Neotectonic activity in the Sierra Baja de San Marcos-Cruz del Eje area, west flank of Sierras Pampeanas Orientales

Abstract

The San Marcos Sierra-Cruz del Eje mountain-piedmont (Córdoba province, Argentina) is a key area in order to analyse the neotectonic behaviour of the Sierras Pampeanas Orientales. In this place, the evolution of recent Andean faulting activity has been temporally and spatially determined by multiple control of structural, geomorphological, sedimentological, palaeontological and radiometric data taken from the morphostructural Sierra Baja de San Marcos unit and surrounding areas. Evidence of the Late Quaternary reactivation in the Sierra Baja de San Marcos fault, a striking reverse fault with a western vergence, and strike and dip displacements, is here presented. As a result, a series of tectonic events and landscape modifications are described. The last ones are demonstrated by avulsion deposits of the Quilpo river, by terrace levels linked to the present channels of the la Costa (San Marcos) and Quilpo rivers, and by changes in the main drainage pattern of the region. A ¹⁴C age of 2560± 120 years before present for the avulsion deposits of Quilpo river allows to define a first Late Holocene step in the Sierra Baja de San Marcos fault activity. The observations carried out in an excavated trench confirm its north-western extension, a second Late Holocene movement and determine that it exhibits characteristics alike others transpressive faults with neotectonic activity in the Sierras Pampeanas Orientales.