【作者】 王旖旎；

【导师】 张梅生；

【作者基本信息】 吉林大学 ， 古生物学与地层学， 2014， 博士

【摘要】 辽宁兴城地区中元古界长城系地层发育较好，在基底太古宙绥中花岗岩之上沉积了常州沟组、串岭沟组、团山子组和大红峪组。近年来在中国地质调查局《辽宁1:25万锦西市幅区调修测》项目的支持下，本文对研究区内长城系岩石地层特征进行了详细研究，在大红峪组底部发现了极为难得且罕见的古海啸岩，可能是目前华北克拉通已知最古老的海啸事件报道。通过沉积学分析与对比，对古海啸岩的识别特征、海啸事件的引发机制及海啸等级进行了系统分析，并讨论了它的全球构造背景和古地理意义。本文对兴城地区长城系岩石地层的划分和特征进行了总结和修订，选择兴城东部夹山地区公路西侧长城系剖面为代表，并对大红峪组岩石地层特征展开详细研究。该剖面地层序列的特征与天津蓟县标准剖面基本可以对比，但由于地处燕山裂陷槽东部边缘，也具有一定特色，可划分为4个岩性段：一段为灰白色厚层石英砂岩质砾岩和含砾长石石英砂岩，其最底部发育复成分角砾岩（海啸岩）；二段为灰白色厚层石英砂岩和厚层—巨厚层长石石英砂岩，夹薄层灰白色粉细砂岩及凝灰岩；三段为灰黑色粉砂质页岩夹灰白色长石石英砂岩及凝灰质粉砂岩；四段为岩屑长石石英砂岩夹粉砂岩。区内大红峪组可以角度不整合覆盖在常州沟组、串岭沟组或团山子组之上，也可直接覆盖在太古宙基底花岗岩之上，前人曾将这一现象解释为一次地壳运动—“兴城运动”，但尚存争议，本文对这一角度不整合接触关系进行了详细观测和分析。兴城地区大红峪组中保留有古海啸事件。本文详细描述了出露在茶棚庵、月亮山和夹山地区该组底部一套特殊的复成分角砾岩，它们明显异于正常的背景沉积。通过沉积岩石学、沉积结构、沉积序列和沉积环境等方面的研究得出该复成分角砾岩为准原地或短距离搬运的异地沉积，形成于异常高能的条件中，属于海啸沉积物，并对其进行了系统研究。通过与古海啸和大量现代海啸事件研究实例的对比，结合兴城地区中元古代古地理环境，总结了海岸古海啸岩的识别特征，如撕裂的碎屑；巨砾出现在沉积物中；砾石极差的分选性；向上变细的层序；复杂的沉积物来自下伏地层；侵蚀的基底。这些特征组合在一起，也适用于其他古海啸岩的识别，具有一定的普遍意义。论文分析了中元古代兴城地区在华北克拉通所处的构造环境，它靠近燕山—汎河古地震带（1700~1200Ma）东部界线。在大红峪组沉积早期，燕山裂陷槽南界发育滦县—建昌断裂带，该断裂以突发性和剧烈性为特征。兴城地区距离该断裂约50km，受其活动的影响，可能引发地震，属于地震海啸。结合区内古地理环境，讨论海啸岩可能经历了以下沉积过程：（1）产生和传播；（2）洪泛及沉积；（3）回流；（4）正常的背景沉积。根据现代国际海啸级别的判别标准，对该古海啸的级别和规模进行了推测。本文对兴城地区团山子期末期—大红峪期初期的沉积环境进行了详细分析。团山子组顶部白云岩中发育有叠层石，均属于燕山、太行地区长城系Gruneria-Eucapsiphora组合。根据岩石组合特征和叠层石形态垂向分布规律得出该组沉积环境演化为海退沉积序列（浅滩到潮间、潮上带）到海侵沉积序列（潮间、潮上带到潮间、潮下带），团山子期末期应属于潮坪环境。大红峪期沉积环境属于滨海相—浅海相沉积，海啸事件发生在两者过渡在海岸环境，海岸带开阔，地势平坦。海啸来自南西方向，与后期海侵方向相同。将区域构造活动与全球动力学背景相结合分析，认为燕山裂陷槽、华北克拉通以及哥伦比亚超大陆（Columbia）是处于同一全球伸展、拉张构造背景之下，考虑到大红峪组沉积时代与Columbia超大陆裂解时代的一致性，可以认为，华北克拉通上记录的一系列地质事件，比如海啸事件、火山喷发事件等是哥伦比亚超大陆的裂解在华北克拉通上的微观响应。更多还原

