Composition and Properties of Estonian Palaeozoic and Ediacaran Sedimentary Rocks

Abstract

Primary composition, diagenetic changes and physical properties of Neoproterozoic (Ediacaran) and Palaeozoic (Cambrian, Ordovician, Silurian, Devonian) sedimentary rocks of the shallow part of the Baltic Sedimentary basin, located in Estonia have been studied during last decades. Chemical and physical parameters, lithology and mineralogy of the rocks were analysed together using statistical methods. Common approach, based on chemical parameters, was applied here for classification of sedimentary rocks. Primary Ordovician and Silurian carbonate rocks (limestones and calcitic marlstones) were compared to secondary rocks (dolostones and dolomitic marlstones). The last were compared to Devonian secondary rocks. Cambrian, Ordovician and Devonian siliciclastic rocks were compared to mixed carbonate-siliciclastic and to Ediacaran rocks. Sedimentation processes determined detrital input, clay, primary iron minerals content, and primary porosity of the rocks. Dolomitization of different genesis caused an increase in grain density, secondary porosity and remagnetization of carbonate rocks. Dolomite cementation, in places rich in iron compounds, caused decrease in porosity of Devonian and Cambrian siliciclastic rocks. Porosity of rocks formed during both primary and secondary processes correlates with their density, acoustic velocity and thermal conductivity. In contrast to pure limestones chemical composition and properties of dolostones depend on diagenesis and especially on composition of dolomitizing fluids.