**5.5 Froude number (Fr)**

The validity of paleoflow bankfull depth and paleo-velocity estimates was assessed by ensuring that the Froude number, Fr, mathematically written as:

$$\mathbf{F\_r = V\_c/\sqrt{g} \, D\_c} \tag{26}$$

Where Vc = water flow velocity, *D*<sup>c</sup> = Bankfull channel depth, and g = acceleration due to gravity (approximately half of the present during Permian times, i.e. 4.9 m/ sec2 . The Froude number is a dimensionless parameter that describes different flow regimen of an open channel flow and is a ratio of inertial and gravitational forces. In open channel flow, the nature of the flow (supercritical or subcritical) depends upon whether the Froude number is greater than or less than unity. When previously determined values of *D*<sup>c</sup> and Vc are substituted, Eq. (26) indicates that Froude number was in between 0.149 and 0.208 indicating the flow was tranquil (subcritical) and of lower flow regimen as substantiated by the profuse development of small and large scale bedforms in the sandstone bodies. Subcritical flow (Fr < 1) is also consistent with field observations of normal fluvial cross beds in paleochannel deposits, whereas antidunes (not observed in study area) form in cohesion-less sedimentary beds under supercritical flow (Fr > 1) conditions ([13], p.120). Subcritical flow was considered acceptable for this study based on observed bedforms at the outcrop site and because of it is the most common type of flow in natural streams. The maximum Froude value calculated by putting respective values in Eq. (26) was 0.267, consistent with subcritical flow in all Gondwana sub-basin of Rajmahal basins.
