柴达木盆地自然伽玛曲线在古气候及沉积环境研究中的应用

应用自然伽玛测井（GR）曲线反演古气候和古环境的方法在国际上逐渐得到重视并取得了进展，柴达木盆地第四纪应用其反演2.85Ma B.P来的古气候变化也取得了成功。本文以柴达木盆地侏罗系冷科1井和雨33井自然伽玛曲线并结合孢粉等地质资料进行了古气候与沉积环境分析，证明GR曲线是有价值的古气候研究参数。GR值的大小及古气候的干湿变化和沉积水体的深浅变化均有内在联系，GR曲线振幅与频率的变化快慢反映出沉积环境动荡与稳定的相对特征，据此对两口井的沉积环境演变作了具体分析。结合古气候与沉积环境综合分析，GR曲线的异常波动还具有特殊的指相意义。GR值增大-古气候加湿-沉积水体加深的同步表现特征是一般性规律，构造-古地理背景的变动可改变这一对应关系，因而提供了研究古地理演变的信息，进一步丰富了GR曲线研究的地质涵义。说明在侏罗纪古气候和古环境研究上，GR曲线是一有价值的参考指标。

APPLICATION OF GAMMA RAY LOG TO STUDY ON PALAEOCLIMATE AND SEDIMENTARY ENVIRONMENTS OF THE JURASSIC IN QAIDAM BASIN

Inversion of climate and palaeoenvironment using gamma ray (GR) log has been highlighted and developed increasingly in the world.Application of inversion to the palaeoclimate changes before 2.85 million years has succeeded in Quaternary in Qaidam Basin.It is shown that gamma ray log is an important parameter for palaeoclimate research and an analysis of palaeoclimate and palaeosedimentary environment in combination of gamma ray log with sporopollen data and other geological data from two wells in Quaternary Qaidam Basin. Both value sizes of GR and dry/wet changes of palaeoclimate have internally related to the depth of depositional water body. Quick/slow variations of the frequency and amplitude of GR log can show relatively the active and stable characteristics of sedimentary environment. For this, a specific analysis on the evolution of sedimentary environment of the two wells was made. The inversion of the palaeoclimate and sedimentary environment shows that the abnormal variation of GR curve is of a special implication in sedimentary facies. The variations of tectonic-palaeogeography background could change the corresponding relation which is characterized as a general regularity by a synchronization of the GR log value-increasing, the palaeoclimate-wetting, and the depositional water-deepening. Therefore, information of a palaeogeography development is presented, which enriches a geological implication of GR log investigation further. It is demonstrated that GR log is a significant indicator for studying the Jurassic palaeoclimate and palaeoenvironment.