Tuesday August 6, 2024
USGS via Maven’s Notebook —
A new study conducted by the University of Texas, the San Francisco Estuary Institute, and USGS investigates how sand supply in San Francisco Bay reversed from largely fluvial sources to offshore sources as sea level rose during the early Holocene.
San Francisco Bay (Bay) is a large structurally controlled estuarine system heavily influenced by bedrock structures at its mouth. The prevailing hypothesis for sand transport across the Bay system has been that sediment (including sand-sized sediment) carried by the Sacramento and San Joaquin Rivers is delivered to the bay and transported to the Pacific coast. In the study, the researchers used a comprehensive sand provenance analysis to test this hypothesis, seeking to better understand origins and transport pathways of sand within the Bay.
Analyzing and dating sediment samples from the Bay and its smaller embayments revealed a significant shift in sand sources over time, particularly in the Holocene epoch from 11,700 years ago to present.