Petrographic and Geochemical Characteristics of the Kamthi and Lower Maleri Formations Adilabad and Karimnagar Dts (A.P.)

Upper Kamthi sandstones are distinct being unimodal, less feldspathic, texturally more mature with a dominant ferruginous cement when compared with the Lower and Middle Kamthi sandstones which are bimodal, feldspathic with abundant carbonate cement. The bimodality and textural inversion in the latter is attributed to their derivation from both metasedimentary and plutonic sources. This is also reflected in the erratic distribution of Al₂O₃ total iron and Na₂O contents. The Yerrapalli sandstones are petrographically not very different from the Lower and Middle Kamthi sandstones, but show finer grained feldspar, abundant carbonate cement and lime pellets. The Bhimaram sand'stones, however, show lesser carbonate content and are characterized by the presence of pyrite and ferruginous cement. In general, the Yerrapalli and Bhimaram sandstones show a greater mineralogical and textural maturity than the Lower and Middle Kamthi units. The distribution of CaO shows a maxima in. the middle portion of the Lower Maleri sequence, other major elements donot show any systematic variation.