辽西下白垩统义县组湖相碳酸盐岩中的燧石成因

Mechanism of the Chert Formation within the Lacustrine Carbonates of the Lower Cretaceous Yixian Formation, Western Liaoning

辽西义县鹰窝山下白垩统义县组砖城子层中部发育一套湖相碳酸盐岩,可识别出4种岩相类型,其中角砾化团块灰岩相中含有大量燧石,所含的燧石可据形态划分为结核状、透镜状和团块状3种类型,据颜色和透明度识别出两种类型。燧石以微晶石英和玉髓为主,含少量的白云石和方解石晶粒。该岩相系相对干旱气候背景下的洪积-漫湖沉积体系中较浅储水洼地沉积,火山活动也具一定的影响力。

Four types of lacustrine facies carbonate developed within the Zhuanchengzi section of the Lower Cretaceous Yixian Formation have been recognized in Yixian County of western Liaoning Province. Among them, plenty of chert occurs in brecciated nodular limestone-facies carbonate. The chert can be divided into three types： nodular, lenticular and glaebule based on its configuration, while two types of chert can be defined based on color and transparency. The chert consists mainly of microcrystalline quartz and chalcedony with small amount of calcite and dolomite crystals. Our study suggests that the sedimentary environment of carbonates might be relatively-dry, shallow short-lived isolated sags on the floodplain partially accompanied with volcanic activity.