利用镜质体反射率恢复地层剥蚀厚度的新方法

Dow在1977年提出的利用上下构造层镜质体反射率 (Ro) 差值来估算不整合面地层剥蚀厚度的方法，在国内仍有广泛的应用。但国内有些学者已认识到了该方法的不合理性并提出了一些改进方法，其中最高古地温法因其思想合理而具有代表性。为了能更合理和更简便地利用Ro数据来估算不整合面地层剥蚀厚度，对最高古地温法作了改进，得到了一种利用Ro数据恢复剥蚀厚度的新方法。新方法不仅继承了最高古地温法的合理思想，而且大大简化了具体操作过程。对某一构造层恢复其顶面剥蚀厚度时，在使用Ro数据恢复剥蚀厚度的前提条件得到满足的情况下，直接将该构造层的ln (Ro)－H线性回归关系外推至ln (0.2) 处而得到近似的古地表位置，古地表位置和不整合面位置的差值即为剥蚀厚度。用最高古地温法和新方法对Dow (1977) 的实例数据进行了重新计算，分别得到2 735 m和2 537 m的剥蚀厚度，相近的结果说明了新方法的实际可行性，并且相比之下新方法操作起来更加简便。但与Dow (1977) 得出的500m剥蚀厚度相差甚远。从多个方面讨论了Dow (1977) 结果和原理的不合理性。新方法将广泛应用于多个地质分支学科中。

A new method by vitrinite reflectance to estimate thickness of eroded strata

Dow proposed a method by using the differential of vitrinite reflectance of the upper and lower strata to estimate the eroded strata thickness at an unconformity surface in 1977. This method is still widely used in China. But some Chinese scholars have already recognized the irrationality of the method and then have proposed some revising methods. Among them, the “method of the highest paleotemperature(MHP)” is representative due to its rational idea. In order to estimate the eroded strata thickness at an unconformity surface by using vitrinite reflectance data more reasonably and more conveniently, the author has improved the MHP in this paper and got a new method. The improved new method not only inherited the rational idea of MHP but also much simplified calculation process. There are some premises in estimating the eroded strata thickness of the top surface of a structural layer by using Ro data. If all the premises are established, we can directly project the linear regressive relationship between ln (Ro) and H of this structural layer upward to the value of ln (0.2) and get the approximate paleosurface’s position. The distance between paleosurface and unconformity surface is the expected erodedstrata thickness. Recalculating the Dow’s original data with MHP and the new method, we can get the results of 2735 m and 2537 m respectively. These two close results show the feasibility of the new method. And compared with MHP, the new method is more convenient. Both of the close results are far away from Dow’s result of 500 m. Then the author discusses the irrationality of Dow’s result and principle from several aspects. The new method will be widely applied in many branch disciplines of geology.