四川甘溪泥盆系观雾山组白云岩特征与其形成条件的关系(英文)

本文通过沉积环境分析,X射线衍射、扫描电镜、同位素及阴极发光分析,讨论了甘溪泥盆系观雾山组白云石的晶体形态及大小、有序度、碳酸钙克分子含量,同位素特征及阴极发光特征与形成条件的关系。中晶白云岩及细晶白云岩分别产于生物层及潮坪环境,为成岩早期地下淡水与海水混合白云岩化作用的产物。低的碳酸钙克分子含量,中-弱的阴极发光强度及低的δ18O、δ13C值。微晶白云岩形成于泻湖环境。白云石具他形粒状晶,差的有序度,高的碳酸钙克分子含量,强的阴极发光强度及高的δ18O、δ13C值,为准同生期高Mg2+/Ca2+值卤水交代碳酸钙软泥形成。

THE CORRELATION BETWEEN THE DOLOMITES AND THEIR FORMING CONDITIONS IN THE GUANWUSHAN FORMATION (MIDDLE DEVONIAN)GANXI,SICHUAN, CHINA

The Guanwushan Formation consists of three types of dolomite; medium crystal line dolomite which occurred in biostrome environment, micrite dolomite in lagoon and fine crystalline dolomite in tidal flat. The first type of dolomite, distributed in the lower part of Guanwushan Formation, is characterized as follow: 1 ) containing abundant reef-forming organisms and other fossils, 2 ) 100-500μm in size, euhedral rhombohedral crystal forms. 3 ) very good ordering degree and low CaCO₃ mole content, 4 ) low δ18O values and 5 ) dull intensity of cathodoluminescence. Second type of dolomite, distributed in middle part of Guanwushan Formation, is characterized as follow: 1 ) containing few fossils but a lot of pyrite, 2 ) 5-60μm in size, dominantly xenomorphic granular crystal form, 3 ) poor ordering degree and high CaCO₃mole content, 4 ) relatively high 618O values and 5 ) bright intensity of cathodoluminescence. Third type of dolomite distributed in the upper part of Guanwushan Formation, is characterized as follow: 1 ) containing some fossils, 2 ) 40-200μm in size, dominantly hypidiomorphic granular crystal form, 3 ) very good ordering degree and lower CaCO₃ mole content, 4 ) relatively low δ18O values, low δ13Cvalues and 5 ) medium intensity of cathodoluminescence. The micrite dolomite in the lagoon resulted from the dolomitization by the solution having a high Mg2+/Ca2+ ratio during penecontemporaneous stage. The medium crystalline dolomite in biostrome and the fine crystalline dolomite in tidal flat resulted from the dolomitization by meteoric ground waters mixing with sea water during the early diagenetic stage.