GONDWANA PALEOSURFACES IN ARGENTINA: AN INTRODUCTION

Resumo

Gondwana paleosurfaces in Argentina were already identified by Juan Keidel and Walther Penck at the beginnings of the 20th century, as well as by other geologists and naturalists of the different European schools that worked in this country. These studies were continued at a very good level in Brazil, thanks to the work of Lester C. King, later on intensively followed by João José Bigarella. However, these concepts gradually disappeared from the Argentine geological scene, dominated by the influence of American geomorphologists, and particularly William Thornbury, who doubted about the existence of such ancient landforms, when one of the main paradigms of the time was that "practically there is no landscape older than the Pleistocene". These landforms are the result of deep chemical weathering and/or pedimentation processes, developed in very stable tectonic and climatic environments, mostly under hypertropical climates, extremely wet, extremely arid or seasonally changing. The Gondwana paleosurfaces or their fragmented remnants have been recognized in Argentina, from north to south, in the basaltic hills of the province of Misiones, the Sierras Pampeanas of the provinces of Catamarca, La Rioja and San Juan, the Sierras Chicas, Sierras Grandes and Sierra Norte of Córdoba province, the Sierras de San Luis, the Sierra Pintada or San Rafael Block of Mendoza province, the Sierras de Tandil, Sierra de la Ventana and the Pampa Interserrana of Buenos Aires province, the Sierras de Lihuel Calel of the province of La Pampa, the Somuncurá or Northern Patagonian Massif in the provinces of Río Negro and Chubut, the Deseado Massif of Santa Cruz province, and the Malvinas/Falklands archipelago. In other regions of Argentina, these surfaces have been down-warped in tectonic basins and are covered by sedimentary and/or volcanic units of various ages. The age for the Gondwana paleosurfaces have been estimated in between the middle Jurassic and the Paleogene. The Gondwana paleosurfaces were uplifted, fragmented, denudated and isolated during the middle to late Tertiary due to the Andean orogeny, and they have remained as mute testimony of the past above extensive pediplains and piedmont deposits, while climate and environments changed to more arid and cooler, approaching the present conditions.