Field trips of the 9th International Conference on Fossil Insects, Arthropods, and Amber—a overview on Mesozoic palaeontology and stratigraphy of the Ordos Basin

The field trips will cover the Mesozoic stratigraphy and palaeontology of the Ordos Basin and the Loess Plateau (Fig. 1). The towering Qinling Mountains developed in the southern part of Xi’an. This investigation has entered the Loess Plateau from the Guanzhong Basin, where Xi’an is located, to the Tongchuan area, and the northernmost city of Yulin is a former desert area. The purpose of the investigation is to understand the Mesozoic strata, palaeontology, palaeoclimate and tectonic movements in the Ordos Basin. From the dry hot environment of the Red Bed in the mid-Triassic, it experienced a large cycle of warm and humid environment and then to the dry climate of the Early Cretaceous. Specifically, the middle and lower parts of the Middle Triassic Ermaying Formation are red beds, and coal seams begin to appear in the upper part of the formation; the overlying Middle-Upper Triassic Yanchang Formation has extensive oil and gas resources, and the lower strata are called by some authors the Tongchuan Formation and yielded a large number of insect fossils. At the turn of the Triassic and Jurassic, the area was elevated and lacked deposit. The Fuxian Formation of coal-bearing strata developed in the Early Jurassic. In the Lower-Middle Jurassic, the Yan’an Formation was a set of coal-bearing strata, which developed the largest coal mine in China. The Middle-Upper Jurassic Zhiluo Formation is a glutenite deposit. The unconformity between the Zhiluo Formation and the conglomerate at the bottom of the Lower Cretaceous Yijun Formation in this area indicates the Yanshan Movement Phase B. The Zhiluo Formation and the Yijun Formation is disconformity, and the Upper Jurassic-Lower Cretaceous Anding and Fengfanghe formations between the former two were missing. The Mesozoic fossil assemblages of the Ordos Basin are briefly introduced below, along with a composite column diagram (Fig. 2) depicting the Mesozoic strata of the Ordos Basin.