Tipo e intensidad de los procesos pedogenéticos en los sedimentos aluviales y lacustres de la primera secuencia de depósito del Semigraben de Rupelo

Abstract

In the Rupelo Halfgraben (NW Cameros Basin), several pedogenetic processes and elements have been described in three alluvial (Ntra. Sra de Brezales Fm.) and lacustrine sequences (Boleras Fm). In the channel abandonment sequences, the dominant process is bioturbation, whose intensity depended on the periods of sedimentary interruption. Within the alluvial flood-plain sequences, there are well developed paleosoils in which a sequence upwards consisting of nodules, coalescent nodules and a carbonate nodular or laminar horizon can be distinguished. In them, modification related to vegetal and microorganism activity (pedotubules and rhizocretions) and to the water table fluctuations (mottling) are superimposed. In the lacustrine-palustrine sequences desiccation and nodulization are the dominant process. There are pedotubules widened by dissolution and filled by vadose and phreatic cements (pseudomicrokarst). In conclusion, the processes and elements related to the water table fluctuations are dominant in the areas near to the lake, whereas in more distant areas of the alluvial fan, these processes loose intensity in favour of those related to plant and microorganism activity.