Abstract
Recent palaeontological and microfacies studies carried out on the Lancara Formation (early Cambrian) provide evidence for an interesting, previously undescribed association of archaeocyaths (Salce locality) and microbialites (Salce and Barrios de Luna localities). The archaeocyathan assemblage consists of Archaeocyathus laqueus (Vologdin, 1932) and Pycnoidocyathus erbiensis (Zhurav leva , 1955), indicating an early Bilbilian age (Stage 4, Series 2, Cambrian) for these materials. The analysis of the upper part of the lower member has allowed differentiation of eleven carbonate facies that have been grouped into: i) non-skeletal grain packstone-grainstone, ii) fenestral mudstone-packstone, iii) heterolithic stylonodular facies, iv) microbialites, v) bioclast-intraclast packstone-grainstone. Archaeocyaths occur reworked in stylonodular facies as well as forming small archaeocyaths-thrombolitic patches (centimetre-scale). The archaeocyath-rich thrombolitic microbialites from Salce were developed in very shallow subtidal conditions surrounded by other microbialites and small lenticular intertidal bars in the inner ramp. Toyonian biostratigraphic and paleobiogeographic analyses have also been carried out. After the comparison with Toyonian archaeocyathan rich facies from Gondwana, it has become evident that the early Cambrian record from the Cantabrian Mountains provides the richest generic assemblage from Gondwana for Toyonian time.
Highlights
The lower-middle Cambrian Láncara Formation (Oele, 1964) is mainly composed of dolostone, limestone and occasional shale interbeds, ranging from 150 m up to 225 m in thickness (Aramburu et al, 1992)
The present paper describes the first recorded occurrence of archaeocyaths in the Somiedo-Correcilla Subunit at Salce and their lateral equivalents in the nearby Barrios de Luna section; carbonate facies descriptions are focused on the upper levels of the lower member of the Láncara Formation
The water-sediment interface was prolifically colonized by microbial benthic communities that built up a variety of micro- and mesostructures such as microbial peloids, calcimicrobes, spongiostromata oncoids and a diversity of microbialites
Summary
The lower-middle Cambrian Láncara Formation (Oele, 1964) is mainly composed of dolostone, limestone and occasional shale interbeds, ranging from 150 m up to 225 m in thickness (Aramburu et al, 1992). The most recent taxonomic study from these localities was done by Perejón and Moreno-Eiris (2003), who reported the presence of Archaeocyathus laqueus (Vologdin, 1932), Pycnoidocyathus erbiensis (Zhuravleva, 1955), Polythalamia sp. Okulitchicyathus valdorensis Perejón and Moreno-Eiris, 2003 This archaeocyathan assemblage is characteristic of an early Bilbilian or Toyonian age (Spanish and Russian stages respectively). With the exception of the occurrences in the Láncara Formation at Esla nappe (Crémenes and Valdoré localities), the presence of archaeocyaths at Somiedo-
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