The eolian beds of the Famatina Range: Middle Miocene Paleoclimate-tectonic interaction in the Central Andean broken foreland ?

Abstract

The sedimentary history and uplift evolution of the Famatina System, Central Andean broken foreland, is poorly known. Within its central region a thick Cenozoic synorogenic stratigraphic succession ('Calchaquence') is exposed, including Early Miocene to Pleistocene deposits. The aim of this study is to describe and analyze the meaning of a dominantly eolian package (Santo Domingo Member, 266 m) within the El Durazno Formation (1122 m). The stratigraphic position and nature of these deposits allow their correlation with Mid-Miocene units of the Argentine Precordillera, considered to be part of the early foreland basin fill. This member comprises: 1- sandstones with megacross-stratification interpreted as eolian packages, 2- lenticular conglomeradic sandstones and sandy conglomerates interpreted as braided stream deposits, and 3- mudstones with common desiccation cracks formed in playa lake environments. The facies association suggests eolian-fluvial interaction depositional systems developed under a semiarid paleoclimate. Paleowinds trend towards the south with a bimodal pattern to the southwest and southeast consistent with the architecture of longitudinal dunes. Comparison between eolian sands of different geographic contexts leads to the interpretation that the eolianites in Famatina are similar to those presently developing in intermontane regions within the broken foreland. Provenance analysis of the fluvial conglomerates suggests an uplifted granitic basement approximately along the present location of the Sierra de Famatina. This high would have separated the Vinchina depocenter from the eastern Famatina depocenter from its inception. The eolianites of Famatina suggest a severe climatic restriction implying high topographic barriers to the east that prevented the influence of humid eastern winds. A similar situation occurred to the north and northeast in the northwestern Sierras Pampeanas. These intermontane basins would have triggered the climatic restriction favoring local sand seas development and meridional paleowind corridors. This study supports a Mid-Miocene paleoclimatic change previously suggested for northwestern Argentina and introduces new clues with which to consider the Andean foreland partitioning.