The transdimensional Bayesian method AH-RJMCMC applied to archeomagnetic intensity data available in the Balkans and the Near East allows us to estimate the variations in intensity of the geomagnetic field in Upper Mesopotamia during the 7 th and 6 th millennia BCE (Late Neolithic), with adequate treatment of the dating and intensity uncertainties. The results for the 6 th millennium BCE appear particularly interesting because there is enough data to trace rapid geomagnetic field intensity variations, with two century-scale peaks around 5800 BCE and 5550 BCE, associated with rates of changes (>0.2 µT/year) higher than the maximum rate observed in the current geomagnetic field. We show that these variations could help decipher the correlations between different archeological sequences or periodizations established from scattered sites in Upper Mesopotamia. So far documented only from the Balkan data, the intensity peak occurring around 5800 BCE may provide accurate chronological constraints for the Early Halaf phase. New insights are also obtained for the Halaf-Ubaid Transitional phase (end of the 6 th millennium BCE), which remains poorly defined from an archeological point of view. The AH-RJMCMC results imply that either the archeointensity data currently available from Upper Mesopotamia document only the beginning of this phase, or that this phase occurred between ~5400 and ~5200 BCE, shorter 2 than often considered. Such preliminary archeological inferences will progress and broaden with the addition of new archeointensity data.