【摘要】：巨鮞的產(chǎn)出時(shí)代多為新元古代和早三疊世,而寒武紀(jì)的巨鮞卻較少報(bào)道。近期我們?cè)谥貞c石柱地區(qū)野外剖面中發(fā)現(xiàn)下寒武統(tǒng)天河板組含厚約35cm的透鏡狀巨鮞灰?guī)r,這也巨鮞的研究提供了最新的素材。通過(guò)對(duì)川西北地區(qū)早三疊世沉積的巨鮞灰?guī)r與早寒武世巨鮞灰?guī)r在結(jié)構(gòu)特征、顆粒組分、沉積環(huán)境、古氣候特征、古生態(tài)背景以及古海洋水化學(xué)性質(zhì)等方面作對(duì)比綜合研究分析了其成因機(jī)理。認(rèn)為巨鮞的形成必須滿足以下條件:具有一個(gè)可以圍繞的核心,核心可以為藻球粒、生物碎屑以及鮞粒;且在兩者的沉積時(shí)期大氣中均表現(xiàn)出CO2濃度顯著偏高,高濃度的CO2會(huì)產(chǎn)生兩方面的作用:一是催生頻繁的強(qiáng)風(fēng)暴作用為巨鮞的形成提供了較強(qiáng)的水動(dòng)力條件,再者便是海洋水在頻繁的強(qiáng)風(fēng)作用影響下會(huì)持續(xù)翻滾攪動(dòng),致使大氣中高濃度的CO2溶解其中,形成化學(xué)性質(zhì)呈CO2過(guò)飽和的海洋水;由于兩者的沉積背景均是極度惡劣的海洋沉積環(huán)境,主要變現(xiàn)為缺乏后生動(dòng)物存在而微生物趁機(jī)得到繁盛,CO2過(guò)飽和的海洋水為大量的微生物生存提供了有利條件,同時(shí)大量的微生物新陳代謝活動(dòng)也影響了巨鮞生長(zhǎng)時(shí)的局部微環(huán)境,即海洋水呈堿性致使CaCO3圍繞其核心高速沉淀;二者在沉積環(huán)境方面亦有相似性,雖然早寒武世巨鮞發(fā)育地帶處于碳酸鹽緩坡沉積環(huán)境中的內(nèi)緩坡外緣—中緩坡內(nèi)側(cè),而早三疊世時(shí)期處于碳酸鹽臺(tái)地沉積環(huán)境開(kāi)闊臺(tái)地,但是可見(jiàn)兩者沉積帶水體深度均較淺,都可以受到頻繁的強(qiáng)風(fēng)暴作用的影響�？傊�,巨鮞的形成是微生物的積極參與、極端的古氣候背景和有利的沉積環(huán)境綜合作用的結(jié)果。此外,筆者在對(duì)兩個(gè)時(shí)代巨鮞成因機(jī)理研究的基礎(chǔ)上,還對(duì)巨鮞衍生出來(lái)的問(wèn)題進(jìn)行了相關(guān)探討。早三疊世巨鮞看似與“錯(cuò)時(shí)相”沉積在沉積時(shí)期是完全吻合的,但是巨鮞在早三疊世無(wú)論是分布范圍還是出現(xiàn)頻率均遠(yuǎn)遠(yuǎn)不如其它早三疊世“錯(cuò)時(shí)相”沉積。由此可見(jiàn),關(guān)于巨鮞是否能做為一種新的早三疊世“錯(cuò)時(shí)相”沉積來(lái)看待,還需要做進(jìn)一步分析研究。同時(shí),微生物在巨鮞的形成中扮演了至關(guān)主要的角色,不僅構(gòu)成了巖石主要組分,而且通過(guò)其生理活動(dòng)改變沉積環(huán)境水體介質(zhì)的化學(xué)性質(zhì)等促進(jìn)了巨鮞灰?guī)r的沉積,因此認(rèn)為巨鮞灰?guī)r也應(yīng)歸屬于微生物巖的范疇。
[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.
【學(xué)位授予單位】：成都理工大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2015
【分類號(hào)】：P588.248

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