Weathering indexes are useful to estimate the intensity or the duration of a weathering process in geological materials as soils. But what are the pros and cons? What are the methodological issues about these indexes? And, finally, why aren't they popular? For soils there are two interesting indexes: the Ki (Silicate to Al-oxides ratio) and the Kr (Silicate to oxides ratio). In simple words: How intenser and/or longer the weathering process, more intense the loss of silicates will be and more oxides will remain in the soil. Therefore, higher the Kr or Ki ratio. As a rule of thumb, soils with Ki < 2 (devoid of 2:1 phyllosilicates) are the highly weathered ones. The highly weathered soils from Brazil very often presents Ki and Kr < 1.
Hi My dear Guilherme Sobrinho; The following links could be helpful to you. Thanks
http://geology.gsapubs.org/content/38/5/407.short
http://www.sciencedirect.com/science/article/pii/0037073888901376
Here are some papers for you help...
and some links
http://www.ingentaconnect.com/content/els/08832927/2001/00000016/00000007/art00071
(The influence of mineralogy on weathering rates and processes in an acid-sensitive granitic catchment)
http://link.springer.com/article/10.1007%2FBF00477973#page-1
(Chemical and mineralogical weathering rates and processes in an upland granitic till catchment in Scotland)
you can also search for Sr isotopes use in weathering indices.
Dear Mr. Sobrinho,
the approach you will have to take, strongly depends on the mineral assemblage of your weathering profile. I have used clay minerals and heavy minerals. The latter group is rather sensitive and even can show you the intensity by the crystal morphology (see file attached). In your environment, newly formed APS minerals may also be of help (Aluminium-Phosphat-Sulfate minerals/ crandallite group), which can be used in combination with sequioxides (Al oxides) and phyllosilicates (kandite-group + halloysite). The following paper may give you an introduction into the matter
DILL, H.G. (1998) A review of heavy minerals in clastic sediments with case studies from the alluvial fan through the near-shore marine environments.- Earth Science Review, 45: 103-132.
DILL, H.G. (1995) Heavy mineral response to the progradation of an alluvial fan: implications concerning unroofing of source area, chemical weathering, and paleo-relief (Upper Cretaceous Parkstein fan complex / SE Germany).- Sedimentary Geology, 95: 39-56
DILL, H.G. (2001) The geology of aluminium phosphates and sulphates of the alunite supergoup: A review.- Earth Science Reviews, 53: 35-93.
Should you have further questions feel free to contact me on this matter.
Best regards
Harald G. Dill
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