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Cryogenian postglacial climate revealed by dolomite triple oxygen isotopes

Quantitative paleotemperature estimates from the Precambrian are rare due to the scarcity of well-preserved sediments and uncertainties about the isotope composition of ancient oceans. Carbonate triple oxygen isotope measurements (δ18O and ∆’17O), however, can be used to overcome these challenges and estimate climate conditions in deep time.

In this study, we investigated interglacial carbonates from the Cryogenian Oodnaminta Reef Complex in Australia, deposited between the Sturtian and Marinoan Snowball Earth events. According to petrological and sedimentary analyses, dolomitization of originally aragonitic reef components occurred immediately after deposition, along with the precipitation of primary dolomite cements.

Our dolomite data display a negative trend in triple oxygen isotope space that cannot be explained by diagenesis, yet it can be attributed to precipitation from a single fluid at various temperatures. To be able to calculate carbonate precipitation temperatures, we first modelled the oxygen isotope composition of the seawater. Initially, we simulated a range of conceivable seawater compositions using an extended oxygen mass balance model. Subsequently, from the modelled values, we selected those compositions that best fit our samples. The resulting seawaters exhibit δ18O values of around -5‰ and ∆’17O values of around -10 ppm. Such seawater compositions are feasible when considering the fluxes of silicification and carbonatization. Finally, we derived seawater temperatures of 10 °C to 50 °C, indicative of a temperate Cryogenian interglacial climate.

Details

Author
David Bajnai1, Jack Stacey2, Axel Balsliemke1, Malcolm W. Wallace2, Andreas Pack1, Daniel Herwartz3, Ashleigh van Smeerdijk Hood2
Institutionen
1Geoscience Center, University of Göttingen, Germany; 2School of Geography, Earth and Atmospheric Sciences, University of Melbourne, Australia; 3Institute for Geology, Mineralogy and Geophysics, Ruhr University Bochum, Germany
Veranstaltung
GeoSaxonia 2024
Datum
2024
DOI
10.48380/8pch-f375