## 1 Introduction  
Volcanic rocks, evaporites, and clastic rocks deposited in the same stratum indicate information about climatic conditions, marine environment, topography, and geomorphology during the sedimentary period of the stratum. It is an important rock combination for global oil and gas exploration. At the same time, sequence research on different rocks developed in the same stratum has been a research hotspot in recent years [1, 2]. The southern part of Laizhou Bay, located in the Laizhou Bay Sag in the southern Bohai Sea, is a typical continental rift lake basin [3] and is a symbiotic sedimentary area of volcanic rock, evaporite, and clastic rock [4, 5, 6]. The Shahejie Formation is a key stratum of oil and gas exploration [7]. In recent years, more than 20 wells have been drilled in this zone, and many large oil fields have been discovered one after another, further showing that the southern part of Laizhou Bay still has great exploration potential [8]; therefore, predecessors have conducted much research on the Laizhou Bay Sag. [PERSON] identified and divided the isochronous sequence stratigraphic interface of the Paleogene Shahejie Formation, established the sequence stratigraphic framework,and then constructed a sedimentary model of \"paleogeomorphology-fault-salt structure-sedimentary body-sand control [9]\". Based on the sequence division of the Laizhou Bay Sag and the exploration of the fault system in the study area, [PERSON] determined that the strike-slip fault zones controlled the formation of sedimentary facies and the injection of eastern provenance [10]. By studying the structural characteristics and genetic mechanism of the slope belt in the Laizhou Bay Sag, [PERSON] et al. summarized the evolution model of the slope belt with the \"frequent transformation of slope uplift and tilting of strata [11]\". [PERSON]'s research showed that the Paleogene high-quality reservoirs in the southern Bohai Sea greatly differ under the influence of multistage volcanic activities [12]. [PERSON] et al. confirmed the existence of volcanic activity in this area through their study on the siliceous clastic rocks of the Shahejie Formation in the Laizhou Bay Sag [13]. The previous research results reveal that most of the studies are aimed at local areas or a certain interval, and no unified sequence division and correlation scheme have been formed in the whole area. The development intervals and areas of different sequence types have not been carefully defined, which restricts the establishment of a unified sequence stratigraphic framework in the whole area and the summary of the filling evolution law in sequence strata. At present, the primary research difficulties are that the joint influence of the strike-slip activity, salt rock activity, and volcanic activity of the Tanlu fault zone has a large degree of stratum deformation and denudation thickness, and the sequence development of different structural units is varied. Frequent structural activities and less drilling data hinder stratigraphic correlation. The identification standard of the key sequence interfaces of the Shahejie Formation has not been unified, and the development characteristics of the sequence strata are not clear. The sequence stratigraphy study of the volcanic rock-evaporite-clastic rock symbiotic system is more complicated mainly because the particularity of sedimentation principle and the diversity of the superposition relationship affect the definition of the sequence boundary [14; 15]. In the continuous sedimentary strata, the conversion surface of the progradation-degradation stacking mode of the parasequence set in the vertical direction and its corresponding sedimentary discontinuity surface in the paleo uplift edge area in the horizontal direction are some of the main bases for the identification of the sequence interface [16; 17; 18].