Sedimentary particles supplied from exposed areas are of a diverse nature, but essentially dominated by silicates, which in the coarser fractions are mainly quartz, and in the finer ones mainly clay minerals. These are predominantly the siliciclastic particles resulting from the physical and chemical attack on continental surface rocks by the action of water, temperature, biologic activity, etc. Weathering constitutes a combination of mechanisms liberating rock particles and removing the dissolved elements from the surface of the earth prior to the process of erosion taking over, which leads to transport and eventually to sedimentation. The susceptibility to weathering depends mainly on the type of source rock. Thus a porous sandstone is much more subject to weathering than a recrystallized one, a pure chalk more than a siliceous one, and a surface clay more than a shale resulting from deep diagenesis. A heterogeneous finely laminated or fractured rock will weather more readily than a homogeneous or compact one.
KeywordsClay Sedimentation Pyrite Jurassic Miocene
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