Accommodation space in a high-wave-energy inner-shelf during the Holocene marine transgression: Correlation of onshore and offshore inner-shelf deposits (0-12Â ka) in the Columbia River littoral cell system, Washington and Oregon, USA

The Columbia River Littoral Cell (CRLC), a high-wave-energy littoral system, extends 160 km alongshore, generally north of the large Columbia River, and 10-15 km in across-shelf distance from paleo-beach backshores to about 50 m present water depths. Onshore drill holes (19 in number and 5-35 m in subsurface depth) and offshore vibracores (33 in number and 1-5 m in subsurface depth) constrain inner-shelf sand grain sizes (sample means 0.13-0.25 mm) and heavy mineral source indicators (> 90% Holocene Columbia River sand) of the inner-shelf facies (≥ 90% fine sand). Stratigraphic correlation of the transgressive ravinement surface in onshore drill holes and in offshore seismic reflection profiles provide age constraints (0-12 ka) on post-ravinement inner-shelf deposits, using paleo-sea level curves and radiocarbon dates. Post-ravinement deposit thickness (1-50 m) and long-term sedimentation rates (0.4-4.4 m ka− 1) are positively correlated to the cross-shelf gradients (0.36-0.63%) of the transgressive ravinement surface. The total post-ravinement fill volume of fine littoral sand (2.48 × 1010 m3) in the inner-shelf represents about 2.07 × 106 m3 year− 1 fine sand accumulation rate during the last 12 ka, or about one third of the estimated middle- to late-Holocene Columbia River bedload or sand discharge (5-6 × 106 m3 year− 1) to the littoral zone. The fine sand accumulation in the inner-shelf represents post-ravinement accommodation space resulting from 1) geometry and depth of the transgressive ravinement surface, 2) post-ravinement sea-level rise, and 3) fine sand dispersal in the inner-shelf by combined high-wave-energy and geostrophic flow/down-welling drift currents during major winter storms.