DISTINGUISHING DIAMICTONS USING TILL MACROFABRIC AND GRAIN SIZE ANALYSIS: A CASE STUDY IN THE NORTHERN SERRA DO GERES MOUNTAINS, NW IBERIAN PENINSULA

Till macrofabric and grain size analysis of glacial diamictons present in several valleys of the Northern Serra do Gerês Mountains in the Iberian Peninsula northwest were used to interpret till types and to reconstruct the glacial paleoprocess history of this mountainous region. Slope deposits, subglacial deformation and supraglacial melt-out tills are dominant in the northern portion of this range. Supraglacial melt-out tills, representative of periods of glacial stability followed by recession, present weaker fabric data and coarser, poorly sorted sediments. Slope deposits, representative of postglacial mass wasting activity, present weaker to strong fabric data and coarser, poorly sorted sediments. Subglacial deformation tills, representative of glacial readvance stages followed by stability, present poorly sorted fine sediments, folding, and striated clasts. These diamictons are of importance in the reconstruction of the glacial dynamics and history of the Northern Serra do Gerês Mountains due to poor preservation of glacial landforms related to the Last Glacial Maximum in several glaciated valleys.