微生物形成的原生沉积构造研究进展综述

Overview of advances in studies of primary sedimentary structures formed by microbes

早在上世纪60年代,沉积学家Pettijohn和Potter曾经将形成原生沉积构造的地质作用划分为剥蚀作用、搬运作用、沉积作用和变形作用。在沉积期间和沉积之后到沉积物还未固结之前由上述作用所产生的沉积构造被定义为"原生沉积构造",包括各种类型的层理、层面上的各种作用痕迹以及各种变形现象。在该分类之中,叠层石被定义为突出沉积面的正生长构造,这种构造由微生物与同沉积胶结作用共同构建而成。上世纪90年代中期至今,随着研究程度的深入,沉积学家们越来越认识到除了叠层石以外,微生物还会形成一种并不突出于底层面的原生沉积构造,并被认为是微生物席或微生物膜与各种物理作用营力共同作用的产物。这些作用营力包括剥蚀作用、搬运作用、沉积作用和变形作用。该类沉积构造被定义为微生物形成的原生沉积构造并被归为第五类原生沉积构造。正如叠层石主要产在前寒武纪以及显生宙未受到后生动物强烈改造的浅水环境中一样,微生物形成的原生沉积构造也主要发育在前寒武纪,以及显生宙的一些未受到后生动物强烈改造的潮坪和潟湖等环境之中。因此,该类沉积构造(第五类原生沉积构造)的研究,对于前寒武纪沉积环境重塑具有重要意义。燕山地区元古界串岭沟组和大红峪组碎屑岩中的变余波痕、皱饰构造和纺锤状裂缝,是碎屑岩中微生物形成的原生沉积构造的代表;高于庄组第三段非叠层石碳酸盐岩(以灰岩为主)层面上发育大型皱饰构造和变余波痕,是碳酸盐岩中微生物形成的原生沉积构造的代表。这些沉积构造的发现和初步研究,为今后进一步深入研究奠定了良好的基础。

In the 1960s, Pettijohn and Potter classified the geologic processes which formed primary structures into erosion, transportation, deposition, and deformation. The primary sedimentary structures are defined as those structures formed by the above processes during sedimentation or after sedimentation while before consolidation. They include various types of bedding, marks on the bedding surface, and deformational phenomena. In their classification on the primary sedimentary structures, stromatolites are defined as positive growth structures projecting from the former depositional surfaces, and are formed by the combined action of microbes and synsedimentary cementation. From the middle 1990s to the present day, sedimentologists realized that microbes can also form a kind of primary sedimentary structures which do not project from the sedimentary surface, and they are formed by the combined action of microbial mat （or film） and all kinds of physical actions such as erosion, transportation, deposition and deformation. This kind of sedimentary structures are defined as the primary sedimentary structures formed by microbes, which belong to the fifth kind of primary sedimentary structures. Stromatolites were mainly developed in the Precambrian and the Phanerozoic shallow water environments which were not strongly changed by metazoan. Similar to that, the sedimentary structures formed by microbes were also mainly developed in the Precambrian and the tidal fiat and lagoon environments in the Phanerozoic which were not strongly changed by metazoan. Therefore, the studies of this kind of sedimentary structures （the fifth kind of primary sedimentary structures） have great significance in the reconstruction of the Precambrian environments. The observation and preliminary study of the primary sedimentary structures formed by microbes in the Mesoproterozoic in Yanshan area provide a useful basis for the further study in the future. These structures include the palimpsest ripple, the wrinkle structure, the microbial sand chip and the spindle crack developed in the Chuanlinggou and Dahongyu formations. They represent the primary sedimentary structures formed by microbes in clastic rocks. The large-scale palimpsest ripple and wrinkle structure developed in the non-stromatolitic limestones of the Member 3 of the Gaoyuzhuang Formation represent the primary sedimentary structures formed by microbes in carbonate rocks of the Mesoproterozoic.