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强迫型海退是海平面(或基准面)下降产生的海退过程,从而区别于正常海退。在克拉通盆地中,强迫型海退常产生沉积基底的暴露并且产生沉积间断,在特定背景下,也会留下相应的沉积记录,北京西郊下苇甸剖面张夏组就是一个典型实例。在该张夏组由一个三级层序构成,进一步可划分为3个四级层序。有序的沉积相序列形成的张夏组,快速加深事件不但产生淹没不整合型层序界面,而且形成了张夏组中下部更多的陆棚相泥岩和泥灰岩沉积;但是,在其顶部,鲕粒滩灰岩的发育就成为对强迫型海退进程的响应。因此,上述现象为研究张夏组鲕粒滩的发育特征提供了重要线索,也为大范围的研究提供了一个概念性模型。
Forced regression is the regression of sea level (or datum) decline, which is different from the normal regression. In the craton, forced-type seafloor often generates sedimentary basement exposures and produces sedimentary discontinuities, leaving corresponding sedimentary records under certain background. The Zhangxia Formation of the reedmetric section in the western suburbs of Beijing is a typical example. The summer group consists of a three-level sequence, which can be further divided into three fourth-level sequences. In the Zhangxia Formation formed by the sequence of sedimentary facies, the rapid deepening events not only resulted in submerged unconformity-type sequence boundaries but also formed more shelf facies mudstones and marl deposits in the middle and lower parts of the Zhangxia Formation. However, At the top, the development of oolitic beach limestone became a response to the forced reversion process. Therefore, the above phenomena provide important clues for studying the developmental characteristics of oolitic beach in Zhangxia Formation and also provide a conceptual model for a large-scale study.