Grains of detrital apatite develop syntaxial apatite cement overgrowths during burial. Petrographic analysis of the distribution of such overgrowths in 453 thin sections from dominantly marine sandstones of late Triassic to Paleogene age on the Norwegian continental shelf shows that apatite overgrowths are present only in samples with formation temperatures above approximately 90°C, suggesting that authigenic apatite starts to form at this temperature. Apatite grains and apatite overgrowths are easily identified with a cathodoluminescence microscope thanks to the intense yellow-green and orange cathodoluminescence colors shown by grains and overgrowths, respectively. Presence of apatite overgrowths may therefore be a useful indicator of paleotemperatures above ca. 90°C, at least in marine sandstones.