Acta Carsologica (Dec 2022)
Clustered stone forest in Pu Dou Chun (Yunnan, China)
Abstract
One of the unique examples of the development of subsoil karren into a stone forest on the varied geological bedrock of the Lunan surface is revealed to us. Originally of subsoil formation and later denuded, the rounded hills that dissect the karst surface have transformed into a clustered stone forest whose central part usually consists of a larger dissected rock mass with individual stone pillars and teeth at the edge. The geologic profile contains beds of dense, homogeneous and compact fine-grained limestones that alternate with beds of mostly coarse-grained and just as compact dolomitised limestones. These bed properties are also reflected in the exterior of the rock as a diverse relief. The average calcium carbonate content in both types of rocks combined is 97.3%. The rock is thickly bedded to massive; beds are mainly positioned subhorizontally. The contacts between the beds of limestone and dolomitised limestone are sharp and clearly visible, especially in the bottom part of the geologic profile, whereas in the central part, they are often blurred and one type of rock grades continuously into the other. In the areas containing limestone, individual bedding planes are especially visible. As can be inferred, the slightly more porous dolomitised rock, made up of larger particles, disintegrates faster in a more permanently waterlogged acid subsoil environment, where the moisture penetrates it deeper. However, as it takes longer to dissolve, it protrudes from the surface of the dolomitic limestone rock when exposed to moisture from occasional rain. The composition and fracturing of the diverse rock strata decisively influences the shape of the pillars and their rock relief. Larger subsoil rock forms (channels, notches, half-bells) have developed on all rock strata. The diversity of the rock is also reflected by the notches that have formed under the soil along the more rapidly soluble partly dolomite rock strata. Denuded subsoil-shaped pillars are reshaped by rainwater and trickling water. Smaller rock forms carved by rainwater have formed mostly only on evenly composed, fine- grained limestone rock. The tops on such rock are more distinctly conical and blade-like and wider on more slowly soluble rock.
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