  A simplified, pseudoplastic rheology characterized by constant viscosity
plateaus above and below a transition strain rate is applied to axisymmetric,
gravitationally driven spreading of a thin fluid film with constant volume flux
source in planar and spherical geometries. The model admits analytical
solutions for flow velocity and volume flux. Shear thinning influence on layer
evolution is investigated via numerical simulation. Isoviscous, asymptotic
behaviors are recovered in small and large transition stress limits. The effect
of viscosity ratio on layer extent agrees with scaling arguments. For
intermediate transition stress, a flow behavior adjustment is observed
consistent with heuristic arguments. Planar and spherical geometry solutions
are in agreement for sufficiently small polar angle.
