鲁西南地区官庄群的地层对比及时代讨论

STRATIGRAPHIC DIVISION AND CORRELATION OF THE GUANZHUANG GROUP IN SOUTHWEST SHANDONG

官庄群主要出露于鲁西南地区的平邑盆地和蒙阴盆地,由于盆地范围较小,岩性横向变化大,地层划分对比较为困难,加之露头区植被覆盖严重,以往发现的生物化石较少,时代归属上各家观点不一。在野外剖面实测及钻井剖面系统采样分析的基础上,依据所获大量的介形虫、轮藻和腹足类化石(其中许多系首次发现),与国内外同期沉积盆地进行了横向对比,提出与以往地层划分意见相比有重大改动的新方案,即:鲁西南地区官庄群固城组和卞桥组底部地层属上白垩统,卞桥组其余部分属下古新统,常路组为中、上古新统,朱家沟组为下始新统,大汶口组划归下始新统至中始新统。

The Guanzhuang Group crops out in the Pingyi and Mengyin Basins in southwestern Shandong Province. The Guangzhuang Group is difficult to correlate because of the small size of the basins and significant facies variations. In addition, the age of the Guangzhuang Group is not well constrained because of poor outcrop exposure and lack of diagnostic fossils. We collected abundant ostracod, charophyte, and gastropod fossils from outcrop and drill core samples. These new data form the basis of revised biostratigraphic correlation with other basins. The revised correlation suggests that the constituent formations of the Guangzhuang Group range from Upper Cretaceous to Middle Eocence. In ascending order, the Gucheng Formation and basal Bianqiao Formation are Upper Cretaceous, the rest of the Bianqiao Formation is Lower Paleocene, the Changlu Formation is Middle-Upper Paleocene, the Zhujiagou Formation is Lower Eocene, and the Dawenkou Formation is Lower-Middle Eocene.