沉积学报2017，Vol.35Issue(4)：681-690,10.DOI:10.14027/j.cnki.cjxb.2017.04.003
川北地区下寒武统筇竹寺组钙质结核特征及成因机制
Characteristics and Genetic Mechanism of Calcareous Concretions in the Early Cambrian Qiongzhusi Formation of Northern Sichuan Basin
摘要
Abstract
Calcareous concretions of different genesis have a great significance in the study of early diagenetic environment, the sedimentary water body and shale of compacted degree.By polishing, the calcareous concretion shows the interior textures including bedding, dark circles structure and tension cracks during the lower Cambrian Qiongzhusi stage in Wangcang, north of Sichuan Basin.The relationship of concretions and surrounding rock of bedding and the preservation of sedimentological micro-features in the concretion matrix point to an early diagenetic concretions and forming before compaction.Not obvious systematic geochemical variations including Al, Ti, Ca, K, Na from concretion center to edge suggests that the element distribution of concretions are affected by cracks.The rich bioclastic and forming about tens meters under the sediment-water interface suggest the concretions may primarily grow during sulfate-reduction.The two characteristics which the beddings are not deformed among the concentric circles and the move of elements reveal that the concretions are pervasive growth which the calcium crystallites of the concretions nucleated at virtually the same time across the entire concretion.The ratios of Mg/Ca and Sr/Ca indicate that the internal calcium components of concretions is magnesium-rich calcite and biogenic calcite.The large migration of calcium in the biogenic calcite of the surrounding rock lead to the rich calcium component in the concretions.Fracture morphology shows the crack is tension cracks.The rapid transportation and deposition of turbidite at the top of Qiongzhusi Formation and analogous-nodular limestone at the bottom of Canglangpu Formation may be the cause of tension cracks.关键词
钙质结核/裂缝/筇竹寺组/成因机制/川北地区Key words
calcareous concretions/crack/Qiongzhusi Formation/genetic mechanism/northern Sichuan Basin分类
天文与地球科学引用本文复制引用
庞谦,李凌,胡广,谭秀成,马腾,赵东方,芦飞凡,陈虹宇,熊鹰..川北地区下寒武统筇竹寺组钙质结核特征及成因机制[J].沉积学报,2017,35(4):681-690,10.基金项目
中国石油科技创新基金项目计划(2016D-5007-0102) （2016D-5007-0102）
国家科技重大专项(2016ZX05004002-001)Science and Technology Innovation Foundation of CNPC, No.2016D-5007-0102 （2016ZX05004002-001）
National Science and Technology Major Project of the Ministry of Science and Technology of China, No.2016ZX05004002-001 （）
