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Modelling Syntectonic Sedimentation in a Relay Ramp of an Extensional Fault System

Abstract

The sedimentary infill under an active extensional fault system with a relay ramp is controlled by different factors (e.g., the source area or the fault system geometry). The main purpose of this contribution is to analyse the affection of different geological scenarios in the sedimentary infill considering a shallow water extensional system. The study is carried out using a novel program that merges a discrete element (DE) code for tectonic deformation, and a stratigraphic modelling code (the SIMSAFADIMCLASTIC program) for sedimentation. The former is widely used to study deformation in the upper crust, both small and large scale, due to tectonic movements. The latter models fluid flow, sub-aquatic clastic sediment transport and sedimentation, and carbonate sediment production. The combination of these two models allows us to reproduce syntectonic sedimentation.

To perform the study a system of two normal faults and a relay ramp has been designed. Various parameters of the DE configuration can be modified (the position of the faults, movement rates, the overlap distance of the two faults as well as the distance between them). The scenario has been considered as initially submerged. The sedimentation program allows us to play also with different parameters: different boundary conditions (e.g., positions for the incoming water and sediments), different initial conditions (e.g., different types and incoming rates for sediment materials) and also variations of the sea level position, among others.

Figure 1 shows the results of one possible configuration for this initial design. In this example the fluid flow (fig 1A) has the same direction than the main deformation direction (fig 1D). Consequently, the sediment material is transported mainly in the same direction.

It is worthy to note in figure 1C an asymmetric deposition pattern due to the position of the two faults. We can observe how sedimentation migrates basinwards and it takes place mainly in the region where subsidence is more relevant since more accommodation space is available (fig 1F). In the figure 1G it is observed the deformation of the pretectonic materials due the influence of a relay ramp (fig 1D) created between the two faults. New syntectonic materials also cover this area.

Fig 1- Results of modelling syntectonic sedimentation in a two normal faults system for a specific configuration. A- Initial conditions for the sedimentary model. B- Initial configuration for the deformation model. C- Final stage of the deformation model with the addition of the new materials added by the sedimentary model. D- Final stage of the boundary box of the DE model, in order to show position and movement of the two faults as well as the relay ramp. E- Final stage showing the two cross-sections below specified. D- Cross-section of the final stage cutting perpendicularly the two faults planes at the midpoint of the overlap region. E- Cross-section of the final stage cutting the relay ramp between the two faults planes.