Tectonic and climatic controls on the development of foreland fan deltas: Montserrat and Sant Llorenc del Munt systems (Middle Eocene, Ebro Basin, NESpain)

Along an early Cenozoic foreland-hinterland boundary in northeastern Spain, we synthesize the depositional environment, climatic conditions, structura l evolution, age, catchment geometry, and altitudinal characteristics from sedimentologic, palynologic, stratigraphic, structural, and paleomagnetic d ata. As the transpressional Catalan Coastal Ranges rose during the Paleogen e, two large fan deltas prograded into the Ebro foreland basin adjacent to the northeastern part of the range. The apices of the fans likely were loca lized by lateral ramps or tear faults along which rivers from hinterland ca tchments debouched into the foreland. Beginning in the late Lutetian, proxi mal debris-flow, sheetflood, and distal fluvial deposits maintained the fan surface at or above sea level, despite rapid basin subsidence during the s ucceeding 4.4 my. Palynological data suggest that a warm, humid climate pre vailed throughout this interval. The mapped extent of the two fans permits an estimation of their volumes, whereas the spatial distribution of distinc tive lithologies within the ancestral Catalan Coastal Ranges serves to deli mit the approximate catchment areas for each of the fans. We estimate mean hinterland denudation rates to range from 100 to 180 m/my and mean catchmen t elevation to range from 700 to 1250 m. The steep gradients between these catchments and the low-lying fan deltas is attributed to the tectonic style of the ancestral Catalan Coastal Ranges, which are characterized by an upl ifted basement block along a steep frontal thrust accompanied by folding of cover rocks. The considerable topographic relief of these catchments is in ferred to have combined with co-seismic shaking to produce landslides and r ockfalls, which were reworked as debris- and fluid-gravity deposits on the fan surfaces. (C) 2000 Elsevier Science B.V. All rights reserved.