Cistoideos rombíferos (Echinodermata) de la Caliza Urbana (Ordovícico Superior) de la Zona Centroibérica, España

Abstract

Cystoids are very rare fossils in the Urbana Limestone of the southern Central Iberian Zone, in contrast to the fossil content of the remaining Kralodvorian («mid» Ashgill) limestones cropping out in the Iberian peninsula, where these echinoderms display a more abundant and diverse record. After a complete recapitulation and discussion about all findings of cystoids in the Urbana Limestone (only 7 specimens derived from 4 localities among dozens of sections examined), two different species of Heliocrinites (Heliocrinites cf. minutes CHAUVEL and Heliocrinites sp. the latter perhaps related with H. jaekeli? CHAUVEL-) and one undetermined rhombiferan (Rombifera indet.) have been identified. From a palaeogeographic point of view, these elements belong to the «Heliocrinites Fauna» and its extreme rarity in the Urbana Limestone may be consequence of non-favourable environmental factors, such as a high energetic gradient and terrigenous influx, or the predominance of semiconsolidate substrates within a very shallow and nearly flat inner shelf setting. The opposite scenario, much more suitable to be colonyzed by echinoderms, is characteristic of the «pelmatozoan limestones» known in other Iberian areas, which generally were deposited in quieter and deeper environments of the outer shelf ermos.