The first occurrence of Silurian sponge spicules of the Precordillera, San Juan Province, Argentina

An association of silicified spicules of hexactinellid sponges was collected from Silurian sandstones at the top of the La Chilca Formation, outcropping at Cerro del Fuerte, near Jáchal, San Juan Province. These spicules are the first to be recorded from the Silurian of the Precordillera. The spicul...

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Detalles Bibliográficos
Autor principal: Beresi, Matilde S.
Formato: Objeto de conferencia Resumen
Lenguaje:Inglés
Publicado: 2010
Materias:
Ciencias Naturales
Paleontología
San Juan, Argentina
Silúrico
Acceso en línea:http://sedici.unlp.edu.ar/handle/10915/16621
Aporte de:
SEDICI (UNLP) de Universidad Nacional de La Plata
id I19-R120-10915-16621
record_format dspace
institution Universidad Nacional de La Plata
institution_str I-19
repository_str R-120
collection SEDICI (UNLP)
language Inglés
topic Ciencias Naturales
Paleontología
San Juan, Argentina
Silúrico
spellingShingle Ciencias Naturales
Paleontología
San Juan, Argentina
Silúrico
Beresi, Matilde S.
The first occurrence of Silurian sponge spicules of the Precordillera, San Juan Province, Argentina
topic_facet Ciencias Naturales
Paleontología
San Juan, Argentina
Silúrico
description An association of silicified spicules of hexactinellid sponges was collected from Silurian sandstones at the top of the La Chilca Formation, outcropping at Cerro del Fuerte, near Jáchal, San Juan Province. These spicules are the first to be recorded from the Silurian of the Precordillera. The spicules were extracted by means of acetic acid treatment from yellowish coarse sandstones with carbonate cement and associated fragmented braquiopod shells. The age of the upper La Chilca Formation ranges from late Llandovery to early Wenlock, based on graptolites and brachiopods. The spicule association is only composed by hexactins (triaxons), the basic type of megasclere of the class Hexactinellida (Phylum Porifera). These sponges secrete siliceous elements that confer strength and protect them from physical perturbations. The spicules can subsequently fuse in rigid dictyonal frameworks. In the hexactins here studied, some rays are somewhat broken, but they clearly show the six rays with 90º angles between their rays. These spicules are the only microfauna found in the sandstones. No conodonts have been recovered in these levels. These spicules are common within the Class Hexactinellida, and they cannot be attributed to any specific hexactinellid taxon. These sponges are mostly confined to quiet, deep and silicon-rich environments which have no lithological record in this Silurian section. Consequently, these spicules restricted to outer platform and peri-platform were transported towards the shallow sandstone environments. Its occurrence reveals the existence of a hexactinellid fauna, which flourished in deep waters with low energy and mud substratum during the Early Silurian of the Precordillera. The greater abundance of sponge skeletons in the fossil record corresponds to periods of high sea level of the Phanerozoic oceans, whereas almost no sponge spicules have been found during the periods of low sea level as for example could have occurred during the Llandovery of the Precordillera.
format Objeto de conferencia
Resumen
author Beresi, Matilde S.
author_facet Beresi, Matilde S.
author_sort Beresi, Matilde S.
title The first occurrence of Silurian sponge spicules of the Precordillera, San Juan Province, Argentina
title_short The first occurrence of Silurian sponge spicules of the Precordillera, San Juan Province, Argentina
title_full The first occurrence of Silurian sponge spicules of the Precordillera, San Juan Province, Argentina
title_fullStr The first occurrence of Silurian sponge spicules of the Precordillera, San Juan Province, Argentina
title_full_unstemmed The first occurrence of Silurian sponge spicules of the Precordillera, San Juan Province, Argentina
title_sort first occurrence of silurian sponge spicules of the precordillera, san juan province, argentina
publishDate 2010
url http://sedici.unlp.edu.ar/handle/10915/16621
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bdutipo_str Repositorios
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