陆相断陷盆地二级层序时限构造沉降与湖平面变化的响应关系

Lake-level Variation Response to Tectonic Subsidence in a Second-Order Sequence of Continental Rift Basin

针对陆相断陷盆地构造沉降与湖平面变化的响应关系问题,笔者通过二维回剥分析,并引入沉降通量和沉降速率通量两个参数以评价盆地沉降的整体特征。黄骅坳陷中区东营组二级层序内三角洲体系发育,可细分为4个三级层序,构造沉降上呈减弱到增强的变化,并具有断陷作用逐渐减弱、坳陷作用加强的特点。拟合构造沉降、沉积演化、层序结构的关系表明,湖平面下降、三角洲的繁盛与快速构造沉降耦合一致,湖平面下降是不均衡的强烈构造沉降导致湖水体积向控凹断层或坳陷中心重新分配、且四周水系的补充滞后于构造沉降产生的新增可容纳空间的结果。相反,湖平面上升和深湖相发育与慢速构造沉降耦合一致。此外,湖平面变化与构造沉降总量的大小无关。

To pursue the lake-level variation response to tectonic subsidence in the continental rift basin, this paper introduced two parameters （subsidence flux and subsidence velocity flux） to show the whole characteristics of basement subsidence by using two-dimensional stripping-back analysis. In the Dongying Formation of the middle Huanghua depression, the delta depositional system is well developed. The Dongying Formation, as a second-order sequence, can be subdivided into four third-order sequences. Tectonic subsidence gradually weakened and subsequently strengthened during the development of the Dongying Formation, characterized by intense rift faulting followed by later increasing down-warping. Combined with tectonic subsidence, depositional evolution and se- quence framework of the Dongying Formation, this paper holds that the fall of the lake-level and the flourishing of the delta depositional system were eoupled with rapid tectonic subsidence, and the lake-level fall resulted from violent unbalanced tectonic subsidence, causing redistribution of lake-water towards main faults or down-warping centers. The lake-water supplement was insufficient compared with the newly increased accommodation space due to tectonic subsidence. As a result, the rise of the lake-level and the development of the deep lake corresponded to slow tectonic subsidence, and the lake-level variation had nothing to do with the gross of tectonic subsidence.