Geochronologies and environmental records of Quaternary fluvial sequences in the Guadalope Basin, northeast Spain, based on luminescence dating

Geomorphological investigations of Quaternary fluvial deposits in the Guadalope basin, NE Spain, have revealed an extended record of river and drainage basin response to long term environmental change. Investigations have focused on a 13 km long reach centred on the town of Castelseras and a 4 km long reach at Mas de Las Matas. The study reach at Mas de Las Matas is located at the confluence of the Rio Guadalope and its principal tributary the Rio Bergantes. The Castelseras reach is situated 16 km downstream from the Bergantes confluence within a relatively narrow bedrock-confined valley. Luminescence dating provides a geochronology indicating that deposits in both study reaches span the Mid-Pleistocene through to the historic period. The Mid-Pleistocene was characterized by large-scale (locally up to 40 m) aggradation and incision cycles associated with tributary stream and slope input of sediment. More gradual alluviation in oxygen isotope stages 4 and 5 was followed by renewed dissection and aggradation immediately preceding the Last Glacial Maximum. At least four river terraces were formed during this period, with heights above present river level of between 10 and 15 m. River instability continued after the glacial maximum and into the Holocene, when the most recent major alluvial unit was formed 3000 to 5000 yr ago. Progressive entrenchment of the Guadalope valley floor during the Pleistocene would appear to reflect long-term regional uplift with channel aggradation and dissection episodes linked to the climate changes shown by vegetation and oxygen isotope records. Rates of downcutting increased during oxygen isotope stages 2 and 3. This change probably occurred in response to a reduction of coarse sediment delivery to the main channel from tributary catchments, an increase in trunk stream competence and/or catchment uplift.