Metamorphosed Permian vertebrate fossils: geochemistry and mineralogy of “white” sharksArns, A.a,c,d,1, Tomaschek, F.b, Alig E.c, Weber, K.a, Vonhof, H.d, Fischer, J.e, Voigt, S.e, Tütken, T.a

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Figure 1: Quarry wall exposing the Kuselit intrusion (marked with +) into Lower PermiansiliciclasAc/calcareous lake sediments at the Remigiusberg quarry within the SNB, SWGermany. The near-concordant contact of the sill and sediments is indicated by a dashed line.The straAgraphic posiAon of white fossils within the sedimentary sequence is highlighted by astar.

1aarns@students.uni-mainz.de, a Applied and Analy4cal Paleontology, Ins4tute of Geosciences, Johannes Gutenberg University, 55128 Mainz, Germany, b Ins4tute of Geosciences,University of Bonn, 53115 Bonn, Germany, c Ins4tute of Inorganic and Analy4cal Chemistry, J. W. Goethe University, Frankfurt am Main, 60438 Frankfurt am Main, Germany, dDepartment ofClimate Geochemistry, Max Planck Ins4tute for Chemistry, 55128 Mainz, Germany, e Urweltmuseum GEOSKOP / Burg Lichtenberg (Pfalz), 66871 Thallichtenberg, Germany

Figure 2: Photomicrographs of cross-sections of white Lebachacanthus sharkteeth from the Remigiusberg quarry.Note that LA-ICP-MS spots and lines arevisible.

Figure 5: Black shark teeth ofLebachacanthus from a synchronousblack shale formaAon within the SNB,for comparison. Note that LA-ICP-MSspots and lines are visible.

Figure 4: X-ray diffracAon paXerns of a) shark tooth denAne from fossil black(SZ1, black line) and white (WZ1, grey line) Lebachacanthus, as well as a recentshark (green line) for comparison, and b) cow bone, tempered in air at 55 to900 °C. A higher crystallinity is reflected by lower FWHM of reflexes.

Figure 3: Dimensionless thermal model of peak temperature depending on thedistance to sill’s centre. Peak metamorphic temperature T is given in relaAon tointrusion temperature TK and corrected against background temperature TS.Typical parameters for crustal lithologies have been chosen. The half width of thesill was taken as 30 m, the rock density was taken equal to 2400 kg m-3 and thespecific heat capacity was 1000 J K-1 kg-1. At esAmated Kuselit (i.e. andesite)intrusion temperature of 1000 °C and TS of 100 °C, the fossils will experience apeak temperature of around 500 °C. The posiAon of the fossils with respect tothe sill centre is indicated by a star.

The Saar-Nahe Basin (SNB) is an intra-mountainous basin in SWGermany, that was formed during the Variscan orogeny and hasaccommodated a freshwater lake-system during the LateCarboniferous/Early Permian. Intense syn- and post-sedimentarymagmatic activity has affected the basin (von Seckendorff et al., 2004).From the Remigiusberg Formation at Remigiusberg quarry (Fig. 1),vertebrate fossils in exceptional white-coloured preservation have beenrecovered, among them the oldest amniote fossil of Germany (Voigt etal., 2014).Due to close proximity to an andesitic sill, the Kuselit, fossil remainshave likely been affected by hydrothermal/contact metamorphism,causing the special type of preservation. Here we analysed teeth fromthe extinct freshwater shark Lebachacanthus, to assess geochemicaland mineralogical aspects of this particular diagenetic setting.

Preliminary results

TS 1.1 | D1168 | EGU2020-18533 | 06.05.2020

Fossil white-coloured shark teeth from the Remigiusberg quarry(Fig. 2, Fig. 6), display intense alteraUon due to high temperaturehydrothermal/contact metamorphism, clearly disUnguishablefrom that of contemporaneous black-coloured shark teethdiageneUcally altered at low temperature in black shale facies(Fig. 5).Element and isotope data indicate different diageneUc historiesfor black and white teeth. Elements associated withhydrothermal fluid acUvity such as U, Cu, Fe, Zn and Al areenriched in white teeth. Other elements, such as Sr, Ba and Y aredepleted. REE pa^erns are similar, however, REE concentraUonsare lower in white teeth.In situ LA-ICP-MS U-Pb daUng yielded none-deposiUonal ages forshark teeth of both preservaUon types due to open-systembehaviour of the U-Pb system and high U mobility.Stable isotopes (13C, 18O) point to different types and intensiUesof diageneUc alteraUon for black and white teeth. Nevertheless,all shark teeth are preserved as carbonated fluorapaUte,however, with clearly elevated crystallite dimensions in the whiteteeth (Fig. 4).

