摘要： 在现代和古代碳酸盐沉积物中,碳酸盐鲕粒的包壳结构类型均较多,因其常被用于恢复古海洋的化学、物理性质演化而备受关注。对碳酸盐鲕粒包壳的研究始于 1879年,此后现代和古代鲕粒包壳的原生和次生结构特征和成因均得到了详细描述和深入探讨;然而,目前仍存在对现代鲕粒包壳原生结构的部分术语定义不明确、对古代鲕粒包壳原生结构的特征识别和分类不尽准确等问题。文中归纳了现代鲕粒包壳的原生结构类型及其主要特征,指出鲕粒包壳结构组合的常见类型包括放射状、同心状、同心—放射状等,且对包壳结构组合类型的识别是鲕粒包壳结构研究的关键。古代鲕粒受成岩作用影响,包壳原生结构保存程度可能不尽相同,甚至完全被次生结构所替代,但其原生结构类型与现代鲕粒类似,以放射状和同心状结构为主,只是同心状结构中的切线状纹层难以识别。中国的古代鲕粒研究虽已取得大量成果,但在对包壳原生结构的识别和应用方面尚存在一些误区,故在借鉴现代鲕粒包壳结构研究成果的基础上,笔者以华南下奥陶统鲕粒为例,论述了对古代鲕粒包壳结构如何进行特征描述、如何识别出保存较好的原生结构及如何利用包壳结构组合类型进行鲕粒分类等问题,展示了古代鲕粒包壳原生结构研究的重要科学意义。

关键词: 鲕粒, 包壳, 原生结构, 放射状结构, 同心状结构

Abstract: Carbonate ooids in modern and ancient carbonate sediments have varieties of cortical structures,which have been intensively studied because of its applications in reconstruction of chemical and physical changes of the ancient ocean. Research on cortices of carbonate ooids started in 1879. Since then,the features and origins of primary and secondary cortical structures of modern and ancient ooids have been described in detail and discussed in depth. However,definitions of terms are unclear in the studies on primary cortical structures of modern ooids; the descriptions and classification of primary cortical structures of ancient ooids are also inaccurate and require further determination. This article summarizes previous researches on modern ooids,concludes the types of primary cortical structures and their main features,and points out that the recognition of assemblage types of cortical structures is a key step to the studies on cortical structures. Normal assemblage types of cortical structures include radial,concentric and radial-concentric. Affected by diagenesis,primary cortical structures in ancient ooids may be preserved at different degrees,or totally replaced by secondary structures. Primary cortical structure types preserved in ancient ooids resemble those in modern ooids of which the dominant are radial structure and concentric structure. However,among concentric structures in ancient ooids,the tangential laminae is hard to recognized. Domestic research on ooids has obtained a lot of achievements,some of which however still misrecognized or misused primary cortical structures. On the basis of reference to researches on cortical structures of modern ooids,we take the Lower Ordovician ooids in South China as a case to show how to describe the features of cortical structures of ancient ooids,recognize well-preserved primary cortical structures,and classify the ooids by assemblage types of cortical structures.

Key words: ooid, cortices, primary structure, radial structure, concentric structure

中图分类号: 

• P588.24+5