Cavities, pores and crystal pseudomorphs which are lined or filled by calcite are ubiquitous in Raisby Formation dolostones at outcrop in north-east England. Their distribution in most exposures is random on a metre scale. On a smaller scale, cavities, pores and crystal pseudomorphs are most numerous in bioclastic and resedimented beds. Deep borehole cores of the Raisby Formation contain nodules and euhedral crystals of gypsum and anhydrite of very similar size and shape to the cavities and pseudomorphs. This indicates that calcium sulphates were once abundant in the Raisby Formation at outcrop, but almost all have been removed subsequently.Calcium sulphate minerals were formed early in the diagenetic history of the Raisby Formation, predominantly by selective replacement of carbonate rocks. Gypsum was precipitated first, probably as a by-product of dolomitization, by brines refluxing basinwards through the Raisby Formation from the hypersaline Zechstein Sea during deposition of the Edlington Formation and the Hartlepool Anhydrite Formation. Later, replacive anhydrite formed following both pressure-solution and dehydration of the gypsum. During further burial, some anhydrite was replaced by barite, dolomite and sphalerite. Upon uplift of the Raisby Formation during the Tertiary, anhydrite rehydrated to porphyroblastic gypsum and this was then dissolved by meteoric groundwaters. The resultant pores were lined or filled by two generations of calcite and also, locally, by kaolinite. The earlier calcite generation is luminescent and was precipitated partly as a passive cement and partly by replacement of surviving gypsum and anhydrite, a reaction thought to have been mediated by sulphate-reducing bacteria. The later calcite generation is predominantly non-luminescent and was precipitated from near-surface meteoric groundwaters.