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义县组岩性以基性、中基性火山岩、火山碎屑岩为主，局部发育有富含“热河生物群”化石的沉积层。在这些沉积层之下、义县组复成分底砾岩之上，发现有 4个沉凝灰岩层，与基性、中基性火山岩呈互层状产出，其岩性以沉凝灰岩或含砾凝灰质粉砂岩为主。这些凝灰岩层厚度虽小，但分布较广泛，走向延伸稳定。根据辽西地区中生代火山岩活动的基本规律，沉凝灰岩层与基性、中基性火山岩的空间展布特征及野外地质综合研究将义县组早期火山活动划分出 5个火山作用旋回，并确认四合屯、黄半吉沟、尖山沟、以及上园、大康堡、河夹心等地富含“热河生物群”化石的沉积层均属于同一火山旋回（第五旋回）的产物。这一发现极大地丰富了辽西地区中生代陆相盆地火山—沉积作用的研究内容，并将促进火山活动与生物灭绝事件方面的研究工作。
The Yixian Formation lithology is mainly composed of basic, intermediate-basic volcanic rocks and pyroclastic rocks, and locally developed sediments rich in fossils of “Rehe Biota”. Below these sediments, the Yixian Formation is subdivided into basal conglomerates and four sedimentary tuffaceous layers are found, which are interbedded with the basic and intermediate-basic volcanic rocks. The lithology is characterized by tuff or gravel Tuff siltstone based. The thickness of these tuff formation is small, but the distribution is more extensive and the direction of extension and stability. According to the basic laws of Mesozoic volcanic activity in western Liaoning Province, the spatial distribution of sedimentary tuff stratum, basic and volcanic rocks, and the field geology comprehensive study divided the early volcanic activity of Yixian Formation into five volcanic cycles and confirmed that Sihe Tuen Mun, Huangbangyegou and Jianshangou, as well as the sediments of the “Rehe Biota” fossils in Shangyuan, Da Kangbao and Hechuan are all belong to the same volcanic cycle (5th cycle). This discovery greatly enriched the study on the volcanic-sedimentary facies in the Mesozoic continental basins in western Liaoning Province and will promote volcanic activity and biological extinction.