Importance of porosity and transfer of matter in the rock weathering processes: two examples in central Spain |
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| Authors: | E Molina Ballesteros J García Talegón A C I?igo I?igo M González Sánchez and H Herrero Fernández |
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| Institution: | (1) Dpto. de Geolog?a, Universidad de Salamanca, Salamanca, Spain;(2) Insto. de Recursos Naturales y Agrobiolog?a de Salamanca (IRNASA-CSIC), Salamanca, Spain;(3) Unidad Asociada de Investigaci?n Universidad de Salamanca-CSIC, Salamanca, Spain |
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| Abstract: | Some physical properties (bulk and free porosity, pore size distribution), and the chemical composition and mass balance of
two deeply weathered profiles one developed on Hercynian granodiorite and the other on pre-Cambrian slates were studied. Hydric
and mercury porosimetry, nitrogen adsorption techniques, chemical analyses and XRD techniques were used. On granodiorite,
weathering has created increased porosity with a pore diameter <5 μm, whereas on slates the weathering has produced of ca.
1 μm in diameter. These pore sizes have played an important role in the weathering processes. Assuming that weathering preserves
volumes, except in the uppermost part of the profiles, it brought about a loss of matter of more than 12% (~300 kg/m3) on granodiorite and ca. 30% (~800 kg/m3) on slates. These changes are related to shifts in the mineralogical evolution, with the appearance of new 2:1 and 1:1 phyllosilicates
and Fe oxy-hydroxides as the main authigenic minerals. The release of matter, at least since the upper Neogene until the present,
has led to the lowering of relief in a more or less homogeneous way, giving rise to gentle hillsides and flat surfaces below
which the current river networks are incised. Porosity studies have the potential to explain several specific landforms as
well as affecting landscape development in general. |
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