On oxide-Al2O3variation diagrams
for TiO2(Fig. 3b), MgO (Fig. 3c), Fe2O3T, and P2O5(not illustrated)
trends in the Barail and Surma Groups are tighter and at differing
inclinations than those in the Tipam and Dupitila Groups. In the
Jaintia, Tipam and Dupitila Group abundances of MgO, Fe2O3T, and
P2O5at a given Al2O3are generally less than in the Barail and Surma
Groups. This is also the case for K2O(Fig. 3d). These features suggest
that some contrasts in composition are present within the succession.