Abstract:
Differences in the fracture type of limestone rocks have resulted in the formation of several main plant soil ecosystems in the montane and subalpine zones of the Jura (800-1 700 m). The sites were on stable landscape with slope < 5%. Locations were chosen to reflect the variation in physical properties of the bedrock and lithic contact. The rock fractures (densities and size), the shape and size of the fragments and the hydraulic conductivities were described and analyzed to characterize the 3 main bedrocks in the area studied (table 1): 1), lapiaz, ie, large rock fragments separated from each other by wide fractures (figs 1-2), 'broken' rocks traversed by numerous fine fractures (fig 2-3), paving-stones crossed by infrequent narrow fractures (fig 3). The effects of rock fracturing on vegetation (table II) and soil formation were significant in reference to porosity and permeability relationships (figs 6-7). Under similar precipitation, meteoric waters flow through the soil and porosity is relative to fracture systems (figs 4, 5). The weathering of cobbles in the soil profiles and along the lithic contacts maintains different soil solution Ca levels and is an important variable in soil and ecosystem formation (table III). Regarding the regional orogenic phases and the tectonic origin of the fractures, we postulate that the different types of fracturation originated from the different chemical and mineralogic composition of the rocks. Significant differences exist in both the calcite and dolomite content, in the insoluble residue content (table IV) and in the percentage of organic matter of the carbonate-free residues (table V, fig 8). The results indicate that the differences in rock composition arose early at about the period of sedimentation. The origin of the differentiation might be due to the sedimentation conditions and environment (fig 9). It is concluded that the present-day plant soil ecosystems may be related to the marine sediment environments of the Jurassic period (fig 10)