Los materiales del tránsito Triásico-Jurásico en la región de Villaviciosa (Asturias, España). Caracterización palinológica.

Abstract

A lithostratigraphic and palynologie study of the sediments corresponding to the Triassic-Jurassic transition at the Barzana section, located in the Villaviciosa region (Asturias), has been carried out. Four lithostratigraphic units have been distinguished: A) Black and maroon lutites with evaporites Unit; B) Weil bedded dolomites and limestones Unit; C) Lutites, evaporites and carbonates Unit, and D) Grey lutites and carbonate breccias Unit. Samples containing fossils of pollen and spores have been collected in successive levels. The 0 level, with Corollina meyeriana as dominant element, associated to Ovalipollis cf. pseudoalatus, and in neighbouring sections also with Rhaetipollis germanicus and Cerebropollenites pseudomasulae, can be considered as Triassic (Rhaetian). Level 18, with Cyathidites min or and Todisporites minor, associated to Corollina torosus and in adjacent areas to Ischyosporites variegatus and Cerebropollenites mesozoicus is Lower Jurassic in age. The biochronostratigraphic analysis indicate that the levels of the upper portion of the A Unit are Rhaetian. The Triassic-Jurassic boundary should be located inside the B Unit, below the level equivalent to the lumachellic bed which furnished a specimen of Caloceras pirondi (Reynès) south of Avilés. The sampled level at the base of the C Unit is considered as Hettangian by the persistence of Rhaetipollis germanicus Schulz.