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Objective The Upper Paleozoic Yanghugou Formation-Taiyuan Formation in the northwestern margin of the Ordos Basin is a good prospect for oil and gas exploration. The strata are completely developed and continuous， with large thickness changes and various types of sedimentary facies. Defining the distribution characteristics of sand bodies and clarifying the law of sedimentary evolution directly affect the selection of preferred exploration zones for oil and gas. Methods This study takes the Yanghugou Formation to Taiyuan Formation in the northwestern margin of Ordos Basin as the target horizon. Based on previous studies， through typical field profile measurement， drilling core observation， paleocurrent direction analysis， logging data， and test data analysis， the sedimentary environment， facies type characteristics， evolution， and model of the study area were evaluated. ［Results and Conclusions］ There are 19 lithofacies types and three sedimentary systems in the study area， including four sedimentary facies types， and 13 sedimentary microfacies are further divided. The Yanghugou Formation-Taiyuan Formation in the study area is supplied by the two provenance systems of the Alxa ancient land in the northwest of the basin and the Yinshan ancient land in the northeast. The Dickinson triangle plot reveals that the tectonic background of the provenance area is dominated by the recycled orogenic belt. The characteristics of heavy mineral assemblages are clear. The northwestern margin of the basin has a clear affinity with the Alashan Group （Ar3-Pt1）， Archean Jining Group （Ar3）， and the Wulashan Group （Ar1-2）. The ZTR index shows that the unstable minerals gradually decrease from north to south； analysis of the paleocurrent direction also reflects the material sources from northwest to southeast and from northeast to southwest. Based on the above provenance analysis， paleo-sedimentary environment evolution and sedimentary facies type characteristics， it is clear that the main body of the Yanghugou Formation-Taiyuan Formation in the study area is the coexistence stage of sea and land. During the sedimentary deposition of the Yanghugou Formation， under the background of the revival of Helan aulacogen and the backlog of north-south tectonics， the sea water enters rapidly. The whole study area is controlled by the delta-clastic coastal sedimentary system. The northern source supply is sufficient， resulting in the development of tidal-controlled delta deposits in the north. Affected by tides and waves， tidal flat-barrier island-desalination of lagoons-shelf sedimentary microfacies are developed in the south. During the deposition of the Taiyuan Formation， the crust continued to sink and seawater invaded. During this period， the basin became the most widely distributed period of the sea area. The sedimentary environment was similar to that of the Yanghugou Formation. The overall performance was the coexistence of tidal-controlled delta， tidal flat， desalination of lagoons-barrier island sedimentary environment， and the erosion range in the northern region was relatively reduced， the source supply continued to increase， and the tidal-controlled delta range extended wider to the south.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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