正星介(Cyprideis)初现面对柴达木盆地上油砂山组和下油砂山组分界的意义

Significance of First Appearance Datum of Cyprideis for Division of Shangyoushashan and Xiayoushashan Formations in Qaidam Basin

柴达木盆地磁性生物地层柱上标定介形类浪花介科正星介属(Cyprideis)出现,其爆发的时代为中中新世晚期,大约距今12Ma。这是该盆地上油砂山组/下油砂山组分界对比的重要依据,也是地震T2′反射界面在全盆地追索对比和验证的重要标志。正星介属爆发点在塔里木盆地和准噶尔盆地也清晰可辨,对该两盆地新近系内部对比划分以及与柴达木盆地对比发挥了重要作用。油气勘探过程中大量钻井少取心,多取岩屑,并绘制分析自岩屑的正星介丰度曲线,基本上可以划定上油砂山组和下油砂山组之间的分界。

The appearance of fossil Cyprideis was demarcated on the magnetic biostratigraphic column in Qaidam Basin. The eruptible time of Cyprideis is at the later Middle Miocene, about 12Ma ago, which is the important evidence to divide the boundary between Shangyoushashan Formation and Xiayoushashan Formation, and also key mark that seismic T2 reflect interface is used to trace and validate whole basin. The eruptible point of Cyprideis can be recognized clearly in Tarim and Junggar Basins, which has been played an important role in the stratum classification and contrasting of Neogene inside in these two basins as well as comparing with that in Qaidam Basin. It is suggested that the boundary between Shangyoushashan and Xiayoushashan Formation would be determined basically through sampling few core and much debris and drawing the abundant curve of Cyprideis existed in debris.