Conodont thermometry by Raman spectroscopy on carbonaceous material: a case study from the Northern Calcareous Alps (Mürzalpen Nappe, Eastern Alps)

Abstract

Carnian metapelites from the southeastern segment of the Mürzalpen Nappe (Northern Calcareous Alps, Eastern Alps) were heated to 280-310 °C, estimated by Raman spectroscopy of carbonaceous material (RSCM). This temperature range is correlated to a Color Alteration Index of 5.0-6.5, determined on conodonts from adjacent Anisian to Norian carbonates. Average RSCM temperatures estimated on the conodonts are biased towards higher temperatures. The spectral characteristics of the conodont apatite suggest a composition altered during progressive recrystallization, influencing the band parameters of the included carbonaceous matter. Consequently, accurate conodont RSCM thermometry needs an assessment of apatite alteration.

Raman Spectroscopy of carbonaceous material thermometry in the Carnic Alps (Austria, Italy)

“…3). Remarkably, the correlation between CAI and RSCM temperatures resembles the correlation established for Triassic conodonts (Rantitsch et al, 2020b).…”

Increasing control over biomineralization in conodont evolution

“…Both slope and intercept differed significantly between these two datasets at a confidence level of 0.05. In contrast, our dataset and that by Zhang et al 15 showed strong clustering close (Zhang et al) or directly on the regression line fitted to the values measured by Rantitsch et al 42 . Compared to the other studies, positions of the ν 1 -PO 4 3− band measured for our specimens showed consistently high values with a mean of 964.00 (median 963.99, standard deviation 0.13, n = 30).…”

“…5 ). The datasets by both McMillan and Golding 41 and Rantitsch et al 42 showed high variability in the position and widths of the ν 1 -PO 4 3− band. Model II regression was fitted to the relationship for these two datasets, producing slopes equal to −0.92 (R 2 = 0.63, N = 41) and −1.30 (R 2 = 0.90, N = 153), respectively (Fig.…”

“…Yet highly porous bioapatite tissues, such as bone and dentine, are still known to be susceptible to substantial diagenetic changes 45 , 46 . Conodont crown and its analog tissue, enamel, are the least susceptible tissues to diagenesis 9 owing to their low porosity 47 and low organic contents, but even in these tissues diagenetic exchange of ions and isotopes 9 , 40 and changes in crystallinity 42 can occur. As there are no other studies yet that would assess the crystallographic texture of fossil bioapatite quantitatively, no insights are available yet as to how diagenesis might affect our conclusions.…”

“…4 ). The ν 1 -PO 4 3− band parameters were then compared with those published in other studies 15 , 41 , 42 . Ranged major axis regression of FWHM over PCMI was calculated for each study using the package lmodel2 39 , 81 .…”