Basin infill architecture and evolution from magnetostratigraphic cross-basin correlations in the southeastern Pyrenean foreland basin

Magnetostratigraphy, numerical dating, and facies mapping have been combined to provide the first cross-basin correlation of the Eocene southeastern Pyrenean foreland basin in northeastern Spain. This has enabled (1) depositional systems on the northern and southern margins of the basin to be dated and correlated across the basin and (2) changes in the rates of sediment accumulation in time and space to be evaluated. By sampling correlative intervals at several locations in a transect across the basin, magnetozones were detected that otherwise may have been misinterpreted due to recent magnetic overprinting, or missed by wide sampling intervals in previous magnetostratigraphic surveys. Results of this study indicate that marginal marine strata of the southeastern part of the foreland near the Vic area of Spain are 5 m.y. older than previously thought, the base of the interval (46 Ma) being middle Lutetian in age. By proposing an age of at least 35.68 Ma for the overlying Cardona evaporite unit, the age span of the marine interval in the studied part of the foreland is [approximately] 10 m.y. Contrary to earlier interpretations, no major southward migration of the southeastern Pyrenean foreland basin depocenter is recorded by the basin stratigraphy during the initial stages of middle Eocene marine sedimentation in the southern margin of the basin. However, marked basin asymmetry is observed later in its evolution as the top of the marine deposits records northward increase in the thickness of chron C17n.1n (37.47-36.61 Ma). This asymmetry is also proved by the presence of a larger number of magnetozones within marine strata at the top of the marine interval in the northern sector. These results imply that previous age calibrations and the estimated rates of tectonic processes and sedimentation within the foreland need to be reassessed. The implications for basin infill architecture evolution through time and space, subsidence analysis, and depocenter evolution through time are addressed.