## 2 Geological Background  
The Liupanshan Basin is located in the southern Ningxia Hui Autonomous Region in Northwest China. Tectonically, it belongs to the southwestern region of the North China Plate, where several major regional faults intersect or merge. As a junction, it connects different geotectonic units in the western and eastern parts of Northern China [25; 26; 27] (Figure 1). Before the Middle Jurassic, the Liupanshan Basin, which is part of the GreatOrdos Basin, had undergone the same evolution as the present-day Ordos Basin (Figure 2a). Since the Middle to Upper Jurassic, due to regional tectonic activities, an intermittent tectonic uplift zone (paleo-uplift hereafter) had started to form along a line connecting the Liupan, Helan, and Zhuozi mountains in the Middle to Upper Jurassic. Its activity may have lasted from the Callovian in the Middle Jurassic to the Albian in the Early Cretaceous. With the emergence of the paleo-uplift, the Liupanshan Basin separated from the Great Ordos Basin in the Early Cretaceous and began to develop independently (Figure 2b). Extremely thick Mesozoic and Cenozoic sedimentary strata are present in the Liupanshan Basin, whereas the Upper Cretaceous system is often absent. The vertical stratigraphy consists of Upper Triassic, Middle Jurassic, Lower Cretaceous, Paleogene, Neogene, and Quaternary strata. While the Lower and Upper Jurassic systems can only be observed at some locations, other strata are widely distributed throughout the region. In the Liupanshan Basin, there are five sedimentary formations in the Lower Cretaceous Liupanshan Group, the Sanqiao, Heshangpu, Liwaxia, Madongshan, and Naijiahe Formations, from the bottom to the top. The Sanqiao Formation is a set of sedimentary units mainly composed of coarse clastic rocks belonging to alluvial fan deposits. The Heshangpu Formation is composed of sandstone and a small amount of conglomerate, belonging to fluvial deposits. The Liwaxia Formation is composed of mudstone, limestone, and a small amount of siltstone and fine sandstone. The Madongshan Formation is composed of mudstone, shale, and a small amount of limestone. The Madongshan Formation includes mudstone, shale, and a small amount of limestone; it represents the peak period of lake development in deep-lake facies. The Naijiahe Formation comprises heterogeneous shale as well as carbonate, gypsum, and salt rocks; it relates to lake extinction and semi-deep and shallow-lake facies [28; 29].  
Figure 1: Structural sketch map of the North China Plate (based on [30]). The sampled Haijjiazhuang section is located at 35\({}^{\circ}\)53\({}^{\prime}\)47\({}^{\prime\prime}\) N and 106\({}^{\circ}\)12\({}^{\prime}\)11\({}^{\prime\prime}\) in [29; 31; 32; 33].  
In the section of the Ordos Basin adjacent to the Liupanshan Basin, the Lower Cretaceous strata consist of the Yijun, Luohe, Huanhehuachi, Luohandong, and Jingchuan Formations (from bottom to top). During the Early Cretaceous, the Ordos Basin was a half-graben with a gentle eastern slope and a steep western slope, exhibiting a north-south-oriented distribution of sedimentary systems: alluvial fan-braided river-lake systems on steep banks, desert-river-delta-lake systems on gentle slopes, and alluvial fan-river-lake systems on the northern margin [11; 31; 34].