Contemporary and fossil foraminifera from isolation basins in northwest Scotland

Abstract

Isolation basins are widely used in sea-level reconstructions, but contemporary analogues have been poorly studied comparatively. Recent research has identified isolation basins with extended transitional isolation contacts that pose problems in sea-level interpretations. This paper presents foraminiferal results from 24 contemporary isolation basins combined with data from two isolation basins with extended isolation contacts. Foraminiferal associations identified from the contemporary basins show a clear relationship with water salinity and sill altitude that supports interpretation of the extended fossil sequences. An association dominated by Miliammina fusca, Mf, signifies a basin close to final isolation from marine influence. Increasing marine inundation of basins is signified by a series of associations dominated by the following foraminifera; Ja, Jadammina macrescens and M. fusca; ME, M. fusca and Elphidium williamsoni; Ew, E. williamsoni; HE, Haynesina germanica and E. williamsoni; Nd, Nonion depressulus. These associations can be used to interpret the sedimentary isolation sequences from Loch nan Corr and Rumach VI. A pilot study of the stable isotope signature from the two species H. germanica and E. williamsoni is reported from Rumach VI and Loch nan Corr. The results show the potential of stable isotope analysis for environmental reconstruction from isolation basins, in particular using 18O for salinity reconstruction.