Tectonic and climatic controls on the development of foreland fan deltas: Montserrat and Sant Llorenç del Munt systems (Middle Eocene, Ebro Basin, NE Spain)
Along an early Cenozoic foreland-hinterland boundary in northeastern Spain, we synthesize the depositional environment, climatic conditions, structural evolution, age, catchment geometry, and altitudinal characteristics from sedimentologic, palynologic, stratigraphic, structural, and paleomagnetic data. As the transpressional Catalan Coastal Ranges rose during the Paleogene, 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 localized by lateral ramps or tear faults along which rivers from hinterland catchments debouched into the foreland. Beginning in the late Lutetian, proximal debris-flow, sheetflood, and distal fluvial deposits maintained the fan surface at or above sea level, despite rapid basin subsidence during the succeeding 4.4 my. Palynological data suggest that a warm, humid climate prevailed throughout this interval. The mapped extent of the two fans permits an estimation of their volumes, whereas the spatial distribution of distinctive lithologies within the ancestral Catalan Coastal Ranges serves to delimit 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 catchment 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 uplifted basement block along a steep frontal thrust accompanied by folding of cover rocks. The considerable topographic relief of these catchments is inferred to have combined with co-seismic shaking to produce landslides and rockfalls, which were reworked as debris- and fluid-gravity deposits on the fan surfaces.