Provenance, Stratigraphic Architecture, and Hydrogeologic Influence of Turbidites on the Mid-Ocean Ridge Flank of Northwestern Cascadia Basin, Pacific Ocean

Abstract

The northwestern edge of Cascadia Basin (North Pacific Ocean) is unusual because late Pliocene to Holocene turbidites lap onto juvenile oceanic crust of the Juan de Fuca Ridge. Subsidence of the ridge flank combines with irregular westward progradation of the turbidite facies to create a stratigraphic section that coarsens and thickens upward. The sand provenance is mixed. Individual turbidity currents have funneled into the area through several shelf-slope and abyssalfloor conduits, including Vancouver Valley, Juan de Fuca Channel, Barkley Canyon, and Nitinat Canyon. Local bathymetric blockage, deflection and reflection of flow paths by basement relief, remobilization by intrabasinal submarine slides and debris flows, episodic channel switching, and sporadic overbank flooding have combined to produce erratic recurrence intervals for the turbidity currents. Only the tallest basement highs have remained isolated from turbidite deposition during the last 500,000 years. Spatial and temporal differences in sediment accumulation are important because they modulate the three-dimensional responses of compaction and consolidation. Those changes in physical properties govern where and when hydraulic communication with the underlying basement shuts down. The basal hemipelagic layer of Cascadia Basin transforms to an effective hydrologic seal (seepage rates Ͻ 1 mm/yr) once the sediment-basalt interface is buried by 100-150 m of strata. Rapid accumulation of turbidites, therefore, accelerates the hydrogeologic conversion of igneous basement from open to sealed.

Physical properties of young (3.5 Ma) oceanic crust from the eastern flank of the Juan de Fuca Ridge: Comparison of wireline and core measurements with global data

“…Rapid turbidite deposition during Pleistocene sea level low-stands has buried much of the oceanic basement on the eastern flank of the JFR, except close to the active ridge and where a few seamounts and other basement outcrops penetrate regionally thick sediments [Davis et al, 1992;Underwood et al, 2005;Zühlsdorff et al, 2005]. Nearly complete burial of this ridge at an unusually young age makes this an ideal area to study ridge flank hydrothermal processes, where the rates and patterns of circulation are intense and particularly wellconstrained [e.g., Davis et al, 1997b;Fisher et al, 2003a;Hutnak et al, 2006].…”

Spatial and temporal dynamics of biogeochemical processes in the Fraser River, Canada : a coupled organic-inorganic perspective

“…The Nechako basin also lies in the heart of the mountain pine beetle outbreak of British Columbia (Safranyik and Wilson, 2006 River averted a substantial portion of the basin downstream of the Fraser Canyon, flowing northward rather than south (Andrews et al, 2012). The reversal to the modern configuration resulted in a massive increase in the delivery of terrigenous sediment to the North American continental shelf, leading to the creation of the deep sea Nitinat Fan (Underwood et al, 2005;Andrews et al, 2012). The temperate rain forest of the Coast Range became established around 9-6.5 ka while the Aleutian Low pressure system dominated over the Pacific High, creating a pattern of relatively cool and wet weather in the region (Hallett et al, 2003).…”

Site U1301

“…Sediment structures and the sediment/basalt interface are clearly visible, as are steeply dipping normal faults to the west of the holes (indicated with vertical lines that show total depth penetration). Both holes are located over the peak of a buried basement high, near the western edge of a major distributary channel for turbidites that flowed off the North American continental shelf (Davis et al, 1992;Zühlsdorff et al, 2005;Underwood et al, 2005;Hutnak et al, 2006). Proc.…”