Middle and upper jurassic foraminifera and radiolaria of Scotland : an integrated biostratigraphical and palaeoenvironmental approach
This study is an integrated biostratigraphical and palaeoenvironmental analysis of foraminiferal and radiolarian distribution from all the major Middle and Upper Jurassic marine deposits of Scotland. These sampled sites are divided between two basins with Staffin Bay and Bearreraig Bay within the Inner Hebrides Basin, North West Scotland; and Brora, Balintore, Helmsdale and Eathie Haven representing the Inner Moray Firth Basin, North East Scotland.A detailed taxonomic section is presented, which provides the means of comparison of microfaunal events between sites. A combined total of 212 species are described, of which 183 are foraminifera and 29 radiolaria; this includes a total of 23 species not previously recorded, comprising 16 foraminiferal and 7 radiolarian taxa.A Callovian to Lower Kimmeridgian biozonal scheme, the first detailed attempted for the onshore UK, is constructed primarily using the Staffin Bay succession as the type section. It is based upon an integration of distinct foraminiferal and radiolarian taxa and events. This microbiostratigraphy is implicitly tied to the Boreal type ammonite scheme and comprises a total of 9 biozones and 12 sub-biozones. The new biozones are then correlated and compared with the other Scottish sites as well as other world-wide schemes.A sequential palaeoenvironmental analysis is outlined, firstly by pinpointing microfaunal assemblages that are based upon a combination of the distribution of the major suborders, the species diversity and faunal abundances, as well as integrating the facies types and probable prevalent substrate conditions. These assemblages are then used to define palaeoenvironmental models for each recorded succession, and are related to prevailing substrate and sea water conditions and distance from the 'palaeoshoreline'. As the assemblages are shown to reflect particular conditions this allows a generalised basin development model to be assessed, related to sea-level changes (transgressions and regressions). All the sites are subsequently correlated palaeoenvironmentally.The relevance of facies dependant distribution is also examined, particularly for benthic foraminiferids. The main conclusion reached is that facies dependence restricts the occurrences of taxa. However, this is not a constant feature as some specific taxa show the ability to colonise several facies types. It is this factor that permits a biostratigraphy to be constructed. Overall, assemblages appear to be related directly to a particular facies, which permits palaeoenvironmental changes to be assessed.Finally the extensive Middle and Upper Jurassic literature is examined and a generalised world wide biogeography constructed. Four provinces are defined based on characteristic foraminiferal and radiolarian assemblages.