Cherts formed from siliceous sponge spicule accumulations as recorders of changing environmental conditions in the shallow marine realm after the End Triassic ecological crisis

• Applicants: Professor Dr. Joachim Reitner; Professor Dr. Michael Tatzel
• Subject Area: Palaeontology ; Geology ; Mineralogy, Petrology and Geochemistry
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 558923374

The End Triassic extinction event was caused by unprecedented high CO2-emmission rates resulting from CAMP volcanism (Central Atlantic Magmatic Province) associated with the opening of the Central Atlantic Ocean. This major crisis for marine invertebrates and calcifiers during the Triassic-Jurassic transition thus serves as partial analogue for the present-day situation in which we just begin to see the effects of even higher CO2-emmission rates. Long-term effects on marine ecosystems are uniquely recorded in sedimentary archives of the Triassic-Jurassic boundary that we target here to answer fundamental questions on the recovery of marine ecosystems following CO2-induced biological crises. Siliceous sponge meadows established as alternate ecosystem subsequent to the ecological crisis. We will investigate if sponges have reduced dissolved Si concentrations and possibly modified (micro)nutrient element concentrations. As sessile filter-feeders that impact marine nutrient cycling and dissolved silica levels, siliceous sponges are predicted to have played a crucial role to moderate high levels of nutrients and dissolved silica, which resulted from a high weathering intensity under greenhouse climate conditions. To date we still mostly lack evidence for such geosphere-biosphere coupling in the Earth System. It is also unknown which mechanisms have led to the decline of sponge meadows and to the return to the initial ecosystem state. To fill these gaps in our understanding, we exploit the characteristic fractionation of Si isotopes by siliceous sponges that will have left a unique signature in Lower Jurassic cherts and spicules dispersed in carbonate rocks. We will study the excellent exposures of the Triassic-Jurassic boundary at field sites in Nevada and the Northern Alps. To reconstruct changes in the silica cycle during high nutrient and Si-fluxes to the ocean under strong greenhouse conditions, we will analyze and model the Si isotope evolution across the depositional records. How sponge proliferation may have affected nutrient cycling will be assessed using isotopes of carbon and nitrogen that respond to changes in nutrients, primary productivity, carbon burial as well as to the seawater redox state. Overall this work will provide basic knowledge on the role of siliceous sponges following CO2-induced marine biotic crises and thus provide an essential contribution to our understanding of the biosphere-geosphere coupling in the Earth System.

• DFG Programme: Research Grants
• International Connection: USA
• Co-Investigator: Dr. Jens Dyckmans
• Cooperation Partners: Professor Frank A. Corsetti, Ph.D.; Professor Dr. Josh West