Trends in Aragonite Dissolution through the Phanerozoic

Different calcium carbonate polymorphs, such as aragonite and calcite, participate differentially in early marine diagenesis due to their different thermodynamic stability. The microbial decay of organic matter causes distinct redox zones during the early stages of burial. In these conditions aragonite is unstable and dissolves, while the dissolved calcium carbonate can then reprecipitate as calcite cement. This results in areas or layers of calcium carbonate export (i.e., marl) and areas or layers of calcium carbonate import (i.e., limestone). The implications for the interpretation of carbonate rock sequences are highly debated, and the potential influences of this redistribution of carbon and other elements on global geochemical cycles remains underexplored. The intensity of this early diagenetic carbon redistribution is largely driven by availability of aragonite in the original sediment. As the seawater Mg/Ca ratio and temperature strongly impact inorganic calcium carbonate mineralogy and skeletal mineralogy (at least before the Jurassic), we expect that the intensity of the redistribution varies throughout the Phanerozoic with seawater Mg/Ca and temperature, i.e. aragonite-calcite sea conditions. In this study we evaluate the intensity of early diagenetic overprint and aragonite dissolution through the Phanerozoic by comparing diagenetically inert Al/Ti ratios of limestone-marl alternations from published datasets in the context of available shelf area and palaeotemperature. We identify time intervals with higher or lower diagenetic overprint and discuss the implications for stratigraphy, palaeoenvironmental reconstructions and carbon cycling.