MagNetZ With Augusto Rapalini (2025/12/10) - Constraint on the End of the Dinosaurs Era in Patagonia

Magnetic Polarity of the Upper Cretaceous Chorrillo Formation, Argentina: Geochronologic Constraints on the End of the Dinosaurs Era in Patagonia The video is also available for download at: https://earthref.org/ERDA/2775/ and can be referenced with the doi: 10.7288/V4/ERDA/2775 Title: Magnetic Polarity of the Upper Cretaceous Chorrillo Formation, Argentina: Geochronologic Constraints on the End of the Dinosaurs Era in Patagonia Author: Augusto Rapalini from Universidad de Buenos Aires, Argentina The Late Cretaceous Chorrillo Formation, exposed in southernmost Patagonia, is a mainly fluvial sedimentary succession of around 500 m thick. It is characterized by an outstanding content of fossil remains that include both vertebrates and invertebrates as well as mega and micro flora. On this basis, it is considered as a key formation to study the biological and ecological evolution immediately before the end-Cretaceous massive extinction event in Patagonia. The Chorrillo Formation has been lately assigned to the Maastrichtian (s.l.), however age of deposition is not determined accurately. To improve its geochronological constraints, a paleomagnetic sampling was carried out along a remotely located and well-exposed cross-section of the formation in March 2024. Despite unexpected snowstorms that limited sampling, we were able to sample eighteen sites distributed along the lower and middle sections of the succession, encompassing a thickness of around 320 meters. After detailed alternating field and thermal demagnetizations a characteristic remanent magnetization was determined at 15 sites. Petrographic observations, rock magnetic experiments and anisotropy of magnetic susceptibility (AMS) and of anhysteretic remanence (AARM) suggest that PSD detrital Ti(poor)-magnetite is the main carrier of the remanence. Correction of inclination shallowing determined by AARM yields a mean direction consistent with that correspondent to the 70 Ma reference poles for South America. Sampled sites showed a single polarity that better constrain the age of the formation, suggesting quite stable environmental and ecological conditions in southern Patagonia not long before the mass extinction. ----------------------------------------------------------- 00:00 - Intro 00:25 - Presentation 36:06 - Questions 40:37 - Announcements