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Secular variations in the proportion of Mg and Ca ions in seawater during the Phanerozoic have driven alternations between calcite seas (Mg:Ca < 2) and aragonite seas (Mg:Ca > 2). There is mounting evidence that these changes in seawater chemistry have impacted the evolution of marine organisms constructing calcareous skeletons, favouring calcite as the CaCO3 biomineral during times of calcite...
A Middle Devonian section in the Blankenheim Syncline (northern Eifel, Rheinisches Schiefergebirge) contains a rather diverse fauna dominated by bryozoans, brachiopods, corals and other taxa, such as calcimicrobes. The section covers sediments of the Junkerberg Formation and the transition to the Freilingen Formation. The transition between the Junkerberg and Freilingen formations coincides with the...
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