浙江石浦下白垩统灰岩微相分析与锆石U-Pb年代学研究

摘要

Through the synthetic lithofacies studies for the Shipu limestone section located in Xiangshan, Zhejiang Province, four types microfacies can be recognized, i. e. bioclasts micrite, oolite micritic limestone, stromatolite marlite, and thin lamina-banded limestone, and they formed in tidal flat, oolitic beach and shallow environments, accordingly. Based on the researches of the cyclostratigrapy, the Shipu limestone can be divided into four sedimentary cycles which record three major transgressions. Furthermore, zircon LA-ICP-MS U-Pb dating has been conduced for the tuff beds from the base and top of the section for the first time. The new radiometric age data indicated that the Shipu limestones deposited in the Early Cretaceous age from 114. 2 Ma to 96. 3Ma. We believe that these results should stir up a new thought on the depositional environment and tectonic background of Early Cretaceous in southeast of China%通过对浙江象山石浦灰岩剖面系统的岩相学研究,总结出4种基本灰岩微相类型,即生物碎屑泥晶灰岩、泥晶鲕粒灰岩或鲕粒泥晶灰岩、叠层石泥灰岩、薄层一条带状泥灰岩,其形成于潮坪、鲕粒滩和浅海等三种沉积环境.结合整个剖面岩性变化规律,划分出4个沉积旋回,反映了3次主要海侵过程.并利用LA-ICP-MS锆石U-Pb 同位素定年技术,首次获得了该剖面下部凝灰岩夹层中锆石U-Pb年龄为114±2Ma,确定了该剖面形成时代为早白垩世.这一成果对于深化我国东南沿海早白垩世构造—沉积环境的研究具有重要意义.