浙江石浦下白垩统石浦群沉积相、层序及相对海平面变化

The Sedimentary Facies,Sequences and Relative Sea Level Change of the Lower Cretaceous in the Shipu,Zhejiang

通过对浙江石浦下白垩统石浦群的野外和镜下分析,划分出19个岩石微相,进一步细分出14个碎屑岩岩石微相和5个碳酸盐岩岩石微相。综合相关沉积构造特征,岩石微相横纵向组合特征,以及对沉积过程的推测,识别出3个主要的沉积相:扇三角洲相、潮坪相和滨海—浅海相。根据剖面上发育的4个不整合面,以及1个沉积趋势由向上变浅到向上变深转换的突变面识别出5个层序界面,结合各层序内部特征,将石浦剖面划分出5个发育海侵体系域和海退体系域的T-R层序,以及1个仅发育海退体系域的层序。根据各层序内沉积相类型的变化特征、体系域叠置方式初步重建石浦地区早白垩世相对海平面升降曲线。发现阿普特阶—阿尔必阶,该地区相对海平面在四级旋回多次波动叠加的基础上,在三级旋回尺度上呈现逐渐上升的趋势。结合前人在该剖面建立的同位素年龄格架以及全球海平面变化,发现石浦剖面的相对海平面变化和全球海平面变化高度耦合,仅在119~116 Ma和104~100 Ma存在差异。结合石浦剖面火山岩的发育特征,以及出现海平面变化差异的时间段与大规模火山岩发育的时间段耦合,推测全球海平面变化和区域构造是影响石浦地区相对海平面变化的两个主要因素。

Based on detailed study on the macroscopic and microscopic sedimentary features of the Shipu Group in the Xiangshan,19 lithofacies were recognized(including 14 detrital rock lithofacies and 5 carbonate lithofacies).According to the sedimentary interpretations of lithofacies,sedimentary structures,and microfacies associations,we recognized three major facies for the Shipu Group(i.e.,fan delta,tidal flat,and the offshore-shallow sea).Based on the unconformity and sedimentary trend mutants identified in the Shipu section,5 intact T-R sequences and 1 poor-preserved T-R sequence which only contains the regressive systems tract were suggested in the Shipu section,and the regional change of relative sea level was established by the superposition mode of systems tract and types of facies.The results indicated that the third-order changes of the relative sea level in the Shipu area is characterized by persistent transgression during the period from the Aptian to the Albian,but the forth-order changes of relative sea level fluctuate frequently.The changes of relative sea level in the Shipu section largely coincided with the changes of eustatic sea level during Aptian-Albian.However,the relative sea level elevated during the time of 119-116 Ma and 104-100 Ma which deviated from the eustatic sea level.Considering the intense volcanic activity in these periods,we suggested that the changes of the relative sea level in the Shipu section were controlled by the eustatic sea level and regional tectonic activity.