The Steinsfjord Formation (Wenlock) of the Ringerike district, southeastern Norway contains marls and carbonates which were deposited in supratidal, intertidal, and restricted subtidal environments. Rhythmic lithological variations seen within the unit represent small transgressive and regressive events. Red arenaceous and argillaceous dolomite reflects minor progradations of the adjacent continental facies from the overlying formation. Celestite is found in two associations within the strata: 1) as aggregates of tiny celestite crystals in dolomicrite of high intertidal facies, or 2) as anhedral or euhedral prismatic crystals infilling intrapores and interpores of low intertidal to subtidal facies. Celestite may have been formed from porewater enriched in SO 4 (super 2-) by solution of calcium sulphate in the high intertidal-supratidal environment. This sulphate has then reacted with Sr (super 2+) released during aragonite to dolomicrite transformation (high intertidal) and aragonite to calcite transformation (low intertidal-subtidal). The occurrence of celestite in these deposits is evidence for evaporitic conditions in the uppermost marine sequence of the Oslo Region's Lower Paleozoic succession.