下扬子巢湖地区下三叠统瘤状灰岩成因再探讨

巢湖地区下三叠统整体沉积于较深水环境，广泛发育瘤状灰岩。针对目前该瘤状灰岩成因机制认识争议较大的现状，文中依据野外实地观测及室内宏观、微观的系统观察，结合沉积环境和成岩作用与瘤状灰岩形成的关系分析，对瘤状灰岩的成因机制进行综合的探讨。研究表明瘤状灰岩的形成是沉积和成岩作用综合作用的产物，沉积时期不平整CCD界面的周期性浮动是造成瘤状灰岩细颈化的基础，而CCD界面的周期性浮动可能与早三叠世气侯冷暖周期性变化以及海底底流作用有关。后期基质泥岩中酸性孔隙水的溶蚀是造成瘤状灰岩细颈处折断的重要原因，压溶作用产生的局部应力场变动造成瘤状灰岩瘤体杂乱状分布。而前人总结的3种瘤状灰岩，即顺层串珠型、断续型和杂乱型瘤状灰岩，是在沉积与成岩改造作用逐渐加强条件下依次形成。

Reappraisal of the Origin of Lower Triassic Nodular Limestonein the Chaohu area,Lower Yangtze Region

The Lower Triassic deposited in deep-water environment in Chaohu area, in which nodular limestone was widely developed.Some previous genetic analysis of Lower Triassic nodular limestone had not come to consensus. Based on the method of fieldobservation, indoor macro, micro observation and the consideration of the relationship between sedimentation and diagenesis within nodular limestone genesis, we made a comprehensive analysis of the nodular limestone genesis. The research results indicated that nodular limestone was a product of both sedimentation and diagenesis. The periodic fluctuation of carbonate compensation depth (CCD) interface is the basis of the nodular limestone necking phenomenon occured in the sedimentary period, while the periodic fluctuation of CCD interface was related to periodic change of climate and dissolution of bottom current in the Early Triassic. The dissolution of acid pore water was an important reason which causes the break of nodular limestone necking phenomenon. The disorder distribution of nodular limestone was mainly caused by the local stress field resulting from pressolution. Three kinds of nodular limestone summarized before, namely, banded nodular limestone, discontinuous nodular limestone and random nodular limestone, were formed by gradually enhancement of sedimentation and diagenesis.