The chronology of the Eocene tectonic and stratigraphic development of the eastern Pyrenean foreland basin, northeast Spain

摘要

Abundant and clearly exposed relationships between structures and syntectonic sedimentary rocks in the southern Pyrenees make this area particularly suitable for detailed studies of the sequential development of a collisional orogenic belt. During the Pyrenean orogeny, major shortening occurred in the eastern Pyrenees in Eocene and early Oligocene times. Until now, individual tectonic and depositional events have been only loosely defined temporally by biostratigraphic data. In order to provide a more precise chronological framework, four new magnetostratigraphic sections, spanning 8 km of Eocene strata and encompassing 18 m.y., have been developed in the eastern Pyrenees of northern Spain. The ages of nine major depositional sequences in the eastern Pyrenean foreland have been specified within the context of these chronologic data, beginning with the early Eocene transgression that commenced at 58 Ma. The timing of numerous tectonic events that occurred during the subsequent 16 m.y. can also be delineated, including the initial emplacement of the Pedraforca thrust sheet (58-54 Ma), the development of the Pedraforca breakback thrusts (47.5-40 Ma) at a mean shortening rate of 2.4 mm/yr, rotation of the Pedraforca footwall, three intervals of motion along the Vallfogona thrust (42.5-44.0, 40.5-41.5, and <40 Ma), creation of the Ripoll piggyback basin at 44 Ma, and the emplacement of the Ribes-Camprodon thrust sheet, beginning at 42 Ma. Extensive evaporitic deposition, apparently coincident with sea-level lowering, occurred twice during Eocene times in the eastern Pyrenees: the Beuda sequence at 49 Ma and the Cardona sequence at 40 Ma. In response to continued tectonic encroachment on the northern margin of the foreland, the Eocene depocenter migrated southward 80 km at a mean rate of 5 mm/yr, whereas individual facies migrated at rates as high as 1 cm/yr. In the context of recent models of foreland basins, most of the major grain-size changes appear to be modulated by changes in subsidence rates, except in areas very close to active thrusts.