Maastrichtian soils and climate from southern Patagonia, Argentina

M. SOL RAIGEMBORN; LIZZOLI, SABRINA; DAMIAN MOYANO PAZ; VARELA AUGUSTO; POIRE DANIEL; PEREZ LOINAZE, VALERIA; VERA, EZEQUIEL; MANABE, MAKOTO; TSUIHIJI T; SANO T; NOVAS, FERNANDO

la plata

Congreso; XVIII Reunión Argentina de Sedimentología y IX Congreso Latinoamericano de Sedimentología; 2023

AAS

The Maastrichtian dinosaur-bearing Chorrillo Formation in southern Patagonia (⁓50° S, Austral-Magallanes Basin, Argentina) is a pedogenically modified fluvial succession, which records sedimentdeposition at mid-high paleolatitudes in the Southern Hemisphere. In order to reconstruct thepaleoenvironment and paleoclimate of the Chorrillo Formation, we performed a paleopedological studyof the unit within a well-defined sedimentological and paleontological context, and considering newpaleobotanical 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 geochemistryanalysis) of the paleosols, we show that the Chorrillo Formation paleosols are overall smectite-rich soilswith vertic and redoximorphic features. They are named and classified as: P1: moderately developedhydromorphic Vertisol- like paleosols, P2: calcic Vertisol- like paleosols, P3: poorly developedhydromorphic Vertisol- like paleosols, P4: Histosol- like paleosols, and P5: argillic Vertisol-likepaleosols.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 annualtemperatures (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 ⁓1000mm/year ± 182 and 108 mm/year, respectively, on average.Paleobotanical remains (i.e., macroflora and palynology) through the Chorrillo succession demonstratesdifferent ecological requirements for the inhabited part of the fluvial floodplain, and temperate-warm andseasonally 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 withthe temperate humid subtropical paleo-Köppen climate zone.Overall, these combined data record environmental and climatic conditions during the uppermostCretaceous, and preserve a record of Maastrichtian terrestrial conditions in the mid–high paleolatitudesof the Southern Hemisphere.