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Part III: Case Studies |
Department of Earth Sciences, The Open University, Walton Hall, Milton Keynes MK7 6AA, UK
Department of Earth Sciences, The University of Leeds, Leeds LS2 9JT, UK
The Western Alpine foreland fold and thrust belt developed in late Miocene times through the Neogene foredeep basin, superimposed on an early Mesozoic and local Palaeogene shelf-basin system. The relative timing between subsidence, tectonic burial and thermal maturation is examined along a section line through the Annecy district of the French Alps. Available stratigraphic data are used to define burial-time paths, using suitable decompaction parameters. The tectonic burial history is determined from regional structural sections. These burial histories are used with a simple thermal model (geothermal gradients: 28°C km–1 before thrusting, 30°C km–1 for the post-orogenic period) to establish hypothetical time-temperature histories. Both the Lopatin method and peak temperature model of source rock maturation suggest that the Jura anticlines are undermature while the Subalpine chains are overmature. However, Subalpine maturation occurred during foredeep subsidence with overmaturation during thrust sheet loading. Large-scale lateral migration of hydrocarbons is required to explain the distribution of bitumen accumulations in the foreland basin offering the possibility of a series of structural and stratigraphic traps in the palaeo-foreland which are not associated with the thrust belt. A complex secondary and remigration history would be needed if liquid hydrocarbons are to have accumulated in traps associated with compressional structures in this part of the thrust belt.
