Middle Miocene Climate Transition as reflected by changes in ichnofacies and palaeosols from Patagonia, Argentina

Abstract

The ichnofacies and palaeosols from the La Pava and Collón Curá formations were studied to shed light on the evolution of terrestrial ecosystems from Patagonia (Argentina) during the Middle Miocene Climate Transition. At Paso del Sapo, Cerrito Terciario and El Petiso localities (Chubut province), the La Pava Formation included Coprinisphaera ispp., Rosellichnus patagonicus, Rebuffoichnus casamiquelai, Feoichnus challa and burrows of spiders and earthworms, representing a case of the Rosellichnus ichnoassemblage of the Coprinisphaera Ichnofacies. Some of the components of this ichnoassemblage, scarce or absent in Cenozoic formations older than La Pava, are present in extant Patagonian habitats, pointing in the direction of extant invertebrate fauna. At El Petiso locality, the Collón Curá Formation included Celliforma ispp., Rosellichnus patagonicus, Fictovichnus ispp., Teisseirei barattinia and Teisseirei paladinco isp. nov., representing a case of the Celliforma Ichnofacies. The La Pava Formation comprises brownish, argillic, granular and strongly-developed palaeosols (Mollisols and Alfisols) formed in mildly stable to long-lasting landscapes, whereas the Collón Curá Formation comprises calcic, tuffaceous, paler and weakly-developed palaeosols (Andisols, Aridisols) formed in unsteady and ashy environments. The ichnofacies and palaeosols from the La Pava Formation indicate wooded grasslands developed in seasonal, subhumid and temperate-warm conditions, whereas those from the Collón Curá Formation indicate a habitat with reduced plant cover similar to semiarid and temperate-warm dry woodlands or bushlands. This shift towards more arid conditions in Patagonian landscapes would have been coeval with climatic changes corresponding to the Middle Miocene Climate Transition, a lapse of global temperature decrease associated with extensive drying.