Corestone caves and their relationship to other types of caves in granite rocks – a study from Queshi Mountains, Shantou, southeastern China

Compared to caves in carbonate rocks, granite caves are significantly less common worldwide. The existing literature identifies three types of granite caves: i) crack caves developed along major faults; ii) boulder caves associated with debris or residual block fields; and iii) caves or grooves resulting from mechanical and chemical weathering acting on rock surfaces. However, our field investigations reveal an additional type of granite cave beyond the three aforementioned types, formed by the excretion of weathering residues during in-situ corestone or spheroidal weathering processes. Despite their geological significance, these caves have been only occasionally mentioned in the global literature, lacking both clear classification and comprehensive study. In this study, this previously underrecognized cave type is formally designated as a "corestone cave" for the first time. In the 4A-rated tourist area of Queshi, Shantou City, China, various granite caves have developed on Queshi Mountain. The granite caves on the mountain have not been comprehensively documented. Notably, a rare but representative corestone cave is present in Queshi Mountain and has long been misclassified as a talus cave—a common type of granite cave. This study investigates the formation mechanisms of granite talus caves and corestone caves on Qushishan Mountain and identifies the key factors responsible for their differences based on the characteristics of contact types between boulders or between corestones. A conceptual model, developed based on previous research, is proposed to elucidate the cave formation processes, and a Particle Flow Code (PFC) model is employed to simulate and reconstruct these processes. The simulation results validate the differences in formation mechanisms—proposed by the conceptual model—between corestone caves and talus caves, and confirm that variations in rock block contacts constitute a reliable and objective criterion for distinguishing these two distinct cave types.