  In this paper we tackle the issue of causality in quantum gravity, in the
context of 3d spin foam models. We identify the correct procedure for
implementing the causality/orientation dependence restriction that reduces the
path integral for BF theory to that of quantum gravity in first order form. We
construct explicitly the resulting causal spin foam model. We then add matter
degrees of freedom to it and construct a causal spin foam model for 3d quantum
gravity coupled to matter fields. Finally, we show that the corresponding spin
foam amplitudes admit a natural approximation as the Feynman amplitudes of a
non-commutative quantum field theory, with the appropriate Feynman propagators
weighting the lines of propagation, and that this effective field theory
reduces to usual QFT in flat space in the no-gravity limit.
