Architecture of intereruptive and syneruptive facies in an Andean Quaternary palaeovalley: the Huarenchenque Formation, western Argentina

ABSTRACT The Huarenchenque Formation is a volcano sedimentary unit deposited to the east of the Plio-Quaternary Andean Magmatic Arc. In order to define depositional settings, two lithofacies associations (fluvial and pyroclastic) were defined. The fluvial facies association is composed of polymictic...

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Autores principales:	Spalletti,Luis A., Colombo Piñol,Ferrán
Lenguaje:	English
Publicado:	Servicio Nacional de Geología y Minería (SERNAGEOMIN) 2019
Materias:	Bed load fluvial systems Pyroclastic processes Intereruptive Syneruptive Quaternary Argentina
Acceso en línea:	http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0718-71062019000300471
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spelling	oai:scielo:S0718-710620190003004712019-10-21Architecture of intereruptive and syneruptive facies in an Andean Quaternary palaeovalley: the Huarenchenque Formation, western ArgentinaSpalletti,Luis A.Colombo Piñol,Ferrán Bed load fluvial systems Pyroclastic processes Intereruptive Syneruptive Quaternary Argentina ABSTRACT The Huarenchenque Formation is a volcano sedimentary unit deposited to the east of the Plio-Quaternary Andean Magmatic Arc. In order to define depositional settings, two lithofacies associations (fluvial and pyroclastic) were defined. The fluvial facies association is composed of polymictic conglomerates with the predominance of basalt-dominated clasts, coarse- medium-grained conglomeratic sandstones and medium- to coarse-grained sandstones. These deposits occur as stacked or single bodies, display both sheet and channelized geometries, and contain a range of internal sedimentary structures, such as planar, low angle stratification and cross-bedding. This facies association is interpreted as the deposit of a multichannel fluvial system characterized by high bed load, steep gradient and non-cohesive bank materials. Facies and architecture of the fluvial deposits are the result of high bank full discharge related to rapid deglaciation of the Andean Last Glacial Maximum. The pyroclastic facies association is characterized by lapilli and ash tuffs deposited from air fall, pyroclastic density current, and density stratified surge mechanisms. In the Huarenchenque Formation the fluvial and the pyroclastic facies associations show a clear physical separation, suggesting that sedimentation occurred in two distinct (intereruptive and syneruptive) phases. During the long-lived intereruptive phases the sedimentary record corresponds mainly to the deposits of the gravelly braided fluvial system, whereas during syneruptive phases the fluvial valley was almost entirely occupied by primary pyroclastic deposits related to high-explosive episodes of the neighbor Andean strato-volcanoes. Although most of the cross-bedded sandstones and conglomerate sandstones are rich in basaltic fragments, some strata are composed almost entirely of pumiceous fragments, while in others there is a marked alternation between “basalt” and “pumiceous” foresets. These attributes reflect the preservation of intrabasinal pyroclastic fragments and allow suggest that: i. explosive volcanic events could be more frequent than reflected by the pyroclastic deposits themselves; ii. syneruptive pyroclastic materials could be eroded (even eliminated) by the fluvial system; iii. contributions of primary pyroclastic material persisted during intereruptive (fluvial-dominated) phases.info:eu-repo/semantics/openAccessServicio Nacional de Geología y Minería (SERNAGEOMIN)Andean geology v.46 n.3 20192019-09-01text/htmlhttp://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0718-71062019000300471en10.5027/andgeov46n3-3170
institution	Scielo Chile
collection	Scielo Chile
language	English
topic	Bed load fluvial systems Pyroclastic processes Intereruptive Syneruptive Quaternary Argentina
spellingShingle	Bed load fluvial systems Pyroclastic processes Intereruptive Syneruptive Quaternary Argentina Spalletti,Luis A. Colombo Piñol,Ferrán Architecture of intereruptive and syneruptive facies in an Andean Quaternary palaeovalley: the Huarenchenque Formation, western Argentina
description	ABSTRACT The Huarenchenque Formation is a volcano sedimentary unit deposited to the east of the Plio-Quaternary Andean Magmatic Arc. In order to define depositional settings, two lithofacies associations (fluvial and pyroclastic) were defined. The fluvial facies association is composed of polymictic conglomerates with the predominance of basalt-dominated clasts, coarse- medium-grained conglomeratic sandstones and medium- to coarse-grained sandstones. These deposits occur as stacked or single bodies, display both sheet and channelized geometries, and contain a range of internal sedimentary structures, such as planar, low angle stratification and cross-bedding. This facies association is interpreted as the deposit of a multichannel fluvial system characterized by high bed load, steep gradient and non-cohesive bank materials. Facies and architecture of the fluvial deposits are the result of high bank full discharge related to rapid deglaciation of the Andean Last Glacial Maximum. The pyroclastic facies association is characterized by lapilli and ash tuffs deposited from air fall, pyroclastic density current, and density stratified surge mechanisms. In the Huarenchenque Formation the fluvial and the pyroclastic facies associations show a clear physical separation, suggesting that sedimentation occurred in two distinct (intereruptive and syneruptive) phases. During the long-lived intereruptive phases the sedimentary record corresponds mainly to the deposits of the gravelly braided fluvial system, whereas during syneruptive phases the fluvial valley was almost entirely occupied by primary pyroclastic deposits related to high-explosive episodes of the neighbor Andean strato-volcanoes. Although most of the cross-bedded sandstones and conglomerate sandstones are rich in basaltic fragments, some strata are composed almost entirely of pumiceous fragments, while in others there is a marked alternation between “basalt” and “pumiceous” foresets. These attributes reflect the preservation of intrabasinal pyroclastic fragments and allow suggest that: i. explosive volcanic events could be more frequent than reflected by the pyroclastic deposits themselves; ii. syneruptive pyroclastic materials could be eroded (even eliminated) by the fluvial system; iii. contributions of primary pyroclastic material persisted during intereruptive (fluvial-dominated) phases.
author	Spalletti,Luis A. Colombo Piñol,Ferrán
author_facet	Spalletti,Luis A. Colombo Piñol,Ferrán
author_sort	Spalletti,Luis A.
title	Architecture of intereruptive and syneruptive facies in an Andean Quaternary palaeovalley: the Huarenchenque Formation, western Argentina
title_short	Architecture of intereruptive and syneruptive facies in an Andean Quaternary palaeovalley: the Huarenchenque Formation, western Argentina
title_full	Architecture of intereruptive and syneruptive facies in an Andean Quaternary palaeovalley: the Huarenchenque Formation, western Argentina
title_fullStr	Architecture of intereruptive and syneruptive facies in an Andean Quaternary palaeovalley: the Huarenchenque Formation, western Argentina
title_full_unstemmed	Architecture of intereruptive and syneruptive facies in an Andean Quaternary palaeovalley: the Huarenchenque Formation, western Argentina
title_sort	architecture of intereruptive and syneruptive facies in an andean quaternary palaeovalley: the huarenchenque formation, western argentina
publisher	Servicio Nacional de Geología y Minería (SERNAGEOMIN)
publishDate	2019
url	http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0718-71062019000300471
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_version_	1714205863447625728

Architecture of intereruptive and syneruptive facies in an Andean Quaternary palaeovalley: the Huarenchenque Formation, western Argentina

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