Deglaciation of the inner Scotian Shelf, Nova Scotia: correlation of terrestrial and marine glacial events

Abstract

Abstract The inner continental shelf off Nova Scotia is an important region for correlating glacial events across the terrestrial-marine transition. The inner Scotian Shelf can be subdivided into five coast-parallel terrain zones which record glaciation and the rise and fall of relative sea levels during the late glacial period. During the initial deglaciation phase ( c. 17–15 ka) ice was drawn out of the Gulf of Maine, isolating an ice mass over Nova Scotia which later became an active centre of outflow (Scotian Ice Divide). The Scotian Shelf End-Moraine Complex (SSEMC) formed at the margin of this glacier. Landward of the end moraine complex is a series of linear depositional basins termed the Basin Zone, containing a complete sedimentary record of events after deposition of the SSEMC. The lowest depositional sequences (sequences 1 and 2) in these basins are interpreted to be ice-proximal sediment, deposited by overflow and interflow meltwater plumes emanating from the retreating ice margin. From 13–12 ka, the sea level dropped rapidly due to glacial isostatic recovery. Ice receded out of marine areas, depositing the glacial-marine sequence 3 in the Basin Zone. A lowstand shoreline ( c. 11.6 ka) at −65 m is marked by the landward transition from morainal topography to a shoreface ramp, terrace and wave-cut platform. Enhanced current erosion during the lowstand was recorded in the inner Scotian Shelf basins by erosional truncation of sequence 3. After this erosional event the sea level rose rapidly, concomitant with climatic warming, as indicated by foraminifera within the Basin Zone and increases in spruce pollen in cores from Nova Scotia lakes. In the Basin Zone a seismic sequence characterized by indistinct, low-amplitude reflections (sequence 4) was deposited. Increased storminess and current sediment delivery with increased sea ice and icebergs during the Younger Dryas climatic cooling ( c. 11–10.0 ka) produced sequence 5 in the Basin Zone. Sequence 5 is correlative with a distinctive mineralic layer in lakes and periglacial and glacial sediments that overlie peat in land sections. The terrestrial and marine sections record a transition from organic-rich to inorganic sedimentation events initiated c. 10.8 ka. Climatic cooling and snowfield/glacier build-up on land, with increased meltwater runoff and storm-induced sedimentation in the marine realm, were the principal causes of these sedimentation events.