A feature commonly associated with growth faults and of extreme importance to [[petroleum]] trapping is the association of rollovers or reverse drag with the downthrown side of a growth fault ([[:file:M31F25.jpg|Figure 10A, B]]). These features are common on the contemporaneous faults presently active in the delta. Rollover structures tend to form soon after deposition of sediment on the downthrown side and do not require a considerable amount of overburden and weighting to form. Mass-moved material flowing downslope from higher levels on the delta front (sands, silts, and clays) contains high water and gas contents. It is speculated that, as sediment accumulates slightly more thickly on the downthrown side of the fault, early degassing and dewatering associated with movement along the fault take place. Pore waters and pore gases are permitted to escape upward in the zone of movement associated with the fault, thereby decreasing the volume of sediment and allowing an early change in density to occur nearly contemporaneously with the fault. As greater and greater amounts of sediment are added and overburden pressures become increasingly larger, this feature is then amplified and becomes more pronounced with time and depth. | A feature commonly associated with growth faults and of extreme importance to [[petroleum]] trapping is the association of rollovers or reverse drag with the downthrown side of a growth fault ([[:file:M31F25.jpg|Figure 10A, B]]). These features are common on the contemporaneous faults presently active in the delta. Rollover structures tend to form soon after deposition of sediment on the downthrown side and do not require a considerable amount of overburden and weighting to form. Mass-moved material flowing downslope from higher levels on the delta front (sands, silts, and clays) contains high water and gas contents. It is speculated that, as sediment accumulates slightly more thickly on the downthrown side of the fault, early degassing and dewatering associated with movement along the fault take place. Pore waters and pore gases are permitted to escape upward in the zone of movement associated with the fault, thereby decreasing the volume of sediment and allowing an early change in density to occur nearly contemporaneously with the fault. As greater and greater amounts of sediment are added and overburden pressures become increasingly larger, this feature is then amplified and becomes more pronounced with time and depth. |