Maastrichtian climate of southern Patagonia (Argentina): An approach from paleosols of the dinosaur-bearing Chorrillo Formation

Abstract

The upper Maastrichtian dinosaur-bearing Chorrillo Formation in southern Patagonia (~50 S, Austral-Magallanes Basin, Argentina) preserves successions of paleosols dominated by vertic features (i.e., the Argentino Lake hydromorphic Vertisols, the Perito Moreno Glacier calcic Vertisols, the Anita Farm Vertisols, the Centinela River Histosols, and the Chorrillo Malo Farm argillic Vertisols). To shed new light on and improve our understanding of the climate conditions that prevailed in southern Patagonia prior to the K/Pg extinction event, we used bulk geochemistry of the Chorrillo Formation paleosols to quantitatively reconstruct the latest Cretaceous climate at midehigh paleolatitudes of the Southern Hemisphere and compare them with late Maastrichtian global climate data derived from paleosols-based geochemical records. Bulk geochemical data indicate that pedogenesis occurred under moderate chemical weathering rates, which operated in a humid climate with a thermic regime (temperate-subtropical). These conditions align with previous qualitative interpretations based on macro- and micromorphological and mineralogical analyses of these paleosols, as well as palynological analyses of the Chorrillo Formation, which further demonstrate seasonality in rainfall. The climate data presented here are consistent with global paleoclimate reconstructions, where our study area (paleo-54 S) lies within the Maastrichtian paleo-Kooppen climate zone “Temperate humid subtropical,” suggesting that during the Maastrichtian, subtropical conditions extended toward the poles by at least 22 of latitude in South America. This research provides new, relevant quantitative paleoclimatological data from the poorly constrained midehigh paleolatitudes of the Southern Hemisphere, refining current latest-Cretaceous climate reconstructions.