Acritarch assemblages from the Oville and Barrios Formations, northern Spain: A pilot proposal of a middle Cambrian (Series 3) acritarch biozonation in northwestern Gondwana

This paper presents a re-study of acritarchs from the Cambrian Oville and Barrios Formations in the Cantabrian Zone, northern Spain. The excellent preservation of the acritarchs, their great abundance and diversity, and good stratigraphic control of the sections examined allows one to establish a detailed middle Cambrian (Series 3) acritarch biozonation, and to consider their potential usefulness for global Cambrian chronostratigraphy. Six middle Cambrian (Series 3) zones (IMC1-IMC6), and one Furongian assemblage in the Barrios Formation are recognized. The IMC1-IMC5 zones, previously described in a preliminary manner (Palacios, 2008), are now characterized in detail, and a new IMC6 Zone is defined which is characterized by the first occurrence of Stelliferidium magnum, Timofeevia phosphoritica and T. microretis. The co-occurrence in the study area of acritarchs and trilobites makes it possible to correlate the two types of biozone. New species (Comasphaeridium maximum sp. nov., Eliasum fombellae sp. nov., Timofeevia simplex sp. nov. Timofeevia heteromorpha sp. nov., Timofeevia densa sp. nov., Tubulosphaera craterae sp. nov., and Vulcanisphaera cantabrica sp. nov.) are recognized, and the diagnoses of Eliasum, and Symplassosphaeridium cambriense are emended. (C) 2015 Elsevier B.V. All rights reserved.