Foraminifera from the Toarcian-Aalenian boundary (Lower-Middle Jurassic) of the Barranco de Agua Larga section (Betic Cordillera, Spain) - biostratigraphic significance
This work describes, in detail and for the first time, the benthic foraminifera assemblages from the Upper Toarcian-Middle Aalenian (Lower-Middle Jurassic transition) interval of the Barranco de Agua Larga outcrop, a reference section located in the Subbetic domain of the Betic Cordillera (Southern Spain).
Taken into account the biostratigraphic framework, based on an abundant and diversified ammonite record, a total of 17 samples have been collected from the Upper Toarcian (Aalensis Zone, Aalensis Subzone), Lower Aalenian (Opalinum Zone, Opalinum and Comptum subzones) and Middle Aalenian (Murchisonae Zone, Murchisonae Subzone). The foraminiferal assemblages, which are relatively abundant and diverse, are composed of well-preserved specimens, similar to those already recognized in the Jurassic carbonate platforms of the Boreal Realm. The representatives of the Suborder Lagenina are the most abundant whereas the forms of the Suborder Textulariina are scarce.
From a biostratigraphic point of view, the occurrence of Astacolus dorbignyi (Roemer) has enabled the recognition of the Astacolus dorbignyi Zone for this time interval. This biozone has also been recognized in other basins of the Iberia, namely in Portugal, in the Northern and Central Sector of the Lusitanian Basin (Murtinheira, São Gião, Maria Pares and Zambujal de Alcaria sections), and in Spain, in the Basque-Cantabrian Basin (Cillamayor, San Andrés, Camino, San Miguel de Aguayo, Pujayo, Tudanca and Castillo Pedroso sections) and in the Iberian Cordillera (Moyuela, Sierra de los Cameros and Muro de Águas sections, as well as in the Fuentelsaz section, where the Aalenian GSSP was established).
Variations in the relative abundance of some taxa and in the diversity of the recorded assemblages have enabled the recognition of several bioevents with biostratigraphical significance along the studied stratigraphic interval. They represent useful proxies that can be applied to determinate both the age and depositional environment assigned to core samples in current activities of oil exploration.
AAPG Datapages/Search and Discovery Article #90226 © 2015 European Regional Conference and Exhibition, Lisbon, Portugal, May 18-19, 2015