臼齿构造主要成因模式及时空分布意义

在综述臼齿碳酸盐岩成因研究历程和国内外最新研究成果的基础上,总结评述了6种主要的臼齿构造成因模式,其核心问题是在元古代正常潮下浅海环境中构建成岩作用早期臼齿构造裂缝形成及等粒微亮晶方解石快速沉淀充填的物理、化学及微生物条件。其中,气泡扩张裂缝模式、微生物-地球化学模式和同沉积地震脱水模式等具有一定的代表性。臼齿构造多产出于正常浅海潮下环境,并且呈幕式特点产出于前寒武纪地层记录中,其时空发育特点似乎表明与叠层石发育的不相容性。臼齿碳酸盐岩在中新元古代集中发育的事实可能反映了有利的物理、化学和生物条件在地质历史上的唯一结合。理清臼齿构造成因问题是认识前寒武纪复杂的碳酸盐岩世界的重要线索。

Origin Models of Molar Tooth Structures and Their Temporal Spatial Distribution Significances

Molar tooth carbonate is a category of fine-grained cryptocrystalline mud carbonate in the Precambrian era with molar tooth structure,which are characterized by various morphologic features and different sizes filled with equigranular microspar calcite,and there is no analog in the Phanerozoic.On the basis of the research course analysis and the latest investigation on molar tooth structures,six dominating origin models are outlined.The core issue is how to construct a reasonable physical,chemical and microbial condition for early rapid precipitationand filling of molar tooth cracks in the subtidal shallow marine. Of these, three models of gas bubble and expansion crack origin, microbial-geochemical origin and synsedimentary seismic origin are the most representative ones. Molar tooth structures are episodically located in Precambrian subtidal shallow marine environment, and their temporal and spatial characteristics indicate incompatibility with stromatolites. The fact that molar tooth carbonates were concentrated in the period of Mid- and Neo-Proterozoic may reflect the only combination of favorable physical, chemical and biological conditions in the entire geological history. Understanding the genetic origin of molar tooth structures is a crucial clue to the complicated Precamhrian carbonate world.