Inoceramid sclerochronology - Advancing Late Cretaceous climate reconstructions
Final Report Abstract
The goal of this project was to establish inoceramid shells as proxy archives for seasonally resolved environmental reconstructions and advance our understanding of the climate variability of the greenhouse Late Cretaceous world. New diagenetic screening techniques, sampling strategies, and data handling approaches were developed to access the life history traits of these organisms and extract unbiased environmental information from their geochemical proxy records. Information on seawater seasonality provided an unprecedented insight into the atmospheric and oceanic feedbacks to global climate changes of this epoch. The main results were as follows: (1) We have demonstrated that, when carefully screened for diagenetic alteration, inoceramid shells are a powerful archive for ultra-high-resolution climate reconstructions. The studied species recorded full seasonal amplitudes in their shells. Facies analysis combined with a multi-taxon stable isotope analysis enabled the recognition of chemosymbiosis and related vital effects on the geochemical record. Unbiased inoceramid δ18O values provided sea surface temperature of great reliability. Through the use of different bivalve species, we were able to estimate seasonal temperatures in different water depths. (2) Some inoceramid species harbored thioautotrophic bacteria, which allowed the host bivalves to survive in oxygen-depleted and H2S-rich environments. Fossils from cold seeps can retain the aragonitic shell layer. However, because of the exposure to 16O-enriched pore fluids during the life of the organisms, their δ18O-record cannot be used for temperature estimates. (3) Altered LMC rims around individual prisms formed during early burial and contain geochemical information of pore fluids near the seafloor. The shell volume occupied by this altered phase can be estimated using cps-resolved LA-ICP-MS data. If rims do not exceed 8% of the shell volume, the specimens are suitable for δ18O-derived temperature reconstructions. (4) Late Turonian benthic temperatures of the Bohemian Cretaceous Basin were reconstructed for the first time. Water temperatures during and after the Hyphantoceras Event were on average 19 °C and 21 °C, respectively. Climate warming, however, predominantly affected the summer temperatures (at least +4.0 °C), whereas winter temperatures remained more or less invariant (not more than +1.0 °C). (5) Strong vertical gradient in water temperature (15 °C) at the northwestern margin of Tethys suggests the existence of cold bottom water currents from North Atlantic high latitudes. The strong vertical difference in annual temperature amplitudes (ΔTsurface = 11°C; ΔTbottom < 2°C) hints to the existence of a steady thermocline and contrasts with the active coastal upwelling system postulated by previous authors. (6) Density/salinity-driven vertical migration of surface water masses controlled the seasonal temperature oscillations (up to 14°C) in the outer shelf setting of the Western Interior Seaway. To survive to the limited oxygen and food supply at the bottom sea, inoceramid harbored sulfide-oxidizing chemosymbionts. In the future, similar studies should be conducted in other regions and other time intervals of Late Cretaceous during which major climate shifts occurred. The single-prism sclerochronology approach can be particularly powerful. It may also be worthwhile to further investigate how the trace and minor element content of the shells as well as heavy isotopes (e.g., Nd) can be put at work.
Publications
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2018. The giant inoceramid Platyceramus platinus as a high-resolution paleoclimate archive for the Late Cretaceous of the Western Interior Seaway. Cretaceous Research 86, 73-90
Walliser EO, Mertz-Kraus R and Schöne BR
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2019. Sclerochronological study of the gigantic inoceramids Sphenoceramus schmidti and S. sachalinensis from Hokkaido, northern Japan. Lethaia, 52, 410-428
Walliser EO, Tanabe K, Hikida Y, Shirai K and Schöne BR
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2020. An evaluation of inoceramid single-prism sclerochronology. Palaeogeography, Palaeoclimatology, Palaeoecology, 547, 109690
Walliser EO, Fröhlich L, Vonhof H and Schöne BR
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2020. Late Turonian climate variability in the Bohemian Cretaceous Basin –A sclerochronological study of Inoceramus hercules shells from the Úpohlavy working quarry (Czech Republic). Palaeogeography, Palaeoclimatology, Palaeoecology, 560, 109996
Walliser EO, Vodrážka R, Höche N, Voigt S and Schöne BR
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Paleoceanography of the Late Cretaceous northwestern Tethys Ocean: seasonal upwelling or steady thermocline?. PLoS ONE 15, e0238040
Walliser EO and Schöne BR 2020
