--> ABSTRACT: Questioning The Concept Of Relative Sea Level, by R. W. C. Arnott; #91019 (1996)

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Questioning The Concept Of Relative Sea Level

R. W. C. Arnott

The concept of relative sea level is widely used to interpret the stratigraphic record. Specifically, relative sea level describes the vertical movement of the basin's bounding surfaces, which in turn is interpreted to have an major influence on the space made available for sediment to accumulate. Although seemingly simple and straightfonward concept of relative sea level is commonly confused. One reason may be that relative sea level defines a two-dimensional space, or areas implicit in the concept, however, is the variation of accommodation space, which is a measure of volume (three dimensional ]Lacking in the concept of relative sea level is a parameter that describes the third dimension -- the depositional basin. Although this inadequacy has been recently recognized, t has been poorly integrated into the concept of relative sea level. For example, for a given sea level change, the stratigraphic response may be more significantly influenced by basin physiography than the relative sea level change. An source of confusion is the counterintuitive idea of progradation during a relative sea level rise. Progradation, however, indicates basin filling, and hence should always be associated with a loss of accommodation space. One way to eliminate these inconsistencies is to consider instead the RATE of basin volume change. By doing so there always a 1:1 relationship between the stratigraphic response, such as transgression or progradation, and variation in the rate of basin volume change. In addition, normal and forced regressions can be easil differentiated. Also, the rate of change provides insight into the physiographic nature of the basin. Finally, sediment flux, which is excluded from the concept of relative sea level, is included because it influences significantly the rate of basin volume change. The inclusion of sediment flux also makes intuitive sense, for after all it is the sediment of the basin fill that make up the sedimentary record, not the sedimentary basin itself.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California