Abstract
The sequence of the Purana formations of Bastar, in the ascending order of (1) Tiratgarh subarkose and orthoquartzite, with purple shale towards the top, (2) Kanger grey laminated limestone, and (3) Jagdalpur purple shale and shale-limestone, with intercalations of quartzites and limestones, in one conformable series, is established. The name "Indravati Series", is proposed for this succession after the name of the river draining the largest patch where the entire sequence is exposed.
On lithological, successional and structural considerations, the 'Tiratgarh' is corre¬lated with the Paniam of Kurnool and the Chandarpur of Chhattisgarh; the 'Kanger' with the Koilkuntla of Kurnool, and the 'Charmuria' of Chhattisgarh and the 'Jagdalpur' with the Nandyal of Kurnool and the 'Gunderdehi, Khairagarh and Raipur' of Chhattisgarh. The 'Tiratgarh' is tentatively correlated with the Sullavai of the Godavari valley. An upper Kurnool age is thus assigned to the Indravati series.
Various structural considerations indicate that the basin, which was continuous from Sukma to Chhattisgarh, was separated from the basin along the Godavari valley by a landmass with shore lines roughly trending N.W.-S.E. The south-eastern boundary of the Indravatis and the eastern boundary of the Kurnools indicate the limits of the basin in this direction.
