Paleosols as paleoclimate proxies to reconstruct mid-Cretaceous paleoclimate conditions in Central Patagonia, Argentina

Abstract

The paleosols preserved in the Bajo Barreal Formation in central Patagonia (Argentina) provide valuable insightsinto mid-Cretaceous paleoclimatic conditions at mid-paleolatitudes in the Southern Hemisphere. This study integratesmacro-, micro-, and nanomorphological analyses, clay mineralogy, and geochemical data to characterizeand classify the Bajo Barreal’s paleosols and reconstruct their paleoclimate conditions. The Cerro Ballena anticline’sexposure begins with isolated, small-scale channel belts of low connectivity within siliciclastic mudstones(Section A). Upwards, it transitions into sheet-like, interconnected channel-belt complexes interbedded withthinner volcaniclastic floodplain deposits (Section B). We identified four pedotypes in stratigraphic order ofappearance: Cerro Guacho (vertic Alfisols-like paleosols), Ca˜nad´on Vasco (Vertisols-like paleosols), San Bernardo(Ultisols-like paleosols), and Río Deseado (hydromorphic Inceptisols-like paleosols). Section A contains smectiterichvertic Alfisols-like paleosols and Vertisols-like paleosols formed under moderate weathering, dominated byargilluviation, vertization, hydromorphism, and calcification. Section B, in contrast, contains kaolinite-richUltisols-like paleosols and hydromorphic Inceptisols-like paleosols formed under intense weathering conditions,dominated by lixiviation (ferruginization) accompanied by argilluviation and hydromorphism. This progressionreflects a transition from temperate and subhumid conditions with seasonal rainfall (Section A) towarmer (temperate) and humid conditions with perennial rainfall (Section B). This vertical progression parallelsmid-Cretaceous global climate dynamics and potentially reflects changes near the Cenomanian–Turonianboundary and OAE 2, offering valuable contributions to refine Southern Hemisphere paleoclimatereconstructions.