USING MAGNETOSTRATIGRAPHY TO FIND THE CRETACEOUS-PALEOGENE BOUNDARY IN LA COLONIA FORMATION, PATAGONIA, ARGENTINA

The Cretaceous-Paleogene (K-Pg) boundary marks the occurrence of one of the largest mass extinctions in Earth’s history. The primary cause is thought to be an asteroid impact at Chicxulub, Mexico, approximately 66 Ma. This impact caused a change in global climate and widespread deposition of material ejected from the crater. Currently, there are few continental records of the K-Pg boundary in South America, resulting in poor understanding of its effects there. Globally, boundary markers include ejecta deposits, high iridium concentration, and tsunami deposits. Another method for finding the boundary uses magnetostratigraphy. Chron C29r is an interval of reversed geomagnetic polarity that encompasses the K-Pg boundary, therefore serving as a record of it. This project seeks to determine whether Chron C29r is preserved in the Upper Cretaceous to Paleogene La Colonia Formation in Patagonia, Argentina. Fossils from this formation potentially allow for investigating the extent of the extinction and the pace of biotic recovery in this region after the impact. Samples taken from strata in La Colonia were analyzed to find their paleomagnetic polarity. Results indicate that chron C29r is preserved within an 11-meter interval in the upper portion of La Colonia. Isothermal remnant magnetization experiments indicate that magnetite is the dominant ferromagnetic mineral preserving magnetic remanence in La Colonia facies. Studying the K-Pg boundary in La Colonia Formation contributes knowledge of the K-Pg boundary in South America and therefore contributes to our understanding of how the Earth system reacts to cataclysmic events.