From Buenos Aires to Santa Fe: Darwin's observations and modern knowledge.

Abstract

During his historical voyage around the world, Darwin raided deeply in the South American interior, travelling over 600 kilometers from Buenos Aires to the north along the Río Paraná. During that journey, he crossed a vast plain characterized by aeolian sediments, something unfamiliar to a European naturalist. However, Darwin's acute observation powers and precise descriptions are noteworthy. After more than 170 years since his visit, modern geological knowledge identifies several sectors in the Buenos Aires-Santa Fe region. One of them (the Tertiary at La Bajada) he described admirably and others such as the Paraná flood plain were brilliantly abstracted in only two sentences. In short, Darwin traversed a first sector (Buenos Aires-Rosario) characterized by aeolian and paludal Early Pleistocene sediments. From Rosario to Santa Fe the plain is formed by Late Pleistocene aeolian and fluvial units. At La Bajada (presently Paraná city) lies exposed the marine Miocene and in SW Entre Ríos is a reconstructed loess-paleosol sequence generated at the Early/Middle Pleistocene transition. The Paraná flood plain and the littoral complex at the mouth (practically not observed by Darwin) underwent rather complex Holocene episodes.