  We develop a general strategy for the detection of nonclassical
system-environment correlations in the initial states of an open quantum
system. The method employs a dephasing map which operates locally on the open
system and leads to an experimentally accessible witness for genuine quantum
correlations, measuring the Hilbert-Schmidt distance between pairs of open
system states. We further derive the expectation value of the witness for
various random matrix ensembles modeling generic features of complex quantum
systems. This expectation value is shown to be proportional to a measure for
the quantum discord which reduces to the concurrence for pure initial states.
