Bryan D. Ritchie¹, Rob L. Gawthorpe¹, Stuart Hardy¹

(1) Manchester University, Manchester, United Kingdom

ABSTRACT: Three-Dimensional Sequence Stratigraphy; Insights from Numerical Modelling; Global versus Local Controls

A three-dimensional numerical model of clastic deposition in sedimentary basins is used to investigate the controlling processes on coarse-grained deltas and to highlight the sequence variability that may occur. The influence of base-level change, sediment supply, subsidence rate, fault slip rate and physiography on delta geometry and internal stratigraphic architecture are investigated.

Analysis of the model results indicate the importance of base-level in controlling the three-dimensional evolution of deltaic depositional systems, but also clearly illustrates the importance of local controls in causing sequence variability. Local controls may have a strong influence on when and how much incision occurs. This is turn has a significant effect on the erosional and depositional features that develop. The modelling results show that local controls such as a low sediment supply, a high rate of hinged subsidence and a shelf-slope physiography are likely to produce more incision. These controls will result in incision occurring earlier in a base-level fall and lead to increased localisation of sediment deposition at the mouths of the incised channels and more pronounced sequence variability. Conversely, less incision is produced by a high rate of sediment supply, a high fault slip rate and a ramp physiography. These controls will offset the start of channel incision and result in the deposition of a continuous fringe of sediment along the delta front. The effects of local controls on incision and deposition during base-level fall have important implications for sequence stratigraphic concepts and models.

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