ИСТИНА

Iceberg rafted debris (IbRD) consisting of rock fragments is widely used as a proxy for reconstruction of deglaciation environments at high latitudes. This study is focused on petrography of the coarse IbRD (>2 mm) to reveal its provenances and deposition conditions. The material was collected by several Russian expeditions : (1) from the glaciomarine; diamicton that was deposited during the early deglaciation of the Barents Sea ice sheet, and (2) from the contourites and channel floor deposits on the Argentine continental slope adjacent to the Malvina Strait. The most variable IbRD (more than 10 rock types per a core sample) occur in the diamicton from the narrow troughs of the eastern Svalbard area where grounded glacier ice flows drained different provenances. In a core from the Franz-Victoria Trough, subglacial till with fragments of organic-rich black shale is overlain by glaciomarine diamicton that contains various rock types including the black shale. Granite fragments dominate among IbRD from the SW Argentine continental slope both among dropstones within the glauconitic sand contourites deposited during the last glaciation and in the residual coarse debris from the channel floor. Hence, the IbRD composition suggests drainage of a single provenance by an ice flow of the Patagonia ice sheet during early deglaciation when glacioeustatic sea level rise led to detachment of the grounded ice sheet from the bottom and related iceberg calving.