Large, buried glacial moraines revealed by TOPAS sub-bottom profiling, South Orkney Islands, South Atlantic Ocean

Abstract

Subglacial and ice-marginal landforms produced during the Last Glacial Maximum and subsequent regional deglaciation become progressively more buried, especially when postglacial sedimentation rates are high. Sub-bottom profiling is usually used to examine the stratigraphy of submarine glacial deposits, but is only rarely exploited to visualize the topography beneath postglacial infill. By picking and gridding the basal reflector from a relatively dense network (spacing of <1.5 km) of TOPAS parametric sub-bottom profiles, we visualize both the modern seafloor of Orwell Trough, South Orkney (SO) Islands, and reconstruct the glacial landforms buried beneath up to c. 54 m of subsequent fine-grained sedimentation (Fig. 1). Based on accompanying sedimentological evidence and the shallow acoustic stratigraphy, the basal reflector is interpreted as the upper surface of either a subglacial till or coarse-grained ice-proximal debris (Fig. 1d). Fig. 1. ( a ) Perspective view of large, buried moraines, revealed through gridding of a sub-bottom reflector (basal reflector a′), interpreted as the upper surface of a subglacial or glacial proximal till. Pink and black arrows are locations of moraine crests marked in (d) and (e), respectively. Corresponding water depths for vertical scale are c. 240 and 480 m. Horizontal scale bars and north arrows on all 3D images provide approximate scale …