摘要
本文应用多种技术方法,对微亮晶碳酸盐岩的成岩作用及其成因从宏观至微观进行了分析。根据岩石矿物学、地球化学和有机地球化学等研究证明,它是早期成岩过程中,在超高压的大气 CO_2,水平急剧下降的转折期,快速石化作用形成的具等粒结构μm级的微亮晶方解石集合体。MT 碳酸盐岩微亮晶成岩作用有两种类型:一是主要发生在海底沉积软泥中,在其底基质软泥中经差异压实作用形成褶皱肠状及复杂形的 MT 构造;二是直接在海水中或重力流搬运过程中形成的微亮晶球粒(核)。简言之,MT 碳酸盐岩石是在地球早期浅海环境下,由于微生物自养作用形成的地球化学成因产物。微亮晶碳酸盐岩是约束古大气圈和古海洋环境变化的最灵敏标志。通过详测 MT 丰度值和编制地球古大气圈 CO_2水平演化模式等,在前寒武纪发现有太古宙末期、早元古宙末期、中元古宙中期和新元古宙早-中期四个 MT 碳酸盐岩发育高峰值期,证明全球古大气圈 CO_2水平发生过四次不连续性、跳跃式下降周期,直到晚新元古宙未,全球雪球事件的发生,导致了 MT 碳酸盐岩的消失。其后,才进入显生宙的 CO_2低水平状态。MT 碳酸盐岩具有重要的油气资源远景,应予以重视。
The diagenesis and origin of Microsparite（MT-molar tooth）carbonates have been analyzed based on macroscopic and microscopic characteristics obtained with a variety of techniques.The study on petrology,mineralogy,geochemistry and organic geochemistry of the MT carbonates demonstrated that the MT carbonates were composed of micrometer-scale,equigranular and hexahedron microspars,and were formed by the early and fast lithificaiton during a rapid drop of atmospheric CO2 pressure.There were two types of diagenesis which had been involved in formation of the MT carbonates;one took place in the soft mud of the sea floor where the differential compaction formed the ptygmatic fold structures or other complex shaped structures.another was the microsparite core of globules which were directly precipitated from sea water or was carried in by the carbonate gravity.All of above confirmed that MT atmospheric and formed by biogeochemical reaction in shallow sea.The MT carbonates were the most sensitive indicator of the paleoatmospheric and paleo-oceanic conditions.The abundance of the MT carbonates can be measured and used to model the evoltion of CO2 level in paleo-atmosphere.Four-peak development stages of the MT carbonates were found in the Precambrian,including the Late Archaecan Era,last stage of the Early Proterozoic,middle period of the Mesoproterozoic and Neoproterozoic.These four stages were coincident with the four stepping -down events of the CO2 level in paleo-atmosphere.After these four stages.the CO2 level dropped down to a lowest level in the Phanerozoic.Moreover,the MT carbonates are of importance for oil-gas resources perspective.
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2006年第8期2133-2143,共11页
Acta Petrologica Sinica
基金
国际地质对比计划 IGCP447项目(编号:SC/GEO/546/447)
科技部国家重点基础研究项目(001CB7 11002)
国家自然科学基金(编号:40172043
40572073)
中国地质调查局项目(编号:200313000055)资助
