Oxidative conditions can lead to exceptional preservation through phosphatization

Abstract

Exceptional preservation through phosphatization is primarily controlled by a reduction in pH, favoring the precipitation of apatite over that of calcite. Laboratory experiments have suggested that phosphatization results from anoxic decay. Here we report results of the fine-scale mineralogical characterization of Cretaceous phosphatized fossils of teleost fishes and crustaceans from the Jebel oum Tkout Lagerstätte (Morocco). Data collected using complementary laboratory and synchrotron-based X-ray techniques reveal that oxidative conditions were established at a certain step of decay. Supporting these conclusions are the presence, covering and embedded in the phosphatized tissues, of Fe(III)-rich mineral phases, the precipitation of which was likely biologically induced during decay. The present study highlights that the establishment of oxidative conditions during decay can be compatible with exceptional preservation of fossils through phosphatization.

Pushing Raman spectroscopy over the edge: purported signatures of organic molecules in fossil animals are instrumental artefacts

“…3b) preserved as a mixture of calcium phosphates and iron oxides in an illite mudstone ( Fig. S1; see also Gueriau et al [35] and references therein), and (ii) a specimen of the modern shrimp Neocaridina davidii (Fig. 3c) dried after death and still rich in organic carbon, likely in the form of chitin (Fig.…”

“…In order to further assess the impact of the sample's chemical composition on the measured spectra, we also performed Raman spectroscopy on (i) a specimen of the penaeid shrimp Cretapenaeus berberus from the Cretaceous of Morocco (Figure 3b) preserved as a mixture of calcium phosphates and iron oxides in an illite mudstone (Figure S1; see also Gueriau et al. [ 35 ] and references therein), and (ii) a specimen of the modern shrimp Neocaridina davidii (Figure 3c) dried after death and still rich in organic carbon, likely in the form of chitin (Figure S1). Whether or not organic carbon is present, and whatever the mineralogical composition of the specimen or its mineral matrix, all the measured spectra (Figure 3d, solid lines) display broad bands, which all occur at the same wavenumber shifts and add up to a significant background (Figure 3d, dotted lines).…”

Insights into soft-part preservation from the Early Ordovician Fezouata Biota

“…6D, E) (Hancy and Antcliffe, 2020). This post-burial degradation can be mitigated by authigenic mineralization such as pyrite or phosphate precipitation (Saleh et al, 2020c;Gueriau et al, 2020) or even by the association of clay minerals such as kaolinite to certain labile anatomies (Anderson et al 2020b). Authigenic pyritization happens when iron is available and anoxic conditions are established in sediments, but oxidants from the water column (i.e.…”

Pushing Raman spectroscopy over the edge: purported signatures of organic molecules in fossils are instrumental artefacts

“…3b) preserved as a mixture of calcium phosphates and iron oxides in an illite mudstone (Fig. S1; see also Gueriau et al [34] and references therein), and (ii) a specimen of the modern shrimp Neocaridina davidii (Fig. 3c) dried after death and still rich in organic carbon, likely in the form of chitin (Fig.…”