Darriwilian (Middle Ordovician) conodonts and graptolites from the Cerro La Chilca Section, Central Precordillera, Argentina

ABSTRACT The Ordovician System is extensively represented in the Precordillera of San Juan Province, Argentina. At the Cerro La Chilca in the Jáchal area, the limestone of the San Juan Formation is paraconformably overlain by interbedded limestone and shale of the Gualcamayo Formation. The present c...

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Autores principales:	Serra,Fernanda, Feltes,Nicolás A., Mango,Matías, Henderson,Miles A., Albanesi,Guillermo L., Ortega,Gladys
Lenguaje:	English
Publicado:	Servicio Nacional de Geología y Minería (SERNAGEOMIN) 2020
Materias:	Conodonts Biostratigraphy Graptolites Middle Ordovician Argentine Precordillera
Acceso en línea:	http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0718-71062020000100125
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spelling	oai:scielo:S0718-710620200001001252020-02-20Darriwilian (Middle Ordovician) conodonts and graptolites from the Cerro La Chilca Section, Central Precordillera, ArgentinaSerra,FernandaFeltes,Nicolás A.Mango,MatíasHenderson,Miles A.Albanesi,Guillermo L.Ortega,Gladys Conodonts Biostratigraphy Graptolites Middle Ordovician Argentine Precordillera ABSTRACT The Ordovician System is extensively represented in the Precordillera of San Juan Province, Argentina. At the Cerro La Chilca in the Jáchal area, the limestone of the San Juan Formation is paraconformably overlain by interbedded limestone and shale of the Gualcamayo Formation. The present contribution reports new data on the conodont fauna and biostratigraphy of these darriwilian units, revising local and regional chronostratigraphic relationships. New information on the composition of conodont and graptolite associations through the stratigraphic sequence is presented. The presence of Paroistodus horridus horridus, Yangtzeplacognathus crassus, and Histiodella sinuosa constrain the uppermost strata of the San Juan Formation to the lower part of the Y. crassus Zone, according to the Baltoscandian scheme, and to the H. sinuosa Subzone of the Periodon macrodentatus Zone of the North American scheme. In the overlying Gualcamayo Formation the co-occurrence of Y. crassus with Histiodella holodentata enable the recognition of the Y. crassus Zone and the H. holodentata Subzone of the P. macrodentatus Zone. The identification of these zones allows for precise global and regional correlation. A graptolite assemblage that belongs to the epipelagic and deep-water biotopes with some components restricted to low paleolatitudes is recognized. This diverse assemblage is characteristic of the pelagic biofacies. The important diversity of graptolites in this section suggests a favorable environment for their development. Local changes in the taxonomic composition are recognized through the Gualcamayo Formation. When comparing this fauna with that of different study localities from the Central Precordillera (Cerro Potrerillo, Oculta Creek, Cerro Viejo de Huaco and Las Aguaditas Creek) slight differences in the generic composition are observed. Taxonomic differences support the preference of certain associations for particular environments; though, graptolites are more diverse in black shales facies, which represent deeper environments (the Los Azules Formation), in relation to the calcareous-shale facies of the Gualcamayo Formation from Cerro La Chilca and correlative unit at Las Aguaditas Creek.info:eu-repo/semantics/openAccessServicio Nacional de Geología y Minería (SERNAGEOMIN)Andean geology v.47 n.1 20202020-01-01text/htmlhttp://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0718-71062020000100125en10.5027/andgeov47n1-3229
institution	Scielo Chile
collection	Scielo Chile
language	English
topic	Conodonts Biostratigraphy Graptolites Middle Ordovician Argentine Precordillera
spellingShingle	Conodonts Biostratigraphy Graptolites Middle Ordovician Argentine Precordillera Serra,Fernanda Feltes,Nicolás A. Mango,Matías Henderson,Miles A. Albanesi,Guillermo L. Ortega,Gladys Darriwilian (Middle Ordovician) conodonts and graptolites from the Cerro La Chilca Section, Central Precordillera, Argentina
description	ABSTRACT The Ordovician System is extensively represented in the Precordillera of San Juan Province, Argentina. At the Cerro La Chilca in the Jáchal area, the limestone of the San Juan Formation is paraconformably overlain by interbedded limestone and shale of the Gualcamayo Formation. The present contribution reports new data on the conodont fauna and biostratigraphy of these darriwilian units, revising local and regional chronostratigraphic relationships. New information on the composition of conodont and graptolite associations through the stratigraphic sequence is presented. The presence of Paroistodus horridus horridus, Yangtzeplacognathus crassus, and Histiodella sinuosa constrain the uppermost strata of the San Juan Formation to the lower part of the Y. crassus Zone, according to the Baltoscandian scheme, and to the H. sinuosa Subzone of the Periodon macrodentatus Zone of the North American scheme. In the overlying Gualcamayo Formation the co-occurrence of Y. crassus with Histiodella holodentata enable the recognition of the Y. crassus Zone and the H. holodentata Subzone of the P. macrodentatus Zone. The identification of these zones allows for precise global and regional correlation. A graptolite assemblage that belongs to the epipelagic and deep-water biotopes with some components restricted to low paleolatitudes is recognized. This diverse assemblage is characteristic of the pelagic biofacies. The important diversity of graptolites in this section suggests a favorable environment for their development. Local changes in the taxonomic composition are recognized through the Gualcamayo Formation. When comparing this fauna with that of different study localities from the Central Precordillera (Cerro Potrerillo, Oculta Creek, Cerro Viejo de Huaco and Las Aguaditas Creek) slight differences in the generic composition are observed. Taxonomic differences support the preference of certain associations for particular environments; though, graptolites are more diverse in black shales facies, which represent deeper environments (the Los Azules Formation), in relation to the calcareous-shale facies of the Gualcamayo Formation from Cerro La Chilca and correlative unit at Las Aguaditas Creek.
author	Serra,Fernanda Feltes,Nicolás A. Mango,Matías Henderson,Miles A. Albanesi,Guillermo L. Ortega,Gladys
author_facet	Serra,Fernanda Feltes,Nicolás A. Mango,Matías Henderson,Miles A. Albanesi,Guillermo L. Ortega,Gladys
author_sort	Serra,Fernanda
title	Darriwilian (Middle Ordovician) conodonts and graptolites from the Cerro La Chilca Section, Central Precordillera, Argentina
title_short	Darriwilian (Middle Ordovician) conodonts and graptolites from the Cerro La Chilca Section, Central Precordillera, Argentina
title_full	Darriwilian (Middle Ordovician) conodonts and graptolites from the Cerro La Chilca Section, Central Precordillera, Argentina
title_fullStr	Darriwilian (Middle Ordovician) conodonts and graptolites from the Cerro La Chilca Section, Central Precordillera, Argentina
title_full_unstemmed	Darriwilian (Middle Ordovician) conodonts and graptolites from the Cerro La Chilca Section, Central Precordillera, Argentina
title_sort	darriwilian (middle ordovician) conodonts and graptolites from the cerro la chilca section, central precordillera, argentina
publisher	Servicio Nacional de Geología y Minería (SERNAGEOMIN)
publishDate	2020
url	http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0718-71062020000100125
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Darriwilian (Middle Ordovician) conodonts and graptolites from the Cerro La Chilca Section, Central Precordillera, Argentina

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