Speaker: Prof. Dr. Steven Goderis

Language: English

Abstract:

In 1980, the finding of a major positive iridium (Ir) anomaly of several parts per billion (ppb) at the Cretaceous-Paleogene (K-Pg) boundary in Gubbio (Italy) and Caravacca (Spain) was the key observation that triggered the hypothesis that a large asteroid or comet collided with Earth inducing the last major mass extinction, and the subsequent demise of the non-avian dinosaurs. The fine (cm thick) boundary clay layer that records the Ir anomaly is also enriched in the other highly siderophile elements (HSE) and shows a less radiogenic value of 187Os/188Os unmistakably supporting an extraterrestrial contribution. Over the years, this anomalous Ir-HSE enrichment has been reported at more than 200 K-Pg boundaries worldwide, including continental and marine sections. In close proximity to the Chicxulub crater, identified as the impact site in the 1990s, the Ir-HSE anomaly is detected at the very top of expanded K-Pg sequences. Interestingly, there is no apparent major fractionation between the HSE according to the distance to the crater. At the rim of the Gulf of Mexico, tsunami, seiche and huge debris flows made the K-Pg boundary considerably thicker (up to several meters) and a high influx of sediments dilutes and vertically spreads the extraterrestrial signature. The HSE ratios, together with Os and Cr isotope ratios and a fossil meteorite fragment, made it possible to constrain nature of the impacting asteroid to a specific type of a carbonaceous chondritic projectile (CM- or CO-type). The recent IODP-ICDP Expedition 364 recovered a ~ 1300 m near-continuous core within the peak-ring of the Chicxulub crater. In this core, a ~75 m thick succession of post-impact sediments was deposited on top of the Chicxulub peak-ring suevite sequence, just before the appearance of Paleocene pelagic carbonates. This layer is composed of generally fining-upward, laminated dark brown to dark grayish brown carbonate-rich silty claystone to micrite. A clear positive Ir anomaly in excess of 1 ppb is measured towards its very top, together with a negative shift towards less radiogenic values of 187Os/188Os. Clearly, the fine Ir dust that engulfed the whole planet also settled within the newly formed crater, placing strict time constraints (< 20 years) on the deposition of the transitional unit, and the whole cratering process. Most of all, the identification of the world-famous Ir anomaly on top of the crater sequence conclusively ties Chicxulub to the global Ir layer and all the K-Pg boundary sections worldwide, unequivocally connecting the impact event to the sedimentary sections that record the K-Pg mass extinction.

Practical information:

Location: VUB, campus Etterbeek, Auditorium E0.09

Participation is free of charge for KVCV-members, WK-members pay 2 EUR and non-members 4 EUR.

Payment is made on site, in cash or electronically (Maestro/Visa/Mastercard, also contactless).

Following the lecture, the youth division of KVCV courteously invites you to a reception in the hallways.

Registration is mandatory. Register here.