ABSTRACT

Two Holocene sediment budgets have been compiled for the California Continental Borderland. The first detailed budget includes the six northern inshore and central basins that capture almost 40% of the total sediment input to the entire borderland. In the second budget, the data for the six basins has been added to estimates of accumulation for the remaining borderland area to produce a total regional budget of lower precision than the smaller, six-basin region.

Natural river influx to the borderland approximates 13 10¹⁰ tons for the Holocene epoch, and biological input has been estimated at about 2 10¹⁰ tons. Eolian and ocean current influx have each been estimated at about 1 10¹⁰ tons. In sum, the total deposited volume for 10⁴ yrs is about 14 10¹⁰ tons, and the estimated total influx is of the order of 17 10¹⁰ tons, which suggests that a net of 1-3 10¹⁰10 tons for the Holocene high sea-level period.

The six high-accumulation-rate basins are located adjacent to the largest river sources, the major zones of coastal upwelling, and the main northern eddies of the California Current. These high-accumulation sites are typically also areas where mass movement and fan development are localized. The sediment-accumulation rate is much larger than subsidence rate, and flat-floored basins are typical. In contrast, the southern and outer, low-accumulation basins are areas of draped sediment, with accumulation rate less than subsidence rate, and are the sites of penecontemporaneous deformation of the accumulating, fine hemipelagic sediments. Few fans or major mass movements are seen.

Significant sedimentation is mainly confined by topography to less than 20% of total margin area. Thus, the moderate to low total sediment influx is amplified by the restricted receiving area to produce locally thick deposits of limited areal extent. This pattern is characteristic of Neogene southern California basins and illustrates that stratigraphic thickness is not a valid indicator of sediment influx.