Seawater properties based on clumped isotope analyses of macrofossil assemblages from the Upper Cretaceous–lower Paleocene Type-Maastrichtian area

Abstract

Carbonate fossils from the Maastrichtian Type area offer important insights into climate dynamics across the Cretaceous/Paleogene boundary. While previous research has established the biostratigraphy and a carbon isotope-based geochronological timescale, allowing for global data comparison, constraints on the local seawater properties remain limited. Our study utilizes oxygen and carbon isotopes, as well as clumped isotope thermometry to reconstruct seawater temperature and its oxygen isotope composition based on carbonate fossil assemblages. Novel analyses of fossil echinoderms, brachiopods, gastropods, bivalves, bryozoans and existing studies were clustered according to their stratigraphy and show temperature fluctuations ranging between 18.3 − 3.2 + 3.4 to 22.7 − 4.9 + 5.1 °C (±95 % CI) that together with existing studies temporary match varying activity of Deccan Trap volcanism. The mean temperature estimate for the late Maastrichtian–early Danian of 20.6 − 1.2 + 1.2 °C is slightly warmer than modern annual sea surface temperatures at the same latitude and in line with palaeoclimate simulations using 3 times the preindustrial atmospheric pCO2 as model input. The oxygen isotope composition of the shallow sea environment fluctuate between 0.3 − 0.9 + 0.9 to 1.0 − 0.9 + 1.0 ‰, together with existing data even to slightly negative values. These fluctuations reflect the highly dynamic hydrologic conditions linked to variations in the evaporation/precipitation budget, sea-level fluctuations and eventual changes in seawater circulation. This study on fossil assemblages from the Maastrichtian Type area shows the dynamic seawater conditions in shallow sea systems and the urgent need for higher spatial and subseasonal resolution when reconstructing regional climate conditions in epeiric marine environments.