Foraminíferos del Toarciense inferior en el sector occidental de la Cuenca Vasco-Cantábrica

Abstract

This dissertation contains the results of a research focusing on the Upper Pliensbachian-Middle Toarcian foraminifera from five stratigraphic sections located in the western sector of the Basque-Cantabrian Basin (N of Spain). The sections from west to east are Tudanca, Camino, San Andrés, San Miguel de Aguayo and Castillo Pedroso. This mainly marine group is very abundant in the fossil record and has a wide stratigraphic, geographical and environmental distribution. As a result, they serve as an important tool in geological studies of varying nature including, biostratigraphic, chronostratigraphic, paleoenvironmental and palaeoecological analyses.A number of papers and monographs dealing with the study of this group in the Lower Jurassic have been published. In Spain, the foraminiferal assemblages of the Iberian Range and the Subbetic (Betic Cordillera) have been analyzed. Publications from this period in the Basque-Cantabrian Basin are limited. However, there are representative outcrops with favorable facies, few discontinuities, and a high-resolution chronostratigraphic framework provided by ammonoids that warrant its use. In addition, a mass extinction event that affected marine fauna has been described in the Lower Toarcian. Thus, the results here seek to contribute to the systematic knowledge of the group in order to clarify part of the taxonomic confusion that still surrounds some of the generic or specific categories and also to provide data on the influence that this extinction event had on the studied microfauna...