Lithosphere rheology and sedimentary basins

Abstract

Introduction The dynamics of sedimentary basins is re- flected in the wide range of observational scales inside sedimentary basins. The advent of high-qu- ality data sets have significantly improved the resolution of the record of near-surface tectonic processes. Crustal thinning, mechanical and thermal sub- sidence, sediment filling, are involved in exten- sional basin evolution, and controlled by complex interactions between ductile and brittle modes of deformation of the whole lithosphere. The rate of loading (extension and sediment filling) and the thermal evolution are among the most important controlling parameters. These nonlinear interac- tions do possess a memory of the evolution his- tory and loading. Quantitative understanding of basin subsidence (and the offlap/onlap strati- graphic patterns of a specific basin) obviously benefits from progress in understanding the geo- dynamical context (HorvLth, 1993-this issue). In compressional settings, foreland basins re- sult from the flexural lithospheric response to loading. Most of the models proposed so far have considered the lithosphere as a rheological unit and have been based on classical elastic and viscoelastic plate theory. The wavelength and am- plitude of the flexural response is not an intrinsic property of the lithosphere but result from the history of the competitive interactions between rate of loading and rate of viscous dissipation (thermally activated). A clear physical description of this flexural mode has not yet been proposed, even though some recent results on the mecha- nisms of uplift shoulder formation during rifting evolution may be considered (Bassi, 1991; Chery et al., 1992). The geodynamical context of those basins is complex, and the relationship between the transition of extensional and compressional domains is a topic of vigorous research. Current models for extensional and compressional basins are strongly based on a bulk rheological descrip- tion of the whole lithosphere and on a kinematic description of the deformation mechanisms (Sawyer, 1985; Houseman and England, 1986; Quinlan et al., 1993-this issue). The basin record does reveal to some extend the memory of the deformation history starting from the construction of the internal structure of the basins (i.e. from the processes leading to the formation of rocks: sedimentation, diagenesis, compaction; including possible buildup of fluid overpressures), and the pattern of the large de- formations by faulting or folding. To enhance the understanding of the formation and evolution of sedimentary basins it is important to fully address the physical mechanisms operating at different scale in the continental lithosphere. For example, faulting forms a most important expression (at least at the surface) of large scale deformation in the basins. How those basins are related to the faulting process and the fault interactions is an unsolved question. Pull-apart basins are certainly