中文摘要：

塔里木盆地北缘奥陶系发育典型的古岩溶,笔者在其中发现了一种非常特殊的沉积物或沉积构造：包壳砾石和包壳砾岩,且这种包壳砾岩之前从未见报道。该包壳砾石和包壳砾岩的结构类似鲕粒或核形石,可分为核心和包壳2部分,大部分呈近圆形或扁圆形,少数形态不规则,直径为数厘米到数十厘米。核心可分为4种,分别是：（1）与溶洞围岩相同的灰岩砾石;（2）由砂岩形成的核心;（3）由砾岩构成的复合核心;（4）由古钙华碎块形成的核心。包壳也可分为4种类型,分别是：（1）具有圈层的包壳;（2）颗粒状包壳;（3）均质包壳;（4）由颗粒状包壳和圈层状包壳组合形成的复合包壳。包壳砾石和包壳砾岩是溶洞和岩溶沉积中的典型产物,其不仅可以作为识别溶洞和岩溶的标志之一,而且具有一定的储集能力,是一种有效的油气储集体。

英文摘要：

Coated gravels and coated conglomerates,a specific type of sediment from karst caves and palaeokarsts,were found in the Ordovician in northern margin of Tarim Basin. These coated gravels and coated conglomerates,not been documented previously,are characterized by oolith-or oncolite-like textures,i.e.,a core and coat around the core. The core is divided into four types：（ 1） limestone gravel identical to the country rock of the karst cave;（ 2） core composed of sandstone;（ 3） composite core of conglomerates and（ 4） core comprised by palaeotravertine clasts. The coat is also divided into four types：（ 1） coat with cycles;（ 2） granular coat;（ 3） homogeneous coat and（ 4） composite coat comprised by granular coats and cycle-like coats. Coated gravels and coated conglomerates are typical products of karst caves and palaeokarsts,which can be served as markers of the presence of karsts and karst caves.Furthermore,the inherent storage capability in coated gravels and coated conglomerates make them effective hydrocarbon reservoirs,and thus a target for oil and gas exploration and development.