Palynological evidence for prolonged cooling along the Tunisian continental shelf following the K-Pg boundary impact

Abstract

The Cretaceous-Palaeogene (K-Pg) boundary mass extinction event is related to major global environmental changes resulting from a large extraterrestrial impact. Organic-walled cyst-producing marine dinoflagellates (dinocysts) survived the K-Pg mass-extinction relatively unscathed, making them ideally suited for reconstructing these environmental changes. So far, one of the best dinocyst records available is from the K-Pg boundary Global Stratotype Section and Point (GSSP) at El Kef (NW Tunisia). There, the dinocyst record shows major fluctuations across the boundary, likely reflecting strong responses to environmental changes. These fluctuations have so far not been confirmed by other studies. Therefore, in this study we performed a high-resolution marine palynological study on a closely spaced sample set from the Elles section, some 75km south of El Kef, in order to generate a palaeoenvironmental and palaeoclimatic record across the K-Pg boundary to allow verification and refinement of earlier reported environmental changes. To better constrain the reconstructions based on qualitative biotic proxies we employed the quantitative sea surface temperature proxy TEX<inf>86</inf>. Unfortunately, the TEX<inf>86</inf> proxy record of the studied section is compromised because of post-depositional oxidation. However, the diverse dinocyst assemblages at Elles show strong fluctuations similar to the El Kef record, therefore confirming the earlier recorded signals, showing rapid, regionally consistent changes. These records imply that the latest Cretaceous was characterized by a gradual cooling trend and the onset of relative sea level fall. Within the immediate post-extinction interval, in the first thousands of years after the impact, dinocyst assemblages reveal multiple incursions of higher-latitude dinocyst species implying repeated pulses of cooling. These results signify that the earliest Danian climatic and environmental conditions were relatively unstable across the Tunisian shelf.