Tethyan carbonate carbon isotope stratigraphy across the Jurassic‐Cretaceous boundary: An indicator of decelerated global carbon cycling?

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Abstract
The carbon isotope record in four pelagic carbonate sections from the Southern Alps (northern Italy) across the Jurassic‐Cretaceous boundary has been correlated to biostratigraphy and magnetostratigraphy. The carbon isotope curve from bulk carbonates shows a decrease from Kimmeridgian to Early Tithonian (CM24–CM22) values of δ13C=+2.07 (± 0.14)‰ to Late Tithonian and Berriasian (CM18–CM14) values of δ13C=+1.26 (± 0.16)‰. The change in the carbon isotope record coincides with changes in Tethyan calcite and silica accumulation rates, with a drop in the calcite compensation depth in the Atlantic and Tethys oceans and with changes in organic carbon burial along the Eurasian margin of the Tethys. Reduced surface water productivity due to diminished transfer rates of biolimiting elements into the Atlantic and Tethys oceans can explain these observations. The decreased transfer rates of elements such as silica or phosphorus from continents into the oceans resulted from drier climatic conditions and decreased water runoff on continents bordering the Tethys and Atlantic oceans. The proposed changes in Tithonian ‐ Berriasian ocean chemistry and paleoclimate suggest that variations in the global carbon cycle were coupled with changes in the global hydrological cycle and in associated material cycles.