In experimentally tempered cow bone, which structurally resemblestooth denUne, bioapaUte crystallinity, indicated by the sharpness ofXRD reflexes (Fig. 4), increases strongly above 500 °C due tosintering and loss of organic compounds (e.g. Munro et al., 2007).The significant difference in black and white fossil shark teethcrystallinity is believed to reflect likewise intensely elevatedtemperature affecUng white fossil shark teeth (Fig. 4). Followingthat, a preliminary peak temperature of ≥ 500 °C was reconstructedfor the Remigiusberg seeng, which is in good agreement withthermal condiUons calculated from a simple thermal model (Fig. 3).High temperature, and possibly hydrothermal fluid overprint, likelydisintegrated and removed organic ma^er from the teeth, whichprobably led to increased apaUte crystallinity and the white colour.Fossil bioapaUte crystallinity may serve as a proxy for reconstrucUngdiageneUc thermal history, especially for high temperatures.However, to reach more accurate temperature esUmates forsedimentary basins based on bioapaUte crystallinity of fossils, moreexperimental constraints are needed to be^er represent geologicalcondiUons.

Voigt, S., Schindler, T., Wuttke, M., Spindler, F., Rinehart, L., 2014. On a potential fossil hotspot for Pennsylvanian – Permian non-aquatic vertebrates in central Europe. Freiberger Forschungshefte C 458, 39–44.von Seckendorff, V., Arz, C., Lorenz, V., 2004. Magmatism of the late Variscan intermontane Saar-Nahe Basin (Germany): A review. Geological Society Special Publication 223, 361–391. Munro, L.E., Longstaffe, F.J., White, C.D., 2007. Burning and boiling of modern deer bone: Effects on crystallinity and oxygen isotope composition of bioapatite phosphate. Palaeogeography, Palaeoclimatology, Palaeoecology 249, 90–102.

Figure 6: ArAculated whitefossil Lebachacanthus, asshown at GEOSKOP.

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For an esAmated Kuselitintrusion temperature of1000 °C, a peak metamorphictemperature of 500 °C affectssediments in 5 m distancefrom contact.

T

STOE Powder Diffraction System 04-May-2020

Range 1 : 2Theta(begin,end,step) = 3.000, 99.990, 0.010 3100.0 sec/step Imax = 3111 (PSD Step 0.20 100.0 sec/step)Detector : Linear PSD / Moving / Fixed Omega Scan Mode : Debye-ScherrerDiffract.: Transmission Monochrom. : Curved Germanium (111) Radiation : 1.54060 Copper Generator : 40 kV, 30 mA Stoe 5 Messung am 25.11.2019; 120s/step; psd-step 0.2 Comment : geglühte rezente Rinderknochen (55°C) aus Tübingen (2001); 0.7 mm Kap.: Title : KRi_055File : X:\pub-data\Carina...\KRi_55-KL.raw Created : 25-Nov-19 15:45 by POWDAT

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STOE Powder Diffraction System 04-May-2020

Range 1 : 2Theta(begin,end,step) = 3.000, 99.990, 0.010 3100.0 sec/step Imax = 3288 (PSD Step 0.20 100.0 sec/step)Detector : Linear PSD / Moving / Fixed Omega Scan Mode : Debye-ScherrerDiffract.: Transmission Monochrom. : Curved Germanium (111) Radiation : 1.54060 Copper Generator : 40 kV, 30 mA Stoe 5 Messung am 21.11.2019; 120s/step; psd-step 0.2 Comment : Schwarzer Zahn; 0.5 mm in 0.7 mm Kap.: neue Probe Title : SZ1-dFile : X:\pub-data\Carin...\SZ1-d_2-KL.raw Created : 21-Nov-19 16:00 by POWDAT

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