**2. Study area, stratigraphy and sedimentological sketch**

The Rajmahal sub- basin of eastern India is part of the Gondwana Master basin and covers a large area of Bengal basin, North Bengal and Purnea. There are four sub basins (coalfields) from south to north i.e. Brahmini, Pachwara, Chuperbhita and Hurra (**Figure 1A**). The Gondwana rocks are bounded by the river Ganga to the north, by Rajmahal volcanic to the east, by rugged metamorphic to the west and by laterite and recent alluvium to the south. The unclassified Archean rocks form the basement of the Gondwana rocks in the Rajmahal sub-basin with a pronounced unconformity, though at places the contact is faulted. Isolated patches of Talchir rocks are seen along the western periphery of the basin. This formation is succeeded by the Karharbari Formation, composed of grits, conglomerates and sandstones. The overlying coal bearing Barakar Formation directly rests over the Archean basement at most places and is exposed along the river valleys where the overlying traps and Triassic sediments are denuded. The Early Permian Barakar rocks are overlain by the Dubrajpur Formation (Late Triassic), which is, intern, followed by Rajmahal traps and Inter-trappean rocks (Early Cretaceous to Early Jurassic).The contacts between Early Permian, Late Triassic and Early Cretaceous are unconformable. A generalized stratigraphic sequence of the Gondwana rocks of Rajmahal sub-basin is shown in **Figure 1B**.

Gondwana sedimentation in Rajmahal sub-basin commenced with the deposition of the Talchir sediments under glacial and fluvio-glacial, glacio-lacustrine and/or shallow marine environments [9]. Following retreat of Talchir ice, the rejuvenated rivers flowed dominantly towards the northwest and northeast and deposited shallow waters gravelly and sandy sediments as discontinuous patches gradationally above Talchir as Karharbari Formation. The overlying Barakar rocks are characterized by fining upward cycles of coarse to medium sandstones with interbedded siltstone, shale and thick to thin coal seams [10, 11]. These rocks were deposited by laterally migrating river channels in response to varying discharge and/or intermittent differential subsidence/tectonism, and led to the development of peat swamps in the flood plains and protected lakes.

*Analyzing Sedimentary Rocks to Evaluate Paleo Dimensions and Flow Dynamics of Permian… DOI: http://dx.doi.org/10.5772/intechopen.106994*

#### **Figure 1.**

*(A) Location and geological map; and (B) subsurface Gondwana stratigraphy of Rajmahal sub-basin of eastern India (based on bore hole log).*
