Abstract:

According to the studies on unconformity structures,it can be concluded that the rocks in unconformity structural layer are rich in Fe,Al and Ti while poor in Ca,Mg and Na,so indices (I_WP、V、I_CA、I_CW、I_PA，etc.) that can be used to study the weathering crust is also applicable in unconformity structure.Because the applicability and the threshold value of the indices change as the elements of mother rocks,the V,I_CA,I_CW,I_PA is suitable for carbonate rocks in weathered clay rocks,I_CA>90，I_CW>95，V>10，I_PA>95，in semi-weathered rocks,I_CA=50～90,I_CW=50～95,V=1～10，I_PA=50～95),and the V,I_CW is suitable for clastic rock(semi-weathered rock:V>5,I_CW>90;semi-weathered rocks,V=1～5，I_CW=50～95.The unconformity in the Jiyang depression is quantitatively classified with the chemical weathering index,which can further improve the accuracy of the structure research on the unconformity.

Key words: chemical weathering index, unconformity, structure classification, carbonate rock, clastic rock