摘要:
中—晚侏罗世是东亚大地构造发展的重要转折时期,鄂尔多斯盆地周缘构造带记录了强烈的陆内多向挤压变形,其发生的动力学背景与古太平洋、西伯利亚、特提斯同时向东亚大陆汇聚产生的远程效应有关。鄂尔多斯盆地侏罗纪沉积记录了该期构造事件的发生、发展过程:(1)自早侏罗世富县期至晚侏罗世芬芳河期,鄂尔多斯盆地岩相古地理演化经历了河流-冲积扇、湖泊-沼泽、河流-三角洲和冲积扇,中侏罗统直罗组底部砾岩发育时期为湖进序列向湖退序列转换的关键时期;(2)Qm-F-Lt图解中,中侏罗统延安组砂岩投点落入了稳定克拉通范围,中侏罗统直罗组和安定组的投点落入了石英再造山旋回范围内,预示着中侏罗世直罗期,鄂尔多斯盆地周缘构造活动性迅速增强;(3)中侏罗统安定组内部发育了一套全区可以稳定对比的泥晶碳酸盐岩,生物化石发育,该套泥晶碳酸盐岩上下地层的颜色由早期的灰绿色突变为紫红色,古盐度突然升高,预示着古气候环境突变,构造活动更为强烈;(4)根据盆地内热流体的记录及相邻区碎屑锆石年龄谱特征,中晚侏罗世构造事件发生的起始、强烈活动时限分别为168.0 Ma和161.0 Ma。
Abstract:
The Jurassic era was an important period of tectonic evolution in the East Asia continent. The boundary structural belts around the Ordos Basin have recorded multi-directional compressions during the Middle to Late Jurassic period, which was dynamically associated with distant field effects that resulted from synchronous convergences of different plates (Siberia, Paleo-Pacific and Tethys) toward the East Asia continent. The generation and development of Middle–Late Jurassic tectonic events were recorded by the Jurassic sedimentation in the Ordos Basin: (1) The Jurassic sedimentary sequence from the Lower Jurassic Fuxian Formation to the Upper Jurassic Fenfanghe Formation represents a complete sedimentary cycle from the lacustrine transgression to the lacustrine regression, and the sedimentary facies include fluvial facies (Fuxian Formation), lacustrine-swampy facies (Yanan Formation), fluvial-deltaic facies (Zhiluo Formation and Anding Formation) and alluvial fan (Fengfanghe Formation). Among these facies, the Middle Jurassic Zhiluo Formation basal conglomerates mark the key period of transition from the lacustrine transgression to the lacustrine regression; (2) In the Qm-F-Lt diagram, the sandstone projection points of Yan’an Formation and Zhiluo Formation fall into the stable craton interior and quartzose recycle, respectively, which indicates that the tectonic activity increased quickly during Zhiluo Formation; (3) A set of regional contrast stable micritic carbonates was developed in the middle Jurassic Anding Formation, the stratigraphic color near the micritic carbonate changes from grayish green into purple, and the paleosalinity increases suddenly, which indicates that the ancient climate changed suddenly and the tectonic activity was enhanced quickly. (4) The Middle–Late Jurassic tectonic events initially occurred at about 168 Ma and their intensive activities took place at about 161 Ma, as evidenced by the tectonic thermal events developed in the basin and detrital zircon age spectrum obtained in the neighboring areas.
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