Influence of Sediment Supply in Shelf Margin Accretion and Sand Bypass to Deep-Water
Despite the obvious importance of sediment supply for studies on shelf margin architecture and on the potential of margins to contain and by-pass deep-water sands, the role of supply in such studies has received limited attention. To draw attention to the supply parameter we therefore suggest a methodology for inferring ‘high’ or ‘low’ sediment supply rates on margins, based on measurement of shelf-edge progradation and aggradation rates. In the review cases, there are two broad types of shelf margin, based on structural style, water depth and proneness to sediment failure: (1) Moderately deep-water (<1000 m maximum water depth) margins produce clinoforms 100s of m high and show rates of shelf-edge progradation <61 km/my and aggradation <270 m/my. On these margins, rates of shelf-edge progradation of several 10’s of km/my are typically linked to the recurrent dispersal of large volumes of sand into the basin including the slope and basin floor indicating that supply (and not just fall of sea level) is likely to have been critical in growing the margin. We refer to these margins as ‘supply dominated’ margins. High supply is especially important for driving deltas to shelf-edge to produce deep-water sand accumulations when sea level is rising, i.e., during highstand conditions. (2) Very deep-water (>1000 m maximum water depth) margins, in contrast, create much higher but more complex clinoforms, and tend to show rates of shelf-edge progradation <37 km/my and aggradation <2500 m/my. These margins aggrade faster and prograde more slowly than moderately deep margins because they are fronted by much deeper water, subside at higher rates, and are prone to large-scale, growth-fault development and large-scale mass failure. This mass failure tendency, and the larger scale of these margins, however, make it difficult to correlate their accretion rates with supply and delivery of sand to deep-water areas, although the Gulf of Mexico offers some encouraging results.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009