现代地质Issue(3)：501-511,11.
安徽巢湖地区中二叠统栖霞组灰岩中燧石成因
Origin of Nodular Cherts in Limestones in Middle Permian Qixia Formation,Chaohu,Anhui Province
摘要
Abstract
The Middle Permian Qixia Formation in Chaohu area,Anhui Province,was mainly composed of fine-grained clastic rocks and limestones which were deposited in the coastal marsh and carbonate platform. Limestones were characterized by nodular and banded cherts.Most of cherts were axiolitic and moniliform in outcrops.Among some cherts and limestones developed transitional belts with 0.5 cm width around cherts.The limestones were composed of packstone and wackestone which consisted mainly of fragments of fossils and micro-crystalline calcite through polarizing microscope observation.The transitional belts were mainly composed of mi-crites and the aragonite-shell fragments which were replaced or half replaced by quartz prior to the micrites. Meanwhile the amorphous silica was found to be precipitated into the pores due to the micrites'dissolution under SEM observation in the transition belts.The chert consists of microcrystalline or cryptocrystalline quartz together with the fossil fragments.The categories of the organic matter and fossil fragments in the cherts were similar to those found in limestones,however,most of them were replaced by quartz completely.The petrology analysis of the cherts and limstones indicates that the organic acid which was produced by degradation of organic matters, would greatly increase the saturation of CaCO3 ,promote the dissolution of aragonitic fossils and marls in the sed-iment.As a result,the calcium precipitation was inhibited yet gelatinous silica precipitated as well.The geo-chemistry of nodular cherts revealed that the average ratio of Al/(Al+Fe+Mn)was 0.63,which was higher than the maximum value (0.35 )of hydrothermal deposition.The average ratio of Fe/Ti was 9.5 also lower than the minimum value (20 )of hydrothermal deposition.The Al-Fe-Mn data of the cherts fell into in the non-hydrothermal field in the Al-Fe-Mn ternary diagram.The Al2 O3 value (average 0.20%)was far beyond the other contents such as MgO,Na2 O,K2 O in the cherts and similar to the terrigenous silicon.Such geochemistry features indicated that the silica of the cherts in limestones was probably sourced from the continental materials in research area.关键词
燧石结核/过渡带/灰岩/硅质来源/中二叠统栖霞组/安徽巢湖地区Key words
nodular chert/transitional belt/limestone/source of silica/Middle Permian Qixia Formation/Chaohu,Anhui Province分类
天文与地球科学引用本文复制引用
杨锐,李红,柳益群,雷川,雷云,冯诗海..安徽巢湖地区中二叠统栖霞组灰岩中燧石成因[J].现代地质,2014,(3):501-511,11.基金项目
国家自然科学基金项目（40802024，41272115，41272116）。 （）
