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许多现象可用于估算海水的绝对深度，进而建立志留纪近岸至远岸的海水深度的变化序列（ＢＡ１一５）。如一些海洋生物化石和一些原始沉积结构（特别是风暴沉积）间的合谐程度，其次，对光的灵敏度高的生物体和礁体化石的分布。其中最重要的是钙藻（包括中奥陶世至早志留世的环毛海绵），现代藻类分布很局限。现代钙藻分布的最大海水深度为９０ｍ，最浅为３０ｍ左右。志留纪的藻类是很丰富的（ＢＡ３和４），少数的环毛海绵和粗枝藻目前有在下志留统中发现的。这些现象限定了志留纪藻类化石的分布深度区间（ＢＡ１一５），即分布在透光带之内。基于分类均衡论原则，志留纪海水深度从ＢＡＩ至ＢＡ４可估算为０ｍ至４０～６０ｍ之间。浪基面和最低透光带是一致的，代表水深为５０ｍ左右。其它可作为证据的，如被厚度已知的玄武岩层所穿切的藻类表面带的孔隙度和广度，为ＢＡ１一４提供了相对的浅水分布区域深度变化序列。在一些较大型的地台区域内，风暴的干扰很少见到，如ＢＡ３一４；在滨海区内志留纪时要比现在的风暴弱得多，可能是由于气候差异所致。
Many phenomena can be used to estimate the absolute depth of seawater and to establish a sequence of seawater depths (BA1-5) from the Silurian to the far shore. Such as the degree of harmony between some marine fossils and some primitive sedimentary structures (especially storm deposits), and secondly, the distribution of highly sensitive organisms and reef fossils. One of the most important is the calcium algae (including Central Ordovician to Ascension Central hair sponge), the distribution of modern algae is very limited. The distribution of modern calcium algae maximum seawater depth of 90m, the most shallow about 30m. Silurian algae are abundant (BA3 and 4), and a few ring-fur sponges and cursive algae are currently found in the lower Silurian. These phenomena limit the depth of distribution of the Silurian algae fossils (BA1-5), which is distributed within the light transmission band. Based on the principle of classification equilibrium, the seawater depth of the Silurian can be estimated from BAI to BA4 to be between 0 m and 40-60 m. Wave base and the lowest light transmission band is the same, representing the water depth of about 50m. Other evidence, such as the porosity and breadth of algae surface strands worn by basalts of known thickness, provides BA1-4 with a sequence of relative shallow water depth changes. Storm disturbance is rare in some large terrain areas, such as BA3-IV; the Silurian in the coastal area is much weaker than the current storm, possibly due to climatic variability.