Abstract: Two basic shell structures are recognized based on study of brachiopods across the Frasnian-Famennian (F/F) boundary (Upper Devonian) in Hunan Province, South China, which are characterized respectively by the presence and absence of a tertiary columnar layer. For excluding poorly preserved shells, a shell alteration index is suggested to estimate the state of preservation of brachiopod shells through examination under cathodoluminescence and scanning electron microscopes. This study shows brachiopod taxa (e.g., Atrypida) with both secondary and tertiary layers have better state of shell preservation and more concentrate carbon and oxygen isotopic distribution than those only with secondary layers and consequently, are more reliable material to determine stable isotopic composition of the Devonian seawater.

Key words: brachiopods, preservation state, carbon and oxygen isotopes, Frasnian-Famennian, South China

摘要： 对华南湘中地区上泥盆统弗拉/法门(F/F)界线附近的几种腕足动物化石壳体结构所进行的详细研究表明，其原始结构主要表现为两种类型：一是具有棱柱状第三层，二是缺失棱柱状第三层。基于壳体保存程度的详细分析，以阴极发光程度、壳体显微结构为参数建立了壳体成岩作用改造程度的量化模式，经化石壳体氧、碳同位素值的验证，这一模式基本可以用来对不同保存环境下的样品进行筛选。在对比研究中发现，以无洞贝目(Atrypida)为代表的具有柱状第三层结构的样品不仅在保存状况上优于只具有纤维层结构的壳体，而且其氧、碳同位素数值的分布也较为集中，从而说明无洞贝目的壳体是进行氧、碳同位素研究较为理想的材料。

关键词: 腕足动物, 壳体保存状态, 碳, 氧同位素, 弗拉/法门界线, 华南