Distribución y ordenación de Microcodium en la Formación Tremp: anticlinal de Campllong (Pirineos Orientales, provincia de Barcelona)

Abstract

The excepcional abundance of Microcodium in the continental sediments of the Tremp Formation along the Campllong anticline (Llinás de Berga, Provincia de Barcelona) is a characteristic feature of these deposits, the same as in others localities of the Pyrenees. The Tremp Formation materials of this area show different lithological facies (silts, limestones, sandstones and conglomerates) rich in Microcodium which can be associated in three sedimentological sequences: a) lacustrine somerization, b) palaeosol and c) fluviatile channel. The petrological study of these sediments shows a great number of prismatic calcite structures of Microcodium both in situ or reworked. Likewise, Microcodium occur with great variety: disperse, massive, filling root structures or at the top of some levels like a mat. The percentage of Microcodium in each sequence and within each interval can vary considerably (5-100%), generally increasing towards the top. The exceptional abundance of Microcodium suggest major subaerial exposure in the most distal part of a flood-plain, where calcitic rhizocretions formed beneath a cover vegetation.