Cephalopod Septal Strength Indices (SSI) and the depositional depth of Swedish Orthoceratite limestone

SSI was calculated for 2,994 individual septa measured in seetioned cephalopod conchs from Iimestones of Arenig to Llandeilo age (Ordovician) in Sweden. Minimum depths assumed on the basis of these calculations serve to illustra te variations in sea-leve! through time. The sealeve! curve for the lower Llanvirn regressive stage agrees with the curve obtained by the same method for the Yangtze Platform.