Quaternary geology of the northeast Baffin Island continental shelf, Cape Aston to Buchan Gulf (70° to 72°N)

Shallow geophysical and geological data acquired from 1974-1985 across a part of the northeast Baffin Island continental shelf provide information on its morphologic and stratigraphic development since the late Tertiary, culminating in the deposition of late Quaternary glacial to post-glacial sediments. The study area contains four transverse troughs, up to 36 km wide and incised up to 800 m through bedrock units of Precambrian to Tertiary age, with glacial erosion indicated by axial overdeepening (including elongate depressions at the bedrock surface, up to 180 m in relief). Bedrock units are unconformably overlain by strata up to 180 m thick, divided into six stratigraphic units to which informal names have been applied. The Cape Adair Sediments, an irregularly stratified subsurface unit with thicknesses up to 100 m, is observed beneath inter-trough areas and within Clyde and Sam Ford troughs and is tentatively correlated to the glacial to glacial marine successions of the adjacent coastal forelands of Baffin Island, which in places date back to the Pliocene. An unconformity at the surface of the Cape Adair Sediments, in places resistant to iceberg scouring, corresponds to a mainly transverse system of depressions and ridges recognised within inter-trough areas. The Scott Trough Sediments, a well-stratified subsurface unit with thicknesses up to 75 m, onlaps bedrock depressions in Scott and Buchan troughs and may record either a long period of marine deposition prior to the last glaciation, or rapid glacial marine deposition during the last deglaciation of the shelf. A conformable succession of four units that outcrop at seabed is interpreted to record a late Quaternary cycle of glacial ice-contact through glacial marine to post-glacial sedimentation. The Baffin Shelf Drift (unstratified, irregular geometry, up to 75 m thick) extends to the shelf edge and to depths of 850 m in Buchan Trough, consistent with full glacial occupation of the shelf. The unit interfingers in places with the Davis Strait Silt (stratified, mantling geometry, up to 7 m thick), which is inferred to record iceproximal to distal marine deposition during deglacial withdrawal from the shelf. A single core sample of the Davis Strait Silt comprises mud with locally derived sand and gravel, yielding no dateable material. However, downward extrapolation of radiocarbon dates in cores of overlying post-glacial muds to the top of the unit yields an age of c. 15 ka for the end of glacial conditions on the shelf. Postglacial deposition is recorded by the Tiniktartuq Mud (hemipelagic deposits in the troughs and intertrough depressions, up to 7 m thick) and the Cape Aston Sand (coarse-grained deposits =1 m thick above depths of 80-120 m). Core samples indicate both units include significant components of deposition from ice rafting and, for the Cape Aston Sand, probable reworking of glacial sediments. Grab samples from the two post-glacial units yield seabed muds and sands, consistent with ongoing deposition. Samples from the surfaces of the two glacial units yield variable textures, inferred to reflect the effects of current reworking, ice rafting and iceberg scouring. Iceberg scours (locally up to 8 m deep over glacial units) have extensively modified the seabed over most of the shelf, although abundances are reduced in inter-trough depressions and in Sam Ford and Clyde troughs. Scours extend to depths of 600 m on the upper continental slope and the outer walls of Scott and Buchan troughs. Most scours below depths of c. 300 m are inferred to be relict, whereas modern scours are recognized in shallower depths, including one observed in the process of formation in c. 90 m depth. Sediments on the floors of Scott and Buchan troughs contain a record of mass failure from the adjacent steep (up to 25°) slopes. Seepage of hydrocarbons from the seabed is also recognized on the walls of Scott and Buchan troughs, where it has resulted in indurated crusts, bacterial mats and possible pockmarks.

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