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Fluvial Deposition in a Sequence Stratigraphic Framework: Abstract
Fluvial deposition occurs in response to changes in relative sea level and can therefore be predicted within a sequence-stratigraphic context. In this presentation only fluvial deposition within the Type 1 sequence will be considered. Widespread fluvial deposition is believed to occur during the late highstand when the seaward shift of the shoreline or bayline results in a seaward shift of the point to which stream profiles are adjusted (i.e., the mouth of the stream). The initial response of the stream will be to straighten and deepen its channel to adapt to a lengthening of its stream profile. Ultimately the original stream pattern should re-establish itself, however, and result in a seaward shift of the steam profile. This seaward shift of the stream profile creates subaerial accommodation between the initial position of the equilibrium profile and the new shifted position of the profile.
During early lowstand systems tract time, which is characterized by relative sea-level fall, stream rejuvenation and downcutting occur. At this time fluvial deposition does not occur. Subsequently, when sea level stabilizes and starts to rise, fluvial deposition once more occurs. At this time, however, fluvial deposition is restricted to within incised valleys. Once again fluvial deposition is believed to occur in response to a seaward shift of stream equilibrium profiles. Fluvial deposition ceases with the onset of the transgressive systems tract. At this time incised valleys are flooded and the mouths of the streams are shifted landward. It is suggested that the streams respond by maintaining a steady state condition of no net erosion or deposition.
Modern analogues are presented to illustrate the proposed fluvial response to changes of base level. These include examples of the effects on streams of changing water level within man-made reservoirs as well as examples of the hypothetical response of streams to changing base level.
Acknowledgments and Associated Footnotes
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