有孔虫壳体内草莓状黄铁矿成因及其地质意义——以湖北雁门口地区栖霞组有孔虫化石为例

Formation of Pyrite Framboids in the Chamber of Foraminiferas and Its Geological Significance:A Case Study of the Foraminiferas Fossilsi n the Qixia Formation in the Yanmenkou Area,Hubei Province

在湖北省京山县雁门口地区栖霞组上部的含泥灰岩中存在丰富的节房虫科底栖有孔虫化石,主要有节房虫属、厚壁虫属和郎格虫属,壳体均被草莓状黄铁矿充填。对其系统的显微镜、扫描电镜观察和黄铁矿的能谱分析结果发现,黄铁矿草莓体直径最大为15μm,平均约10μm,硫铁原子比值(S/Fe)为1.90±0.10,表明在黄铁矿形成过程中,有孔虫壳体空腔内呈轻度-中度贫氧的微环境。在分析该类黄铁矿成因的基础上,认为有孔虫壳体内的黄铁矿在指示沉积环境和保存环境方面具有局限性。

Abundant benthic foraminiferas, identified mainly as Nodosaria, Pachyphloia and Langella, were discovered in the muddy limestone of the Qixia Formation in Yanmenkou area, Jingshan County, Hubei Province. Most of the foraminiferas chamber were filled by pyrite framboids. Systematic microscopic, scanning electron microscopic observations and energy spectrum analysis of pyrite were catTied out. The maximum diameter of pyrite framboids is 15 μm, and the average is about 10 μm. The sulfur to iron atom ratio （S/Fe） is 1.90 ±0.10. All these features indicate that these chamber were formed under a weak to moderate dysoxic micro-environments. Based on the discussion of the formation mechanisms of pyrite framboids, it is thought that these pyrite framboids in foraminiferas chamber have restricted significance in the study of deposition and diagenesis environment.