Late Pleistocene channel incisions in the southern Eel River Basin, northern California: implications for tectonic vs. eustatic influences on shelf sedimentation patterns

High-resolution multichannel seismic (MCS) profiles from the southern offsh ore Eel River Basin off northern California show multiple, superimposed bur ied channels beneath the continental shelf. These channels display consiste nt southwest orientations. Their dendritic map pattern and low but consiste nt cross-shelf gradients suggest that they formed by fluvial erosion during periods of shelf exposure associated with relative sea-level lowstands. Al l of the channels were incised after similar to 500 ka, the age of the onsh ore-offshore Hookton Datum. Their frequency of incision exceeds that of kno wn glacioeustatic lowstands since similar to 500 ka, confirming that some o f the surfaces must have formed during relative lowstands initiated by loca l tectonic uplift. Sedimentation patterns in the Eel River Basin shift dramatically in respons e to relative sea-level fluctuations. Today, sediments from the Eel River m ove north and west on the shelf, in response mainly to large winter storm e vents. In contrast, fluvial incision on the exposed shelf during relative l owstands directed sediments to the southwest, most likely into the head of the Eel Canyon. Shelf channels were probably fed not only by ancestral rive rs, but also by local uplifts like the Table Bluff Anticline. Increases in gradient and channel depths at the southern end of the MCS coverage indicat e that canyon-forming processes modified fluvial channels as they converge towards embayments near the head of the Eel Canyon. Cyclic recurrence and c onsistent orientation of these channels demonstrate that the Eel Canyon has been extant through numerous relative sea level cycles, and is perhaps as old as similar to 500 ka. (C) 2001 Elsevier Science B.V. All rights reserve d.