SEA-LEVEL CONTROLS ON THE TEXTURAL CHARACTERISTICS AND DEPOSITIONAL ARCHITECTURE OF THE HUENEME AND ASSOCIATED SUBMARINE FAN SYSTEMS, SANTA-MONICA BASIN, CALIFORNIA

Hueneme and Dume submarine fans in Santa Monica Basin consist of sandy channel and muddy levee facies on the upper fan, lenticular sand shee ts on the middle fan, and thinly bedded turbidite and hemipelagic faci es elsewhere. Fifteen widely correlatable key seismic reflections in h igh-resolution airgun and deep-towed boomer profiles subdivide the fan and basin deposits into time-slices that show different thickness and seismic-facies distributions, inferred to result from changes in Quat ernary sea level and sediment supply. At times of low sea level, highl y efficient turbidity currents generated by hyperpycnal flows or sedim ent failures at river deltas carry sand well out onto the middle-fan a rea. Thick, muddy flows formed rapidly prograding high levees mainly o n the western (right-hand) side of three valleys that fed Hueneme fan at different times; the most recently active of the lowstand fan valle ys, Hueneme fan valley, now heads in Hueneme Canyon. At times of high sea level, fans receive sand from submarine canyons that intercept lit toral-drift cells and mixed sediment from earthquake-triggered slumps. Turbidity currents are confined to 'underfit' talweg channels in fan valleys and to steep, small, basin-margin fans like Dume fan. Mud is e ffectively separated from sand at high sea level and moves basinward a cross the shelf in plumes and in storm-generated lutite flows, contrib uting to a basin-floor blanket that is locally thicker than contempora ry fan deposits and that onlaps older fans at the basin margin. The in filling of Santa Monica Basin has involved both fan and basin-floor ag gradation accompanied by landward and basinward facies shifts. Prograd ation was restricted to the downslope growth of high muddy levees and the periodic basinward advance of the toe of the steeper and sandier D ume fan. Although the region is tectonically active, major sedimentati on changes can be related to eustatic sea-level changes. The primary c ontrols on facies shifts and fan growth appear to be an interplay of t exture of source sediment, the efficiency with which turbidity current s transport sand, and the effects of delta distributary switching, all of which reflect sea-level changes.