  In this paper some new tools for the study of evolution problems in the
framework of Young measures are introduced. A suitable notion of time-dependent
system of generalized Young measures is defined, which allows to extend the
classical notions of total variation and absolute continuity with respect to
time, as well as the notion of time derivative. The main results are a Helly
type theorem for sequences of systems of generalized Young measures and a
theorem about the existence of the time derivative for systems with bounded
variation with respect to time.
