Structural History as an Aid in Precambrian Stratigraphic Correlation: An Example from the Gangpur Group in Eastern India

Gangpur Group, an important Precambrian metasedimentary sequence near Rourkela in eastern India shows an easterly antiformal closure, but the northerly younging towards the core shown by cross beds in the southern limb proves large scale inversion. Three generations of folds F₁, F₂ and F₃ are proved on mesoscopic and macroscopic scales by structural analysis. The limbs and axial planes of low easterly plunging isoclinal reclined folds (F₁) along with schistosity developed parallel to these axial planes are coaxially folded by upright F₂ folds; N-S trending upright F₃ folds cause culminations and depressions in axes of F₁ and F₂ folds. The stratigraphy of the complexly folded Precambrian Group is worked out on the basis of the structural model. One important marker horizon of carbonaceous quartz phyllite and banded quartzite recurs four times because of large scale axial plane folding.