  We study type IIB brane configurations engineering 3d flavoured ABJ(M)
theories with Yang-Mills kinetic terms, which flow to IR fixed points
describing M2 branes at a class of toric Calabi-Yau fourfold singularities. The
type IIB construction provides a bridge between M-theory geometry and field
theory, and allows to identify the superconformal field theories with fixed
quiver diagram, Chern-Simons levels and superpotential, differing by the ranks
of the gauge groups, which we associate to dual AdS_4\timesY_7 backgrounds of
M-theory without or with torsion G-fluxes sourced by fractional M2 branes in
Y_7, when Y_7 is smooth. The analysis includes the Q^{1,1,1} and Y^{1,2}(CP^2)
geometries. We also comment on duality cascades and on the interplay between
torsion G-fluxes in M-theory and partial resolutions.
