Indo Gangetic alluvium is a consequence of the Indian- Eurasian plates collision that was initiated in the Paleogene. The Ganga basin is an active foreland basin having an east-west elongated shape.
- The Ganga basin is characterized by three subsurface ridges –
- Delhi-Haridwar ridge in the West
- Faizabad ridge in the middle
- Monghyr – Saharsa ridge in the east
- In the area between the Delhi-Haridwar ridge & Faizabad ridge, the sediments rest on Late Proterozoic unmetamorphosed sediments, which are part of the Vindhyan basin in the south and Karol basin in the north.
- East of the Monhgyr – Saharsa ridge, the foreland sediments lie on a thick succession of Gondwana rocks.