A sedimentary facies model for stepped, fluvial tufa systems in the Iberian Range (Spain): the Quaternary Piedra and Mesa valleys

摘要: Stratigraphic and sedimentological analyses of the Quaternary tufa associated deposits in Piedra Mesa river valleys allowed a number stages their sedimentary evolution to be characterized, depositional model for this north-central sector Iberian Range (Spain) established. The proposed facies may explain arrangements other medium high gradient, stepped, fluvial systems with narrow transverse profiles occurring temperate, semi-arid areas, both recent past scenarios. There are several within that, over maximum thickness about 90 m, record one or more deposition produced following incision bedrock previous deposits. Each stage begins coarse detrital sedimentation. Six fundamental, vertical sequences small amounts material reveal processes that occurred different environments: channel areas with: (i) free-flowing water; (ii) barrages and/or cascades; (iii) dammed water palustrine floodplains. involves narrow, which cascades were common. Alternating intervals bryophyte stromatolite commonly formed at some cascades. Many these represented barrage-cascade structures consisted phytoclast rudstones, thick phytoherms mosses stromatolites, curtain-shaped stems. Upstream structures, bioclastic sands silts developed vegetation grew. stretches between loci extensive growth fast flowing water. floodplain was home pools drainage channels. also explains River surpassed height divide, diffluence main into secondary course forming area. distribution abundance certain types basins an indicator differences gradients. studied work suggest gradient ancient steeper than Mesa. Assuming similar scenarios climate hydrology, settings mentioned above dimensions would have been determined mainly by width valleys. This useful inferring variations basin slopes, as well accounting presence tufas normally no permanent input.