Biostratigraphy of the Ribota and Huérmeda formations (Cambrian Series 2) in the Comarca del Aranda (Zaragoza province), Iberian Chains (NE Spain)

Resumen

This article presents a detailed biostratigraphic analysis of the Cambrian Series 2 Ribota and Huérmeda formations of four sections of the Iberian Chains (NE Spain), and a systematic study of their trilobite faunas. We identified four major assemblages: two in the middle part of the Ribota Formation, one at the base of the Huérmeda Formation and one at the top of the Huérmeda Formation. The studied species permit the assignment of these formations to the middle and upper Marianian and probably lower Bilbilian stages in the regional stratigraphic chart for the Iberian Peninsula, which correlates with an interval around the Cambrian Stage 3–4 boundary. The assemblages exhibit a great correlation potential with the presence of Termierella and the first figured material of Andalusiana from the Iberian Chains, two characteristic taxa of the Marianian of the Ossa-Morena Zone, having been also recorded from the Central Iberian Zone and Morocco. In addition, specimens tentatively assigned to Hebediscus are recorded for the first time from the region, a taxon with a wide geographic distribution which allows a good international correlation in the Cambrian Series 2.