Palaeoecological distribution pattern of Early–Middle Jurassic benthic foraminifera in the Lusitanian Basin (Portugal) based on multivariate analysis
Abstract Paleontologists have favoured univariate statistical methods over multivariate ones, using information-rich data to derive diversity measures such as the Simpson's index. However, such palaeontological datasets may benefit from flexible multivariate methods that exploit data directly. Hence in this work, with the aim of quantifying and characterising the spatio-temporal change in the species composition and abundance of benthic foraminiferal assemblages, univariate and multivariate statistical techniques are applied on a Lusitanian Basin dataset from the Lower–Middle Jurassic transition. This paper presents the trends identified at spatial and temporal scales, i.e. among sections corresponding to distal, middle and proximal palaeogeographical positions within the platform and between two successive stratigraphic intervals (upper Toarcian and lower Aalenian). It also compares the results obtained by univariate and multivariate methods. Samples in the reference sections are composed by taxa typical of the Jurassic carbonate marine platforms of the Boreal Realm, such as Vaginulinidae and Lenticulina species. Univariate analysis only found significant change in species diversity between the two most distant sections and failed to detect any temporal change. In contrast, multivariate analysis (PERMANOVA and NMDS) revealed that spatial change in assemblage structure (22%) quadruples temporal change (5%). CAP analysis identified characteristic species for each section along the palaeogradient, with a posterior cross-validation procedure that classified correctly 97% of the samples. In fact, multivariate results suggest the existence of stable palaeoecological conditions across the Lower–Middle Jurassic transition in the Lusitanian Basin. Future work in the field may benefit from multivariate analysis, including hydrocarbon exploration activities where only core samples are available and foraminifera are currently used.