上扬子地区早寒武世及早三叠世巨鲕灰岩对比研究
发布时间：2019-01-06 17:00
【摘要】：巨鲕的产出时代多为新元古代和早三叠世,而寒武纪的巨鲕却较少报道。近期我们在重庆石柱地区野外剖面中发现下寒武统天河板组含厚约35cm的透镜状巨鲕灰岩,这也巨鲕的研究提供了最新的素材。通过对川西北地区早三叠世沉积的巨鲕灰岩与早寒武世巨鲕灰岩在结构特征、颗粒组分、沉积环境、古气候特征、古生态背景以及古海洋水化学性质等方面作对比综合研究分析了其成因机理。认为巨鲕的形成必须满足以下条件:具有一个可以围绕的核心,核心可以为藻球粒、生物碎屑以及鲕粒;且在两者的沉积时期大气中均表现出CO2浓度显著偏高,高浓度的CO2会产生两方面的作用:一是催生频繁的强风暴作用为巨鲕的形成提供了较强的水动力条件,再者便是海洋水在频繁的强风作用影响下会持续翻滚搅动,致使大气中高浓度的CO2溶解其中,形成化学性质呈CO2过饱和的海洋水;由于两者的沉积背景均是极度恶劣的海洋沉积环境,主要变现为缺乏后生动物存在而微生物趁机得到繁盛,CO2过饱和的海洋水为大量的微生物生存提供了有利条件,同时大量的微生物新陈代谢活动也影响了巨鲕生长时的局部微环境,即海洋水呈碱性致使CaCO3围绕其核心高速沉淀;二者在沉积环境方面亦有相似性,虽然早寒武世巨鲕发育地带处于碳酸盐缓坡沉积环境中的内缓坡外缘—中缓坡内侧,而早三叠世时期处于碳酸盐台地沉积环境开阔台地,但是可见两者沉积带水体深度均较浅,都可以受到频繁的强风暴作用的影响。总之,巨鲕的形成是微生物的积极参与、极端的古气候背景和有利的沉积环境综合作用的结果。此外,笔者在对两个时代巨鲕成因机理研究的基础上,还对巨鲕衍生出来的问题进行了相关探讨。早三叠世巨鲕看似与“错时相”沉积在沉积时期是完全吻合的,但是巨鲕在早三叠世无论是分布范围还是出现频率均远远不如其它早三叠世“错时相”沉积。由此可见,关于巨鲕是否能做为一种新的早三叠世“错时相”沉积来看待,还需要做进一步分析研究。同时,微生物在巨鲕的形成中扮演了至关主要的角色,不仅构成了岩石主要组分,而且通过其生理活动改变沉积环境水体介质的化学性质等促进了巨鲕灰岩的沉积,因此认为巨鲕灰岩也应归属于微生物岩的范畴。
[Abstract]:The oolitic age was mostly Neoproterozoic and early Triassic, but the Cambrian giant oolitic was seldom reported. Recently we found lenticular giant oolitic limestone in the Lower Cambrian Tianheban formation in the Shizhu area of Chongqing which contains about 35cm thick which also provides the latest material for the study of giant oolitic rocks. Based on the structural characteristics, grain composition, sedimentary environment and paleoclimate characteristics of the giant oolitic limestone deposited in the early Triassic and the giant oolitic limestone of the early Cambrian in northwestern Sichuan, The genetic mechanism of paleo-ecological background and paleo-marine hydrochemistry were studied and analyzed. It is considered that the formation of giant oolitic must satisfy the following conditions: there is a core which can be surrounded by algal globules bioclasts and oolitic particles; The concentration of CO2 is significantly higher in the atmosphere during the deposition period, and the high concentration of CO2 can produce two effects: one is that the frequent strong storms provide strong hydrodynamic conditions for the formation of giant oolitic. Furthermore, under the influence of frequent strong winds, ocean water will continuously roll and stir, resulting in the dissolution of high concentration of CO2 in the atmosphere and the formation of marine water with chemical properties of CO2 supersaturation; Because the sedimentary background of both is extremely bad marine sedimentary environment, mainly because of the lack of metazoan and the flourishing of microbes, the CO2 supersaturated marine water provides favorable conditions for the survival of a large number of microbes. At the same time, a large number of microbial metabolic activities also affect the local microenvironment of giant oolitic growth, that is, the alkaline marine water causes CaCO3 to precipitate around its core at high speed. They are also similar in sedimentary environment, although the early Cambrian giant oolitic development zone is located in the inner gentle slope and the middle gentle slope in the carbonate gentle slope sedimentary environment, while in the early Triassic period it is located in the open platform of carbonate platform sedimentary environment. However, it can be seen that both sedimentary zones have shallow water depth and can be affected by frequent strong storms. In a word, the formation of giant oolitic is the result of the active participation of microbes, the extreme paleoclimate background and the favorable sedimentary environment. In addition, on the basis of studying the mechanism of the formation of giant oolitic in two times, the author also discusses the derivation of giant oolitic. The early Triassic giant oolitic deposits seem to coincide well with the "staggered facies" deposition in the sedimentary period, but the distribution and frequency of the giant oolitic facies in the early Triassic epoch are far less than those of other early Triassic "staggered facies" deposits. It can be seen that whether the giant oolitic facies can be regarded as a new early Triassic "staggered facies" deposit needs further analysis and study. At the same time, microbes play an important role in the formation of giant oolitic rocks, which not only constitute the main components of rocks, but also promote the deposition of giant oolitic limestone by changing the chemical properties of the water media in the sedimentary environment through its physiological activities. Therefore, the giant oolitic limestone should also belong to the category of microbial rocks.
