Characterization of Paleochannels offshore from the Northern Channels Islands, California USA

Howasta Tahiry

Howasta Tahiry
MS Candidate
Advisor: Dr. Jillian Maloney

Friday, December 6th, 2019
CSL 422 – 9am

The continental shelf offshore from the Northern Channel Islands (NCI) provides a glimpse into fluvial response to eustatic sea level changes since the last glacial maximum (LGM, ~20 ka). During the LGM, the NCI shoreline fell to 106 m below the present-day shoreline, affecting drainage systems as they adjusted to a lower base level. The response of the terrestrial reaches of these systems has been investigated and used to infer changes to their offshore extensions, but direct investigations of paleochannel morphology on the now submerged NCI shelf have not been conducted. The island setting of the NCI provides an excellent study area as external forcings on fluvial morphology (climate, tectonics, and sea level) are uniform across the many drainage basins of the island chain. Using newly available high-resolution bathymetric and seismic data, we located and characterized four submerged paleovalleys on the NCI shelf. Observed paleovalley morphology is variable, including a wide terraced valley, a series of narrow and shallow channels, and small shelf delta deposits cut by narrow channels. The variable morphology could be a response to internal forcings such as shelf and basin morphology, or could be related to preservation in the marine environment. These results demonstrate the variability of paleovalley morphology in uniform environments along an active margin, which has significance for sequence stratigraphic models, energy exploration studies, archaeological resources, and paleoenvironmental reconstructions.