A phenomenological analysis is made of the role of nucleon and quark correlations in the nuclear ground state on the quark momentum distribution in nuclei. The analysis is based on the recent observations in deep-inelastic lepton nuclear scattering of an anomalous nuclear effect. The discussion is framed in the QCD-improved quark parton model. The incoherent nucleon contribution is augmented by contributions representative of correlation effects which are described in a simple cluster model. Two distinct mechanisms are considered: one invoking two-nucleon and three-nucleon clusters with high intrinsic momenta and the other invoking six-quark correlated clusters. It is found that the second six-quark cluster mechanism provides a viable explanation of the anomaly, especially the depletion at large x. The enhancement observed at small x remains problematical in this cluster approach and an explanation of it is attempted in a parton-model approach of Regge behaviour for the sea-quark distribution in nuclei.