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Climatic Geomorphology
the distinct degree of leaching of the varnish constituents. A leaching index has been
proposed: Ca + K/Ti, but it presents many treatment and analytical determination
problems. All of these methods have been used in studies of fault activity, rate of sea cliff
erosion, Quaternary deposit ages and lithic artefacts (Oberlander, 1994).
4.2. Formation processes
Previously, investigators believed that the constituents of varnishes came from the
weathering of the supporting rock. Solutions rich in Fe and Mn were thought to rise to the
rock surface via capillary action, where they were deposited after humid and rainy periods.
Nowadays no one doubts that the constituents derive from external sources, through
aeolian dust transport or water transport in solution (Figure 12.19). Electron microscope
Figure 12.19. Rock varnish developed on a sandstone, probably due to the precipitation of waters with
silica on the surface. This sandstone is affected by cavernous weathering features (tafoni). Petra, Jordan.
Photo by J.L. Pefia.