Las unidades carbonatadas y evaporíticas del tránsito Triásico-Jurásico en la región de Lécera (Zaragoza, España)

Abstract

One of the main challenges for the stratigraphy of the Mcsozoic sediments of the Iberian Basin is the recognition of the Triassic-Jurassic boundary. Subsurface data provided by the hydrocarbon boreholes drilled from the not outcropping areas of the basin show the presence of a thick interbedded evaporitic section located between the Imón Fm, an Upper Triassic dolomitic unit, and the Cuevas Labradas Fm, a thick Lower Jurassic carbonate unit. These evaporúes are normally dissolved in the surface, where they are represented by the not dissolved carbonates, which constitute the Camiolas of the Cortes de Tajuña Fm. However, the recent finding of unusual cropping out of this evaporitic succession at the Lécera region has provided a good opportunity to study a surface section of the evaporitic materials of the Lécera Formation (Gómez y Coy, 1998) which is composed of gypsum, anhydrite and carbonates. Palynological data confirms a Carnian age for the Keuper facies and an Hettangian age for the Carniolas of the Cortes de Tajuña Fm located in this outcrop on top of the Lécera Fm. Regional data indicate a Rhaetian age for the carbonates of the underlying Imón Fm. AII these data suggest that the Triassic-Jurassic boundary should be located inside the Lécera Fm.