Resumen de Características sedimentológicas de los materiales volcaniclásticos de la zona de La Fortaleza (Tenerife, Islas Canarias, España).
Ferrán Colombo Piñol, Joan Martí Molist, Feliciano Plana, Ignasi Queralt Mitjans
Near the Teide volcano National Park (La Fortaleza area), some Plio-Quaternary pyroclastic materials with different types of sedimentary structures are preserved. The outcrop is made up of coarse pyroclastic materials largely consisting of subrounded and subangular pumice clasts. In this outcrop the materials are preserved like a large deposit restricted to a previous topographical valley, o f 3 0 m w id th , 8 - 7 Om maximum height and WNW-ESE general orientation. This is filled mainly by pumice material with large scale (3 - 4,5 m of height) cross bedding and great lateral continuity (8-1 Om). The cross bedding shows m ed ia l dips o f 0 8 ° - l5 ° w it h m ain paleocurrents towards the E and ENE approximately. Locally there are interfingered deposits that show orthogonal paleocurrents and some oblique ones (240°-350°) with unitary lenticular geometries. Their internal granulometric distribution show a certain coarsening-upwards vertical tendency. The general interpretation suggests the intermittent generation of a large sedimentary structure (like aeolian dune-type), which infills the previous valley. Episodically and perhaps due to the own instability of the deposits, some rapid gravitative falling small events could occur (granular flow). This events with a transversal p a le o flo w tendency could modify the frontal portion of the aeolian dune developed in pyroclastic materials. These deposits could be accumulated by intermittent episodes and could be affected by some rains producing chemical alteration thereby leading to the excavation of very small channels. Humidity-dessication cycles alter the most external partof the deposit units, giving rise to the presence of clay materials infilling all the pores and vesicles producing a hard surface with a compact texture. In the central part of the lobes the materials show small empty hollows that produce their marked friability. Afterwards and before the arrival of the subsequent deposits which could accommodate the previous irregularities, a short episode of small pumices deposit that show the previous discontinuities occur. Finally, the arrival of the main granular deposit which shows a decreasing upwards lithic tendency and which could locally be affected by small channels generated by intermittent rain fall episodes could be produced. All of this transverse accumulation could be controlled by locally large topographical landscapes (sharp margins of the previous valley) in a very short time span, as suggested by a high speed chemical alteration of the pyroclastic materials
