Tectonic controls on drainage evolution and development of terminal alluvial fans, southern Pyrenees, Spain

An understanding of how drainage patterns respond to tectonics can provide an insight into past deformational events within mountain belts and where sediment flux is supplied to depositional basins. The transverse rivers draining the Spanish Pyrenees show sudden diversions to axial courses and the capture of lateral systems producing large trunk rivers that break through the thrust front at structurally controlled points. The drainage reorganization from the initial regularly spaced pattern in the Late Eocene caused by the growth of thrust‐controlled topography influenced the location of outlets into the Ebro basin. The headward capture and merger of rivers as a result of structural diversion formed two large terminal fan systems during the Oligo‐Miocene along the Pyrenean thrust front. The early structural topographic controls on drainage evolution will have long‐term effects on sedimentation and stratigraphic architecture of foreland basins. This will only be maintained as long as there is tectonic uplift and the river systems strive to re‐attain a regular drainage spacing across the orogenic belt as partly achieved in the Pyrenees.