Principles of calcite macrofossil sampling and analysis for geochemical studies on Mesozoic palaeoenvironments

Macrofossil carbonate is extensively used for palaeoenvironmental and chemostratigraphic research, especially for the reconstruction of Mesozoic and Paleozoic environments, climates and Earth system evolution. Work on such materials has allowed to chart geochemical signatures of biomineralisation and diagenetic overprints. This information, in conjunction with studies on modern analogues, allows placement of newly obtained results into a well-established conceptual framework of geochemical and structural overprints on macrofossils.The reliability of geochemical research using Mesozoic macrofossils can be optimized by taking into account these general patterns of fossil diagenesis and tendency for exhibiting metabolic effects that bias palaeoenvironmental proxy incorporation into biominerals. Such biases are specific to individual taxa and successions and have to be tested in each study to provide quantitative constraints on preservation. Due to the large potential range of the expression of post-depositional alteration, analysis of relevant diagenetic phases and altered fossil materials should always complement study of the best-preserved material. This contribution outlines principles behind this screening approach and provides guidance on general sampling and sample evaluation strategies. These strategies improve the confidence in the validity of analytical data from macrofossil carbonate for palaeoenvironmental interpretation, including for novel and easily altered geochemical proxies.