In addition to tectonic forces, pre-existing structures, fluids and mechanical stratigraphy, the evolution of a thrustbelt is also controlled by syn-orogenic erosion and deposition. Their influence modifies the geometry of both local thrust structures and also the whole thrust wedge. The following sections are devoted to these two aspects.

Role of syn-orogenic erosion and deposition in an evolving thrustbelt

Syn-orogenic erosion and deposition influence both the evolving thrustbelt and basin development at its front, the fill of which is progressively accreted into the thrustbelt and thus controls its structural style.

Direct influence of syn-orogenic erosion and deposition in an evolving thrustbelt

Syn-orogenic deposition can influence the developing thrustbelt by modifying the wedge due to the addition of sediments both between and in front of growing structures, whilst syn-orogenic erosion can modify the wedge by changing the shapes of growing structures.

The addition of new material during syn-tectonic deposition can take place at various stages of thrust development and at various rates (Table 9.1). This material becomes involved in subsequent thrustbelt deformation (Fig. 9.1). Local control of the deposition rate is especially likely in piggyback basins, i.e. those basins that form above, and are transported by, actively deforming thrust sheets. Natural examples in marine settings are present in the Po basin in front of the Apennines (Ori and Friend, 1984; Fig. 9.2), the synorogenic Čelovce Formation in the West Carpathians (Nemčok et al., 1996) and the Paleocene–Middle Eocene Formations of the Balkan Unit in the Balkans. Examples in continental settings have been documented in the Pyrenees (Ori and Friend, 1984; Fig. 9.3; Bentham et al., 1992).