Geomorphology of the Northwest Atlantic Continental Margin: The Role of Deep-water Sedimentary Processes
|Title||Geomorphology of the Northwest Atlantic Continental Margin: The Role of Deep-water Sedimentary Processes|
|Publication Type||Journal Article|
|Authors||Mosher, DC, Campbell, DC, Chaytor, JD, Piper, DJW, Gardner, JV, Rebesco, M|
|Place Published||Amsterdam, North Holland, The Netherlands|
The tectonic history of a margin dictates its general shape; however, its geomorphology is generally transformed by deep-sea sedimentary processes. The objective of this paper is to show the influences of turbidity currents, contour currents and sediment mass failure on the geomorphology of the northwestern Atlantic margin (NWAM) between Blake Ridge and Hudson Trough, spanning about 30 degrees of latitude. This assessment is based on new multibeam echosounder data, global bathymetric models and sub-surface geophysical information.
The geomorphology of the NWAM is a function of the balance between sediment delivery, removal and accumulation and the relative influences of each of the deep sea sedimentary processes involved in these roles. In some locations, a single process dominates, while along most of the margin it is a mix of processes. Much of the NWAM demonstrates a steep (>4o) upper slope followed by a general concave-upwards (graded) shape down to the abyssal plain. The steep upper slope is largely a result of either turbidity current erosion, sediment mass failure or a mix of both. The commonly observed graded profile results from erosion and sediment by-pass, as upper slope material is removed and transported toward the basin. In a turbidity current dominated margin, such as Labrador, material delivered at the shelf edge was moved downslope in the many channels and canyons and removed from the basin by the Northwest Atlantic Mid-Ocean Channel. Bathymetric profiles show a continuous exponential decay shape (graded) indicating sediment removal outpaced sediment delivery, despite high delivery rates in the Quaternary.
At a number of locations along the NWAM, there is departure from this graded profile shape that result from, 1) along-slope sediment transport and deposition (contour currents), which created drifts, such as the Chesapeake and Hatteras drifts along the U.S. margin, and resulted in an above grade (convex) shape to the lower parts of the margin; 2) high sedimentation rate in which sediment delivery outpaced sediment removal, such as seaward of glacial troughs that constructed trough mouth fans, such as Okak and Hawke trough mouth fans. These fans reflect above grade (near-linear) profiles. Similar profiles are formed by detached drifts, such as Blake Ridge and Hamilton Spur, wherein sediment was delivered laterally by contour currents, and construction of the drift outpaced removal of sediment by erosion or mass failure; 3) sediment retention due to physical damming of sediment involved in downslope processes, such as within Orphan Basin, wherein Orphan Knoll (and buried bedrock half-grabens) physical dammed outlet of material shed from the northern Grand Banks (e.g. Trinity Trough) and created an above grade shape to the bathymetric profile. To a similar extent, Chesapeake and Hatteras drifts retain sediments that were shed along the US margin; 4) significant large mass failure events created a steep headscarp and low profile lower slope where the deposit accumulated. A series of large mass failure deposits mapped off of Makkovik Bank along the Labrador margin created a two-stage profile shape, and 5) Sediment starvation or heavy erosion that resulted in exposing original structural tectonic shape; such as along the upper flank of the eastern portion of Flemish Cap. The lower flank hosts plastered drifts but the steep uppermost slope is largely a consequence of its original tectonic structure and the result is a two-stage slope profile.