The highest-latitude Foliomena Fauna (Upper Ordovician, Portugal) and its palaeogeographical and palaeoecological significance

Abstract

Here we report and describe for the first time the Foliomena Fauna fossil record from Portugal (Kralodvorian, upper Katian). This deep-water brachiopod association originates from the uppermost beds of the Porto de Santa Anna Formation (uppermost Katian), cropping out in several localities of the Portuguese Buçaco-Penacova region (Central Iberian Zone). The three studied localities have yielded different associations, composed of 15 species of brachiopods and two trilobites, including both key elements of the deep water Foliomena Fauna and taxa typically from shallower benthic biotas, e.g. the Nicolella Fauna. The mixed character of the associations indicates that they are probably representatives of the atypical Foliomena Fauna, characteristic of relatively shallow benthic assemblages. The Portuguese associations represent the highest-latitude occurrences of the Foliomena Fauna so far and one of the youngest. In the analyses carried out, the two Portuguese associations are grouped together with the other peri-Gondwanan associations (Sardinia and Carnic Alps) and are included within a major grouping including associations previously interpreted as inhabiting deep-water environments and also predominantly late Katian in age. According to these results, the association of Locality 2 may have inhabited a slightly deeper environment than the one present in Locality 3. This agrees with the presence in the former of a greater number of deep-water genera. Despite of the occurrence of a great number of deep-water taxa in the association of Locality 2, the co-occurrence of several elements related to the shallower water Nicolella Fauna, probably transported offshore as a result of the slope of the inclined shelf, suggest that this association probably inhabited slightly shallower environments than those expected for a typical Foliomena Fauna (BA5-6) with no shallow-water elements represented. This inference is also supported by the absence from the association of cyclopygid trilobites.