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鄂尔多斯地区南缘奥陶纪可划分为１２个层序（ｓｅｑｕｅｎｃｅｓ）．本区奥陶纪地壳演化正处于重要关键时期，早奥陶世（冶里－亮甲山期、马家沟期、峰峰期）为被动大陆边缘，划分为７个层序．海平面突然上升，尔后逐渐下降．中、晚奥陶世（赵老峪期、上店期）演化为主动大陆边缘，可划分为５个层序．海平面就鄂尔多斯地区整体而言发生大规模海退，露出海面．但就鄂尔多斯地区南缘则海水突然加深，随后海平面渐渐下降．晚奥陶世卡拉道克世末鄂尔多斯地区海水全部退出．
Ordovician southern margin Ordovician can be divided into 12 sequences (sequences). The Ordovician crustal evolution in this area is at an important and crucial period. The Early Ordovician (Yeli - Liangjishan, Majiagou, and Fengfeng periods) is a passive continental margin and is divided into seven sequences. Sea level suddenly rose, then gradually declined. Middle and Late Ordovician (Zhao Laoyu period, Shangdi period) evolved into active continental margin, can be divided into five sequences. Sea level on the whole Erdos area in large scale regression, exposing the sea. However, on the southern margin of Ordos, seawater suddenly deepened, and then the sea level gradually decreased. Late Ordovician Karadak end of the Ordos region all the water out.