Publication: Conodontos y episodios carbonatados en el Silúrico de la cadena hercínica meridional y el dominio sahariano
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1996
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Sociedad Española de Paleontología
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Abstract
Se han reunido y evaluado los datos (publicados e inéditos) sobre los conodontos silúricos en una región que se extiende desde las Ardenas hasta el Sahara occidental y centraL Su revisión taxonómica ha permitido la identificación de 63 especies y subespecies, que han sido referidas a una biozonación útiL El análisis de los aspectos lito y bioestratigrá ficos de cuarenta secciones sintéticas de este ámbito pone en evidencia asociaciones de faunas características y su relación con la dinámica sedimentaria. El Sistema Silúrico, en la región investigada, presenta dos lifofacies mayores consistentes en, pclitas que gmdan de manera heterócron<la (1) facies siliciclásticas groseras, o bien a (2) calizas de cefalópodos de rampa distal ("facies mediterránea") o a calizas bioelásticas en áreas marginales. Los datos proporcionados por los conodontos en los materiales carbonatados, contrastados con la información ofrecida por graptolitos, han permitido reconocer, con carácter preliminar, la existencia de cuatro episodios carbonatados, cuya edad está indicada por las zonas de conodontos. El primer episodio se registra en el Llandovery, próximo al tl'<\l1 - sito Rhuddaniense-Aeroniense y tiene un carácter local , el segundo se inicia en el Llandovery superior-Wenl ock inferior, el tercero se instala desde el Wenlock más alto-Ludlow y el cuarto en el Prídoli. correspondiendo los dos últimos a la generalización de los intervalos condensados carbonatados y que en las áreas de mayor influjo elástico están representados por determinados horizontes de profundización.
The taxonomic review of published and unpublished data concell1ing silurian conodonts from a large region that extends from Ardennes to western and central Sahara has enabled the idenlification of 63 specific and subspccific laxa; these taxa have been placed in a workable biozonation. The analysis of the fossil and lithological feactures of forty synthetic sections shows several faunal associations Ilnd their relation to the condilions of sedimentation. The Silurian System, in the studied domain, shows two renain lithofacies, consist ing of, pelites whkh progressively and hcterochronously change to (1) coarse si licielastic lithofacies, 0 1' (2) to cephalopod limeslones attributed to dcposits of distal ramp ("medilcITane;:ln facies"), or 10 bioclaslic limestones deposited in marginal areas. Combining the informalion provided by conodonts and graploli tes, a preliminary subdivision in four carbonate episodes is established for the Silurian rocks of the studi ed region; these episodes are chronologically aITanged by using lhe succession of conodont zones. The oldes! episode took place during the L1andovery, dose to the Rhuddanian-Aeronian boundary, and is of local magnitude; the second episode began during the upper L1andovery -lower Wen lock: the third one happened during the uppermost Wenlock-Ludlow and the youngest du ring the Pridoli. The last two episodes correspond to a common sedimentation characterized by condensed carbonate intervals that in areas of greater elastic inflow are represented by distinct deepening horizons.
The taxonomic review of published and unpublished data concell1ing silurian conodonts from a large region that extends from Ardennes to western and central Sahara has enabled the idenlification of 63 specific and subspccific laxa; these taxa have been placed in a workable biozonation. The analysis of the fossil and lithological feactures of forty synthetic sections shows several faunal associations Ilnd their relation to the condilions of sedimentation. The Silurian System, in the studied domain, shows two renain lithofacies, consist ing of, pelites whkh progressively and hcterochronously change to (1) coarse si licielastic lithofacies, 0 1' (2) to cephalopod limeslones attributed to dcposits of distal ramp ("medilcITane;:ln facies"), or 10 bioclaslic limestones deposited in marginal areas. Combining the informalion provided by conodonts and graploli tes, a preliminary subdivision in four carbonate episodes is established for the Silurian rocks of the studi ed region; these episodes are chronologically aITanged by using lhe succession of conodont zones. The oldes! episode took place during the L1andovery, dose to the Rhuddanian-Aeronian boundary, and is of local magnitude; the second episode began during the upper L1andovery -lower Wen lock: the third one happened during the uppermost Wenlock-Ludlow and the youngest du ring the Pridoli. The last two episodes correspond to a common sedimentation characterized by condensed carbonate intervals that in areas of greater elastic inflow are represented by distinct deepening horizons.