OUTCROP EXPRESSION OF CONFINED CHANNEL COMPLEXES

Images from 3-D seismic surveys provide high-resolution architectural details of confined channels in the slope environment. Analog data for many seismically resolved confined channels comes from outcrop studies that provide insight into the lithofacies distribution and architectural features at the bed, bed set, channel, and channel complex scale. Dimensional and lithologic data are incorporated into forward seismic models to assist interpretation of seismic facies in terms of lithology distribution. The Capistrano Formation (Miocene) near San Clemente, California, is a sand-dominated complex of channel fills that is about 15 m thick and 1.2 km wide and serves as a model for seismically defined, single-cycle reservoirs. In contrast, channel fills exposed in northern California, such as the Gravelly Ridge lens (Tithonian) of the Stony Creek Formation, are gravel-dominated and serve as analogs for confined channels defined seismically by multiple cycles.

The Capistrano is made up of laterally amalgamated channels that exhibit a systematic change in sand fraction, facies preservation, and bed architecture from the margin to axis of each channel fill. The channel margin is low net to gross (<50% sand), non-amalgamated, thin-bedded and dominated with low-concentration turbidites. In contrast, the channel axis is high net to gross (>90% sand), thick- bedded, amalgamated, and dominated with high-concentration sandy turbidites and gravel-rich traction deposits. In the Capistrano, the channel-margin facies is 200-300 m wide, whereas the channel-axis facies is 600-700 m wide.

The Gravelly Ridge lens consists of at least 5 stacked channel complexes separated by mudstone intervals. Channel fills are vertically and laterally amalgamated. Channel margins consist of interbedded sandstone and granule conglomerate, whereas the channel axis is dominated with pebble conglomerate displaying traction-related features; imbricate pebbles, cross bedding, and horizontal stratification. These channel complexes are 500 m to 2 km wide, 60-100 m thick and exposed for 30 km in a dip section. Based on outcrop expression and paleocurrent patterns, these deposits are interpreted as filling sinuous channels and are dominated with the channel-axis facies consisting of amalgamated granule and pebble conglomerate.