Analogue models of delta systems above ductile substrates

Abstract

Delta systems developed above ductile substrates such as overpressured shales and salt have been modelled using layered sand-packs above ductile silicone polymer layers. Gravity spreading of progradational sedimentary wedges produces delta-top and upper delta-slope grabens linked to delta-toe contractional fold-thrust and diapir zones. The delta-top grabens are bound by both regional and counter-regional listric growth faults. A basinward-stepping sequence of regional, counter-regional followed by regional faulting is commonly developed. Polymer pillows and ridges commonly develop in the footwalls of the major listric extensional faults and may evolve into reactive diapirs. Successive progradational loads generate new delta-top or upper delta-slope graben systems on top of older contractional belts where the ductile polymer layer has been thickened significantly. The analogue model results in cross-section show many similarities to examples of natural deltas and differential sedimentary load systems such as offshore Angola, the Niger and Nile Deltas, Kutai Basin, Kalimantan, the Baram delta, Brunei and the Orinoco delta, Columbus basin and offshore Trinidad.

Balancing deformation in NW Borneo: Quantifying plate-scale vs. gravitational tectonics in a delta and deepwater fold-thrust belt system

“…For example, the Niger Delta (west Africa) demonstrates more extension than compression . This is consistent with prograding delta systems, whereby the extensional delta top cannibalises the delta toe fold-thrust belt as the delta progrades; resulting in a much larger region of extension than compression (Morley and Guerin, 1996;McClay et al, 2003;Fig. 2B).…”

The influence of pre-existing structure on the growth of syn-sedimentary normal faults in a deltaic setting, Niger Delta

“…10j). This variability contrasts previous studies that have documented either a general seaward-propagating trend of consecutive deltaic growth structures (e.g., Evamy et al, 1978;Rider, 1978;Bruce, 1983;McClay et al, 2003), or a retrogradation of bounding faults into previously undeformed footwall terrain (e.g., Gibbs, 1984;Vendeville, 1991;Bhattacharya and Davies, 2001;Imber et al, 2003;Back et al, 2006).…”

Coeval extension and shortening above and below salt canopies on an uplifted, continental margin: Application to the northern Gulf of Mexico

“…The first three diagrams are based primarily on published physical model results (e.g., Cobbold et al, 1989;McClay et al, 1998McClay et al, , 2003Fort et al, 2004;Rowan et al, 2004;Vendeville, 2005;Dooley et al, 2007). To begin, suppose that a seaward hinge in the midslope affects both the bathymetry and the base of the salt and that the distal part of the basin is subhorizontal ( Figure 11A).…”