Changes

Shelf-margin systems tracts are the lowstand deposits of a type 2 sequence. Type 2 sequences are deposited when relative sea level falls but not below the preceding depositional inflection. Type 1 sequences are deposited when relative sea level falls below the preceding depositional systems tract..<ref name=ch04r70>Mitchum, R., M., Jr., Van Wagoner, J., C., 1990, High-frequency sequences and eustatic cycles in the Gulf of Mexico basin: Proceedings, Gulf Coast Section SEPM 11th Annual Research conference, p. 257–267.</ref> The subsequent transgression may provide effective top seal, but the lateral seal of shelf margin systems tracts shares the same limitations as the highstand systems tract.

Shelf-margin systems tracts are the lowstand deposits of a type 2 sequence. Type 2 sequences are deposited when relative sea level falls but not below the preceding depositional inflection. Type 1 sequences are deposited when relative sea level falls below the preceding depositional systems tract..<ref name=ch04r70>Mitchum, R., M., Jr., Van Wagoner, J., C., 1990, High-frequency sequences and eustatic cycles in the Gulf of Mexico basin: Proceedings, Gulf Coast Section SEPM 11th Annual Research conference, p. 257–267.</ref> The subsequent transgression may provide effective top seal, but the lateral seal of shelf margin systems tracts shares the same limitations as the highstand systems tract.

Early sequence stratigraphic studies, based largely on seismic reflection profiles, used the shelf edge as the depositional inflection reference point.<ref name=ch04r100>Vail, P., R., Todd, R., G., 1981, North Sea Jurassic unconformities, chronostratigraphy and seal-level changes from seismic stratigraphy: Proceedings, Petroleum Geology of the Continental Shelf, Northwest Europe, p. 216–235.</ref><ref name=ch04r102>Vail, P., R., Hardenbol, J., Todd, R., G., 1984, Jurassic unconformities, chronostratigraphy and sea-level changes from seismic stratigraphy and biostratigraphy in Schlee, J., S., ed., Interregional Unconformities and Hydrocarbon Accumulation: AAPG Memoir 36, p. 129–144.</ref> Subsequent work on outcrops and high-resolution seismic reflection profiles redefined the deposition inflection as the shoreline break<ref name=ch04r70 /> The shoreline break is generally coincident with the seaward end of the stream mouth bar in a delta or the upper shoreface in a beach environment. This change in depositional inflection scale results in nearly all seismically recognized lowstand deposits being attributed to type 1 sequences. Because the GOM basin analysis relies largely on seismic reflection profiles, all lowstand deposits are referenced to shelf-edge inflection points.

Early sequence stratigraphic studies, based largely on seismic reflection profiles, used the shelf edge as the depositional inflection reference point.<ref name=ch04r100>Vail, P., R., Todd, R., G., 1981, North Sea Jurassic unconformities, chronostratigraphy and seal-level changes from seismic stratigraphy: Proceedings, Petroleum Geology of the Continental Shelf, Northwest Europe, p. 216–235.</ref><ref name=ch04r102>Vail, P., R., Hardenbol, J., Todd, R., G., 1984, [http://archives.datapages.com/data/specpubs/seismic1/data/a166/a166/0001/0100/0129.htm Jurassic unconformities, chronostratigraphy and sea-level changes from seismic stratigraphy and biostratigraphy] in Schlee, J., S., ed., Interregional Unconformities and Hydrocarbon Accumulation: AAPG Memoir 36, p. 129–144.</ref> Subsequent work on outcrops and high-resolution seismic reflection profiles redefined the deposition inflection as the shoreline break<ref name=ch04r70 /> The shoreline break is generally coincident with the seaward end of the stream mouth bar in a delta or the upper shoreface in a beach environment. This change in depositional inflection scale results in nearly all seismically recognized lowstand deposits being attributed to type 1 sequences. Because the GOM basin analysis relies largely on seismic reflection profiles, all lowstand deposits are referenced to shelf-edge inflection points.

==Systems tracts with greatest trapping potential==

==Systems tracts with greatest trapping potential==