Geomorphic and stratigraphic evidence of Quaternary diapiric activity enhanced by fluvial incision. Navarrés salt wall and graben system, SE Spain

Abstract

The structural and stratigraphic geological features associated with salt structures have received extensive attention from geologists. However, there is limited work on the geomorphic and Quaternary record of diapiric activity despite its practical implications (e.g., salt and hydrocarbon extraction, geostorage activities). This work analyses the Quaternary geomorphic and stratigraphic evidence of diapiric activity in the Navarrés salt wall (SE Spain), developed along the axis of a Neogene graben. This salt system is located in a region characterized by a peculiar network of orthogonal grabens that control the configuration and evolution of the drainage network. The protruding salt walls are spatially associated with the erosionally unloaded and deeply entrenched graben sections situated close to the regional base level. Evidence of recent/current activity in the Navarrés salt wall include: (1) internally drained areas in a marginal withdrawal basin with long-sustained aggradation; (2) distorted drainage network (defeated and deflected streams, wind gaps, knickpoints, changes in fluvial style), which changed from an initial axial longitudinal pattern to a longitudinal marginal distribution at the flanks of the salt wall; (3) development of diapiric fault scarps at the edge of the salt wall; (4) tilted fluvial terraces dipping away from the salt wall and with localized sediment thickening. The available data indicate along-strike variability in deformation style and long-term vertical deformation rates. These range from ≤0.09 mm/yr, to significantly higher values (>0.2–0.4 mm/yr) in the section where the salt wall displays a more prominent relief and is affected by deep fluvial entrenchment. The regional analysis and the characterization of the Navarrés salt wall suggest that Quaternary diapirism in the region is enhanced by erosional unloading related to fluvial entrenchment, which expands from the regional base level through the upstream propagation of an incision wave.