Foraminiferal ecology of contemporary isolation basins in Northwest Scotland

Abstract

Isolation basins contain high-resolution records of environmental change relating to RSL and climate since the last glacial maximum, and provide valuable data in constraining regional and global ice sheet and earth rheology models. A key weakness in current research is a lack of information regarding the identification of the reference tide level of different stages of basin isolation, and the role of factors such as freshwater input in controlling palaeosalinity. To address these issues, this thesis reports data collected from modern isolation basins from twenty sites in northwest Scotland. The basins range in size and elevation of their sill within the tidal cycle. Surface sediment samples were analysed for their foraminiferal composition, and other analyses of water chemistry and sedimentology were completed. Statistical analyses show a poor correlation between sill altitude and fauna. A transfer function was therefore produced based on average salinity, but calibration of this using fossil data was unsuccessful. This research demonstrates that the modern training set lacks adequate analogues for many of the fossil foraminiferal assemblages recorded in previous work. Likely causes for this include differences in the relative abundance of foraminiferal species between the modern and fossil data-sets, and the fact that no modern basin was found which has the water depth and salinity required for reconstruction of the fully marine stage. Because of these factors, foraminiferal data should be used with care in the definition of the indicative meaning of isolation basin sea-level index points. The statistical methods do, however, yield the first detailed understanding of the distributions of foraminifera in contemporary shallow water isolation basins, particularly with reference to their optimum and tolerance values for environmental variables. Variable salinity species such as Miliammina fusca are dominant in the training set, displaying their broad tolerance of environmental conditions.