Boletín de la RSEHN. Sección Geológica

Se realiza un estudio taxonómico preliminar de la flora del afloramiento del Cretácico Superior de Guadalix de la Sierra (Madrid), a partir del cual se han identificado doce taxones diferentes: un helecho Cladophlebis sp., una cicadácea Ctenozamites insignis, cinco coníferas Frenelopsis sp., Pagiophyllum sp., Araucarites aquiensis, Cupressaceae gen. et sp. indet. y Pinaceae gen. et sp. indet. y cinco angiospermas primitivas Magnoliaephyllum sp., Sapindopsis sp., Fabidae gen. et. sp. indet., Eudicot gen. et sp. indet., y Magnoliophyta gen. et sp. indet. Los fósiles se encuentran preservados en forma de compresiones y se atribuyen al Turoniense. Las características de los ejemplares identificados señalan la existencia de dos comunidades vegetales distintas que se desarrollaron en un ambiente deltaico.

The paleobotanical outcrop of Guadalix de la Sierra is located in the “Dolomías Tableadas del Caballar” Formation (Fig. 1). The plant fossils are found in not laminated marls (Fig. 2). The age of the locality corresponds to the upper Turonian and its rocks belong to the II Mesosequence of the Cretaceous of the “Sistema Central” (Gil et al., 2010). On top of the studied materials there are marine sediments of Santonian age, dated by the presence of ammonoids.

A total of 56 specimens have been studied. Most of them belong to the collections of the Museo Geominero (IGME). In addition, some of the studied specimens are housed in the collection of Palaeobotany of the Museo Nacional de Ciencias Naturales (CSIC), and others were collected by the authors in a field trip. The fossil plants are mainly preserved as compressions. Few specimens show preserved cuticle which could be extracted with Schultz´s solution (Kerp, 1990) for its microscopical study.

As a result, 12 taxa have been identified: 1 fern, 1 cycad, 5 conifers and 5 primitive angiosperms. The most abundant species in the outcrop was the cycad Ctenozamites insignis (Lám. I, figs. 1-2 and 4), which had imparipinnately compound leaves and ovate pinnules with dichotomous venation. The study of the cuticles preserved in the branches of the genus Frenelopsis (Lám. II, figs. 1-2, 5-7) confirms that two species coexisted during the upper Turonian in the center of the Iberian Peninsula. Frequently, the angiosperm remains have imparipinnately compound leaves. An example of these angiosperms is the genus Sapindopsis, which had ovate leaflets with a serrate margin (Lám. I, figs. 8-9).

The total of the identified taxa integrated the vegetation that lived near a deltaic zone (Fernández Marrón & Álvarez Ramis, 1999). From a taphonomical point of view, the studied assemblage may be considered mixed, since it exhibits elements from different environments which were mainly transported by waters to the delta. Likewise, the assemblage can be defined as ademic and allochthonous. Two different communities have been inferred from this palaeobotanical study: a xerofitic shrubby formation dominated by Ctenozamites insignis and conifers, and a community related to swampy environments with ferns and angiosperms. Paleofloristically the identified taxa can be related to the Eurosinic region described by Vakhrameev (1991).