【Abstract】 The strata of Mesoproterozoic Changcheng System are well developed in the Xingcheng area, Liaoning Province, China. The successions are composed of the Changzhougou Formation (Fm.), the Chuanlinggou Fm., the Tuanshanzi Fm., and the Dahongyu Fm., and they are sedimentary contact over the basement of Archean’Suizhong Granites’. Recently, under the support of the China Geological Survey (1:250000Scale Regional Geological Mapping Project of Jinxi City, Liaoning Province), the features of the Changcheng System in study area are detailed revised. The rare ancient tsunamite are found in the Dahongyu Fm., which is probably the oldest tsunami event in the North China Craton. The identification of tsunamite, triggering mechanism and magnitude of tsunami event are studied systematically by analysis and comparison in sedimentology. The meaning of the tsunami event in the global tectonic setting and palaeogeography is discussed.The feature of the Changcheng System in the Xingcheng area is summarized and revised, and the section at Jiashan was here proposed as a typical section in this area. The feature of the Dahongyu Fm. is detailed studied, and it could be correlated with that in strata type of the Jixian County, Tianjin. However, it also has some special Characteristics, since the area is tectonically located in the eastern margin of the Yanshan Taphrogenic Trough. The whole of the formation could be subdivided into4members:the1st Member is composed of thick bedded quartz conglomerates, and pebble contained arkose conglomerates, and a suit of specially formed breccia (tsunamite) in some places; the2nd Member is composed of grayish-white thick bedded quartz sandstones and thick to huge thick bedded feldsparthic quartz sandstones, and interbedded with some grayish-white thin bedded fine-silt sandstones and tuff; the3rd Member is grayish-black silt shales and interbedded with grayish-white feldsparthic quartz sandstones; the4th Member is composed of lithic quartz sandstones and fine-silt sandstones. The Dahongyu Fm. unconformably overlays the Changzhougou Fm., the Chuanlinggou Fm. or the Tuanshanzi Fm., and even the Archean granites, it is explained as a crust movement’Xingcheng Movement’, and there is a debate on it. In current thesis, this angular unconformity relationship is re-observed and confirmed.The Dahongyu Fm. preserves the ancient tsunami event in the Xingcheng area. This paper detailed describes the special breccia from the bottom of the Dahongyu Fm. at Chapen’an, Yueliangshan, and Jiashan. These breccia are markedly different from normal sediments, and are analyzed in terms of sedimentary petrology, sedimentary texture and sedimentary sequence, and sedimentary environment. Based on the analyses of sedimentary facies, the special breccia is identified as tsunamite. They were deposited in abnormal high-energy sedimentary conditions, and belonged to parautochthonous and allochthonous deposits. After the comparison with the ancient and modern examples of tsunamite, and based on the lithofacies palaeogeography in the Xingcheng area, there are some features to identify the tsunamite:rip-up clasts; boulders exclusively appear in the deposits; poorly sorted gravels; fining-upward sequences; complex sediment sources of the underlying strata; erosional bases. These combined features also widespread apply to identification of other ancient tsunamite.The tectonic setting of the Xingcheng area is detailedly discussed, and it is close to the eastern edge of the ancient Yanshan-Fanhe Seismic Belt (1700-1200Ma). The Luanxian-Jianchang Fault lies at the southeastern edge of the Taihang-Yanshan Taphrogenic Trough, and occurred at the early stage of the Dahongyu Fm., it is characterized by abrupt and pulsing activities. The study area is about50km from this fault, and is affected by the fault. The tsunami was probably triggered by the earthquake, which resulted from the activities of the Luanxian-Jianchang Fault in the early Mesoproterozoic. Based on the analyses of lithofacies palaeogeography and sedimentary facies, the depositional process was discussed in the following:(1) Generation and propagation;(2) Inundation and deposition;(3) Backwash flow;(4) Normal background deposits. Acorrding to international magnitude of tsunami, the magnitude of the acient tsunami is discussed.The sedimentary environment of the later Tuanshanzi Stage-the later Dahongyu Stage is analysed in the paper. Stromatolites occur in the top of the Tuanshanzi Fm., they belong to the Changcheng System type stromatolite zone(Gruneria-Eucapsiphord) in Yanshan and Taihang Ranges. According to the lithostratigraphic characteristics, and the relationship between the vertical distribution rule of stromatolites’ morphology and the paleoenvironment, the sedimentary environment history of the Tuanshanzi Stage in the Xingcheng area should be from regression (shallows to intertidal zone and supratidal zone) to transgression (intertidal zone and supratidal zone to intertidal zone and subtidal zone). The sedimentary facies was a tidal flat environment in the later Tuanshanzi Stage, and the depth of water cannot exceed50m. The sedimentary facies of the Dahongyu Stage are littoral-shallow marine. Therefore, the studied area was in an open coastal environment, and the terrain was flat in the Mesoproterozoic. The direction of tsunami waves should be from SW to NE, it is the similar direction as the later marine transgression.Based on the analyses of the regional and global tectonic backgrounds, the Yanshan Taphrogenic Trough, the North China Craton and the Columbia Supercontinent were in the same global extensional tectonic setting. Having considered the simultaneity and the consistent geodynamic pattern of regional and global tectonic backgrounds, some events, such as tsunamis and volcanic eruptions should be recognized as effects of the breakup of the Columbia Supercontinent in the North China Craton.更多还原