Detailed investigation of sorted bedforms, or “rippled scour depressions,” within the Martha's Vineyard Coastal Observatory, Massachusetts

Beneath the sorted bedforms lies a shallow, horizontal seismic reflector, a few tens of centimeters below the seafloor in the shallower waters, and>1 m in deeper water. This reflector is consistently present below the fine sands and is often observed, although less defined, beneath the coarse sands. It is often continuous beneath transitions between fine and coarse sands at the surface. In sediment cores, this reflector appears to correlate to a variable-thickness layer of gravel/very coarse sands that is frequently present beneath both coarse and fine surface sands. This surface also caps a buried fluvial channel system. We interpret this horizon as an erosional lag delineating a transgressive ravinement surface and the contact between poorly sorted glacio-fluvial sediments below and reworked, well- to moderately well-sorted fine and coarse sands above.