The Late Ordovician succession of the Baltic Basin contains a characteristic fine-grained limestone, which is rich in calcareous green algae. This limestone occurs in surface outcrops and drill-cores in an extensive belt reaching from Sweden across the Baltic Sea to the Baltic countries. This limestone, which is known in the literature under several different lithological names, is described and interpreted, and the term “Baltic limestone facies” is suggested. The microfacies, from selected outcrops from the Åland Islands, Finland and Estonia, consists of calcareous green algae as the main skeletal component in a bioclastic mudstone-packstone lithology with a pure micritic matrix. Three types of calcitarch, which range in diameter from c. 100–180 μm, are common. Basinward, the youngest sections of the facies belt contain coral-stromatoporoid patch reefs and Palaeoporella-algal mounds. The Baltic limestone facies can be interpreted as representing the shallow part of an open-marine low-latitude carbonate platform.

中文翻译：

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海藻、calcitarchs 和波罗的海盆地晚奥陶世波罗的海石灰岩相

波罗的海盆地晚奥陶世系列含有特征性细粒石灰岩，富含钙质绿藻。这种石灰岩存在于从瑞典穿过波罗的海到达波罗的海国家的广阔地带的地表露头和钻芯中。这种石灰岩在文献中以几种不同的岩性名称为人所知，对其进行了描述和解释，并建议使用术语“波罗的海石灰岩相”。微相来自奥兰群岛、芬兰和爱沙尼亚的精选露头，由钙质绿藻组成，作为具有纯泥晶基质的生物碎屑泥岩-堆积岩岩性中的主要骨骼成分。三种类型的calcitarch，其直径范围从c。100–180 μm，很常见。盆地，相带最年轻的部分包含珊瑚-层孔状斑块礁和古孔藻-藻丘。波罗的海石灰岩相可以解释为代表开阔海相低纬度碳酸盐台地的浅层部分。