Poisson-Pinsker factor and infinite measure preserving group actions

We solve the problem of the existence of a Poisson-Pinsker factor for a conservative ergodic infinite measure preserving action of a countable amenable group by proving the following dichotomy: either the system has totally positive Poisson entropy (and is of zero type) or it possesses a Poisson-Pinsker factor. If $G$ is abelian and the entropy positive, the spectrum is absolutely continuous (Lebesgue countable if $G=\mathbb{Z}$) on the whole $L^{2}$-space in the first case and in the orthocomplement of the $L^{2}$-space of the Poisson-Pinsker factor in the second.