Rob L. Gawthorpe¹, Stuart Hardy¹, Bryan D. Ritchie¹, Dave Hunt¹
(1) The University of Manchester, Manchester, United Kingdom

Abstract: Three-dimensional variability of depositional sequences: insights and developments from numerical models

Seismic and sequence stratigraphic models have significantly enhanced the understanding of the controls on erosion, transportation and deposition in sedimentary basins. Existing conceptual models are principally two-dimensional and attempt to interpret stratal relationships and facies distribution as a function of regional variations in the rate of relative sea-level change. However, many sedimentological and tectonic processes are inherently three-dimensional, yet few studies have attempted to examine the 3D variability of sequences and address the fundamental controls on sequence development in a quantitative way.

We use a 3D numerical model of erosion, sediment transport and deltaic deposition to analyse the 3D variability of depositional sequences and their response to sea-level change, tectonic subsidence/uplift, and varaitions in sediment supply. The model produces realistic stratal geometries and stacking patterns in three dimensions, including aggradation, progradation, offlap and retrogradation, together with truncation and incised valley formation. Even within a single delta system marked variability in the expression of systems tracts and key stratal surfaces are apparent. The results indicate: i) key stratal surfaces may be of limited lateral extent, ii) different stacking patterns may occur contemporaneously, and iii) complex relationships between incision and deposition during sea-level fall. Furthermore, model results suggest that 2D interpretation of an inherently 3D geometry may lead to erroneous interpretation and incorrect prediction.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana