回剥分析(backstripping)是盆地沉降史分析的核心方法, 应用极为广泛; 但对其分析结果的不确定性及参数对分析结果的影响的关注甚少。以珠江口盆地白云凹陷地区为例, 探讨了原始数据和选用参数(包括无钻井揭示的基底埋深和界面年龄、地层划分、孔隙度随深度变化曲线、沉积岩性、古水深和全球海平面变化等)对回剥分析结果的影响。理论分析和灵敏度试验表明, 无钻井揭示的基底埋深的误差影响回剥分析的所有结果; 界面年龄的误差仅影响对沉积速率和构造沉降速率的估计; 岩性的影响反映在选取密度和孔隙度随深度变化的曲线参数之中, 孔隙度在不同地区可能有较大差异; 而古水深是回剥分析参数中不确定性最大的因素, 古水深的误差不影响去压实厚度和沉积速率, 但却100%成为构造沉降量的误差。由于陆坡区古水深和岩性随位置的变化较大, 这两种参数对陆坡区回剥分析结果的影响尤为显著, 需要采用随位置而变的参数, 特别需要综合利用各种地质地球物理资料估计各地层沉积时的古水深变化。数据的不确定性及参数选取的不当有可能导致谬误的结果, 因此发表回剥分析结果时应该说明主要参数的选取依据, 而对于文献中发表的回剥分析结果则必须在考察其数据和参数的不确定性后才能考虑采用与否。
Backstripping is an important and widely used method for basin subsidence analysis. Little attention has been paid on the uncertainty of its results. In this paper, we address this issue based on a study of the Baiyun Sag in the Pearl River Mouth Basin. We demonstrated through theoretical analysis and sensitivity tests that the uncertainty in the non-recovery of the basement depth will pass on to all the results of backstripping, but the uncertainty in age only affects the estimations of sedimentary and subsidence rates. Formation lithology influences the selection of porosity and density parameters. The porosity-depth curves of sandstone and shale vary from area to area. Largest uncertainty comes from paleo-water depth, whose error is 100% inherited by the calculated tectonic subsidence. In the slope area, paleo-water depth and lithology vary significantly with locations. Thus, it is essential to use the paleo-water depth and lithology parameters that are variable with locations. The uncertainty in the source data and inappropriate parameters may lead to erroneous results. Caution should be taken when reading published backstripping results. The quality of parameterization needs to be examined before adopting the results.
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