DECIPHERING CONTROLS ON TURBIDITE CHANNEL SEDIMENTATION PATTERNS ALONG AN ACTIVE MARGIN: UPPER NANAIMO GROUP, BRITISH COLUMBIA, CANADA

Deep-water slope systems represent one of the largest sediment pathways on Earth, delivering terrestrially-derived sediments to deep-ocean basins providing a critical link between sediment source and sink. The delivery of sediment through deep-water conduits is influenced by many local processes (e.g., accretionary prism thrusting) as well as regional marine-basin processes (e.g., basins subsidence, changes in sea-level). Additionally, marine sediment pathways are inherently linked to, and influenced by, upstream controls in the terrestrial realm. Deciphering the relative importance of these processes on sediment routing evolution in deep-time is a subject of current research. To fully isolate tectonic and local controls on depositional patterns, integrated datasets that are spatially and temporally exhaustive must be collected to understand the evolution of the entire source-to-sink system. The Upper Nanaimo Group, exposed in the Gulf Islands of British Columbia, represent a major sediment sink during the final building stages of the Northern Cordillera. Eocene uplift has exposed the basin fill in a depositional strike orientation, allowing for 20 m.y. of sediment routing to be analyzed along the ancient margin. The tectonic history of the Nanaimo basin is quite contentious. As such, deciphering tectonic events from sediment routing systems will help inform this debate.

We present a large dataset that incorporates regional mapping, measured stratigraphic sections, 4082 paleocurrent measurements, 46 detrital zircon samples, and 33 point-counted petrography samples to constrain the mechanisms controlling sedimentation patterns, duration, and stratigraphic architecture of the Upper Nanaimo Group. This dataset shows that each of the lithostratigraphic formations is composed of multiple deep-water conduits and many of the formations are largely diachronous documenting episodic delivery of coarse-grained sediment to the basin. The migration of sediment pathways that compose these systems as well as the initiation of basin wide conglomerate deposition can be linked to initiation of spreading along the Kula-Farallon ridge at ~84 Ma. These results demonstrate the long-term impact of oblique subduction and subsequent subduction erosion in a unique view along the length of a forearc basin.