Climate and sea-level changes across a shallow marine Cretaceous-Palaeogene boundary succession in Patagonia, Argentina

摘要

Upper Maastrichtian to lower Paleocene, coarse-grained deposits of the Lefipan Formation in Chubut Province, (Patagonia, Argentina) provide an opportunity to study environmental changes across the Cretaceous-Palaeogene (K-Pg) boundary in a shallow marine depositional environment. Marine palynological and organic geochemical analyses were performed on the K-Pg boundary interval of the Lefipan Formation at the San Ramon section. The palynological and organic geochemical records from the San Ramon K-Pg boundary section are characteristic of a highly dynamic, nearshore setting. High abundances of terrestrial palynomorphs, high BIT-index values and the occasional presence of plant fossils are indicative of a large input of terrestrial organic material. The organic-walled dinoflagellate cyst (dinocyst) assemblage is generally dominated by Senegalinium and other peridinioid dinocyst taxa, indicative of high-nutrient conditions and decreased salinities, probably associated with a large fluvial input. The reconstructed sea surface temperatures range from 25 degrees C to 27 degrees C, in accordance with the tropical climate inferred by palynological and megafloral studies. As in the Bajada del Jaguel section, similar to 500km north-north-east of San Ramon, peaks of Senegalinium spp. were recorded below and above the K-Pg boundary, possibly related to enhanced runoff resulting from more humid climatic conditions. The lithological, palynological and organic geochemical records suggest the occurrence of a sea-level regression across the K-Pg boundary, resulting in a hiatus directly at the boundary in both sections, followed by a transgression in the Danian.