Foreland-basin stratigraphy and orogen state are determined by the rate of mass accretion to an orogen by thrust tectonics, the efficiency of mass redistribution by surface processes, and lithospheric flexure. Orogen state can be characterized as constructive, steady, or destructive depending on the mass net balance in the orogen (Jamieson and Beaumont, 1988, Tectonics, v. 7, pp. 417-445). We have constructed a kinematic planform foreland-basin model to look for stratigraphic relationships between synthetic foreland basin stratigraphy and orogen state.
The foreland-basin model links thin-skinned tectonic development of an orogen, lithospheric flexure (Beaumont and others, 1988, Tectonics, v. 7, p. 389-416) and mass redistribution by surface processes (Beaumont and others, 1992, Thrust Tectonics, p. 1-18). The tectonic model uses critical wedge principles to construct a two-sided wedge-shaped orogen. Sediments are accreted to the toe of each wedge at a rate proportional to the convergence rate of each leading slip line with the adjacent autochthon. The wedges, which need not be symmetric, grow in proportion to the net rate of mass influx. Their geometry is consistent with flexural adjustment of the lithosphere, conservation of mass, the criticality of each Coulomb wedge and match of wedge heights at their interface. The lithospheric-flexure model includes elastic or thermally activated linear viscoelastic rheologies. The surface process model couples climatic, hillslope (mass diffusion) and fluvial (mass transport) processes to erode, redistribute, and deposit mass across the orogen, its foreland basin and peripheral bulge.
Synthetic stratigraphic assemblages are constructed for a range of tectonic, lithospheric, and surface process model parameters, to determine under what circumstances an assemblage can be considered diagnostic of an orogens's state, or change in state.
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Tectonic and Eustatic Controls on Sedimentary Cycles
The collected volume begins with a brief perspective by one of the conveners, followed by articles in order of increasing stratigraphic age. Eustatic sea-level changes and tectonic warpings of basins are competing mechanisms for explaining many stratigraphic patterns. The model for sea-level changes should be developed first for a basin, since it is allocyclic and leads to a series of time bands in the strata. The residual effects should then be modeled for tectonic patterns affecting the depositional processes. Doing the reverse limits time constraints on the tectonic warping models and will blur the resolution of detailed time surfaces in the strata. Case histories of situations with both tectonic warping and time surfaces marked by sea-level events will lead to improved interpretations of earth history.