Estudio preliminar del yacimiento de macrorrestos vegetales de Caranceja (Reocín, Cantabria, España)

Abstract

It is described for the first time a deposit containing subfossil woods, which was recently discovered near the village of Caranceja (Cantabria, northern Spain, fig. 1) during the removal labours of the construction of a highway (Autovía del Cantábrico). The sediments consist of a fluvial filling in a palaeovalley, shut off, nowadays, from the present valley of the Saja river (fig. 2). The deposit corresponds to the evolution of a positive fluvial macrosequence of channel filling and abandonment (fig. 3, 5). The system starts with a torrential stage follow by a braided system represented by longitudinal gravel bars that evolve to sandy meander stage in which appears most of the vegetal remains. The deposit finally shows a gradual channel abandonment. Considering the lithological facies of the deposit and its relative height over the river (100 m), it is not possible to establish a direct relationship with the system of terraces that appears below 50 m on the Saja valley. However, is possible to associate the outcrop with a much more ancient tracing of the Saja river given the ramble character that the river had in the past at this area, as the morphological features of the terraces show (fig. 6). The deposit presents great interest since the quantity and variety of subfossil materials, especially numerous strobili remains and trunks up to 70 cm of diameter as well as the excellent state of conservation of the vegetal remains. Subfossil remains are placed in different channel levels of the sequence, principally in sandy facies. Strobili remains corresponding to three different species of the Pinus genus have been found, from which two, Strobus (Subsect. strobi) and Pinaster (Subsect. attenuata) are not related with taxons existing today in the Occidental mediterranean region. Moreover pinecones of Picea (Sect. Picea) and Cupressaceae (Cupressus) are present (fig. 7). Among all the withdrawal woods (fig. 8), has been identified by the moment a gimnospermae, not pinacea, which is compatible with anatomical characters of Cupressaceae or Taxodiaceae. In addition leaf remains of a Angiospermae (planifolia of edge crenado), a gymnosperm (Cupressaceae) of thujoideo type, and numerous domes of Fagus have been found. Excepting one of the species of Pinus and the domes of Fagus , that could be related to a subsequent deposit, the other strobili remains that were described do not exist at present in the Peninsula neither in the Western Mediterranean. This fact, as well as the relative altitude of the deposit over the oldest dated terraces, permit to deduce for the deposit an age at least of the middle/lower Pleistocene or even Pliocene. According to archaeological data, the terrace of 60 m correspond to an age of 90-120,000 B.P. On the other hand, the higher level containing remains is older than the upper limit of 14 C dating technique, therefore older than 48.000 BP. In spite of the fact that other dating techniques were applied (racemization) without any result, by the moment it is not possible to determine the precise date. These are preliminary results obtained by the group, but still some work is in progress, specially dating the deposit and finishing the palaeobotanical and geomorphological analysis in order to reconstruct the Pliocene-Quaternary evolution of the area.