Dear Dr. Hanbiao Xian,

In my opinion and according to my practical experience I gathered during 40 years in geosciences, there is no “universal proxy” and even the CIA masks rather than elucidates the issue you are going to address in your question. I have collected good results in having taken a look at the chemical and mineralogical composition and used them in context with geomorphology (shaping the landscape) and geology (interacting with geomorphology in building landforms). I know that geoscientists, including myself, always are striving to find the “philosopher´s stone” and chemical ratios are held to be the savior. They pretend a quick and reliable solution without knowledge and experience, what is never the case.

Have a look at the literature listed in the projects of mine:

- Environment analysis of clay mineral deposits

- Heavy mineral analysis and placer deposits

- Weathering: From the residual ore deposit to the post-mining mineralization

I wish you much success

H.G.Dill

Dear Sir

In addition to the Chemical Index of Alteration (CIA) there are three other factors:

1) Chemical Index of Weathering (CIW)

CIW = (Al2O3 / (Al2O3 + CaO* + Na2O)) 100

2) Plagioclase Index of Alteration (PIA)

PIA = ((Al2O3 – K2O) / ((Al2O3 - K2O) + CaO* + Na2O)) 100

3) A modified version of CIW (CIW´)

CIW´ = (Al2O3 / (Al2O3 + Na2O)) 100

Best Regards

I am also in the favor of Prof. Harald G. Dill. There is no such universal chemical weathering process which can be applicable for all the rocks. The proxy used should be well supported by other geo-chemical or petrographic analysis. But at least these weathering proxies can provide you some idea. Some of these proxies are already mentioned by Dr. Osama Rahil in the above answer. I want to provide some more in this regard along with their references.

There are several proxies proposed for the determination of paleoclimate such as:

i) Chemical index of alteration (CIA)= 100× Al2O3/ (Al2O3+CaO*+ Na2O + K2O) (Nesbitt and Young, 1982)

ii) Chemical index of weathering (CIW)= 100× Al2O3/ (Al2O3+ CaO*+ Na2O) (Harnois, 1988)

iii) Index of composition variability (ICV)= (TiO2+ Fe2O3+ MnO+ MgO+ CaO+ Na2O + K2O)/ Al2O3 (Cox et al., 1995)

In all these equations, oxides are used in molar percentage and the CaO* is the value after removing the effect of apatite and calcite.

According to my observation, there are two possible recordable chemical weathering in the clastic succession, phase 1- Chemical weathering of the clasts ( grains) on the source area before erosion and depostion. In this phase the grains may be partially weathered ( partially leached or corroded) and stain red or brown and gained low specific gravity. Then the sediment (clasts) are eroded by sheet wash to the basin of deposition. The phase 2 , is weathering after exhumation to surface or near surface. In this phase the strata are extensively weathered which changes according to type of mineralogy, cementation, compaction, climate and topography of the outcropped terrain