川北地区下寒武统筇竹寺组钙质结核特征及成因机制

发布时间：2018-04-08 08:11

本文选题：钙质结核　切入点：裂缝　出处：《沉积学报》2017年04期

【摘要】：不同成因的钙质结核在研究沉积水体、早期成岩环境及泥页岩的压实程度方面具有重要意义。通过对川北地区旺苍县下寒武统筇竹寺组钙质结核抛光,发现结核内部具有层理、暗色圈层和张裂缝构造。结核和围岩的层理关系和具有漂浮状的微观结构特征表明,该地区结核是形成于压实作用之前的成岩早期结核。对结核中Al、Ti、Ca、K、Na元素分析表明,结核的元素分布受到结核内部裂缝的影响。结核内部富含生物碎屑和其形成深度为数十米的特征,推测结核主要是在硫酸盐还原带生长。结核具有暗色圈层之间层理不弯曲和元素移动的特征,揭示了结核为透入性生长,在整个结核生长阶段就开始大量同时结晶。Mg/Ca和Sr/Ca的比值说明,结核内部钙质成分为富镁方解石—生物成因方解石。结核中富含钙质成分的原因可能是围岩中的生物成因方解石大量向结核运移所致。裂缝的形态特征表明,裂缝为张裂缝。对结核上部地层的沉积特征研究表明,张裂缝的成因很可能与筇竹寺顶部的浊积岩和沧浪铺组底部的似瘤状灰岩快速搬运沉积有关。
[Abstract]:Calcareous nodules of different origin are of great significance in studying sedimentary water bodies, early diagenetic environments and the compaction degree of shale.By polishing the calcareous nodules of the Lower Cambrian Qiongzhusi formation in WangCang County, northern Sichuan Province, it is found that the inner nodules have bedding, dark layer and tensional fracture structure.The stratigraphic relationship between nodule and surrounding rock and the characteristics of floating microstructure indicate that nodule in this area is an early diagenetic nodule formed before compaction.The element distribution of the nodules is influenced by the internal cracks of the nodules.The nodules are rich in bioclasts and their formation depth is tens of meters. It is assumed that the nodules mainly grow in the sulfate reduction zone.The characteristics of stratification and element movement between dark layers indicate that the nodules are permeable growth, and the ratios of mg / Ca and Sr/Ca in the whole growth phase of the nodules begin to be large amounts at the same time.The internal calcium composition of tuberculosis is magnesium-rich calcite-biogenic calcite.The reason for the rich calcium in the nodules may be the mass migration of biogenic calcite to the nodules.The morphological characteristics of the fracture indicate that the fracture is an extensional fracture.The sedimentary characteristics of the upper nodule strata indicate that the genesis of the Zhang fracture is probably related to the turbidite at the top of Qiongzhusi and the nodular limestone at the bottom of the Canglangpu formation.
【作者单位】：西南石油大学地球科学与技术学院;中石油碳酸盐岩储层重点实验室沉积与成藏分室西南石油大学;
【基金】：中国石油科技创新基金项目计划(2016D-5007-0102) 国家科技重大专项(2016ZX05004002-001)~~
【分类号】：P512.2;P588.2

【参考文献】