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Line 27: − [[file:exploring-for-stratigraphic-traps_fig21-17.png|thumb|{{figure number|1}}See text for explanation.]] + + +
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A transgressive surface forms during a transgression. It is the physical boundary between the lowstand and transgressive systems tracts and is defined by the change from forestepping to backstepping. It merges with the basal unconformity landward of the point where the lowstand systems tract pinches out.<ref name=ch21r48 />
A transgressive surface forms during a transgression. It is the physical boundary between the lowstand and transgressive systems tracts and is defined by the change from forestepping to backstepping. It merges with the basal unconformity landward of the point where the lowstand systems tract pinches out.<ref name=ch21r48 />
==Downlap surface==
==Downlap surface==
[[file:exploring-for-stratigraphic-traps_fig21-17.png|300px|thumb|{{figure number|1}}Planktonic and foraminiferal data taken on a 30-ft (9.1-m) interval show abundance peaks crossing a sharp log break from a thin carbonate to marine shale.]]
A downlap surface (DLS) is a marine flooding surface onto which the toes of prograding clinoforms of the overlying highstand systems tract downlap. The surface represents a change from a retrogradational depositional pattern to an aggradational pattern. It is the surface of maximum flooding, recognized by downlap of overlying units and apparent truncation of underlying units. A downlap surface is common at the base of prograding deltas and the top of submarine fans.
A downlap surface (DLS) is a marine flooding surface onto which the toes of prograding clinoforms of the overlying highstand systems tract downlap. The surface represents a change from a retrogradational depositional pattern to an aggradational pattern. It is the surface of maximum flooding, recognized by downlap of overlying units and apparent truncation of underlying units. A downlap surface is common at the base of prograding deltas and the top of submarine fans.