The genesis of nodular limestones in the Ordovician and Silurian of the Oslo Region (Norway)

Nodular limestones have been studied from the Lower Chasmops Shale (Middle Ordovician) and the Rytteráker Formation (Lower Silurian). Observations on nodule‐host‐rock relations and variations of ferroan/non‐ferroan calcite cements help explain the role of precipitation, dissolution and redistribution of carbonate. Distribution and frequency of nodules depends on environmental parameters such as carbonate/clay ratio, grain size distribution and bioturbation, though final shapes are the result of pressure‐dissolution and cleavage.