Heavy or high-specific gravity minerals make up a small but diagnostic component of sediment that is well suited for determining the provenance and distribution of sediment transported through estuarine and coastal systems worldwide. By this means, we see that surficial sand-sized sediment in the San Francisco Bay Coastal System comes primarily from the Sierra Nevada and associated terranes by way of the Sacramento and San Joaquin Rivers and is transported with little dilution through the San Francisco Bay and out the Golden Gate. Heavy minerals document a slight change from the strictly Sierran-Sacramento mineralogy at the confluence of the two rivers to a composition that includes minor amounts of chert and other Franciscan Complex components west of Carquinez Strait. Between Carquinez Strait and the San Francisco Bar, Sierran sediment is intermingled with Franciscan-modified Sierran sediment. The latter continues out the Gate and turns southward towards beaches of the San Francisco Peninsula. The Sierran sediment also fans out from the San Francisco Bar to merge with a Sierran province on the shelf in the Gulf of the Farallones. Beach-sand sized sediment from the Russian River is transported southward to Point Reyes where it spreads out to define a Franciscan sediment province on the shelf, but does not continue southward to contribute to the sediment in the Golden Gate area.

Sediment samples were selected from the 0.063 and 0.25-mm size fraction (or, if not enough sample was available, from the 0.25 to 0.50 mm size fraction) for heavy mineral analysis. Samples were separated in tetrabromoethane diluted to a specific gravity of 2.90; both the light and heavy (floating and sinking, respectively) grains were retrieved. The heavy grains were microsplit to about 1000 grains and mounted on glass slides. Grains were identified and counted by optical properties determined on a petrographic microscope for 42 samples. The counts were normalized as percent of total non-opaque grains and a cluster analysis was applied.

Supplement to: Wong, Florence L; Woodrow, Donald L; McGann, Mary L (2013): Heavy mineral analysis for assessing the provenance of sandy sediment in the San Francisco Bay Coastal System. Marine Geology, 345, 170-180