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

• Autores: Carlos Morla Juaristi, Alberto González Díez, I. García Amorena, Juan Remondo Tejerina, Fernando Gómez Manzaneque, Ángela Alonso Millán, Guillermina Garzón Heydt, Sonia Roig Gómez
• Localización: Boletín de la Real Sociedad Española de Historia Natural. Sección geológica, ISSN 0583-7510, Tomo 94, Nº 3-4, 1998, págs. 23-40
• Idioma: español
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• Resumen
  • español

    Se describe por primera vez el yacimiento de macrorrestos vegetales de Caranceja, localizado en un paleovalle colmatado de depósitos fluviales. Éstos corresponden a la evolución de una secuencia positiva compleja, que pasa de una etapa torrencial a un sistema braided de gravas, culminado en uno meandriforme arenoso en cuyos materiales aparecen la mayor parte los macrorrestos vegetales. No existe relación entre estos depósitos y el sistema de terrazas del valle del río Saja, ni por sus facies ni por su altura sobre el río. Sí sería posible, sin embargo, asociar el yacimiento con un trazado mucho más antiguo del río Saja dado el carácter divagante que en un pasado ha tenido éste en la zona. El yacimiento presenta enorme interés por la cantidad y variedad de materiales subfósiles (especialmente por los numerosos troncos de hasta 70 cm de diámetro) y su estado de conservación. Se han encontrado estróbilos de tres especies diferentes del género Pinus, de las cuales dos, Strobus (Subsect. Strobi) y Pinus (Subsect. Oocarpae), no tienen correspondencia con táxones existentes en la actualidad en la cuenca mediterránea occidental. Se presentan también piñas de Picea (Sect. Eupicea) así como de una Cupressaceae (Cupressus). Entre todas las maderas recogidas se ha identificado por el momento una gimnosperma, no pinácea, compatible con caracteres anatómicos de Cupressaceae o Taxodiaceae, además de restos foliares de una Angiospermae (planifolia de borde crenado), una gimnosperma (Cupressaceae) de tipo thujoideo, así como numerosas cúpulas de Fagus. Exceptuando una de las especies de Pinus descrita y las cúpulas de Fagus, que serían asociables a un depósito posterior, los demás restos de estróbilos descritos no existen en la actualidad en la Península ni en el Mediterráneo Occidental. Tanto este hecho como la altura morfológica del depósito sobre las terrazas datadas más antiguas, permiten inferir para el yacimiento una edad al menos del Pleistoceno medio/inferior o incluso del Plioceno.

  • English

    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.