Evolution of a fluvial terrace system in a base level-changing scenery within the Jucar Drainage Basin (Valencia, Spain): The Jarafuel-Cautabán case study

The fluvial network of the Júcar river around Cofrentes village (hinterland of the Valencia through, Eastern Iberian Peninsula) presents an overall trellis pattern controlled by a polygonal system of Neogene grabens and salt-walls, some of them showing clear evidence of Quaternary activity. The main rivers of this network are the Júcar itself flowing from the West, the Cabriel from North-West, and the Jarafuel – Cautabán from the South, all three merging around Cofrentes village and showing diverging quaternary evolutionary history. The Júcar and Cabriel rivers are deeply incised into Mesozoic and Cenozoic bedrock, forming striking canyons and wide terrace systems, while the Jarafuel - Cautabán shows a much less developed terrace system, with its upper reaches and main tributaries flowing along broad and non-dissected floors, with scattered badly-drained zones and desiccated lakes.

The quaternary fluvial dissection in the area has been described to be driven not only by base-level changes in the Mediterranean Sea, but also by other external factors such as diapirism, evaporite-dissolution subsidence, volcanism, and neotectonics that have played a singular role in the dissection process. One of the most outstanding differential features observed among these fluvial valleys is the headward erosion that in the Júcar and Cabriel rivers reach distances as far as 160 and 250 km respectively, but along the Jarafuel – Cautabán valley only propagated 22 km. Headward erosion is marked by prominent knickpoints along this valley and tributaries, depicting a relevant change in the landscape style, with staircase terraces downstream and undissected late Neogene tectonic landscape upstream. This remarkable difference in headward erosion, and hence in terrace system development cannot be only explained by differences in variable erodibility of bedrock, but another driver must be invoked such as different timing in the opening of the fluvial network to a closer and active base level, that in this case is the Mediterranean sea level. The Jarafuel – Cautabán valley can thus be considered an active example of the interplay between different actors such as sea-level (base level) changes, differential headward erosion, diapiric uplift, and neotectonics.  This contribution presents the first geochronological data (OSL dating) in the Jarafuel – Cautabán system, indicating that, although headward erosion started during the last glacial cycle at c. 95-85 kyr (end of OIS 5), the most important drainage reorganization and incision took place around the Last Glacial Maximum at c. 22 kyr ago, in response to the significant coetaneous sea-level fall.

Contribution supported by the Spanish Research Project I+D+i PID2021-123510OB-I00 (QTECIBERIA-USAL) funded by the MICINAEI/10.13039/501100011033/