Simulation of Foreland Basin Stratigraphy using a diffusion model of mountain belt uplift and erosion: An example from the central Alps, Switzerland

Abstract

Abs•act, Foreland basin stratigraphy can be considered as the result of three interacting processes:thrust deformation, which builds the tectonic load, sedimentary and erosional processes which redistribute that load, and the flexural response of the lithosphere. The resultant stratigraphy of foreland basins is commonly composed of a small number of shallowing and coarsening upward cycles bounded by regional unconformities. To understand the development of these unconformities, we present a simple model of these three processes, coupling an evolving thrust wedge on a linear elastic plate with erosion and sedimentation defined by the diffusion equation applied to topography. Our model demonstrates the development of regional unconformities without recourse to either eustasy or complex viscoelastic models for the continental lithosphere. The model describes the thrust wedge-foreland basin system in terms of four parameters: (1) the effective elastic thickness of the foreland plate (Te), (2) the sediment transport coefficient (K), (3) the thrust wedge advance rate, (4) the surface slope of the thrust wedge. The model is applied to the Oligocene-Miocene North Alpine Foreland Basin (NAFB) of eastern Switzerland. The stratigraphy of the NAFB can be simplified into two large-scale shallowing upward cycles separated by an unconformity at the base of the Burdigalian (22 Ma). Geological information is taken from the NAFB to estimate suitable values for the parameters listed above. Assuming a linear elastic lithospheric rheology, the Te value is estimated at 10 + 5 km from decompacted sediment columns. Data to constrain the sequential development of the thrust wedge come from structural geology. The early stages (40-24 Ma) of compression involved a relatively low-angle thrust wedge with an advance rate of approximately 2-4 mm/yr. At about 24 Ma the wedge advance slowed down and thickened by underplating crystalline basement of the foreland plate. The value for the transport coefficient has been estimated from previous studies. Prior to attempting to simulate the broad-scale geometry of the NAFB the role of each parameter was assessed individually. The values for Te and K are held constant throughout the simulation of the NAFB at 7.5 km and 500 m2/yr, respectively. The geometry of the base Burdigalian unconformity is reproduced by variations in the parameters describing the thrust wedge. The surface slope angle of the wedge is increased from 2.5 ø to 4 ø over 0.2 m.y., and the rate of thrust advance is decreased from 2 mm/yr to 0.2 mm/yr, during the thickening event between 24 and 23.8 Ma. The rejuvenation of the internal parts of the thrust load causes backtilting of the foreland basin sediments and, after a time lag, erosion of the distal stratigraphy over the forebulge, so simulating the base Burdigalian unconformity. Platt, J.P., Dynamics of orogenic wedges and the uplift of high-pressure metamorphic rocks, Geol. Soc. Am. Bull., 97, 1037-1054, 1986. Price, R.A., Large scale gravitational flow of supracrustal rocks, South...

Neogene sediments and modern depositional environments of the Zagros foreland basin system

“…Sinclair et al 1991;DeCelles et al 1998;Mutti et al 2003), this succession can be interpreted in terms of migrating depozones (see also Alavi, 2004 for the Zagros). In the Zagros, the wedge-top depozone is represented mainly by the Agha Jari and Bakhtyari formations, though in the Fars region, part of the Mishan also occupies a wedge-top position.…”

“…In doing so, we aim to place the various deposits observed within the context of foreland basin depozones (see also Alavi, 2004Alavi, , 2007, as already established for many other foreland basin systems (e.g. Sinclair et al 1991;DeCelles et al 1998;Mutti et al 2003). The Zagros system offers an advantage over many other foreland basins in that it is currently active and has been so for a considerable time period.…”

An Eocene paleodoline in the Morcles Nappe of Anzeindaz (Canton of Vaud, Switzerland)

“…In the Early to Middle Eocene, the bypassing of the forebulge and foreland basin of the alpine orogeny through the southern European continental shelf led to the emersion and extensive continental erosion of ancient seafloors, followed by a renewed submersion (Crampton & Allen 1995, Sinclair et al 1991. Thus, the Eocene erosive unconformity is a major stratigraphic feature that can be observed over large regions throughout the Helvetic Alps, the Jura Mountains and the Swiss Molasse Basin (Burkhard & Sommaruga 1998).…”

“…A much more probable possibility is the existence of a number of alpine faults related to the orogenic flexure of the alpine forebulge (Crampton & Allen 1995, Sinclair et al 1991 that could have provided the necessary weak zone for the Eocene erosion to attack. Indeed, Eocene synsedimentary faults (some of which are very large) are widely known throughout the Helvetic Realm (Menkveld-Gfeller 1993) as well as in the study area.…”

Late Eocene transgressive sedimentation in the western Swiss Alps: Records of autochthonous and quasi-autochthonous biofacies on a karstic rocky shore

“…This regional erosive surface, which was the result of emersion and continental erosion due to tectonic uplift linked to flexural forebulge migration of the Alpine foreland basins, was flooded during Late Eocene-Oligocene times (Sinclair et al, 1991;Crampton and Allen, 1995;Sinclair et al, 1998). The Priabonian transgression in the Swiss and French Alps has been regarded to be mainly the result of rapid tectonic subsidence associated with normal faulting related to flexural bending, caused by the advancing Alpine thrust front.…”