--> ABSTRACT: Delta Types and Sea Level Cycle, by Szczepan Porebski and Ron Steel; #90906(2001)

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Szczepan Porebski1, Ron Steel2

(1) Polish Academy of Sciences, Krakow, Poland
(2) University of Wyoming, Laramie, WY

ABSTRACT: Delta Types and Sea Level Cycle

The commonly used delta classification (fluvial-, wave- and tide-dominated) was erected on the basis of modern examples and thus is biased towards highstand conditions. Deltas can form at any location across the shelf, but those formed on the middle and inner shelf are significantly different from those at the shelf edge. Mid-shelf deltaic clinoforms tend to be thin, with patchy development and low-angle reflectors, whereas deltas located near the shelf margin and on the upper slope are thick, localized, strike-oriented wedges of steeply-dipping strata commonly associated with slope failure. These contrasts reflect the increased accommodation that occurs when the deltas transit the shelf during sea-level fall, and build into deeper water near the shelf break. The other end-member of the delta spectrum, produced by sea-level rise that causes the deltaic shoreline to become estuarine, is a small, dip-elongated and often tide-dominated bayhead delta that forms at the landward end of flooded valleys. Inner-shelf (platform or shoal-water) deltas tend to be wide and are accompanied by thick, paralic facies, which reflects their formation during times of highstand progradation (reduced rate of growth in accommodation and proximity to sediment sources). The deltaic spectrum emphasizes the fundamental role that changes in regional base-level play in producing different delta types, each of which has distinguishable stratigraphic characteristics. For a given sea-level cycle, these types are likely to follow a predictable evolutionary pattern in which they form either intergradational transitions or occur as distinct entities separated in space and time by major discontinuities.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado