Glacial geomorphology of the Northeast Newfoundland Shelf: ice‐stream switching and widespread glaciotectonics

摘要

> Analysis of Olex bathymetry, multibeam sonar and seismic survey data, shows that, perhaps during the mid Pleistocene, grounded ice crossing the Northeast Newfoundland Shelf was topographically steered in Hawke Saddle, occupied a broad trough underlying much of Belle Isle Bank and present‐day Notre Dame Trough, and deposited ~100?m of stacked glacigenic sediment; grounded ice crossed southern Funk Island Bank and occupied Notre Dame Trough. During the Wisconsinan Stage, c . 30?cal. ka BP, flow remained topographically steered in Hawke Saddle, but due to flow switching two convergent ice streams incised the stacked sediments of the earlier phase, creating the modern Notre Dame Trough, and diverging around an erosional remnant near the shelf edge. The ice margin at the Last Glacial Maximum ( c . 18 14 C ka BP) was at the shelf edge in Trinity Trough but far to the west elsewhere. Retreating ice did not stabilize at fjord mouths, but halted several times within fjords. Shelf morphology was shaped by glaciotectonism. The large tectonized zone on the north flank of Notre Dame Trough was created by the northernmost of the two convergent streams. Glaciotectonism was most widespread in the enclosed St. Anthony Basin, where the Quaternary cover has been stripped away, arrays of composite ridges have formed and sediment blocks have been thrust onto the adjacent bank. A large hill‐hole pair was formed on the east side of the basin, extending onto Belle Isle Bank. A hill‐hole pair on the inner shelf was formed by ice flow from the northwest into Notre Dame Channel. Evidence of widespread glaciotectonism distinguishes this relatively deep shelf from the adjoining, relatively shallow, eastern Canadian shelves, but has strong parallels with parts of the Norwegian continental shelf where methane hydrates maybe played a role in regulating ice‐stream flow.