## 3 High-Resolution Sequence Stratigraphic Division
### Long-Term Cycle Identification Based on Well Logging-Seismic Data Combination  
The bottom boundary of the Guantao Formation exhibits characteristics of medium to strong amplitude and medium to high continuity on its seismic profile (interface T1), which can be tracked throughout the region. The seismic down-lap reflection structure can be identified above the T1 interface, and obvious truncation reflection texture can be identified below the interface (Figure 3), indicating an angular unconformity contact relationship between the Guantao Formation and the underlying strata. The obvious unconformity between the upper and lower sedimentary bodies reflects an important tectonic movement and can serve as a marker bed for identifying long-term cycles (third-order sequences). There are two types of contact interfaces between the Guantao Formation and the underlying strata in the study area. One type is the Guantao Formation's contact with the Shahejie Formation (Es), and the other is its contact with the Archean strata. These two types of strata contact interfaces have different well logging curve characteristics. The well logging curves of the contact surface between the Guantao Formation and the Shahejie Formation have the following characteristics (Figure 4c): the well logging curve SP value above the T1 interface is relatively low, while the SP value is relatively high below the T1 interface; the well logging resistivity curve shows an increasing trend below the interface; the well logging CAL and AC curves exhibit more severe serration above the T1 surface, gradually returning to low values below the T1 surface. The well logging curves of the contact surface between the Guantao Formation and the Archean strata have the following characteristics (Figure 4d): the well logging resistivity curve above the T1 interface shows a straight and continuous low value, with an increasing trend under the T1 interface; the well logging AC and CAL curves often exhibit a combination of serrated box-shaped and serrated bell-shaped shapes above the T1 interface, with a downward trend under the T1 surface. The differences in these logging curve shapes indicate the differential sedimentary facies and lithologies on different sides of the interface [26]. The interface between the Guantao Formation and the overlying Minghuazhen Formation in the seismic profile (interface T0) shows characteristics of medium to strong amplitude and medium to low continuity (Figure 3). The T0 interface is a parallel unconformity surface, reflecting geological erosion caused by rapid structural uplift and lake level decline [27]. Under the T0 interface, the well logging GR, SP, CAL, and AC curves are mainly of medium to high values, and the resistivity curve is mainly of medium to low values (Figure 4a,b). Based on comprehensive analysis of seismic and well logging data, it is believed that the bottom interface (T1) and top interface (T0) of the Guantao Formation are typical third-order sequence boundaries, and the entire Guantao Formation corresponds to a long-term cycle (third-order sequence). Figure 3: A typical seismic profile characteristic of the Binxian area. The long-term cycle includes a rising base-level semi-cycle in the lower part and a falling base-level semi-cycle in the upper part. The identification marker of the interface between the rising and falling semi-cycles is the thick mudstone section layer, which was formed in the inter-river floodplain and continuously developed in the upper parts of the Guantao Formation. The thick floodplain mudstone was deposited during a maximal flooding period, which can be recognized in the large number of drilling wells in the study area (Figure 5). Figure 4: Well logging curve characteristics of third-order sequence boundaries: (**a**,**b**) Well logging curve characteristics of the top interface between the Guantao Formation and the Minghuazhen Formation. (**c**) Well logging curve characteristics of the bottom interface between the Guantao Formation and the Shahejie Formation.