Conodont apatite from a shallow-marine Middle Devonian transgressive unit has been investigated in five borehole sections representative of the epicontinental Belarussian Basin located in a near-equatorial setting. The transgression is related to the onset of the late Eifelian Kacak Event, an important biotic episode recorded worldwide. The δ 18 O apatite data were acquired using the secondary ion mass spectrometry (SHRIMP) technique. The mean corrected values in the studied sections are in the range 19.8 ‰ to 20.2 ‰, significantly exceeding the values measured for late Eifelian low-latitude open marine basins. This can be explained by higher average δ 18 O seawater levels related to elevated seawater salinities in the Belarussian epeiric basin, in agreement with the presence of impoverished marine fauna. The intra-specimen δ 18 O variability, with differences ranging up to 2.6 ‰ in some specimens, can be explained by fluctuating δ 18 O seawater and, to a smaller degree, temperature variations in the Belarussian inland sea under a monsoonal climate. The present results demonstrate that local paleoclimate and epeiric paleogeography may considerably obscure the global climatic signature of the conodont apatite isotopic record.