柴达木盆地昆2井古近系下干柴沟组上、下段分界探讨

青海油田和中国石油大学（北京）合作,在柴达木盆地昆2井井深5120～5140 m发现南星介化石带。通过对比柴西地区和柴北缘地区南星介化石带的发现层位,并将该化石带顶界在地震剖面上进行标定追索,认为南星介（Austrocypris）是柴达木盆地下干柴沟组下段上部的标准化石。从发现南星介化石并标定有T4反射界面的冷科1井（或深88井）开始,沿地震测线向昆2井进行追索,经时深转换,将昆2井5040 m处标定为下干柴沟组上段与下段的分界。两井之间T4（下干柴沟组上、下段分界）、南星介化石带顶界和T5 （下干柴沟组底）呈3条平行线,表明其得到闭合验证,下干柴沟组上、下段的分界划分合理。因此,生物地层学与地震地层学相结合,可以有效地对比柴达木盆地陆相新生界红色碎屑岩区的地层。

Discussion on boundary between the upper and lower members of Xiaganchaigou Formation of Paleogene in Well Kun-2, Qaidam Basin

Through the collaboration between Qinghai Oilfield Company and China University of Petroleum(Beijing), ostracoda Austrocypris fossil zone was found in the interval about 5120 m to 5140 m in Well Kun 2, Qaidam Basin. By correlating with the  Austrocypris fossil zone in the western and northern margins of the Qaidam Basin, its top boundary was calibrated with a seismic event and traced on the seismic profile. The results indicate that the Austrocypris is an index fossil of the upper part of Lower Member of Xiaganchaigou Formation in the Qaidam Basin. Tracing along the seismic lines from Well Lengke 1(or Shen 88) in which Austrocypris was found and T4 seismic reflector surface was marked, to Well Kun 2, after time to depth coversion the boundary between the upper and lower members of Xiaganchaigou Formation is determined to be at about 5040 m in Well Kun 2. The T4 seismic reflector surface, the top boundary of Austrocypris fossil zone and the T5 seismic reflector surface（at the bottom of Xiaganchaigou Formation） are always parallel with one another between the two wells. The boundary between the upper and lower members of Xiaganchaigou Formation is reasonable and its position is supported by the loop correlation of seismic events. In conclusion, combining biostratigraphy with seismic stratigraphy, an effective correlation of the Cenozoic stratigraphic succession of  the red continental clastic rocks in the Qaidam Basin has been obtained.