  In this article we investigate mathematically the variant of post-Newtonian
mechanics using generalized fractional derivatives. The relativistic-covariant
generalization of the classical equations for gravitational field is studied.
The equations match to (i) the weak Newtonian limit on the moderate scales,
(ii) deliver a potential higher, that Newtonian, on certain, large-distance
characteristic scales. The perturbation of the gravitational field results in
the tiny secular perihelion shift and exhibits some unusual effects on large
scales. The general representation of the solution for fractional wave equation
is given in form of retarded potentials. The solutions for the Riesz wave
equation and classical wave equation are clearly distinctive in an important
sense. The Riesz wave demonstrates the space diffusion of gravitational wave at
the scales of metric constant. The diffusion leads to the blur of the peak and
disruption of the sharp wave front. This contrasts with the solution of
D'Alembert classi-cal wave equation, which obeys the Huygens principle and does
not diffuse.
