豫西寒武系苗岭统张夏组Talassinoides bacae 中莓状黄铁矿的成因及其生态学意义

豫西寒武系苗岭统张夏组薄层微晶灰岩中发育了大量的Thalassinoides bacae遗迹化石,利用微区X射线荧光光谱仪和扫描电镜观察,并结合能谱分析,对Thalassinoides bacae遗迹化石的元素分布及微观特征进行分析。结果表明:衬壁与围岩的元素特征相似,晕圈的Fe、Mg富集;在填充物与衬壁的边界处Fe的含量高,且有大量的莓状黄铁矿(微晶呈八面体、五角十二面体、立方体、球体和不规则形)、黄铁矿的自形单晶及其铁的氧化物。认为晕圈构造是受到铁白云石流体的影响而形成的成岩晕;莓状黄铁矿的特征表明其为生物成因,为Thalassinoides bacae的耕作行为习性提供了重要依据,表明造迹生物在潜穴衬壁的边缘培植微生物以提供食物来应对食物贫乏,这是早期生物行为习性进化及后生动物向不同环境辐射的重要标志。

FRAMBOIDAL PYRITES IN THALASSINOIDES BACAE FROM THE ZHANGXIA FORMATION (CAMBRIAN MIAOLINGIAN SERIES) IN HENAN PROVINCE: GENESIS AND ITS ECOLOGICAL SIGNIFICANCE

Amounts of Thalassinoides bacae are preserved in micrite of the Zhangxia Formation in western Henan Province. In order to illuminate the element distribution and microscopic characteristics of Thalassinoides bacae, they are observed under micro-X-ray fluorescence spectrometer and scanning electron microscope (SEM) and analyzed by energy dispersive X-ray spectroscopy (EDS). The results show that: the elements in the lining are similar with that in the surrounding sediments, Fe and Mg are enriched in the diagenetic halo indicating that this part was preferentially flowed by the dolomitizing fluids and was dolomitized; Fe is also enriched in the boundary between fill and lining; abundant of framboidal pyrites (microcrystalline pyrites occur as octahedrons, pyritohedrons, cubes, spheres and irregular shapes), single idiomorphic crystals and iron oxides are only found in the boundary of fill and lining. The characters of the framboidal pyrites show that they are likely to be related to biogenesis, and they are an important evidence of the trace maker growing microbes for supply nutrient materials to live in the restricted marine, indicating the behavior evolution and the ecological space radiation in the middle Cambrian period.