Rohr, K. M. M., King, H., Riedel, Michael and Schmidt, U. (2019) From mid-plate to subduction zone: stratigraphy of the northeast Juan de Fuca plate, offshore British Columbia. , 2019 . Geological Survey of Canada Current Research, 2019-4 . Natural Ressources Canada, 14 pp. DOI 10.4095/314906.

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Abstract

Quaternary sedimentary stratigraphy in Ocean Drilling Program site 1027 was tied to three regional multichannel seismic reflection profiles across the northeastern Juan de Fuca plate to the Cascadia subduction zone. A velocity gradient from a refraction study provided a good fit to convert depth of stratigraphic horizons to two-way traveltime. Topography of basement ridges prevents correlating time horizons older than 0.76 Ma on a regional scale on seismic reflection sections. By that time sediments had filled almost to the top of basement ridges and deposition of the Nitinat fan had begun. After 0.46 Ma, coarser sediments and debris flows were deposited from the fan into the seaward reaches of Cascadia Basin, and above the 0.28 Ma time horizon, the reflection character of deposits around the fan is that of poorly sorted mass-transport deposits with intermittent layering. More than half of the sediments in the trench are from the Nitinat fan; they are approximately 2 Ma younger than previously thought. Growth faults created by bending stresses from the sediment load and subduction are primarily observed in intervals that predate the Nitinat fan and accumulated at slower sedimentation rates. These faults appear to be utilizing extensional faults that are part of the original fabric of the igneous crust.

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