摘要
华南中二叠统栖霞组沉积了一套特殊的碳酸盐岩地层,该套地层富含有机质和硅质结核,是中国南方四套区域性海相烃源岩之一.在野外露头上,灰岩-泥灰岩韵律层因为其抗风化能力不同而受到广泛关注,其在整个华南栖霞组分布广泛.其中,灰岩层富含各种生物碎屑,主要包括钙藻、有孔虫和腹足,其次还有腕足,棘皮类和介形虫,偶尔见苔藓虫和三叶虫.灰岩层中较好的保存了易碎的钙质藻类,说明灰岩的胶结作用发生在成岩早期,没有明显压实作用的痕迹.泥灰岩以粒泥生物碎屑灰岩和黑色钙质泥岩为主,主要的生物碎屑以腕足和介形虫为主.生物碎屑都非常破碎,壳体大都平行层面,颗粒之间发育大量压溶缝,说明泥灰岩层经历过强烈的成岩压实作用.基于对灰岩-泥灰岩韵律层的生屑类型和成岩现象的分析,提出差异成岩作用来解释该套地层的形成过程:泥灰岩层中不稳定的文石在早期成岩过程中溶蚀,然后迁移到灰岩层中形成方解石胶结灰岩层;随后机械压实作用和化学压实作用主要发生在泥灰岩层中;最终灰岩-泥灰岩层由于差异成岩作用导致其抗风化能力不同而形成不同的露头特征.其中文石溶蚀发生在海水埋藏环境,有机质的分解为其提供了动力来源,这与栖霞期较高的原始生产力相符合.
The Middle Permian of South China is a unique carbonate succession, which is rich in organic matter and chert nod- ule, and is one set of the most important marine source rocks. Limestone-marl alternations are widely distributed in this area. The limestones are rich in skeletal detritus, dominated by algae, foraminifera, and mollusks with subordinate amounts of bra- chiopods, echinoderms, and ostracods, and minor bryozoans and trilobites. Fragile skeletons such as calcareous algae were well preserved, indicating that cementation took place during early diagenesis with little diagenetic compaction. Marls are bioclastic wackestone or dark mudstone. Bioclasts are diverse, including remnants of brachiopods, ostracods and rare trilobites. Bioclastic flakes are oriented parallel to bedding planes, and thin-shelled fragments, e.g., ostracods, are broken due to compaction of the unlithified sediment. Between the particles are micrite and a large number of dissolution seams. As to the particular features of the limestone-marl alternations, it is inferred that differential diagenesis occurred between limestones and marls. Aragonite in marl layers was dissolved to cement limestone, which took place in shallow-burial realm. Mechanical compaction and then pres- sure dissolution were concentrated in the less cemented strata. The dissolution of aragonite in the shallow marine burial realm is thought to have been initiated by modification of the pore-water chemistry by bacterial oxidation of organic matter.
出处
《地球科学（中国地质大学学报）》
EI
CAS
CSCD
北大核心
2014年第2期155-164,共10页
Earth Science-Journal of China University of Geosciences
基金
国家自然科学基金项目(No.41072078)
国家重点基础研究发展计划(No.2011CB808800)
关键词
灰岩-泥灰岩韵律层
文石
方解石
沉积岩
栖霞组
华南
limestone-marl alternations
aragonite
calcite
sedimentary rocks
Qixia Formation
South China.
