FIGURE 10. Forward seismic model for proximal fan channels from the Skoorsteenberg Formation, Tanqua Karoo Basin, South Africa (Figure 3), built using GXII seismic modeling software. (A) Outcrop photo of the compensationally stacked, erosionally based, narrow (low aspect ratio) channels and interchannel sheets that dominate the most proximal exposures of the Skoorsteenberg Formation at Ongeluks River. (B) Depth model constructed for this outcrop by applying subsurface rock properties (density and velocity) from deep-water reservoirs in the Gulf of Mexico to the digitized interpretation of this outcrop and assuming that the reservoirs are encased by mudstones. (C) The seismic response for a 30-Hz wavelet images these intercutting channels as a single-cycle event. Amplitude, isochron, and dip variations on the base reservoir can yield clues to the net sand and channel locations, as the brightest amplitudes and thickest isochron correspond to the most channelized and highest net-to-gross portion of the outcrop. The distribution of interreservoir mudstones, however, is not resolved by the forward seismic model (modified from Sullivan et al., 2000b).