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Continental or oceanic weathering processes – What controlled the Late Cretaceous lithium cycle?

The lithium isotopic composition (δ7Li) of marine carbonates is known as a proxy for the chemical weathering intensity of silicate rocks. To evaluate the role of weathering as a sink for atmospheric CO2 during the Late Cretaceous, we generated a 20 Ma δ7Li record (86.3–66.0 Ma) using chalk from Northern Germany as an archive. The late Santonian to Maastrichtian record shows an overall increase of ~4.5‰ with superimposed increases in the late Santonian, early Campanian and across the Campanian–Maastrichtian transition.

The overall increase in δ7Li fits with the Late Cretaceous increase in seawater 87Sr/86Sr. Further, the δ7Li record strongly resembles both the evolution of deep-sea temperatures based on benthic oxygen isotopes and modeled changes in the rate of seafloor spreading. Thereby, increases of δ7Li in the early Campanian and across the Campanian–Maastrichtian transition correspond to major sea level falls, and the latter with a negative δ13C excursion.

These coherences allow three interpretative approaches: (1) Climate cooling controlled the weathering congruency and the magnitude of Li isotope fractionation by clay mineral formation on the continents. (2) Lowland exposure promoted erosion together with enhanced soil and clay formation after sea level falls. (3) A temperature-dependent fractionation during low-temperature basalt alteration affected the seawater δ7Li signal in a time, when more fresh oceanic basalts where available due to higher spreading rates. The best possible interpretation for the Late Cretaceous δ7Li record and the often-neglected aspects of basalt alteration and reverse weathering need to be further assessed and discussed.


Sandra J. Huber1, Vanessa Schlidt1, Jorit F. Kniest1, H.-Michael Seitz1, Jacek Raddatz1, Horst R. Marschall1, Silke Voigt1
1Institute of Geosciences, Goethe University Frankfurt, Altenhöferallee 1, 60438 Frankfurt am Main, Germany;Frankfurt Isotope and Element Research Center (FIERCE), Goethe University Frankfurt, 60438 Frankfurt am Main, Germany
GeoBerlin 2023