【摘要】 浙江江山晚石炭世藕塘底组上段发现一种较为特殊的硅质岩。该类岩石呈白色、黄白色,夹于浅海相黄白色长石石英砂岩、粉砂岩和砾岩中。其显著特征是,岩石具残余生物碎屑结构,见大量腕足类、海百合茎、珊瑚等钙质生物假象,主要为mm级完整个体,密集堆积。生物已完全硅化,但内部组构清晰可辨。常见由多个微晶石英交代的自形细晶白云石假象以及碳酸盐交代残余。岩石质地较轻,具大量圆形、菱形和不规则状孔隙,系由海百合茎等生物碎屑、白云石(或钙质成分)风化淋滤流失造成空洞所致。岩石属于交代成因,原岩可能为亮晶(或微晶)生物碎屑灰岩,为潮下浅滩沉积产物。岩石硅化前曾发生过白云化作用。地球化学特征表明,硅质来源于正常地下水,无热水或火山硅质来源的迹象。笔者将这类硅质岩取名为“钙骨假象燧石岩”。更多还原

【Abstract】 There is a peculiar type of bedded siliceous rock in the upper Outangdi Formation of the Late Carboniferous in Jiangshan, Zhejiang Province. The rocks, white or light yellow-white in color, is intercalated in the feldspathic quartz sandstone, siltstone and conglomerate. The prominent characteristic of the siliceous rock is the residual bioclastic structure, with plenty of silicified calcareous organisms, such as brachiopoda, encrinite caudex and coral, which are several millimeters in size. The organisms were all silicified, but their inner structures are visual. It can be seen under microscope that rhombic crystals (dolomite) were replaced by microlitic quartz. The rock is characterized by light in weight and porous nature. The pores, being circular, rhombic or irregular in shape, were formed by weathering and eluvia-ting of bioclasts (such as encrinite caudex) and dolomite (or calcareous matter). This study suggests that the siliceous rocks were originated by replacement of sedimentary carbonates, such as sparry (or micrite) bioclastic limestone, which were formed in subtidal shallow beach environment. Dolomitization took place before silification. The chemical analysis data demonstrate that siliceous matter came from normal underwater, not from hydrothermal or volcanic silicon. The author named this peculiar type of siliceous rock as "silicified calc-bioclastic chert".更多还原