Cenozoic geologic evolution of the lower Colorado River basin, Northern Patagonia, Argentina

ABSTRACT Climatic changes and eustatic sea levels have been assumed to be the most important controllers of the Colorado River alluvial fan in northern Patagonia. Although the alluvial fan occurs in a region considered tectonically stable, there are pieces of evidence that the Miocene Andean orogeny...

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Autores principales:	Seitz,Carina, Vélez,María I., Perillo,Gerardo M.E.
Lenguaje:	English
Publicado:	Servicio Nacional de Geología y Minería (SERNAGEOMIN) 2019
Materias:	Cenozoic sediment Neotectonic activity Colorado river Argentina
Acceso en línea:	http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0718-71062019000100131
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spelling	oai:scielo:S0718-710620190001001312019-02-18Cenozoic geologic evolution of the lower Colorado River basin, Northern Patagonia, ArgentinaSeitz,CarinaVélez,María I.Perillo,Gerardo M.E. Cenozoic sediment Neotectonic activity Colorado river Argentina ABSTRACT Climatic changes and eustatic sea levels have been assumed to be the most important controllers of the Colorado River alluvial fan in northern Patagonia. Although the alluvial fan occurs in a region considered tectonically stable, there are pieces of evidence that the Miocene Andean orogeny has reactivated inherited structures, with subsequent geomorphological changes that date back to the Pleistocene. Besides, the clear evidence of neotectonism in the region and their effects on the evolution of this fan, it has not been studied in detail yet. In this study, we map and analyze six sections outcropping in different terraces of the alluvial fan with the primary aim of disentangling the role of tectonism, climate and eustatic changes on the evolution of the alluvial fan. This study is part of a bigger project aimed to understand the origin of the shallow lakes occurring in northern Patagonia. Our results indicate that the alluvial fan of the Colorado River was established in the area around the Middle Pleistocene. Evidence of deformations in Miocene to Pleistocene units indicates significant neotectonism during the Upper Pleistocene. By the Pleistocene-Holocene transition, tectonism produced incision generating a set of terraces. After this time, an important climate change from semiarid to arid favored the calcretization of some terraces. By the Pleistocene-Middle Holocene, the terraces were covered by ancient eolian sediment accumulated during dry conditions. By the Middle Holocene, a broad alluvial fan developed in the region under a warmer and more humid climate generating the Alluvial Colorado River-III deposit at the T3 terrace. In the late Holocene, aggradation process was favored by a high sea level and temperate-arid climate, producing T4 terrace. At the same time, this climate condition favored the local deflation-sedimentation processes that resulted in the deposition of modern eolian deposits (mE) over the T3 terrace. The depressions generated by the deflation were, later on, occupied by shallow lakes when the climate turn more humid. Subsequently, during regressive sea level condition, ca. 2000 years BP, the T4 terrace was partially eroded and the modern alluvial plain formed.info:eu-repo/semantics/openAccessServicio Nacional de Geología y Minería (SERNAGEOMIN)Andean geology v.46 n.1 20192019-01-01text/htmlhttp://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0718-71062019000100131en10.5027/andgeov46n1-3060
institution	Scielo Chile
collection	Scielo Chile
language	English
topic	Cenozoic sediment Neotectonic activity Colorado river Argentina
spellingShingle	Cenozoic sediment Neotectonic activity Colorado river Argentina Seitz,Carina Vélez,María I. Perillo,Gerardo M.E. Cenozoic geologic evolution of the lower Colorado River basin, Northern Patagonia, Argentina
description	ABSTRACT Climatic changes and eustatic sea levels have been assumed to be the most important controllers of the Colorado River alluvial fan in northern Patagonia. Although the alluvial fan occurs in a region considered tectonically stable, there are pieces of evidence that the Miocene Andean orogeny has reactivated inherited structures, with subsequent geomorphological changes that date back to the Pleistocene. Besides, the clear evidence of neotectonism in the region and their effects on the evolution of this fan, it has not been studied in detail yet. In this study, we map and analyze six sections outcropping in different terraces of the alluvial fan with the primary aim of disentangling the role of tectonism, climate and eustatic changes on the evolution of the alluvial fan. This study is part of a bigger project aimed to understand the origin of the shallow lakes occurring in northern Patagonia. Our results indicate that the alluvial fan of the Colorado River was established in the area around the Middle Pleistocene. Evidence of deformations in Miocene to Pleistocene units indicates significant neotectonism during the Upper Pleistocene. By the Pleistocene-Holocene transition, tectonism produced incision generating a set of terraces. After this time, an important climate change from semiarid to arid favored the calcretization of some terraces. By the Pleistocene-Middle Holocene, the terraces were covered by ancient eolian sediment accumulated during dry conditions. By the Middle Holocene, a broad alluvial fan developed in the region under a warmer and more humid climate generating the Alluvial Colorado River-III deposit at the T3 terrace. In the late Holocene, aggradation process was favored by a high sea level and temperate-arid climate, producing T4 terrace. At the same time, this climate condition favored the local deflation-sedimentation processes that resulted in the deposition of modern eolian deposits (mE) over the T3 terrace. The depressions generated by the deflation were, later on, occupied by shallow lakes when the climate turn more humid. Subsequently, during regressive sea level condition, ca. 2000 years BP, the T4 terrace was partially eroded and the modern alluvial plain formed.
author	Seitz,Carina Vélez,María I. Perillo,Gerardo M.E.
author_facet	Seitz,Carina Vélez,María I. Perillo,Gerardo M.E.
author_sort	Seitz,Carina
title	Cenozoic geologic evolution of the lower Colorado River basin, Northern Patagonia, Argentina
title_short	Cenozoic geologic evolution of the lower Colorado River basin, Northern Patagonia, Argentina
title_full	Cenozoic geologic evolution of the lower Colorado River basin, Northern Patagonia, Argentina
title_fullStr	Cenozoic geologic evolution of the lower Colorado River basin, Northern Patagonia, Argentina
title_full_unstemmed	Cenozoic geologic evolution of the lower Colorado River basin, Northern Patagonia, Argentina
title_sort	cenozoic geologic evolution of the lower colorado river basin, northern patagonia, argentina
publisher	Servicio Nacional de Geología y Minería (SERNAGEOMIN)
publishDate	2019
url	http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0718-71062019000100131
work_keys_str_mv	AT seitzcarina cenozoicgeologicevolutionofthelowercoloradoriverbasinnorthernpatagoniaargentina AT velezmariai cenozoicgeologicevolutionofthelowercoloradoriverbasinnorthernpatagoniaargentina AT perillogerardome cenozoicgeologicevolutionofthelowercoloradoriverbasinnorthernpatagoniaargentina
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Cenozoic geologic evolution of the lower Colorado River basin, Northern Patagonia, Argentina

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