An holistic approach to mapping the Quaternary geology and reconstructing the last glaciation of West County Mayo, Ireland, using satellite remote sensing and 'conventional' mapping techniques

Abstract

The Quaternary geology of West County Mayo, Ireland, has appeared in the literature over 30 times since Close's account in 1867. Various glacial reconstructions have been proposed due to i) the complex sedimentology and morphology of the area, ii) different approaches having been adopted by researchers iii) models being tainted by theory-laden evidence as different glaciological concepts were in vogue at the time of publication. Corroboration of existing information was undertaken in this research along with de novo mapping and identification of new data. An holistic approach was adopted, with 'conventional' mapping techniques integrated with digital image processing of satellite imagery. Over 20OOkm2 were field-mapped where landforms such as drumlins, moraines, roche moutonnées, kames/kettle holes and eskers were recorded along with sedimentological data including till fabric analysis, deformation structure geometry, petrographic components, lithofacies etc. Radar (ERS-1) and optical multitemporal and multispectral Landsat-5 Thematic Mapper imagery were processed, evaluated and interpreted. Due to the absorption of H20 molecules in soil and plants between 1.55-1.751im, winter Landsat TM band 5 provided most information and was used for interpretation. Geological information from conventional mapping and digital remote sensing were integrated using an inversion model. The landscape was spatially divided into assemblages of landforms and relative chronologies were determined by analysing cross-cutting landforms. The data show that there was one ice mass with two 'domes' in the research area. The dome in Clew Bay had a north-south divide with ice flow towards the east in the eastern half of the bay and towards the west in the western half. The eastern margins of this dome diverted the Midlands ice to flow in a northerly direction. An older pattern of flow, towards the northwest, was recorded in the east of the area. The deposits indicate that a staged retreat occurred generally from north to south.