Quartz crystallinity index:New quantitative evidence for biogenic silica of the Late Ordovician to Early Silurian organic-rich shale in the Sichuan Basin and adjacent areas,China  

作　　者：Guoheng LIU Gangyi ZHAI Rui YANG Tingpeng HE Bin WEI 

机构地区：[1]School of Geosciences,China University of Petroleum(East China),Qingdao 266580,China [2]Oil and Gas Survey,China Geological Survey,Beijing 100083,China [3]Key Laboratory of Tectonics and Petroleum Resources,Ministry of Education,China University of Geosciences,Wuhan 430074,China [4]Chongqing Institute of Geology and Mineral Resource,Chongqing 401120,China [5]Liaohe Petroleum Exploration Bureau,Panjin 124010,China

出　　处：《Science China Earth Sciences》2021年第5期773-787,共15页中国科学（地球科学英文版）

基　　金：supported by the National Natural Science Foundation of China for Young Scholar(Grant No.41902148);the National Science and Technology Major Project of the Ministry of Science and Technology of China(Grant No.2016ZX05034-002);the Innovative Special Project of Sino-US Intergovernmental Cooperation in Science and Technology(Carboniferous-Permian shale reservoir evaluation and technology between China and the USA)(Grant No.2017YFE0106300)。

摘　　要：Quartz crystallinity index(QCI)was used to reflect the crystallisation of silica in the Late Ordovician Wufeng(WF)and Early Silurian Longmaxi(LM)Formation shale,as well as the airborne volcanic ash-derived silica in the Lucaogou Formation tuffaceous shale,to distinguish the two types of silica.The silica in different graptolite biozones exhibited different crystallisation.The WF2–3,LM1–4 graptolite biozones showed obviously lower QCI values than the LM5–9 graptolite biozones and the Lucaogou Formation samples.The graptolite organisms played the role of adsorption,fixation,and precipitation in silicon accumulation and enrichment in stratum.The biogenic origin caused the poorest quartz crystallisation in WF2–3 and LM1–4 graptolite biozones samples.The airborne volcanic ash-derived silica in the Lucaogou Formation tuffaceous shale exhibited relatively poor quartz crystallisation because of weaker diagenesis intensity.Generally,although the WF2–3 and LM1–4 graptolite biozones underwent strong diagenesis and contained a small amount of detrital quartz,the silica still exhibited lower QCI values than the airborne volcanic ash-derived silica in the Lucaogou Formation tuffaceous shale.The biogenic silica crystallisation was much poorer than that of the airborne volcanic ash-derived silica.QCI is an effective quantitative index to demonstrate the biogenic silica in the organic-rich and silica-rich shale.

关 键 词：Biogenic silica Volcanic ash-derived silica Quartz crystallinity index Late Ordovician Wufeng Formation Early Silurian Longmaxi Formation 

分 类 号：P618.13[天文地球—矿床学]