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 x 10 10 tons for the Holocene epoch, and biological input has been estimated at about 2 x 10 10 tons. Eolian and ocean current influx have each been estimated at about 1 x 10 10 tons. In sum, the total deposited volume for 10 4 yrs is about 14 x 10 10 tons, and the estimated total influx is of the order of 17 x 10 10 tons, which suggests that a net of 1-3 x 10 10 tons has been passed through the system to the south into coastal deposits of Viscaino Bay or beyond the borderland. The uncertainty for this total approximate budget is probably + or -20%, and so the pass-through is best considered to be of the magnitude of 10 10 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.

First Page Preview

First page PDF preview
You do not currently have access to this article.