Mega-shoaling in carbonate platform of the Middle Triassic Leikoupo Formation,Sichuan Basin, Southwest China

查看全文 作　　者：TAN [1,2]XiuCheng;LI [2]Ling;LIU [2]Hong;CAO [3]Jian;WU [2]XiaoQing;ZHOU [2]SuYan;SHI [4]XueWen

机构地区：[1]State Key Laboratory of Oil and Gas Geology and Exploitation, Southwest Petroleum University;[2]School of Resource and Environment, Southwest Petroleum University;[3]Department of Earth Sciences, Nanjing University;[4]Institute of Petroleum Exploration and Exploitation, PetroChina Southwest Oil and Gas Field Company

出　　处：《Science China Earth Sciences》索引2014年第57卷第3期,共15页

基　　金：supported by National Basic Research Program of China(Grant No.2012CB214803);PetroChina Scientific Innovative Foundation(Grant No.2011D-5006-0105);Key Subject Construction Project of Sichuan Province,China(Grant No.SZD0414) 摘　　要：Shoaling is a common type of sedimentation in the evolution of carbonate platform,and commonly has poor continuity.This paper presents a newly discovered and rare type of shoaling,i.e.,mega-shoaling in nearly basin scale,which is developed in the Middle Triassic Leikoupo Formation of the Sichuan Basin,southwest China.During the Leikoupo time,the studied Sichuan Basin experienced hot and dry climate conditions and developed a carbonate platform within a restricted epicontinental sea.In B sub-layer of the Lei-1-1 sub-member of the Leikoupo Formation a series of grainstones of shoal facies accumulated throughout almost the entire basin,thereby generating features associated with basin-scale mega-shoaling.By detailed core examination and microscopic observation of thin sections,it is shown that the lithology of this set of grainstones is dominated by doloarenite(calcarenite)followed by oolitic dolomite(limestone).In addition,it contains three types of sedimentary sequences characterized by upward-coarsening and upward-shallowing as the followings:restricted lagoon to platform interior beach;restricted lagoon to platform interior beach and to platform flat;and tidal flat to peritidal beach.Subsequently,a multicyclic stratigraphic division and correlation revealed that this set of grainstones can be well traced and compared horizontally,and is generally isochronous.In addition,a template for logging facies,established based on core calibrations and logging data,was employed to analyze the 235 wells in the basin.The results demonstrate the shoal grainstones to be 10–40 m thick with a15×104km2continuous distribution area.These findings indicate that the carbonate platform developed mega-shoals within a short period of time.The genesis of such a mega-shoaling was investigated by focusing on various shoaling conditions,such as paleo-tectonics,paleo-geomorphology,paleo-climate,sea-level changes,and palaeo-hydrodynamics.A specific combination of independent geological factors creates beneficial geomorphologic conditions for the mega-shoaling including a quiescent paleo-tectonic environment,relatively flat paleo-geomorphology and evaporites filling up and leveling off.In addition,a stably settling carbonate platform underwent sea-level fluctuations through swift transgressions and protracted regressions,which is not only conducive to continuous,multicyclic and superimposed vertical development of grain beaches but also beneficial for the horizontal migration,coalescence and superimposition of individual grain beaches.As a consequence,large-scale and continuously-distributed grain beach sedimentation emerges and mega-shoals develop. 关键词：碳酸盐台地中国西南地区四川盆地雷口坡组中三叠统浅水海平面变化古构造环境

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Mega-shoaling in carbonate platform of the Middle Triassic Leikoupo Formation,Sichuan Basin, Southwest China

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