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