Lower Ordovician stromatolite-like columns and thrombolite-like mounds, composed of fossilised keratose sponges (keratolites) and microbial carbonates, are reported from the Tremadocian Mungok Formation, Yeongwol, Korea. The stromatolite-like columns, which are up to 10 cm wide and high, consist of an inner core with low-angled (10–45°) layers that are covered by high-angled (>45°) layers. The inner core is made up of millimetric layers of alternating keratolite and microbial carbonate, and microbial carbonate dominantly comprises the outer cover. The entire columns are surrounded by bioclastic packstone to grainstone. The thrombolite-like mounds are domes a maximum of 100 cm high and 40–60 cm wide embedded within lime mud and shale. These mounds consist of keratolite–microbial carbonate clots and minor lithistid sponge–microbial carbonate clots. The stromatolite-like columns were formed in a high-energy subtidal setting, in which laminoid keratolite and microbial carbonate formed the tight laminar frame columns. Continued growth of the column narrowed the intercolumnar space, resulting in higher-energy hydrodynamic conditions that limited the growth of sponges but promoted growth of microbial organisms. In contrast, thrombolite-like mounds developed in a low-energy environment below fair-weather wave base, where irregular to bulbose keratose sponges with minor lithistid sponge–microstromatolite associations formed cluster reefs. There appear to have been ecological and/or environmental factors that affected the distribution of these sponges; keratose and lithistid sponges rarely occur together in the Mungok reefs, whereas lithistids are pervasive within coeval intermediate-energy microbial reefs elsewhere. These results demonstrate the importance of hydrodynamic controls on overall reef morphology and configurations during the Early Ordovician, and suggest that keratosan–microbial consortia may have been an integral component of the Great Ordovician Biodiversification Event, together with the lithistid sponge–microbial consortium.

据报道，韩国影月的特里玛多克芒格组（Tremadocian Mungok Formation）报道了由化石化的角质海绵（角质岩）和微生物碳酸盐组成的下奥陶纪叠层岩状柱体和类似栓塞岩的土丘。叠层石状的柱状柱体，宽达10厘米，高，由一个内芯和一个低角度（10–45°）的层组成，这些低角度层被高角度（> 45°）的层所覆盖。内芯由角质层和碳酸盐微生物交替的毫米层组成，并且碳酸盐微生物主要构成外壳。整个柱子都被生物碎屑堆积岩到粒岩包围。类似于血栓石的土丘是圆顶，埋在石灰泥和页岩中的最大高度为100厘米，宽为40-60厘米。这些土墩包括角质岩-微生物碳酸盐凝块和较小的直链海绵-微生物碳酸盐凝块。叠层石状柱子是在高能潮下环境中形成的，其中层状角蛋白石和微生物碳酸盐形成了紧密的层状框架柱。柱子的持续增长缩小了柱间空间，导致了高能流体动力学条件，限制了海绵的生长，但促进了微生物的生长。相反，在晴朗天气波峰以下的低能量环境中，形成了类似于血栓石的土堆，在那里，不规则的球状角蛋白海绵与少量的组蛋白海绵-微叠层石的结合形成了珊瑚礁。似乎有生态和/或环境因素影响了这些海绵的分布。在Mungok的礁石中，角质和海绵状的海绵很少一起出现，而在其他地方的中世纪中能微生物礁石中，岩棉和海绵状石棉普遍存在。这些结果表明，在奥陶纪早期，流体动力学控制对整个礁石形态和构造的重要性，并表明，角蛋白聚糖－微生物群落与小卵石－海绵－微生物群落可能是大奥陶纪生物多样性事件的一个不可或缺的组成部分。