Significance for international correlation of the Perapertú Formation in northern Palencia, Cantabrian Mountains. Tectonic/stratigraphic context and description of Mississippian and Upper Bashkirian goniatites.

Abstract

Small ammonoid assemblages are recorded from the Perapertú Formation in northern Palencia. This is a mudstone unit with local platform limestones characterised by carbonate debris flows on the limestone margins. This unit, of Late Bashkirian to Early Moscovian age, participates in a series of southwards verging thrust slices North of a major fault zone which originated as the head leading edge) of a large thrust sheet with an internal deformation consisting of thrust slices and at least one nappe structure. Opposed vergencies at the head of this major thrust sheet Carrionas Thrust Front) and the Ruesga Fault which locally modifies its trace, mark the position where the northern branch of the Cantabric-Asturian arcuate fold belt has overridden the southern branch in early Westphalian Langsettian) times. Two different palaeogeographic areas are found here in juxtaposition, i.e. the Asturian-Leonese Domain to the South and the Palentian Domain to the North. The contrasting stratigraphic developments are summarised in figure 2. Upper Bashkirian and Lower Moscovian formations elsewhere in the Cantabric-Asturian orogen are discussed, and the sporadic records of ammonoids in the lower part of the Pennsylvanian in various parts of the Cantabrian Mountains are commented on. The chronostratigraphic significance of the Perapertú Formation is discussed in the context of marine-terrestrial correlations for the Late Bashkirian-Early Moscovian time interval. It is concluded that the evidence from NW Spain suggests a position of the base of the Moscovian at the level of basal Westphalian or even within the highest Namurian. A brief analysis of the literature shows this position to be different to some of the correlations admitted in recent publications. A newly discovered goniatite fauna from the lower part of the Perapertú Formation contains Branneroceras sp. indicating Late Bashkirian to earliest Moscovian, and Deleshumardites cantabricus Kullmann gen. et sp. nov. This fauna is figured and described in conjunction with the new subfamily Dombaritinae Kullmann family Delepinoceratidae. The new genus Deleshumardites is erected with “Proshumardites” delepinei Schindewolf, 1939 as its type species. Ammonoid descriptions and illustrations include that of Deleshumardites cantabricus sp. nov. from strata of an earlier, Serpukhovian age in northern León.