GNGTS 2023 - Atti del 41° Convegno Nazionale

Session 3.2 ___ GNGTS 2023 compared to ice, so it is straightforward to think it could be somehow related to rocks and/or debris. At first, the hypothesis of the actual interpretation of the layered unit is that it could be possibly related to a development of the moraine, as a collapse of the moraine surface. However, there are no reasons to associate an internal layering with a collapse as it should show a massive and chaotic facies, due to the scattering phenomena caused by the heterogeneous material characterizing a moraine. The following hypothesis is that the evident layering is due to some sedimentary activities, repeated in time and causing the deposition of superimposed layers, as happens in a fluvial delta. Also, the shape and location of such a unit is peculiar: as a matter of fact it is hosted in a depression of the moraine surface, which is an optimal spot for accumulation of sediments. Then, it is remarkable to notice that the extension of this sedimentary deposit corresponds to the white spot highlighting the ice blister on the lake surface (FIG. 3). This correlation could be an evidence in favour of the pushing action of Amorphous Glacier, which is forced to overthrust the sedimentary deposit creating the ice blister just above it, as the shear evidence on GPR profiles seems to suggest (FIG.2A). The hypothesis of the fluvial delta existence is further supported by the evidence of a localised incision, flowing down along the moraine. As shown in FIG. 3, the incision is about 5 m deep in the north-western profiles and flows down reducing its depth and following the inner border of the moraine. In fact, in FIG. 3C,D the incision is localized close to the high-amplitude reflector of the moraine. The idea is that the channel flowed from NW to SE, entered in the depression of the moraine and deposited the sedimentary delta, as it encountered an obstacle to the flowing in Amorphous Glacier in front of it. On GPR profiles, the contact between the glacier ice and the fluvial delta is unclear and we were unable to improve the imaging even by dedicated attribute analysis. The period of the delta activity is still unknow, but it should be related to a warm period of the Antarctic climatic history. Such a geomorphological setting at first could be unexpected as the Antarctic landscape is considered the most stable and conservative environment of the entire planet, at least since 13.6 Myr ( Sugden and Denton, 2004 ), but not so uncommon considering the surroundings of Amorphous Lake area. As a matter of fact, the Amorphous Glacier area presents morphological similarities with Boulder Clay Glacier, a polar glacier partially covered by an heterogeneous ice-cored moraine and located about 2 km South-East from Amorphous Lake. On Boulder Clay Glacier, a channelized system flowing down near a morainic ridge has been imaged in GPR profiles ( Forte et al., submitted ). During the XXXVIII Italian Antarctic Expedition (November 2022), a new GPR survey on Amorphous Lake to increase the previous spatial data coverage, as well as a FDEM induction electromagnetic survey, were performed with the aim to characterize shallow materials on the basis of their electrical characteristics. The research will focus on the integration of these information in order to provide a clearer assessment of the layered unit and a more constrained reconstruction of the structural and geomorphological setting of the area, in relation with a similar setting found in the Boulder Clay Glacier area.