MAASTRICHTIAN SOILS AND CLIMATE FROM SOUTHERN PATAGONIA, ARGENTINA

RAIGEMBORN, M.S.; LIZZOLI, S.; MOYANO-PAZ, D.; VARELA, A.N.; POIRÉ, D.G.; PEREZ LOINAZE, V.S.; VERA, E.I.; MANABE, M.; TSUIHIJI, T.; SANO, N.; NOVAS, F.E.

La Plata

Congreso; XVIII REUNIÓN ARGENTINA DE SEDIMENTOLOGÍA IX CONGRESO LATINOAMERICANO DE SEDIMENTOLOGÍA; 2023

Universidad de La Plata

The Maastrichtian dinosaur-bearing Chorrillo Formation in southern Patagonia (⁓50° S, Austral-Magallanes Basin, Argentina) is a pedogenically modified fluvial succession, which records sediment deposition at mid-high paleolatitudes in the Southern Hemisphere. In order to reconstruct the paleoenvironment and paleoclimate of the Chorrillo Formation, we performed a paleopedological studyof the unit within a well-defined sedimentological and paleontological context, and considering new paleobotanical data of the unit. Using detailed macro- and micromorphological features, clay mineralogy (X-ray diffraction analysis), and molecular weathering indexes of B horizons (whole-rock geochemistry analysis) of the paleosols, we show that the Chorrillo Formation paleosols are overall smectite-rich soils with vertic and redoximorphic features. They are named and classified as: P1: moderately developed hydromorphic Vertisol- like paleosols, P2: calcic Vertisol- like paleosols, P3: poorly developed hydromorphic Vertisol- like paleosols, P4: Histosol- like paleosols, and P5: argillic Vertisol-like paleosols.Such soils took place under a wide range of moderate weathering conditions (CIA-K ⁓76 on average; PWI ⁓25 on average; CALMAG ⁓65 on average; Salinization ⁓0.21 on average). Mean annual temperatures (MAT) calculated based on Salinization and PWI are ⁓13° C ± 4.4 and 2.1° C, respectively, on average. Mean annual precipitations (MAP) estimated based on CIA-K and CLAMG are ⁓1000 mm/year ± 182 and 108 mm/year, respectively, on average.Paleobotanical remains (i.e., macroflora and palynology) through the Chorrillo succession demonstrates different ecological requirements for the inhabited part of the fluvial floodplain, and temperate-warm and seasonally humid conditions. Thus, both abiotic (i.e., paleosols) and biotic (i.e., paleobotanical remains) climate proxies suggest a broadly temperate and seasonally humid climate, which is in agreement with the temperate humid subtropical paleo-Köppen climate zone.Overall, these combined data record environmental and climatic conditions during the uppermost Cretaceous, and preserve a record of Maastrichtian terrestrial conditions in the mid–high paleolatitudes of the Southern Hemisphere.