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La formación radiolarítica Jarropa: definición y significado en el Jurásico Subbético (Cordillera Bética)

By J. A. Vera, J. Sandoval, P. A. Ruiz-Ortiz, J. M. Molina and L. O'Dogherty

Abstract

The Jarropa Radiolarite Formation is defined formally, for the first time, according to the international guide of stratigraphic nomenclature, and the holostratotype and two parastratotypes are described. This is a very characteristic Jurassic unit of the Subbetic (Betic Cordillera) in which point out the presence of radiolarite levels, together with siliceous marlstones, marls and clays. Two members are differentiated: a lower member of green, radiolarites and siliceous marls, and an upper member of red, siliceous clays and marls, both being recognizable in most of the outcrops. The age of this formation in the holostratotype, known mainly from the study of their radiolarians, is Late Callovian-Oxfordian. In other stratigraphic sections (including some parastratotype) is verified that the exact age of the bottom of the formation, and of the boundary between the two before described members are heterochronous, within the Uppermost Bajocian-Lowermost Kimmeridgian. They are pelagic sediments, deposited during the expansive phase of the Southern Iberian Continental Paleomargin, in areas far from the continent with thin continental crust. They have a great analogy with deposits outcropping in others Mediterranean Alpine domains (Apennines, Alps, Dinarids, etc.) also accumulated during Jurassic extensive phases of continental margins adjacent to the Tethys. The depositional bathymetry is estimated in a few hundreds of meters, without a necessary relation with the calcite compensation depth (CCD).<br><br>Se define formalmente, por primera vez, la &#194;&#171;Formaci&#243;n Radiolar&#237;tica Jarropa&#194;&#187; de acuerdo con las normas internacionales de nomenclatura estratigr&#225;fica, y se describen el holoestratotipo y dos paraestratotipos. Se trata de una unidad litoestratigr&#225;fica muy caracter&#237;stica del Jur&#225;sico del Subb&#233;tico (Cordillera B&#233;tica) en la que destacan la presencia de niveles de radiolaritas, junto con margas y arcillas sil&#237;ceas. Se diferencian dos miembros, uno inferior (&#194;&#171;miembro de radiolaritas y margas sil&#237;ceas, verdes&#194;&#187;) y otro superior (&#194;&#171;miembro de arcillas y margas sil&#237;ceas, rojas&#194;&#187;), ambos reconocibles en la mayor&#237;a de los afloramientos. La edad de esta formaci&#243;n en el holoestratotipo, conocida a partir del estudio de los radiolarios, es Calloviense superior-Oxfordiense. Se constata que las edades del muro de la formaci&#243;n y del l&#237;mite entre los dos miembros, en otras secciones estratigr&#225;ficas son diferentes mostrando un car&#225;cter claramente heter&#243;crono, dentro del intervalo Bajociense terminal-Kimmeridgiense basal. Se trata de sedimentos pel&#225;gicos, depositados en &#225;reas alejadas del continente, durante la fase expansiva del margen continental sudib&#233;rico, con sustrato de corteza continental. Presentan una gran analog&#237;a con materiales que aparecen en diferentes dominios alpinos mediterr&#225;neos (Apeninos, Alpes, Din&#225;rides, etc.) tambi&#233;n depositados, durante el Jur&#225;sico, en fases de expansi&#243;n de m&#225;rgenes continentales adyacentes al Tethys. La batimetr&#237;a de su dep&#243;sito se estima en pocos centenares de metros, sin una necesaria relaci&#243;n con el nivel de compensaci&#243;n de la calcita (CCD)

Topics: Formation, Radiolarites, Callovian, Oxfordian, Subbetic, Betic Cordillera, Formaci&#243;n, Radiolaritas, Calloviense, Oxfordiense, Subb&#233;tico, Cordillera B&#233;tica, Geology, QE1-996.5, Science, Q, DOAJ:Earth Sciences, DOAJ:Earth and Environmental Sciences
Publisher: Consejo Superior de Investigaciones Científicas
Year: 1997
DOI identifier: 10.3989/egeol.97533-4239
OAI identifier: oai:doaj.org/article:96be306b15754fea9e2e8e50c7639b94
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