Abstract:
A seismic stratigraphic study of the Upper Neogene and Pleistocene shelf and deep-sea deposits of Southeast Greenland is presented. The depositional environment was controlled by glacial, turbidity current, and contour current processes. Below the mid-and outer shelf a Tertiary sedimentary wedge, as much as 1.7 km thick, is resting on a seaward-dipping volcanic acoustic basement. A lower marine part is separated by a regional unconformity, SB-A, from two seismic sequences of early Pliocene to Pleistocene prograding clinoforms. SB-A is surmised to represent a seaward-dipping palaeo-relief surface, accentuated by modest submarine erosion related to a sea-level lowering. The overlying two Sequences x and y reflect shelf-edge progradation in front of grounded ice during periods of maximum glaciation. The topset beds of the youngest sequence, possibly of Pleistocene age, are characterized by six or more sub-horizontal, landward-dipping internal unconformities, taken to reflect individual glacial cycles of grounded ice erosion. The present-day shelf is overdeepened, landward dipping, and traversed by troughs. These features are characteristic of a shelf sculptured by grounded ice. The position of the transverse troughs, reflecting the positions of former icestreams, seems to have been more or less permanent since the late Neogene. The shelf progradation has been higher in front of the troughs than in front of adjacent banks, resulting in the development of trough-mouth fans (TMF). The strata continue seawards below the shelf break across a crustal monoclinal flexure to the deep sea. Three seismic sequences have been identified within the late Miocene and Pleistocene deep-sea sedimentary succession on the continental rise. They are bounded by unconformities of mid-Pliocene, early Pliocene, and (?) late Miocene ages. The oldest sequence is interpreted as basin floor fans, probably linked to a sea-level lowstand. The two youngest sequences were deposited from interplay of contour and turbidity currents during glacial periods, and they form large sediment ridges on the sea floor, oriented almost perpendicular to the continental rise, nucleated on the older sequence. Inter-ridge channel-levee complexes recognized within the youngest sequence were deposited from turbidity currents. The major turbidity channels are prolongations of the transverse shelf trough-trough-mouth fan systems. A moat zone, at the base of the continental slope, reflects the position of strong modern contour currents. Appreciable contourite deposition did not commence before the early Pliocene, and was probably linked to glaciation of the shelf and onset or intensification of the Labrador Sea Water deep current.