塔里木盆地奥陶系“鹰山组”的解体及中下统界线的划分

THE BREAKUP OF THE ORDOVICIAN YINGSHAN FORMATION AND THE LOWER-MIDDLE ORDOVICIAN BOUNDARY IN THE TARIM BASIN

塔东北鹰山组系从上丘里塔格群中细分出的奥陶系的一个组。由于该组在塔里木盆地分布广泛,是一个重要的碳酸盐岩产油气层,因此,此组的划分和对比极为重要。国际上以牙形刺(Bartoniodus triangularis)的首现为中奥陶统的开始,但在塔里木盆地台地相区至今未发现B.triangularis,在这种状况下,建议选择短翼矢刺(Pteracontiodus exilis)的首现作为划分塔里木盆地中奥陶统界线的生物标志,并讨论鹰山组解体后两组各自在划分和对比中的作用,从而提升塔盆油气地质勘探的深度和广度。

The Yingshan Formation is part of the upper Qiulitag Group in the northeast Tarim Basin. Be- cause the Yingshan Formation is widely distribution, and it is an important carbonate reservoir, its strati- graphic subdivision and correlation is very important. According to international standard, the Lower-Mid- dle Ordovician boundary is defined at the first appearance of the conodont Bartoniodus triangularis. How- ever, B. triangularis has not yet been found in Tarim carbonate platform facies. Thus, we suggest to use the first appearance of Pteracontiodus eacilis to define the Lower-Middle Ordovician boundary within the Yingshan Formation. Accordingly, the Yingshan Formation is broken up into two formations in order to improve the precision of Ordovician stratigraphic correlation for oil and gas exploration in the Tarim Basin.