湘南地区奥陶系岩石组合及其沉积环境

An analysis of Ordovician rock association and sedimentary environment in southern Hunan Province

湘南地区奥陶系的岩石类型以砂岩、泥岩和页岩为主,硅岩、灰岩较少。按照岩石成分,可进一步划分为砂岩-泥岩韵律性互层型和泥(页)岩(板岩)-硅岩型2种岩石组合类型。其中,砂岩-泥岩韵律性互层型岩石组合分布于爵山沟组、桥亭子组、天马山组,泥(页)岩(板岩)-硅岩型岩石组合分布于烟溪组。通过岩性、古生物、沉积构造等相标志分析,认为研究区奥陶系沉积环境为深水斜坡至盆地环境,发育深水原地沉积和浊流沉积,并建立了沉积模式,同时分析其沉积演化过程。研究区奥陶系总体表现为水体逐渐上升,经历过一次完整的海进-海退旋回:第一次海进始于下奥陶统桥亭子组,上奥陶统天马山组海退开始。

The Ordovician strata in southern Hunan Province consist mainly of sandstone and mudstone（slate）,with minor siliceous rocks and limestone.According to the rock components,they can be further divided into two sub-rock association types,i.e.,rhythmically alternate sandstone and mudstone type,which is mainly developed in Jueshangou,Qiaotingzi and Tianmashan formations;and mudstone（slate）-siliceous rocks type,which is mainly developed in Yanxi Formation.According to a comprehensive analysis of lithology,palaeontology and sedimentary structures,it is held that the sedimentary environment should be deep-water slope to basin,where deep-water autochthonous（in situ） deposits and turbidite deposits were developed.On such a basis,the sedimentary model has been built and the sedimentary evolution has been analyzed.The sedimentary evolution indicates that the water became gradually deeper on the whole,and there existed an Ordovician sedimentary cycle of transgression-regression in this section.The first transgression began in Qiaotingzi stage of Early Ordovician,and the regression began in Tianmashan stage of Late Ordovician.