鄂尔多斯盆地晚三叠世延长期古湖盆生物相带划分及地质意义

鄂尔多斯盆地晚三叠世发育大型坳陷型湖盆。湖水的升降影响着湖盆水体面积的大小、深浅以及沉积体系发育分布，进而影响全盆地晚三叠延长统地层生储盖组合的发育特征。通过野外剖面、钻井岩芯中古生物化石的鉴定，结合古生物组合特征对鄂尔多斯盆地晚三叠世湖盆的古生物生态环境进行了恢复。确定鄂尔多斯晚三叠世湖盆是一个最大水深不超过60 m的浅水湖盆，属于温暖潮湿的淡水-半咸水环境。从湖岸到湖心，可以划分为预测古水深1～2 m的河流-沼泽生物相带；预测古水深3～15 m的滨岸-河口三角洲生物相带；预测古水深15～35 m的浅湖生物相带；预测古水深在35～60 m范围的半-深湖生物相带。这些生物相带的划分，为恢复鄂尔多斯盆地晚三叠世时期的岩相古地理奠定了基础，为盆地延长组沉积边界、盆地内沉积体系发育展布以及沉积相带的划分提供了坚实的地质依据，具有理论与实际意义。

The Paleontology Phase Zones and Its Geological Significance on the Late Triassic Yanchang Stage Palaeo-lacustrine Ordos Basin

Ordos Basin in the Late Triassic stage developed large-scale depression lake basin.The rise and fall of Lake water affected the area of the sedimentation, depth and depositional system distribution in the lake basin, thereby affecting the whole basin characteristics of the development of the source rock combination, reservoir and sealling rock in the Late Triassic formation. Through identification of outcrop, drilling rock cores palaeontological fossils, combined with paleontological assemblages of Ordos Basin in the Late Triassic lacustrine paleo-ecological environment were recovered. It is concluded that the Late-Triassic Ordos Basin was a shallow lake in which the depth of the water was less than 60 m, the salinity of the water was freshwater-brackish and the weather was warm and humid. From the shore to the lake centre it can be divided into four paleontology phase:river-marsh biofacies-assemblage zone in which the water depth was predicted within 1~2 m, shore-delta biofacies-assemblage zone in which the water depth was predicted within 3~15 m, shallow lake biofacies-assemblage zone in which the water depth was predicted within 15~35 m and semi-deep lake biofacies-assemblage zone in which the water depth was predicted between 35~60 m. These conclusions have important theoretical significance to understanding the characteristic of the Ordos lake basin in late Triassic Yanchang Stage. These facies division, for the restoration of the Ordos Basin during the Late Triassic lithofacies palaeogeography laid the foundation for the extension of the sedimentary basin boundaries, depositional systems and sedimentary facies division.