上扬子地台中奥陶统“龟裂纹”灰岩成因的新解释  

MIDDLE ORDOVICIAN CRACKED LIMESTONES OF POLYGONAL STRUCTURE IN THE UPPER YANGTZE RIVER AREA, SOUTH CHINA'A NEW INTERPRETATION OF THEIR ORIGIN

作　　者：王尧[1] 

机构地区：[1]中国科学院地质研究所

出　　处：《地质科学》1995年第3期368-374,T002,共8页Chinese Journal of Geology(Scientia Geologica Sinica)

基　　金：国家自然科学基金

摘　　要：本区“龟裂纹”大量发育于碳酸盐台地内的薄－厚层灰岩中，不受沉积环境、岩相和层位的严格控制。其在层面、侧面和底面上均呈不规则多边形。“龟裂纹”是含水的碳酸盐沉积物在构造应力和威岩作用中发生的裂开、脱水收缩，以后又经压溶作用使之改造并复杂化而成，因此“龟裂纹”灰岩是构造－成岩作用的产物。racked limestones of polygonal stucture in the Middle Ordovician Baota Formation are of the so-called 'Tortoise shell' patterns on their surface, and nodularlimestones are widely distributed in the upper reaches of the Yangtze River, whichattain about several handreds of thousand square kilometers in their distribution.They have got great attention for long time, but so far there is no satisfied answersto the interpretation of their. The cracked limestones are mainly developed withinthe Baota Formation, but in western Hunan Province they can also be found inupper Ordovician Linxing Formetion, Middle Ordovician Baota and GoniutanFormation and Lower Ordovician Dawan Formation. These cracks and nodulesusually occur in thin to thick bedded Limestones of Middle Ordovician carbonateplatform in South China, bait these limestones are quite different in their component and lithologies, of which skeletal and intraclastic (attaining about 5%60% in their totol grains) micritic limestones are predominated. Therefore, crackswere not severely controlled by sedimentary environment, lithological factes andstratigraphic horizons.On the top and bottom of these limestones, as well as on their lateral sidesthey often demonstrate irreqular polygonal structure, but are predominated with tetragonal and pentagonal patterns. Under the microscope, these cracks are composedof complicated systems of many fine, curved fissures, which are quite differentfrom those formed by mud crack structures and those produces by subaqueous shrisikages. These cracks were formed during fracturing under the tectonic stress anddewatering-contracting of water-containing lime mud sediments in the course of rookforming process. Enormous evidences have indicated that the Yangtze plate hadundergone great compression not only from the Yunnan-Qinghai-Tibet plate, but also from the Pacific plate in Caledonian movement, thus suffering from intensivedeformation, faulting and uplift during late Middle Ordovician to early Late Ordovician time. These processes must affect

关 键 词：龟裂纹灰岩 构造应力 灰岩 中奥陶世 上扬子地台 

分 类 号：P588.248[天文地球—岩石学]