陆架边缘三角洲体系供源速率的侧向差异对地层叠加样式的控制—以珠江口盆地SQ13.8为例

Currently, two problems in sequence stratigraphic study are need to be solved in the shelf margin delta system. One problem is that mutative stratigraphic stacking patterns such as progradation, aggradation and retrogradation would be simultaneously developed in the lateral direction, due to the influence of δA/δS. As a result, system tracts are difficult to be compared laterally. The other is that the genetic analysis about stratigraphic stacking patterns is dominated by the empirical and qualitative δA analysis. Taking the SQ13.8LST in the Middle-Miocene of the Pearl River Mouth Basin as an example, we will focus on the lateral variation of stratigraphic stacking patterns in the shelf margin delta system, and study the following contents: ① analyze the “hinged systems” and its lateral δA/δS controlling the inner stratigraphic stacking patterns, boundary characteristic (MRS and SB) and sedimentary facies of LST. ② quantitatively calculate T/SF and sedimentation rate in the “hinged systems”, and take the T/SF value into the world's value system. ③ using stratigraphic sequence simulation to reconstruct the dynamic formation process of the LST, and to reveal the influence of δA/δS on lateral stratigraphic stacking patterns in the geological time scale. Results are benefit to re-understand the stratigraphic stacking patterns and boundary characteristics of the LST, and realize the laterally isochronal stratigraphic correlation of the shelf margin delta system, and broaden genesis analysis thoughts about stratigraphic stacking patterns.

关于陆架边缘三角洲体系的层序地层研究目前有2个亟待解决的问题，其一是受控于δA/δS，进积、加积和退积等地层叠加样式在侧向上会同时出现，导致体系域在侧向上难以对比；其二是地层叠加样式的成因分析以定性、经验性的δA分析为主。本研究以珠江口盆地中中新世SQ13.8LST为研究对象，紧密围绕陆架边缘三角洲体系地层叠加样式在侧向上的变化，研究以下内容：①“耦合带”及其两侧的δA/δS对LST内部地层叠加样式、LST边界（MRS和SB）以及沉积相特征的影响；②定量计算“耦合带”及其两侧的T/SF量值和沉积物供给速率，并将T/SF量值纳入全球范围内的LST量值系统；③利用地层层序模拟恢复LST的动态形成过程，揭示不同时空节点δA/δS对LST侧向上地层叠加样式的控制。研究成果有助于重新认识LST的地层叠加样式以及边界特征，实现陆架边缘三角洲体系侧向上的等时地层对比，拓宽地层叠加样式的成因分析思路。

层序地层结构三维空间变化是近年来层序地层学研究的重要命题。以往的层序地层学研究仅仅关注二维的、顺物源的剖面，但是受控于沉积物供给，等时地层单元内部叠置样式在三维空间上会发生明显变化。目前为止，关于地层叠置样式三维变化的研究仍停留在定性的、静态的观测，缺乏动态的研究。本课题聚焦于珠江口盆地SQ13.8LST，通过观测LST地层结构侧向差异，揭示陆架边缘三角洲体系“耦合带”及其两侧“沉积物供给”和“可容空间”对体系域特征、体系域界面特征（MRS和SB）以及沉积相特征的影响。建立了SQ13.8精细层序地层格架，明确了其内部由HST、FSST、LST和TST组成，整体构成了完整了基准面旋回，刻画了层序内部体系域叠置样式和沉积体系的侧向变化过程。分析了层序结构侧向差异对于等时地层对比的影响，修订了层序地层学标准化理论中关于体系域的定义。另外，以湖盆层序地层学为例，通过常规时间域和Wheeler域联合解释，确定了层序结构侧向差异在层序地层学研究中的普遍性。揭示了“沉积物供给侧向变化”和“可容空间不均一分布”对于层序地层界面、体系域叠置样式和体系域内沉积单元侧向变化的控制机理。利用正演模拟，构建LST内部准层序单元叠置的几何模型，量化了地震尺度LST可识别的极限厚度为40m。利用DionisosFlow层序数值模拟恢复了SQ13.8层序及内部体系域的动态形成过程。本研究旨在通过探究层序结构及体系域叠加样式的空间变化过程，明确“沉积物供给”和“可容空间”对其控制作用，解决层序地层学的应用问题，最终为层序地层学理论与应用研究提供重要基础。