RT Journal Article
T1 Foraminifera from the Aalenian and the Bajocian GSSP (Middle Jurassic)of Murtinheira section (Cabo Mondego, West Portugal):Biostratigraphy and paleoenvironmental implications
A1 Canales Fernández, María Luisa
A1 Henriques, María Helena Paiva
AB The detailed study of benthic foraminifera in 28 samples from Late Toarcian–Aalenian–Early Bajocian hemipelagic sedimentsof the Murtinheira section (Cabo Mondego, Lusitanian Basin, West Portugal), has permitted the recognition of the assemblagecomposition and the analysis of their evolution throughout this time interval. The representatives of the Suborder Lageninadominate all the assemblages and, in the majority of them, the most abundant species is Lenticulina münsteri. The Late Toarcianand Early Aalenian assemblages are very similar. From the Comptum Subzone, a gradual replacement of the Early Jurassic formsby characteristic Middle Jurassic taxa takes place. During the Late Aalenian–Early Bajocian interval, a significant number of lastoccurrences (LOs) of taxa are recorded. The assemblages composition, the estimation of the relative taxa abundances and the dataobtained from the calculation of several diversity indexes, together with the previous sedimentological and paleontological worksin this area, indicate that these assemblages were developed in a shelfal basin environment. This platform showed normal marinesalinity values, good oxygenation and was always located above calcite compensation depth (CCD). However, the environmentalconditions were not always the best for the development of rich and diverse foraminiferal assemblages. These conditions wereprobably unstable during the Late Toarcian (Aalensis Subzone)–Early Aalenian (lower part of the Comptum Subzone). From theComptum Subzone to the lower part of the Limitatum Subzone (Late Aalenian), conditions were more stable and more favourablefor the development of foraminiferal communities. However, in the Aalenian–Bajocian transition the environmental conditionschanged again and affected the development of this group. In the Limitatum Subzone a decrease in the diversity of the assemblageswas recorded. This fact seems to be related to a global perturbation in the carbon-cycle that could have affected the foraminifera,together with other marine and continental organism groups.
PB Elsevier Science B.V., Amsterdam.
SN 0377-8398
YR 2008
FD 2008
LK https://hdl.handle.net/20.500.14352/49556
UL https://hdl.handle.net/20.500.14352/49556
LA eng
DS Docta Complutense
RD 5 may 2024