麻豆传媒

The inner continental shelf off Nova Scotia can be subdivided into 5 coast-parallel terrain zones which record glaciation, and sea level rise and fall during the Late-glacial period. At the last glacial maximum an ice mass centred in the Gulf of St. Lawrence extended to the shelf edge (Ice Flow Phase 2). During an initial deglaciation phase (ca. 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-Ice Flow Phase 3). The Scotian Shelf End Moraine Complex (SSEMC) lies at the seaward margin of the inner shelf. The surface SSEMC till is correlated with an autochthonous, stony till on land formed under the Scotian Ice Divide. The SSEMC formed at the ramp margin of a buoyant ice sheet. The Phase 3 ice margin was stabilized by isostatic recovery from Phase 2 ice loads.

Landward of the end moraines is a series of linear depositional basins termed the Basin Zone which contain a complete sedimentary record of events after the deposition of the SSEMC. The lowest depositional sequences (Sequences 1 + 2; Emerald Silt facies A) in these basins are interpreted to be ice proximal sediment, deposited by overflow and interflow meltwater plumes emanating from a retreating ice margin. Periodic stillstands of this ice mass are marked by small, incipient moraines within the Basin Zone. DeGeer moraines are found over a wide area (Morainal Zone) landward of the Basin Zone. Two morphological varieties were defined; symmetrical and asymmetrical moraines. These formed underneath and at the edge of a rapidly advancing local ice cap centred in northern Nova Scotia (Ice Flow Phase 4; ca 13 ka). From l3-l2 ka sea-level dropped rapidly, due to general isostatic recovery. Ice receded out of marine areas depositing ice distal glacial marine Sequences 3 and 4 (Emerald Silt facies B), in the Basin Zone. A lowstand shoreline (ca 11.6 ka) at -65 m is marked by the landward transition from morainal topography to a shoreface ramp, terrace and wave-cut platform. Increased storminess, sea ice and icebergs during the Younger Dryas climatic cooling (ca 11-10.0 ka), produced Sequence 5 in the Basin Zone.

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