Abstract

Seismic reflection profiles, basement structure-contour maps, and bathymetric data are used to analyze sedimentation patterns over a distance of ∼2,300 km along the Kane Fracture Zone and to interpret uplift history of the Bermuda Rise. Sediments within the fracture valley thin seaward on younger crust and with distance from continental sources. Superposed on this pattern are the effects of local and regional basement structure, variations in surface-water productivity, influence of bottom currents, and local effects of sediment redistribution. Preservation of a thicker and more complete sedimentary record within the Kane fracture valley facilitates identification and eastward correlation of seismic reflections, and we have cross-correlated these eflections to synthesize an along-axis transect of the fracture zone. Stratigraphic correlations of key reflections to Deep Sea Drilling Project drill sites determine the composition and ages of the lithologic sequences. Observed pinch-outs of seismic horizons J1, β, and A* on fracture-valley crust extend significantly seaward of previously mapped limits, and the younger pinch-out ages accord better with ages defined by deep-sea drilling.

Paleosedimentation patterns in successive stratigraphic intervals document the growth of the continental margin/basin sedimentary prism from Late Jurassic time and the uplift of the Bermuda Rise beginning in middle Eocene time. Middle Eocene cessation of turbidite deposition atop the Rise, as identified by Horizon At, marks initiation of regional uplift. A seismic discontinuity in turbidite ponds east of the Rise records a probable pulse of uplift during early Oligocene time. Structure of the overlying seismic reflection sequence suggests continued uplift, albeit at decreasing rates, through the late Oligocene and possibly through Miocene time. The anomalous elevation of the Rise subsequently has been maintained, but there is no clear stratigraphic evidence for further growth.

Turbidite ponds fill the Kane fracture valley east of the Bermuda Rise and terminate against a prominent structural dam at 55°20′W. These ponds began to fill with turbidites in middle Eocene to early Oligocene time, and the sediments were derived from local sources. Within the past 10-12 m.y., turbidity currents began to enter the ponds through connections with the encroaching Nares Abyssal Plain, and they probably now constitute the dominant sediment source for the fracture valley.

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