Oxygen isotopes in cherts from the Rhenish Massif record paleo-heat flow and burial rates

Oxygen isotopes in sedimentary rocks have long been used to reconstruct paleo-surface temperatures. Chert, a microcrystalline form of SiO₂, has also been explored as a paleotemperature proxy, but the factors controlling its isotopic composition remained uncertain. A recent numerical model of silica diagenesis has now linked chert oxygen-isotope ratios directly to paleo-heat flow, opening new opportunities for its application [1].

Diagenetic chert forms when amorphous silica (opal-A) dissolves and reprecipitates, passing through an opal-CT intermediate before becoming microcrystalline quartz. The oxygen-isotope ratios (δ¹⁸O, Δ′¹⁷O) in the resulting chert capture the temperature and fluid composition at the depth of the opal-CT to quartz transition. By simulating that diagenetic transition, the new model relates δ¹⁸O_chert and Δ′¹⁷O_chert to burial temperatures, pore fluid alteration and heat flow.

We use the model to reconstruct paleo-heat flow during prograde silica phase transformation and derive burial rates and pore fluid alteration across the Rhenohercynian basin. Our data reveal paleo-heat flow in the order of 50 to 70 mW m^-2, agreeing with a previous model [2] and high burial rates in the east of up to 80 m Myr^-1, agreeing with the thickness of overlying turbidites. Burial rates and clay mineral content coincide with ¹⁸O-depleted compositions of cherts, i.e compositions in three isotope space that deviate from the expected temperature-equilibrium. This dataset lays the foundation for a new tool to study the thermal- and burial histories of sedimentary basins.

[1] Tatzel, et al. (2022) PNAS 119

[2] Littke et al. (2000) Geol. Soc. Spec. Publ. 179

Details

Author

Oskar* Schramm1, Katharina Ebert2, Patrick J. Frings3, Tommaso di Rocco4, Andreas Pack4, Volker Karius5, Nils Keno Lünsdorf5, Dieter Korn6, Daniel Herwartz7, Michael Tatzel5

Institutionen

1Department of Sedimentology and Environmental Geology, Geoscience Center Georg-August-Universität Göttingen, Germany;Department of Sediment Geochemistry, Institute for Geosciences, Ruhr University Bochum, Germany; 2Department of Sedimentology and Environmental Geology, Geoscience Center Georg-August-Universität Göttingen, Germany;Department of Mineralogy, Leibniz University Hannover, Germany; 3Earth Surface Geochemistry, GFZ Helmholtz Centre for Geosciences, Potsdam, Germany; 4Department of Geochemistry and Isotope Geology, Geoscience Center Georg-August-Universität Göttingen, 37077 Göttingen, Germany; 5Department of Sedimentology and Environmental Geology, Geoscience Center Georg-August-Universität Göttingen, Germany; 6Museum für Naturkunde, Leibniz-Institut für Evolutions- und Biodiversitätsforschung, Berlin, Deutschland; 7Department of Sediment Geochemistry, Institute for Geosciences, Ruhr University Bochum, Germany

Veranstaltung

Geo4Göttingen 2025

Datum

2025

DOI

10.48380/e5aw-fr16

Geolocation

Rhenish Massif

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