%0 Journal Article
%A Meléndez Hevia, Alfonso
%A Alonso-Zarza, Ana María
%A Sancho Marcén, Carlos
%T Multi-storey calcrete profiles developed during the initial stages of the configurationof the Ebro Basins exorrheic fluvial network
%D 2011
%@ 0169-555X
%U https://hdl.handle.net/20.500.14352/42523
%X Multi-storey calcrete profiles developed in the Quaternary on strath terraces of the Cinca and Alcanadre rivers,tributaries of the Ebro River inNE Spain. Two calcrete profiles (Tor 1 and Tor 2) near the village of El Tormillo showhorizons with an arrangement that differs from that of commonly described calcrete profiles. Significant lateralchanges occur in these profiles within a distance of less than 200 m, reflecting their pedofacies relationship. TheTor 1 profile on terraceQt1 (the highest and oldest) consists of six horizons (frombottomto top): 1) coarse fluvialgravels; 2) mudstones with carbonate nodules; 3) a chalky horizon; 4) laminar horizons, including one peloidalhorizon; 5) amulti-storey horizon formed of at least six minor sequences, each ofwhich includes a lower detritallayer, a pisolithic horizon, and a thin discontinuous laminar horizon (these sequences indicate several cycles ofbrecciation and/or reworking); and 6) a topmost laminar and brecciated horizon also including reworkedpisoliths. Some200 mto the north of Tor 1, horizon 5 undergoes a lateral change to channel fill-deposits. The infillof the channels shows a fining-upwards sequence ranging fromclasts of about 10 cmin diameter to red siltswithsparse pebbles. All the clasts come fromthe underlying calcrete horizons. Laminar horizons are interbeddedwiththe clastic channel deposits. The youngest calcrete profiles developed on terraceQt3 of the Cinca River and on theQp4 and Qp6mantled pediment levels. All showrelatively simple profiles composedmostly of lower horizons ofcoated gravels, with thin laminar horizons at the top. Most of the horizons, especially the laminar ones, showbiogenic features such as alveolar septal structures, calcified filaments, biofilms, spherulites, micropores andneedle-like calcite crystals. These features indicate the important role of vegetation in the formation of all theabove profiles. The interbedding of clastic sediments and pisolithic horizons within the Tor 2 profile indicatesseveral stages of stabilisation during profile formation. These sequences are an indication of the sedimentation,soil formation and reworking processes operating on the soil surface. The alternation of these processes isinterpreted as the result of climate–vegetation changes. The channel-fills of Tor 2 indicate erosion and reworkingof the hard laminar calcrete horizon. Both Tor 1 and Tor 2 are multi-storey profiles reflecting the complexsedimentation–erosion–pedogenesis relationships at the final stages of the development of its correspondingfluvial terrace. The study of these calcretes shows that these supposedly abandoned terraces continue to be activeeven though the fluvial network is entrenched. Both the pedofacies relationships and the complexity shown byTor 1 and Tor 2 reflect the complex and unstable geomorphic setting inwhich these profiles developed. After theestablishment of the exorrheic network, less complex calcrete profiles were produced in the lower terraces.
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