Abstract Turbidites on active margins represent key archives of great earthquakes, yet turbidity currents triggered by non‐seismic events complicate paleoearthquake records and influence geochemical budgets. Sediment cores collected from highstand‐detached Astoria Canyon address whether non‐seismic turbidity currents are preserved in canyon stratigraphy. Detailed analysis of a core indicates fluvial origin of turbidites based on sedimentology, geochronology, and organic matter composition. Turbidites are ∼15 cm thick, graded, and laminated. Turbidite 210Pb activity is low, and depositional ages align with major Columbia River floods. Turbidite organic matter is terrestrial and modern (−26‰ δ13Corg, 18 C:N, ∼6 mg lignin per 100 mg OC). These deposits provide the first direct evidence of modern non‐seismic turbidite deposition in northern Cascadia, with implications including that highstand stratigraphy preserves non‐seismic events, turbidite composition reflects sediment source, and turbidite deposition represents a significant component of sediment and carbon accumulation.
Observations from the Little Bunker
Last updated: November 30, 2025 04:25 AM
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