A geological survey was carried out on the left side of the middle Susa Valley north of Bussoleno (NW Italy), with the aim of study the relationship between the tributary Moletta Glacier and the main Dora Riparia Glacier in the Last Glaciation. The Moletta catchment is a 5,8 km2 wide tributary south-facing valley, with maximum elevation of 2963 m a.s.l. (M. Palon - Rocciamelone Group). It consists of oceanic crust made of serpentinite and prasinite (Piemontese Zone), oucropping in the upper sector of the valley and tectonically overlying (cargneule) on a continental crust made of paragneiss, micaschist and dolomite marble (Dora Maira Massif) outcropping in the lower sector (Cadoppi et al., 2002). The bedrock, with a diffuse subglacial abrasion shaping, is covered by Lateglacial (19-11.7 ka BP) glacigenic deposits (lodgement till, subglacial melt-out till, ice-marginal flow till, glacio-lacustrine and glacio-fluvial deposits) and by post-glacial gravitative deposits (talus debris and colluvial). The Bussoleno village is located on the T. Moletta alluvial fan which extends downvalley in the trunk valley floor. Thick bodies of well stratified ice-marginal glacio-lacustrine gravelly sand, scattered on the trunk valley side, rest above the subglacial till and are referred mainly to the trunk glacier. Some geomorphological elements have been found on the valley side at the edges of the lower T. Moletta incision (a latero-frontal moraine ending at the valley side-valley floor border; N-S trending glacial-striae on roche moutonnée) and in the apex sector of the T. Moletta alluvial fan (a set of transversal scarps not due to river erosion; a cluster of 1-2 long serpentinite blocks; a big serpentinite erratic boulder). These elements are interpreted as the remnants of an end moraine-system largely buried under the alluvial fan deposits and referred to the Moletta Glacier. This reconstruction attests that the Moletta Glacier joined the Dora Riparia Glacier during the Last Glacial Maximum and reached the main valley floor in the Lateglacial. A greater expansion of the tributary glacier is therefore recognized and reported on a new geological map compared to the previous extent reported in the Susa Sheet of the Geological Map of Italy (Cadoppi et al., 2002). Cadoppi, P., Castelletto, M., Sacchi, R., Baggio, P., Carraro, F., & Giraud, V. (2002). Note illustrative della Carta Geologica d’Italia alla scala 1:50.000 – Foglio 154, Susa. Roma: Servizio Geologico d’Italia, p. 127
The end-moraine system of the Pleistocene Moletta Glacier (Susa Valley, NW Italy)
Gianotti F.Co-first
2021-01-01
Abstract
A geological survey was carried out on the left side of the middle Susa Valley north of Bussoleno (NW Italy), with the aim of study the relationship between the tributary Moletta Glacier and the main Dora Riparia Glacier in the Last Glaciation. The Moletta catchment is a 5,8 km2 wide tributary south-facing valley, with maximum elevation of 2963 m a.s.l. (M. Palon - Rocciamelone Group). It consists of oceanic crust made of serpentinite and prasinite (Piemontese Zone), oucropping in the upper sector of the valley and tectonically overlying (cargneule) on a continental crust made of paragneiss, micaschist and dolomite marble (Dora Maira Massif) outcropping in the lower sector (Cadoppi et al., 2002). The bedrock, with a diffuse subglacial abrasion shaping, is covered by Lateglacial (19-11.7 ka BP) glacigenic deposits (lodgement till, subglacial melt-out till, ice-marginal flow till, glacio-lacustrine and glacio-fluvial deposits) and by post-glacial gravitative deposits (talus debris and colluvial). The Bussoleno village is located on the T. Moletta alluvial fan which extends downvalley in the trunk valley floor. Thick bodies of well stratified ice-marginal glacio-lacustrine gravelly sand, scattered on the trunk valley side, rest above the subglacial till and are referred mainly to the trunk glacier. Some geomorphological elements have been found on the valley side at the edges of the lower T. Moletta incision (a latero-frontal moraine ending at the valley side-valley floor border; N-S trending glacial-striae on roche moutonnée) and in the apex sector of the T. Moletta alluvial fan (a set of transversal scarps not due to river erosion; a cluster of 1-2 long serpentinite blocks; a big serpentinite erratic boulder). These elements are interpreted as the remnants of an end moraine-system largely buried under the alluvial fan deposits and referred to the Moletta Glacier. This reconstruction attests that the Moletta Glacier joined the Dora Riparia Glacier during the Last Glacial Maximum and reached the main valley floor in the Lateglacial. A greater expansion of the tributary glacier is therefore recognized and reported on a new geological map compared to the previous extent reported in the Susa Sheet of the Geological Map of Italy (Cadoppi et al., 2002). Cadoppi, P., Castelletto, M., Sacchi, R., Baggio, P., Carraro, F., & Giraud, V. (2002). Note illustrative della Carta Geologica d’Italia alla scala 1:50.000 – Foglio 154, Susa. Roma: Servizio Geologico d’Italia, p. 127
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