Late Cenozoic evolution of Laurentian Fan: Development of a glacially-fed submarine fan

Abstract

The Late Cenozoic evolution of the upper Laurentian Fan, offshore eastern Canada, was studied by integrating single and multi-channel airgun seismic surveys collected over the past three decades. The upper Laurentian Fan has a complex history, strongly influenced by the growth and decay of continental ice sheets since at least the Middle Pleistocene. Four regional stratigraphic horizons (O, Q, B, and A, in order of increasing sub-bottom depth) were correlated throughout the single channel airgun data set and have been identified in low-resolution, multi-channel data. An additional deeper horizon, L, only identified in the multi-channel data, marks the Pliocene onset of Laurentian Fan development. Correlation of the seismic markers, in conjunction with seismic facies analysis, provided the basis for dividing the evolution of the fan into five major phases: i) initial development of a single, progradational leveed channel; ii) erosional over-deepening of this channel associated with the onset of glaciation; iii) major re-organization of the fan system coinciding with the glacial excavation of Laurentian Channel on the continental shelf; iv) further re-organization of the fan associated with ice streams flowing through Halibut Channel; and v) predominantly aggradational growth of the fan and a progressive westward shift of the upper fan depocentre. A chronology for the fan was determined indirectly using sparse biostratigraphic data from seafloor outcrops, extrapolation of sediment accumulation rates, and correlation to the global oxygen isotope curve. It shows that the regional reflectors O–A correspond to marine isotope stages 4, 6, 12 and (?) 22. Average sediment accumulation rates show a gradual increase through time consistent with the generally progradational character of the fan. Comparison of Laurentian Fan with the Northwestern Atlantic Mid-Ocean Channel in the Labrador Sea, both glacially-fed submarine channel–levee systems, suggests that Eastern Valley of Laurentian Fan is analogous to the submarine braidplain in the Labrador Sea. Ice-margin flow separation, similar to that inferred at the head of NAMOC, resulted in coarse-grained bedload flowing down Eastern Valley as hyperpycnal inflows, whereas Western Valley and the canyons of the East Scotian Slope were fed principally by finer-grained sediment from meltwater plumes. The turbidity currents associated with these plume deposits were initiated either by remobilization of this material due to upper slope failures or through hyperpycnal flows created by double diffusive sedimentation. The stratigraphic evolution of Laurentian Fan records a wealth of glaciogenic and paleoclimatic information that would be further revealed by the collection of long cores (e.g., Integrated Ocean Drilling Program boreholes).