Compositional changes in fish scale hydroxylapatite during early diagenesis; an example from an abandoned meander

Abstract

The chemistry of recent fish scales (tench, common carp, amur and European perch) and subrecent fish scales (European perch and mostly taxonomically not determined) was studied by means of laser ablation inductively coupled plasma mass spectrometry and electron microprobe from shallow boreholes in the abandoned meander Certak near Uherské Hradiste. A detailed study of subfossil fish confirms extremely rapid changes in the chemical composition of hydroxylapatite during very early diagenetic processes in the first 2 years, which does not change significantly in the bottom of the boreholes about 25 years old. While there is an enormous increase in Na, K, Ba and Sr, Fe and Mn, there is a major decrease in Mg. The fish scales from 70 to 78 cm (6-8 years old) are approaching already the level of francolite-type hydroxylapatite. The high Na content indicates carbonate substitutions for OH or PO 4 group. Consequently, environmental interpretations based on the chemistry of fossil hydroxylapatites require extreme caution. In recent fish scales, the element concentrations reflect not only the position in the trophic pyramid but also a complicated interplay of the diet, physiological processes and environmental contamination.

Do fish remains provide reliable palaeoenvironmental records? An examination of the effects of cooking on the morphology and chemistry of fish otoliths, vertebrae and scales

“…These data indicate that the chemistry of the hydroxyapatite in the scale structure reacts differently to the other fish hard-parts when heated. The alkaline earth elements, Mg and Sr were greater in the treatment groups, suggesting that the use of Sr as a palaeothermometer in scales is problematic, in agreement with Kalvoda et al (2009), who found that early diagenetic alteration in fish scales is so profound that palaeoecological interpretations are not possible. Differences may also reflect that scales are in direct contact with the environment unlike otoliths and vertebrae.…”

Application of benchtop micro-XRF to geological materials

“…These energy ranges also show up as green and red flecks in patches of quartz ("Q" on Figure 7A), suggesting that the quartz patches are polycrystalline, and that the quartz grains are randomly oriented. Whilst hydroxyapatite is a common component of fish scales (Lanzing and Wright 1976;Ikoma et al 2003;Kalvoda et al 2009), these scales are practically invisible on the fossil itself. It is not clear whether the scales have simply been preserved in a way that is not visibly obvious, or whether they are preserved beneath a thin layer of limestone, but given the low atomic number of P and the low energy of X-rays it emits, we would expected that P-derived X-rays would be attenuated by just a few micrometers of overlying material and it is more likely that the scales have been preserved but are almost invisible to the naked eye.…”

New Insights in the Ontogeny and Taphonomy of the Devonian Acanthodian Triazeugacanthus affinis From the Miguasha Fossil-Lagerstätte, Eastern Canada

“…Bioapatites usually display small particle sizes and significant carbonate contents [15,52]. In addition, apatite particles in bones of living animals are coated by a poorly-ordered hydrous phosphatic phase [53] and associated with organic polymers (collagen), which transform [54] or decay after an animal's death [55]. In contrast, carbonate-fluorapatite is less soluble than bioapatite [26,54] and often represents an ultimate stage of recrystallization of biomineralized anatomical structures in geological environments [26,28,52,54,56].…”

“…In addition, apatite particles in bones of living animals are coated by a poorly-ordered hydrous phosphatic phase [53] and associated with organic polymers (collagen), which transform [54] or decay after an animal's death [55]. In contrast, carbonate-fluorapatite is less soluble than bioapatite [26,54] and often represents an ultimate stage of recrystallization of biomineralized anatomical structures in geological environments [26,28,52,54,56]. Carbonate-fluorapatite also occurs in sedimentary environments as an authigenic mineral, likely produced from the bacterial decay of organic matter [57][58][59][60].…”