A recent turbidity current event, Hueneme Fan, California: reconstruction of flow properties

ABSTRACT A recent (100 yr old) turbidite is described from Hueneme Fan, California Continental Borderland. Dense sampling over the fan surface has allowed excellent delineation of the characteristics of this deposit. It exhibits Bouna DE sequences and has a distinctly bimodal, sandy silt grain size distribution. Through the use of generalized fluid dynamics equations, it is possible to reconstruct original flow properties of the current which deposited this material. The calculated velocities ranged from 10–90 cm s‐1 and excess density (above ambient seawater) from 0·001–0·005 g cm‐3 in the lower midfan and upper fan channel regions, respectively. Height of the current ranged from 5–15 m, on slopes from 1·5 to 0·15°. A total of 107 m3 of sediment was deposited during 10 days. The turbidity current is conjectured to have originated from direct river input during the floods of 1884. An older event is also described, which has distinctly different properties and origins. The grain sizes of this older deposit are much coarser, and sedimentary structures suggest higher flow regimes. This turbidite is conjectured to have been deposited from a higher density, faster current thought to have been generated by slumping. The need for a better understanding of the controls on the characteristics of turbidity currents and their effect on fan morphology is emphasized.