Depositional environments and sediment partitioning during early stage foreland basin thrusting

Abstract

The Late Ilerdian-Early Cuisian Roda Sequence spans approximately 3 Ma and formed in the South Pyrenean Foreland Basin (Spain). It is mapped in detail across the present-day Tremp-Graus, Ager and Ainsa sub-basins, and across the Boltaña Anticline into the Jaca sub-basin. The South Pyrenean Foreland Basin basin formed during the early stage of oblique collision of the Iberian Plate with the Eurasian Plate, and was bounded to the north by the Pyrenean chain and to the south by the Sierras Marginales. Within the basin, a time-sequenced series of curved thrusts developed (controlled by the location of inverted Mesozoic extensional faults) of which the Montsec thrust was decisive for the development of the Roda Sequence. This thrust sheet was displaced in a mostly southward direction and has an E-W orientation; it carried the Ilerdian-Cuisian sediments of the present-day Tremp-Graus and Ainsa sub-basins. It is well-expressed at the surface as well as partly buried by younger sediments. The Montsec thrust sheet is bounded east and west by the corresponding lateral ramps oriented SW-NW (Segre line), and SE-NW (La Fueba thrust system). Beyond the SE-NW oriented lateral ramp, the present-day Ainsa and Jaca sub-basins are located. The thrust had a significant influence on sediment dispersal patterns and the nature and location of depositional environments during the development of the Roda Sequence.