Changes

==Lowstand systems tract traps==

==Lowstand systems tract traps==

[[file:exploring-for-stratigraphic-traps_fig21-38.jpg|300px|thumb|{{figure number|2}}Play types for shelf-edge and ramp margins.]]

[[file:exploring-for-stratigraphic-traps_fig21-38.jpg|300px|thumb|{{figure number|2}}Play types for shelf-edge and ramp margins. From Van Wagoner et al. 1990;{{citation needed}} courtesy AAPG]]

The diagrammatic cross section ([[:file:exploring-for-stratigraphic-traps_fig21-37.png|Figure 1]]) and the corresponding table describe six potential trap types associated with the lowstand systems tract.

The diagrammatic cross section ([[:file:exploring-for-stratigraphic-traps_fig21-37.png|Figure 1]]) and the corresponding table describe six potential trap types associated with the lowstand systems tract.

{| class = "wikitable"

{| class = "wikitable"

|-

|-

! No.

! No. || Facies || Trap description

! Facies

! Trap description

|-

|-

| 1

| 1 || Incised valley sands || Excellent reservoirs. Traps form where valley incises underlying coastal plain shales.

| Incised valley sands

| Excellent reservoirs. Traps form where valley incises underlying coastal plain shales.

|-

|-

| 2

| 2 || Coastal belt sands || Good reservoirs, commonly very thick. Rollover traps common. Strat traps depend on undip seal. If underlying unit is impermeable, they are present where onlapping sands pinch out below preceding shoreline break.

| Coastal belt sands

| Good reservoirs, commonly very thick. Rollover traps common. Strat traps depend on undip seal. If underlying unit is impermeable, they are present where onlapping sands pinch out below preceding shoreline break.

|-

|-

| 3

| 3 || Channel/overbank channel sands || Excellent reservoirs. Seal provided by toes of overlying low-stand wedge.

| Channel/overbank channel sands

| Excellent reservoirs. Seal provided by toes of overlying low-stand wedge.

|-

|-

| 4

| 4 || Overbank sands || Poor reservoirs. Seal provided by toes of overlying lowstand wedge.

| Overbank sands

| Poor reservoirs. Seal provided by toes of overlying lowstand wedge.

|-

|-

| 5

| 5 || Mounded basin floor fan sands || Sands thin or pinchout over contemporaneous highs. Strat traps depend on top and bottom seal. Overlying slope fan not a good seal. Best traps pinch out in a basinward direction.

| Mounded basin floor fan sands

| Sands thin or pinchout over contemporaneous highs. Strat traps depend on top and bottom seal. Overlying slope fan not a good seal. Best traps pinch out in a basinward direction.

|-

|-

| 6

| 6 || Shingled toe of lowstand prograding wedge sands || Good reservoirs. In sandy systems, basin floor fans are shingled and pinch out between the shale toes of lowstand prograding wedge.

| Shingled toe of lowstand prograding wedge sands

| Good reservoirs. In sandy systems, basin floor fans are shingled and pinch out between the shale toes of lowstand prograding wedge.

|}

|}