Seismic Stratigraphy, Cenozoic Basin Evolution, and Sedimentary History of the Southern Part of Baffin Bay, Canada: Preliminary Results of ODP Leg 105

S. P. Srivastava, M. A. Arthur

Ocean Drilling Program Leg 105 drilled Site 645 (2,018 m water depth) in southern Baffin Bay, recovering 1,147 m of lowermost Miocene to Quaternary sediments. The drilling results, a regional multichannel seismic net, and industry wells on the Greenland margin and in Davis Strait allow us to reconstruct the late Paleogene-Quaternary tectonic and sedimentary history in southern Baffin Bay. A deep regional seismic reflector (R3) that extends across the central part of Baffin Bay and lies at a depth of about 1,540 m below sea floor in the vicinity of Site 645 was not reached, but our results suggest a late Eocene-early Oligocene age for the horizon. That age, depositional sequences in seismic records, and results of a preliminary subsidence model for the site indicate that s bsidence, following rifting of the basin, began between 63 and 55 Ma, and that spreading ceased by the Oligocene, in agreement with plate tectonic models for the region. This basin probably was not a major conduit for water-mass exchange between the Arctic and Atlantic Oceans prior to the Eocene.

Silty and sandy mud and muddy sand (porosities 20-30%), deposited in relatively deep water at rates of 30 to 140 m/m.y., dominate the sedimentary sequence at Site 645. Organic carbon contents average near 1% over much of the sequence, with a maximum of 3%, but the organic matter has low hydrogen indices and is predominantly of terrestrial origin. The paucity of siliceous and calcareous biota, the neritic aspect of diatom and dinocyst floras, and other indicators suggest that cool, subsaline, low-productivity surface waters predominated from at least the Miocene to the present.

Regional reflector (R2) marks the onset of vigorous deep-water circulation in the basin in the middle Miocene--perhaps the first major penetration of cold Arctic water masses into the Labrador Sea via Baffin Bay. Reflector R1 lies at the base of a thick late Pliocene-Pleistocene sediment sequence that onlaps that surface from the Greenland side of the basin. Evidence from Site 645 suggests initiation of major ice rafting at about 2.4 Ma, but with some ice-rafted debris possibly reaching the site as early as 6 Ma.

AAPG Search and Discovery Article #91038©1987 AAPG Annual Convention, Los Angeles, California, June 7-10, 1987.