts liquefaction clastic injections |
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