Towards a better understanding of historic mortar production—burning experiments on calcareous nannofossils

Abstract Calcareous nannofossils are < 30 µm sized calcitic fossil remains of single-celled marine photoautotrophic algae. Carbonate-rich sedimentary rocks, containing these fossils, used as raw material for lime-based mortars. The carbonates (CaCO 3 ) heated up to approx. 900 °C. burning process, which causes the thermal decomposition CaCO into CaO (= quicklime) and CO 2 , destroys fossils. Surprisingly, calcareous algae were recently encountered in historic mortars mortar-based materials. To gain a better understanding behaviour during calcination procedure, four sample sets nine temperature levels (100 °C, 300 500 600 700 750 800 850 °C). For each set, initial all analysed with respect its nannofossil content preservation by using settling slides. Our results show decrease absolute abundance from °C onwards; rare preserved Changes relative individual species document that certain taxa more heat resistant than others. This pattern is explained different crystal sizes forms relevant taxa. Differences assemblages, observed mortar produced it, can be estimate reached quicklime production.