Foraminiferal biostratigraphy across the Visean/Serpukhovian boundary in the Vegas de Sotres section (Cantabrian Mountains, Spain)

Abstract

A continuous succession of the upper part of the Alba Formation is recorded in the Vegas de Sotres section in the Cantabrian Mountains, northern Spain. This section contains slightly shallower-water facies than elsewhere and as a result is particularly rich in foraminifers. Characterization of the late Visean to Serpukhovian interval in coeval deeper water settings is accomplished by means of integrating conodont, ammonoid and foraminiferal data. The foraminiferal assemblages recorded in units 1–4 of the Alba Formation enabled correlation with the Russian substages in the Moscow Basin, Urals and Donets Basin. The upper part of the Canalón Member (unit 1) is correlated with the Venevian, the lower part of unit 2 is correlated with the Tarusian, and the Steshevian is recognized in the middle and upper part of unit 2. Most of unit 3 is correlated with the Protvian and is equivalent to the E2a ammonoid zone. The youngest Millaró Member (unit 4) contains undiagnostic foraminifers and lies within the Gnathodus truyolsi Conodont Zone equivalent to the E2b/E2c ammonoid zones.

The base of the Serpukhovian is defined on the first occurrence of the conodont Lochriea ziegleri. Slightly below this horizon are recorded Neoarchaediscus parvus, N. aff. N. postrugosus, Biseriella paramoderata, Asteroarchaediscus rugosus, Howchinia hemisphaerica and Rectoendothyra latiformis. At the Visean/Serpukhovian (V/S) boundary, species of Tubispirodiscus are recorded and just above, the presence of Asteroarchaediscus baschkiricus is confirmed. The late Serpukhovian is characterized by the occurrence of diverse Eostaffella pseudostruvei, E. sp. cf. E. postmosquensis, Eostaffellina “protvae”, Eost. actuosa and Plectostaffella varvariensis.