%0 Journal Article
%A Tortosa, A.
%A Arribas Mocoroa, José
%A Garzón Heydt, Guillermina
%A Fernández García, Paloma
%A Palomares Herranz, Marta
%T Análisis petrológico de depósitos de terrazas aplicado al estudio de los procesos de captura en los ríos Adaja,Voltoya y Eresma (provincias de Segovia y Valladolid)
%D 1997
%@ 0214-2708
%U https://hdl.handle.net/20.500.14352/57055
%X La caracterización composicionaI y textural de los depósitos arenosos de terrazas de losríos Adaja, Voltoya y Duero ha permitido resolver la procedencia de otras secuencias de terrazas,relacionadas con estos ríos pero hasta ahora de difícil asignación genética, como son las situadas al SEde Pozáldez y en el área de Olmedo. La secuencia de terrazas del área de Pozáldez se ha dividido endos grupos: el primero, correspondiente a las terrazas más antiguas, está relacionado con elretrabajamiento de las terrazas del Duero por el río Voltoya durante su encajamiento. El segundogrupo, formado por las terrazas más modernas, se relaciona con los depósitos del río Adaja, marcandoel límite de ambos grupos el momento de la captura de este último por el Voltoya. Por otra parte, lasecuencia de terrazas del área de Olmedo refleja una gran similitud con las arenas del sistema delVoltoya, pudiendo ser considerado como parte del mismo. La integración de los datos geomorfológicosy petrológicos ha permitido elaborar un modelo de evolución de la red fluvial basado en capturassucesivas entre los ríos Adaja, Voltoya y Eresma.[ABSTRACT]The analysis of the composition and texlures of the sandy deposits of terraces of Adaja,Voltoya and Duero rivers permits to solve the provenance of other terrace sequences, as those appearingat the SE of Pozáldez and near Olmedo, without a clear parentage with the rivers mentioned aboye.TheAdaja terraces are constituted by arkoses with crystalline rock fragments and a light dominance ofk-feIdspar over plagioclase grains, representing the more immature deposits analysed. The Voltoyaterraces al so consist of arkoses with a greater dominance of k-feldspar over plagioclase and with theoccurrence of metamorphic rock fragments. The Duero terraces are formed of subarkoses with lowcontent in rock fragments, showing a great dispersion of the contents in feldspars and rock fragmentstypologies. Based on these data, the upper terraces appearing near Pozáldez are constituted by thereworking product of Duero terraces by lhe Volloya river during the incision of its channel. The lowerterraces are constituted by recent terraces whose origin is related to the Adaja river. Thus the limitbetween these two groups of terraces represents the capture of the Adaja by the Voltoya river. On theother hand, the terrace sequence near Olmedo shows a great similarity with the deposits of the VoItoyaterraces, so that its origin is related to this terrace system. The integration of geomorphologic andpetrologic data permits lhe reconstruction of the evolution of the fluvial network, based on successivechannel piracy. Firslly, lhe Adaja river was captured by the Voltoya river, and subsequently both theAdaja and Voltoya rivers were captured by the Eresma river. The origin of this set of captures is thegeneral trend to the NE of the groundwater flow, caused by tectonic tilting, and improving the hydraulicefficiency of the basin. Finally, the composition of the terrace deposits was greatly influenced by thepiracy processes that produced a new input of sediments with different provenance. Incision of lhechannels also affected composition by reworking of intrabasinal sediments. Both processes acted bymixing sediments producing a homogenisation of its composition. As a consequence, an importantloose of detailed information about the source area of the different feeders occurs.
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