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

Key words: 
• lower Cretaceous /
• Shipu Group /
• sedimentary facies /
• T-R Sequence /
• relative sea level

Abstract: 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.