| 从席底构造到第五类原生沉积构造:沉积学中具有重要意义的概念 |
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| 引用本文： | 梅冥相,高金汉,孟庆芬.从席底构造到第五类原生沉积构造:沉积学中具有重要意义的概念[J].现代地质,2006,20(3):413-422. |
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| 作者姓名： | 梅冥相 高金汉 孟庆芬 |
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| 作者单位： | 1中国地质大学 地质过程与矿产资源国家重点实验室，北京100083；2中国地质大学 岩石圈构造、深部过程及探测技术教育部重点实验室，北京100083；3中国地质大学 地球科学与资源学院，北京100083 |
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| 基金项目： | 国家自然科学基金;高等学校博士学科点专项科研项目 |
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| 摘 要： | 发育微生物席或微生物膜的沉积底被形象地称为席底，在席底上由于微生物席的发育使沉积物富黏性而抗水流改造，并在沉积面和沉积层内形成一系列奇形怪状的原生沉积构造，如变余波痕、皱饰构造、微生物席碎片、纺锤状或次圆状收缩裂缝等等，这些构造都归为席底构造；与席底相对应，那些不发育微生物席或微生物膜的沉积面则称为混合底，在混合底上单个沉积颗粒受到水流剪切与变形作用的改造而形成诸如正常波痕等原生沉积构造，这些沉积构造则归为混合底构造。席底和席底构造的概念很重要，用来专指微生物沉积作用的产物而区别于混合底和混合底构造。从沉积学概念的演变方面分析，混合底构造就是1964年Pettijohn和Potter所定义的原生沉积构造，他们曾经将其归为4大类并且沿用至今；席底构造也就是微生物形成的(或相关的)原生沉积构造，由于其在形成机理和形态上与Pettijohn和Potter所定义的原生沉积构造存在较大的区别，Noffke 2001年认为其应该具有合适的分类位置，所以就将席底构造归为“第五类原生沉积构造”并纳入Pettijohn和Potter 1964年的原生沉积构造的分类体系之中。从席底构造到第五类原生沉积构造，概念的演变表明了万能的微生物在沉积作用过程中的重要性以及沉积学家对微生物沉积作用认识的深入。这些相关的沉积构造及其所形成的席底，就像叠层石(被当作正生长原生沉积构造)一样在前寒武纪地层之中较为普遍。随着后生动物的大规模出现而造成的寒武纪“农艺革命”(Agronomic revolution)的开始，显生宙的席底及其相关的席底构造多出现在那些不适宜后生动物居住的地方并大多被混合底及其相关的混合底构造所替代；因此，与微生物相关的原生沉积构造，除熟知的叠层石以外，在席底上发育的一系列原生沉积构造,由于其具有特别的指相意义并有助于古环境重塑而被很自然地归到“第五类原生沉积构造”。该类构造由于其在前寒武纪的普遍性和显生宙的局限分布性，特别是在生物大灭绝事件之后的灾难性泛滥，对于研究地球表层环境的演变具有重要意义。所以说，从席底构造到第五类原生沉积构造，是近年来沉积学发展过程中所出现的较为重要的基本概念。根据这一重要概念，对前寒武纪地层中一些常常被认为是遗迹化石、长期以来存在的“臼齿状构造谜”(Molar-tooth structure enigma)等奇形怪状的沉积构造的成因以及从前寒武纪到显生宙地层中均有分布的特殊的纹理化构造等，将会得到一些更加合理的认识；另一方面，关于微生物形成的原生沉积构造的研究，对于了解地球表层生物变化与沉积变化之间的复杂关系将会发现更多的新问题而得到进一步的思考与研究。
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| 关 键 词： | 席底构造 微生物形成的原生沉积构造 第五类原生沉积构造 有意义的概念演变 |
| 文章编号： | 1000-8527(2006)03-0413-10 |
| 收稿时间： | 02 20 2006 12:00AM |
| 修稿时间： | 04 20 2006 12:00AM |
From Matground Structures to the Primary Sedimentary Structures of a Fifth Category: Significant Concepts on Sedimentology |
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| MEI Ming-xiang,GAO Jin-han,MENG Qing-fen.From Matground Structures to the Primary Sedimentary Structures of a Fifth Category: Significant Concepts on Sedimentology[J].Geoscience——Journal of Graduate School,China University of Geosciences,2006,20(3):413-422. |
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| Authors: | MEI Ming-xiang GAO Jin-han MENG Qing-fen |
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| Institution: | 1State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing100083, China;
2Key Laboratory of Lithosphere Tectonics and Lithoprobing Technology of Ministry of Education, China University of Geosciences, Beijing100083, China;
3School of Earth Sciences and Resources, China University of Geosciences, Beijing100083, China |
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| Abstract: | The deposits surface with development of a microbial mat or microbial film is called as the matground in imagery.The development microbial mat or microbial film on matground leads to the strong mucosity of(sediments) that are resistant to reformation of current.Resulted from the action of microbes a series of primary sedimentary structures in grotesque shape such as palimpsest ripples,wrinkle structures,microbial mat chip,spindle-shaped or subcircular syneresis cracks and so on are formed both on the bedding plane and within beds;And these primary sedimentary structures are nominated