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Effect of depositional rates on proxies in palaeoenvironmental reconstructions – new article by Jarochowska et al.

Brachiopod shell bed from the Silurian of Gotland

The depositional rate reflects how quickly a given thickness of sedimentary rock forms. Abrupt changes in environmental signals recorded in an interval of strata can be the result of (1) fast changes in environmental conditions and average sedimentation rate or (2) average changes in environmental conditions and slow sedimentation rate. To correct for this effect, age models are used, but they are often not available or lack sufficient resolution to detect rapid changes in the environment. The new study by Dr. Emilia Jarochowska and co-authors, published in Paleoceanography and Paleoclimatology, proposes a method to estimate relative changes in depositional rates and test it in a sedimentary section on the Swedish island of Gotland. The section preserves geochemical records of a carbon cycle perturbation, expressed as shifts in carbon isotopes. It has also been proposed to record periods of oxygen depletion in marine water, detectable as enrichment in elements sensitive to redox conditions. The authors measured these parameters and compared the original values as preserved in the section with values corrected for depositional rates. The study shows that (1) perturbations of the carbon cycle were most likely more rapid than they appear in the section and (2) high depositional rates during the carbon cycle perturbation partly disguised the intervals of oxygen depletion.
This work was co-authored by Dr. Emilia Jarochowska, Dr. Theresa Nohl (currently Vienna University, Madleen Grohganz (currently at Bristol University), Niklas Hohmann, Prof Thijs R. A. Vandenbroucke (Ghent University) and Prof. Axel Munnecke. It employs the DAIME package for R Software developed by Niklas Hohmann in his BSc thesis.

You can also see a presentation on this work on GeoZentrum’s YouTube channel.

Jarochowska, E., Nohl, T., Grohganz, M., Hohmann, N., Vandenbroucke, T. R. A., & Munnecke, A. (2020). Reconstructing depositional rates and their effect on paleoenvironmental proxies: The case of the Lau Carbon Isotope Excursion in Gotland, Sweden. Paleoceanography and Paleoclimatology, 35, e2020PA003979. https://doi.org/10.1029/2020PA003979