Geological interpretation - 3-D Seismic Interpretation - page 116

Fig. 4.8 Composite coherency image showing the Rosetta channel complex (orange), with the
image of the Abu Madi channel complex (56 ms above the Rosetta; yellow) superimposed on the
upper right. Light yellow outlines levee/overbank deposits associated with this channel system.
Reproduced with permission from Wescott & Boucher (2000) .
transporting sediment across the shelf into deeper water. They filled with sediment
as transgression continued, and the system was no longer confined by the resistant
evaporite canyon walls. Eventually the channel avulsed at a meander bend, following
a steeper gradient, and formed the Abu Madi channel system, with higher-sinuosity
channels confined within fan/overbank deposits.
An example of interpretation of downlap geometries is shown in fig. 4.9 . This is
from the San Jorge Basin, Argentina (Wood et al. , 2000). This is a fluvial system; the
successive south-to-north downlap onto the M7 unconformity is attributed to lateral
accretion of migrating point bars. The overlying deposits show accretionary processes
from north to south, with downlap onto an unconformity separating this unit from the
deeper point bars. The top of this interval is a widespread flooding surface, marked by
alluvial deposits. Mapping amplitudes, on both standard reflectivity data and coherency
volumes, in slices parallel to this flooding surface, allowed channel systems to be
mapped and their evolution followed over time.