as the matground structures.On the other hand,(mixground) refers to the deposit surface without a microbial mat or microbial film,where individual sedimentary grain yields to current shear or deformation,forming structures such as normal ripples and so on;And these(primary) sedimentary structures are nominated as mixground structures that are different from and correspond to matground structures.Thus,concepts about matground and relative to matground structure are used to focus on the result of microbial sedimentation and become very important on sedimentology.According to the analysis of(concept) evolvement on sedimentology,mixground structures are actually the primary sedimentary structures that are grouped four categories by Pettijohn and Potter(1964);and matground structures are actually mat-induced structures(or mat-related primary structures).Considering the great difference of both the forming mechanism and configuration between matground structures and mixground structures,the matground structure or mat-(induced) structure(the mat-related primary structure)ought to be placed as its own category in the existing classification of primary sedimentary structures proposed by Pettijohn and Potter(1964),i.e.the primary(sedimentary) structure of a fifth category.The change of concept from the matground structure to the primary sedimentary structure of a fifth category expresses the importance of microbes' sedimentation and the thorough cognition to this kind of sedimentation.Like stromatolites,these primary sedimentary structures and their forming matground were common through the Precambrian.With the onset of Cambrian agronomic revolution,these primary sedimentary structures and their forming matground were replaced by mixground and its relative mixground structures in all but the most inhospitable habitats due to effective grazing and burrowing of metazoa.In addition to the stromatolite,microbial related primary sedimentary structures developed in matground are highly facies-indicative and can aid in paleoenvironmental reconstruction,which is the chief reason for the terminology as "the(primary) sedimentary structure of a fifth category".The widespread distribution in the Precambrian and the(sporadically) distribution in the Phanerozoic,especially for their mischance flowage in sea floor after the mass(extinction) event,make this category of sedimentary structures become meaningful and useful to study the evolutionary change of earth surface.Ultimately,the concept change from the matground structure to the primary(sedimentary) structure of a fifth category is an important change on sedimentology.According to this change of concept,the reasonable cognition for origin of those grotesque sedimentary structures in the Precambrian(e.g.,the spindle or subcircular cracks that are frequently thought as trace fossils,the molar-tooth structure)and the special lamina from the Precambrian to the Phanerozoic can be obtained.On the other hand,the study on the(microbial-induced) primary sedimentary structures should give rise to new questions and perspectives of the(complex) relationship between the biological change and the sedimentary change. |
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| Keywords: | matground structure microbial-induced primary sedimentary structure the primary sedimentary structures of a fifth category meaningful evolvement of concept |
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