Late Quaternary benthonic foraminiferal stratigraphy of the western U.K. Continental Shelf
Late Quaternary deposits have been investigated from three main study areas from 'western Britain in an attempt to define lithological and biostratigraphic changes. Detailed analyses of included benthonic foraminiferal assemblages are presented and a systematic section included which describes and illustrates over 200 distinct forms. Chronostratigraphic control is provided by radiocarbon dates, amino acid analysis and tephrachronology. The three study areas yield distinctive records of the depositional environments characterizing the climatic events of the Late Quaternary. From the Hebridean Shelf, B.G.S. vibrocores have been analysed within the context of a previously established seismostratigraphic sequence. Foraminiferal faunas allow the reconstruction of a regional climatostratigraphic sequence for the Lateglacial period (c. 14,000 to 10,000 BP) and this sequence is correlated, through 9 radiocarbon (AMS) dates, to the established climatostratigraphy of the Lateglacial period from N.W. Europe. Reconstructions of notional water depths during this period allow glacio-isostatic components from the shelf to be estimated and these confirm a generally accepted pattern of changing relative sea-level, from initial regression following deglaciation and subsequent transgression as the eustatic component over-takes the isostatic component. Rising sea-levels are most notable after about 10,000 BP. A cliff section at Aberdaron on the western Lleyn Peninsula provides an insight into the controversy surrounding the question of depositional origin of the "Irish Sea Drift" sequences bordering the Irish Sea. Diamicts and sorted layers from the section contain mixed boreo-arctic, temperate and pre-Quaternary species, and allochthonous/autochthonous elements are identified. While lithological changes within the section are marked, the foraminiferal assemblages maintain relatively constant faunal ratios. None of the foraminifera are considered to be in situ, but instead entrained by the Irish Sea glacier during its passage along the Basin and deposited at the site by basal melt-out processes. The third study area, the southwestern Celtic Sea, records geomorphological evidence of previously extensive glaciation in the region. Microfaunas, both foraminifera and Ostracoda, are analysed and record a transition from grounded ice lodgement facies to quiet, glacial marine facies at about 49°30 N. Amino acid analysis confirms the geomorphological evidence for glacial marine accumulation during the Late Devensian.