广西桂林南边村上泥盆统沉积灰岩脉研究  

Study on Carbonate Limestone Dykes (Neptunian Dykes) of Upper Devonian in Nanbiancun, Guilin, Guangxi

作　　者：彭阳[1] 陆刚[2] 胡贵昂[2] 

机构地区：[1]中国地质科学院地质研究所,北京100037 [2]广西区域地质调查研究院,广西桂林541003

出　　处：《地质论评》2013年第2期217-224,共8页Geological Review

基　　金：中国地质调查局项目(编号1212011120115);中国地质调查局工作项目(编号1212011120794);国家自然科学基金资助项目(编号40372058)的成果

摘　　要：沉积灰岩脉广泛发育在桂林及桂西北右江盆地晚古生代碳酸盐岩台地边缘。广西桂林南边村泥盆纪—石炭纪(层55～56)国际副层型剖面中,沉积灰岩脉分别出现在层50(为多条栉壳状方解石细脉标示拉张的构造背景)和层45(为液化颗粒灰岩脉)。层45中的液化颗粒灰岩脉与在桂林庙头剖面和桂西北右江盆地晚古生代地层中广泛发育的沉积灰岩脉有较大差异:桂林庙头和右江盆地晚古生代碳酸盐岩台地边缘的沉积灰岩脉中充填物大多数为与围岩有时差的后期正常海水沉积物,而层45内的沉积灰岩脉中充填物为上覆软沉积物液化颗粒流。由砂屑、生物屑颗粒组成:砂屑成分为含铁泥质、破碎方解石晶体及细小生物屑,呈暗色,彼此紧密接触,几乎没有填隙物,并常因挤压而变形,表明砂屑为非正常海水沉积物;生物屑主要为腕足类和海百合茎,挤在砂屑颗粒之间,且海百合茎纤细侧剌保存完好、腕足壳完整,被缓慢挤压变形几近U型合拢并原地寸断——佐证颗粒为非正常海水沉积物。脉顶端显示上宽下稍窄V字型,脉壁无侵蚀但贴有红色铁质泥皮(表明短暂间断);而且在周围岩层中找不到与脉内岩性结构相同的沉积地层。因此脉中颗粒物应来源于上覆弱固结沉积物流。晚泥盆世晚期,在拉张的构造背景下,桂林及右江盆地各台地边缘同沉积正断层活动并伴生张裂隙,同时诱发地震;桂林庙头剖面和右江盆地各含沉积灰岩脉剖面多数处在陡峭的台地边缘,是无沉积刚性正地形(bypassing),因此同沉积正断层及地震只在此形成伴生刚性张裂隙,并在下次海侵时接受正常海水沉积物;桂林南边村剖面处于靠近台缘的斜坡位置,因此具有上覆软沉积物;当台缘同沉积正断层及地震活动波及时,形成少量张裂隙,而上覆软沉积物,如准同生灰泥、砂屑、生物屑、亮晶胶结物、铁泥质等,与孔隙水混Carbonate neptunian dykes occurred commonly in Late Palaeozoic carbonate plateform margins in Guilin and Northwestern Youjiang basin, Guangxi Autonomous Region. In the Nanbiancun International Devonian-- Carboniferous （bed 55 ~ 56） Boundary （DCB） Parastratotype Section of Guilin of Guangxi, carbonate neptunian dykes are identified in Bed 45 （ a liquefied grainstone vein） and Bed 50 （ some fine crystal fiber calcite veins, as signal of tension structure background） and is considered far different from those in the Miaotou section of Guilin and Youjiang Basin. In the Miaotou section of Guilin and the Youjiang Basin, the infillings of neptunian dyke are afterwards normal sea water sediments, while in the Nanbiancun section of Guilin are simultaneous overlain liquefied soft-sediment-flow, shown as skeletals and non-skeletal grains （ with dark Fe-bearing clays, fine calcites and fine skeletals） mixture. The non-skeletal grains deformed and impinged each other with very few cements among them That means they are not normal sea water deposits. The skeletal grains are mainly brachiopod and crinoid stems crowded floating in non-skeletal grains. A single Brachiopods shell are folded as ＂U＂ shape and then cut into several continuous parts in situ. That means a slowly soft press surrounding and wholly flowing. The upper part of the carbonate neptunian dyke shaped ＂V＂ and the inside wall of the dike are solid and covered with thin Fe-film （means an instant unconformity）. Additional evidence is that no rock, same as the fillings inside the dykes in contains and structure, are reported in surrounding beds. Therefore the infillings are from overlain softsediments-flow. In the later Late Devonian, the Miaotou section and those of sections with neptunian dykes in Youjiang basin located in high cliff margin without overlain sediments （bypassing）. When the normal fault movement and earthquake had taken place, the cracks occurred here and then filled by next transgression normal sea water sediments

关 键 词：沉积灰岩脉 上泥盆统 广西 

分 类 号：P618.13[天文地球—矿床学]