【学位授予单位】：成都理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P588.248
本文编号：2403071
[Abstract]:The oolitic age was mostly Neoproterozoic and early Triassic, but the Cambrian giant oolitic was seldom reported. Recently we found lenticular giant oolitic limestone in the Lower Cambrian Tianheban formation in the Shizhu area of Chongqing which contains about 35cm thick which also provides the latest material for the study of giant oolitic rocks. Based on the structural characteristics, grain composition, sedimentary environment and paleoclimate characteristics of the giant oolitic limestone deposited in the early Triassic and the giant oolitic limestone of the early Cambrian in northwestern Sichuan, The genetic mechanism of paleo-ecological background and paleo-marine hydrochemistry were studied and analyzed. It is considered that the formation of giant oolitic must satisfy the following conditions: there is a core which can be surrounded by algal globules bioclasts and oolitic particles; The concentration of CO2 is significantly higher in the atmosphere during the deposition period, and the high concentration of CO2 can produce two effects: one is that the frequent strong storms provide strong hydrodynamic conditions for the formation of giant oolitic. Furthermore, under the influence of frequent strong winds, ocean water will continuously roll and stir, resulting in the dissolution of high concentration of CO2 in the atmosphere and the formation of marine water with chemical properties of CO2 supersaturation; Because the sedimentary background of both is extremely bad marine sedimentary environment, mainly because of the lack of metazoan and the flourishing of microbes, the CO2 supersaturated marine water provides favorable conditions for the survival of a large number of microbes. At the same time, a large number of microbial metabolic activities also affect the local microenvironment of giant oolitic growth, that is, the alkaline marine water causes CaCO3 to precipitate around its core at high speed. They are also similar in sedimentary environment, although the early Cambrian giant oolitic development zone is located in the inner gentle slope and the middle gentle slope in the carbonate gentle slope sedimentary environment, while in the early Triassic period it is located in the open platform of carbonate platform sedimentary environment. However, it can be seen that both sedimentary zones have shallow water depth and can be affected by frequent strong storms. In a word, the formation of giant oolitic is the result of the active participation of microbes, the extreme paleoclimate background and the favorable sedimentary environment. In addition, on the basis of studying the mechanism of the formation of giant oolitic in two times, the author also discusses the derivation of giant oolitic. The early Triassic giant oolitic deposits seem to coincide well with the "staggered facies" deposition in the sedimentary period, but the distribution and frequency of the giant oolitic facies in the early Triassic epoch are far less than those of other early Triassic "staggered facies" deposits. It can be seen that whether the giant oolitic facies can be regarded as a new early Triassic "staggered facies" deposit needs further analysis and study. At the same time, microbes play an important role in the formation of giant oolitic rocks, which not only constitute the main components of rocks, but also promote the deposition of giant oolitic limestone by changing the chemical properties of the water media in the sedimentary environment through its physiological activities. Therefore, the giant oolitic limestone should also belong to the category of microbial rocks.
【学位授予单位】：成都理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P588.248
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