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Paleosol barometer indicates extreme fluctuations in atmospheric CO₂ across the Cretaceous-Tertiary boundary

¹ Department of Geology, Baylor University, Waco, Texas 76798, USA

We present an atmospheric pCO₂ (p is partial pressure) curve showing extreme fluctuations for the interval between ca. 77 and 63 Ma in southern Alberta, Canada, using a paleosol barometer. Paleosol carbonate nodules (micrite) were collected from 40 Bk horizons among 6 stratigraphic sections for stable carbon isotope analysis. Based on results from the study area, declining atmospheric pCO₂ from 1200 ppmV (V is volume) in the Campanian to 780 ppmV in the Maastrichtian correlates with Late Cretaceous climate cooling and falling sea level as documented in global records. The remarkable rise in atmospheric pCO₂ near 65.5 Ma (1440 ppmV) correlates with volcanic activity associated with the Deccan Traps, rising sea level, and warmer global climates. The decline in atmospheric pCO₂ (760 ppmV) at the Cretaceous-Tertiary boundary and subsequent sharp rise into the Danian (1000 ppmV) occurred during static terrestrial temperatures and sea level. This work provides compelling evidence that atmospheric pCO₂ curves modeled for the Phanerozoic do not offer the resolution needed to understand environmental conditions during catastrophic events in Earth's history.

Key Words: Cretaceous-Tertiary boundary • paleosol CO₂ barometer • atmospheric CO₂ • carbon isotope ratios • partial pressure

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