Hi, you might look at articles dealing with contact metamorphism. Be aware that in this field people tend to use V-SMOW instead of V-PDB, which might e a bit confounding.
If I remember correctly my results in that field, the lowest values I got directly at the intrusion contact were as low as +7 permil V-SMOW (ca. -23permil V-PDB).
Thanks a lot, Micha, I will certainly look into that. There is a fault with igneous rocks below not far but we are well away from the contact and our lowest values are -28permil V-PDB, which is around +2 permil V-SMOW, still crazy low...
How far away are the igneous rocks? How big is the igneous body? What kind of carbonate did you investigate? It is known that e.g. intrusions emit lots of water during cooling. Thus, if your sediment has (or had during the cooling of the intrusion) a high permeability the water might significantly alter the isotope values.