New evidences of subaerial volcanism as a trigger for the Kilian event (Aptian-Albian transition) and major climatic changes from offshore Morocco (DSDP Site 545)

Abstract

The Aptian-Albian transition is characterized by the presence of four organic-rich intervals all linked with major disturbances of the carbon cycle. Among these, the second subevent of the oceanic anoxic event (OAE) 1b, also called Kilian event, has an Aptian-Albian transition age and is characterized by a negative carbon isotope excursion. On the contrary of the Paquier OAE1b subevent, the Kilian event was not extensively studied and its triggering mechanisms and its consequences on regional climates remain uncertain. Here we present a geochemical (Rock-Eval, Mercury) and mineralogical (clay minerals) study on late Aptian-early Albian sediment cores from the Deep-Sea Drilling Program (DSDP) Site 545 (offshore Morocco, Eastern North Atlantic) where a Kilian level equivalent is present. Mercury (Hg) content results show two main peaks in the late Aptian, immediately below and above the Kilian level equivalent. The absence of correlations between Hg and total organic carbon and Hg and CaCO 3 indicates that the mercury content is mainly related to subaerial volcanic activity, probably issued from the emplacement of the Kerguelen large igneous province in the Indian Ocean. Mineralogical analyses show that the clay content, in our studied interval, mainly reflect the weathering and climatic conditions in Northwest Africa. The evolution in clay mineral assemblages depicts three distinctive climatic intervals: (i) a seasonally contrasted semi-arid climate below the first Hg anomaly; (ii) a moister and warmer climate during the Kilian level equivalent deposition; and (iii) a rapid transition toward more arid climate post Kilian level equivalent deposition that is linked with the second Hg anomaly (large increases in illite and palygorskite). Therefore, our study confirms that the Kerguelen volcanic activity was probably the trigger of the Kilian event and shows that the resulting changes in the carbon cycle caused two major climate changes before and after the Kilian event and a long term aridification of Northwest Africa. • Hg anomalies occurs immediately below and above the Kilian level. • Kerguelen volcanic activity was likely the trigger of the Kilian event • Three distinct climatic periods can be recognized along the late Aptian. • late Aptian represents a turning point for the Cretaceous climate changes.