CONCLUSIONS

1. FAST BASE-LEVEL FALL

 

In case of rapid fall: valley incision begins immediately taking advantage of any pre-existing channel scour.

Incised valley lengthens upstream by headward erosion with attendant flow piracy. Downstream the valley lengthens by forced regression.

 

 

Incised valley lengthens upstream by headward erosion with attendant flow piracy. Downstream the valley lengthens by forced regression.

Gravity flows carry sands to deep basin.

During the rapid fall, focussing of flow into incised valley leads to flow deepening with attendant increase in shear stress. As a result the deposition within the incised valley is better sorted and has enhanced porosity.

Growth faults develop along the prograding delta front. They seem to initiate and continue during the rapid fall phase, but may have begun during the previous highstand systems tract.

Total horizontal displacment along rapid fall growth faults is about 25% of the total length of the basin.


2. SLOW BASE LEVEL FALL

Shoreline incision, leading to valley formation, did not begin until ~ half way through the fall. We suspect that this was due to the subsidence profile and the resulting distribution of relative base level.

The incised valley duration was short, ~ 30 min.

The erosion front migrated headward by nick point retreat, followed by a wave of deposition that migrated headward. Possibly deposition is forced by widening of flow path causing flow shallowing, coupled with relative base level rise in the basin center.

Ultimately valley widens across the basin with penecontemporaneous sedimentation, producing a relatively widespread, albeit subtle, disconformity across the basin.

 

Although the rapid fall lasted only 1 hour (10% of slow fall duration), subaerial exposure lasted twice as long as that formed during the slow fall.

 

The incised valley during the rapid fall was about three times as deep, but much narrower than the valley form during slow fall.

Incision took place over 100% of the time of the rapid fall vs. 4% of the slow fall.

 

 

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