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In the purview of continental masses, intracratonic sag basins and
intracratonic rift basins are formed within cratons(continental).
Intracratonic sag basins are formed possibly as the result of
asthenospheric downwelling or isostatic equilibrium following
termination of rifting. They are rarely fault-bounded with major fault
zones but may contain internal strike-slip faulting (Middleton, 2007).
Sag basins are commonly circular to oval in shape and may have multiple
histories of basin subsidence. They may be large and thick or small and
thin. They may form over older basins and inherit only some of the
previously existing structural grain (USGS).
From the Fig.1., for intracratonic sag basins, younger one might be at
the centre with a steep dip inwards relative to the older one with a
gentle dip inwards depending on the rates of divergence of tectonic
plates. They are structurally less disturbed.