鄂尔多斯地区南缘奥陶纪层序地层及海平面变化

HIGH-FREQUENCY CARBONATE CYCLES OF EARLY PALEOZOIC IN THE SOUTHERN MARGIN OF ORDOS BASIN

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．

Four evolutional stages including low-energy and high-energy ramp, rimmed shelf with restricted inner-shelf basin, rimmed shelf with envoloped inner-shelf basin and carbonate faulted margin can be distinguished for Early Paleozoic carbonate platform in the southern margin of Ordos basin. Each stage developed different high-frequency cycles, suggesting that the depositional setting controlled the diversity of carbonate high-frequency cycles. The 4:1 bunding of fifth-order cycles within fourth-order cycles and the 5:1 bunding of sixth-order cycles within fifth-order cycles as well as calculation of period for cycles within the first stage show that the driving force is related to Milankovitch orbital periodicity.