Benthic foraminiferal assemblages across the Aalenian–Bajocian (Middle Jurassic) in the Barranco de Agua Larga section (Betic Cordillera, Spain) - biostratigraphic considerations
This work reports, for the first time, the benthic foraminiferal assemblages recorded across the Aalenian–Bajocian boundary in the Barranco de Agua Larga section (Betic Cordillera, SE of Spain), where the ammonite record has enabled the recognition of the Gigantea Subzone in the Bradfordensis Zone (Middle Aalenian), the Concavum and Limitatum subzones in the Concavum Zone (Upper Aalenian) and the Discites Zone (Lower Bajocian).
A total of 17 samples have been collected in this reference section, characterized by an alternation of limestones and marly limestones, in order to study the composition of the foraminiferal assemblages throughout the studied stratigraphical interval. The recorded foraminiferal assemblages are moderately abundant and diverse, constituted by well-preserved specimens. Their composition display close similarities to those already described for the Jurassic carbonate platforms of the Boreal Realm. The representatives of the Suborder Lagenina are the most abundant, whereas the Textulariina displays a relatively small number of specimens.
From a biostratigraphic point of view, the occurrence of Lenticulina quenstedti (Gümbel) has enabled the recognition of the Lenticulina quenstedti Zone – ranging from the Bradfordensis Zone (Middle Aalenian) to the lower part of the Discites Zone (Lower Bajocian) – and displaying the same stratigraphical distribution than in other basins of the North Hemisphere, namely in the Lusitanian, Basque-Cantabrian, and Iberian basins of the Iberian Peninsula. Other bioevents of biostratigraphic relevance have been identified throughout the studied interval: an increase in abundance and diversity of the assemblages' composition in the upper part of the Gigantea Subzone (Middle Aalenian); and a decrease in abundance and diversity of the assemblages' composition recognized in the uppermost part of the Limitatum Subzone (Upper Aalenian). The last one was also identified in the above mentioned Iberian basins, and seems to set up a proxy of regional rank, with useful application to determinate both age and depositional environment assigned to core samples in basins regarded as potentially interesting for the oil industry.
AAPG Datapages/Search and Discovery Article #90226 © 2015 European Regional Conference and Exhibition, Lisbon, Portugal, May 18-19, 2015