Experimental burial diagenesis of aragonitic biocarbonates: from organic matter loss to abiogenic calcite formation

Abstract. Carbonate biological hard tissues are valuable archives of environmental information. However, this information can be blurred or even completely lost as undergo diagenetic alteration. This is more likely to occur in aragonitic skeletons because bioaragonite often transforms into calcite during diagenesis. For reliably using geochemical proxies, it necessary understand depth the alteration processes that they undergo. Several works have recently investigated hydrothermal short-term experiments at high temperatures (T > 160 ?C). In study, we conduct long-term (4 and 6 months) 80 ?C burial-like fluids. We document evaluate changes undergone by outer inner layers shell bivalve Arctica islandica, prismatic nacreous tissue gastropod Haliotis ovina, skeleton coral Porites sp. combining a variety analytical tools (X-ray diffraction, thermogravimetry analysis, laser confocal microscopy, scanning electron backscatter diffraction atomic force microscopy). demonstrate approach most adequate trace subtle, diagenetic-alteration-related biocarbonate structural materials. Furthermore, unveil complex multi-step process where major low temperature used well before any aragonite transformation takes place. Alteration starts with biopolymer decomposition concomitant generation secondary porosity. These followed abiogenic precipitation partially totally obliterates Only subsequently does occur. The kinetics highly dependent on primary microstructural features biomineral. While remains virtually unaltered for entire duration conducted experiments, ovina nacre undergoes extensive precipitation. islandica significantly affected calcite. layer ovina. Our results suggest majority fossil overprinted, those free clear signs. finding may implications use these proxies.