Tectonostratigraphic model for underfilled peripheral foreland basins: An Alpine perspective

Abstract

Advances in the development of quantitative models of foreland basin stratigraphy have outpaced the observational data used to constrain the input parameters in such models. Underfilled peripheral foreland basins comprise a broad threefold subdivision of depositional realms that translates into three stratigraphic units which are commonly superimposed during basin migration; these units are here termed the “underfilled trinity.” The three units of the trinity reflect (1) carbonate deposition on the cratonic margin of the basin (the lower unit), (2) hemipelagic mud sedimentation offshore from the cratonic margin of the basin (the middle unit), and (3) deep water turbiditic siliciclastic sedimentation toward the orogenic margin of the basin (the upper unit). Theoretical predictions of how such a complex basin fill initiates and evolves through time are not currently available; hence this study reviews the stratigraphy of underfilled peripheral foreland basins and provides a unique data set comprising rates of thrust advance and basin fill migration for the Tertiary foreland basin of the European Alps. The Paleocene to Oligocene Alpine foreland basin of France and Switzerland comprises a well-developed underfilled trinity that is preserved within the outer deformed margins of the Alpine orogen. Structural restorations of the basin indicate a decrease in the amount of basin shortening from eastern Switzerland (68%) to eastern France (48%), to southeastern France (35%). Structurally restored chronostratigraphic diagrams allow rates of basin migration to be calculated from around the Alpine arc. Paleogeographic restorations of the Nummulitic Limestone (lower unit) illustrate a radial pattern of coastal onlap on to the European craton. Time-averaged rates for northwestward coastal onlap of the underfilled Alpine basin across Switzerland were between 8.5 and 12.9 mm/yr. Time-equivalent westward to southwestward coastal onlap rates in France were between 4.9 and 8.0 mm/yr. The direction of migration of the cratonic coastline of the basin was parallel to the time-equivalent thrust motions, and oblique to the Africa-Europe plate motion vector. By comparing rates of thrust propagation into the orogenic margin of the basin to rates of coastal onlap of the cratonic margin of the basin, it is possible to suggest that the Alpine foreland basin of central Switzerland migrated with an approximately steady state geometry for at least 210 km northwestward over the European craton. The westward and southward decrease in the basin migration rate around the Alpine arc was associated with an increase in the degree of syndepositional normal faulting on the European plate; this is thought to relate to the opening of the Rhine-BresseRhone graben system.