CAJ | 학술논문

巨鲕是指那些直径超过2mm、海相成因的大型鲕粒，它们在结构上与鲕粒相似，但却远没有鲕粒分布广泛，成因也与鲕粒不尽相同。豫西渑池地区寒武系第三统张夏组发育了大量的巨鲕，其核心由粒径小于2mm的放射状鲕粒或泥晶球粒组成，形成于弱搅动的水体环境中；圈层以泥晶或由 Girvanella 丝状体组成的暗色纹层与由微亮晶方解石组成的浅色纹层交替发育为特征。巨鲕是在低、中等能量交替的滩间海环境中由 Girva-nella丝状体的生长、微生物诱导的钙化作用和无机碳酸钙沉淀而成的。Girvanella 丝状体在巨鲕的内、外圈层均有分布，尤以外圈层分布更为密集，显示了微生物在巨鲕形成过程中具有重要作用，这为探讨巨鲕的成因提供了一个重要的实例。
거이시지나사직경초과2mm、해상성인적대형이립，타문재결구상여이립상사，단각원몰유이립분포엄범，성인야여이립불진상동。예서민지지구한무계제삼통장하조발육료대량적거이，기핵심유립경소우2mm적방사상이립혹니정구립조성，형성우약교동적수체배경중；권층이니정혹유 Girvanella 사상체조성적암색문층여유미량정방해석조성적천색문층교체발육위특정。거이시재저、중등능량교체적탄간해배경중유 Girva-nella사상체적생장、미생물유도적개화작용화무궤탄산개침정이성적。Girvanella 사상체재거이적내、외권층균유분포，우이외권층분포경위밀집，현시료미생물재거이형성과정중구유중요작용，저위탐토거이적성인제공료일개중요적실례。
Giant ooids are those large ooids with diameters greater than 2mm formed in marine envi-ronments.They are similar with the normal ooids in structure but have a different origin and limited distri-bution.Abundant giant ooids occur in the Zhangxia Formation of Cambrian Series 3 in Mianchi area,west-ern Henan Province.Their cores consist of micritic pellets or radial ooids with diameters less than 2mm and are formed in weak-agitating environments.Their concentric layers are characterized by the alternations of the dark laminations of micritic calcites or Girvanella filaments and the light laminations of microspar calcites.Giant ooids are formed by the growth of Girvanella filaments, microbially-induced calcification and chemical precipitation of calcium carbonate in the oolitic inter beach banks environments with the al-ternation from low to medium energy conditions.Girvanella filaments distribute both in inner or outer con-centric layers of the giant ooids,especially dense in the latter.It clearly shows that the microbes play an important role in the formation of giant ooids,and provides an important evidence for the study of origin of giant ooids.