Crater Lake, Oregon: A restricted basin with base-of-slope aprons of nonchannelized turbidites

The basin floor of Crater Lake (10-km diameter, 600-m water depth) is covered by up to 75 m of sediment–gravity-flow deposits interbedded with mud. In the upper units (8 m (thick), sand and gravel layers with numerous wedging, strong seismic reflectors characterize the base-of-slope aprons at the basin margin. These layers evolve to turbidites of mainly thin, fine-grained, basin-plain type, characterized by numerous flat and weak seismic reflectors in the central basin floor. Many individual debris-chute sources funnel sediment to base-of-slope aprons: there, coarse-grained parts of the sediment–gravity flows deposit nonchannelized beds attributed to the F, A, B turbidite facies. While traversing the base-of-slope aprons, flows evolve to sheet-flow turbidity currents that deposit D-facies beds over the central basin floor. These processes and patterns of deposition characterize small siliciclastic basins without channelized submarine fans and are common in carbonate basins of all sizes.