DIAGENETIC SIGNAL VS BIOGENIC ULTRASTRUCTURE IN HYPERMINERALIZED FOSSIL FISH SCALES

Analyses using microprobe and laser ablation ICP-MS show that rare earth elements (REE) have accumulated and preserved in variable concentrations in apatites in continental fossil remains if compared to marine remains. The studied hypermineralized hard tissues are from fossil fish scales preserved in bioclasts. The outer layers of these scales are composed of series of periodically deposited enamel-like lamellae (biological apatite) and are original growth structures. Series of growth events do not yield biogenic geochemical signals in fossil fish scales, but reflect depositional, burial and (post)diagenetic events yet are linked to the original ultrastructure of the (biological) apatite. Nevertheless, each biological entity (higher systematic taxon) may reveal a peculiar pattern of biogenic ultrastructure that may be correlated with a different geochemical signal, which closely resembles geological apatite in the fossil fish scales studied. REE concentrations reveal a significantly different pattern in internal lamellae if compared to external lamellae at the bone/enamel and at the matrix/enamel boundaries. It is concluded that REE concentrations preserve original diagenetic and postdiagenetic signals that help identify and reconstruct events in taphonomy, diagenesis and re-deposition of fossil fish remains from bioclasts.