부산대학교 도서관

1 Introduction During the Late Jurassic-Early Cretaceous (Kimmeridgianmiddle Albian), the central and eastern Iberian plate was submitted to a rifting phase associated to the double influence of the spreading of [...]
A review of the onset of the synrift sedimentation and synsedimentary extensional tectonics of the Oliete sub-basin (northwestern Maestrazgo basin, East Spain) is presented here based on new data acquired after extensive sedimentological, structural and palaeontological analysis of the Barremian Blesa Fm. The lower boundary of the Blesa Fm is a prominent basal synrift unconformity overlying Jurassic units. This formation has been divided into three genetic stratigraphic sequences bounded by sub-basin-wide unconformities. The lower Blesa sequence (LBS) is characterized by distal alluvial to palustrine marls/clays grading upward to palustrine-lacustrine limestones. The LBS is bounded on top by a planar to irregular transgressive, hardened ferruginous surface, locally encrusted by oysters. Above this discontinuity, the middle Blesa sequence consists of oyster-rich limestones and marls deposited in a shallow restricted bay, which grade to distal alluvial and palustrine-lacustrine marls/clays and limestones towards the marginal areas of the basin. The boundary between the middle and upper Blesa sequence (UBS) is a regressive surface outlined by the local presence of an erosive conglomeratic bed. The UBS generally starts with red clays deposited in distal alluvial fan environments, which grade upwards to palustrine and lacustrine carbonates and marls/clays. The local presence of heterolithic alternations of clay with fine-to-medium sandstone and of cross-bedded sandstones indicates the local occurrence of siliciclastic coastal environments in the UBS. The upper boundary of the Blesa Fm is marked by widespread transgression, giving rise to the bioclastic limestones of the Alacon Fm. In the present paper, the stratigraphic position and palaeoenvironmental context of the abundant vertebrate remains found across the defined sequences within the Blesa Formation is reviewed. The results obtained are relevant for a further understanding of the tectosedimentary evolution of the studied basin. Successive stages of evolution are distinguished, including the initial uplift, breakup and erosion of the earlier Jurassic carbonate platform that took place during the Tithonian-Hauterivian; the onset of synrift sedimentation during the early Barremian, which was highly controlled by extensional faulting and differential block subsidence; the homogenization of the basin subsidence accompanied by the incursion of marine waters (sourced from southeastern areas) during the middle part of the Barremian; and the significant fall in base level, of possible climatic origin and also involving significant siliciclastic input in the northern areas of the Oliete sub-basin around the middle part of the late Barremian. Keywords Barremian * Iberia * Extensional tectonics * Transitional facies * Vertebrate fossils Este trabajo es una revision de la sedimentacion sin-rift barremiense y la tectonica extensional en la subcuenca de Oliete (noroeste del Maestrazgo, este de Espana), a partir de datos previos y nuevos datos adquiridos despues de un extenso analisis sedimentologico, estructural y paleontologico de la Fm. Blesa. El limite inferior de la Fm. Blesa es una discordancia basal sin-rift que recubre las unidades jurasicas. La unidad se ha dividido en tres secuencias geneticas delimitadas por discontinuidades en toda la subcuenca. La secuencia Blesa inferior (LBS) se caracteriza por margas/arcillas aluviales a palustres y calizas palustres-lacustres hacia techo. Su limite superior es una superficie transgresiva neta representada por una superficie ferruginosa irregular, localmente encostrada por ostras. La secuencia Blesa media (MBS) consiste en calizas y margas ricas en ostras depositadas en una bahia restringida poco profunda, que pasan lateralmente hacia areas marginales de la cuenca a calizas palustres-lacustres y margas/arcillas aluviales distales. El limite con la secuencia Blesa superior (UBS) es una superficie regresiva erosiva asociada localmente a niveles conglomeraticos. La UBS comienza generalmente con arcillas rojas de abanicos aluviales distales, que hacia techo pasan calizas y margas/arcillas palustres-lacustres. La presencia local de alternancias heteroliticas de arcillas y areniscas de grano fino y medio, y de areniscas con estratificacion cruzada, indica ambientes costeros siliciclasticos. El limite superior de la Fm. Blesa esta marcado por una transgresion generalizada (calizas bioclasticas de la Fm. Alacon). En el presente trabajo, se revisa tambien la posicion estratigrafica y el contexto paleoambiental de los abundantes restos de vertebrados encontrados teniendo como base el nuevo esquema de secuencias definido dentro de la Fm. Blesa. Los resultados obtenidos son relevantes para una mayor comprension de la evolucion tectosedimentaria de la subcuenca de Oliete. Se distinguen sucesivas etapas de evolucion, incluyendo: 1) levantamiento inicial, ruptura y erosion del de las calizas de plataforma del Jurasico, que tuvo lugar durante el Titoniense-Hauteriviense; 2) inicio de la sedimentacion durante el Barremiense inferior, controlada por fallas extensionales y hundimiento de bloques diferencial; 3) fase de hundimiento homogeneo acompanada por la incursion de aguas marinas (provenientes del sureste) durante la parte media del Barremiense; y 4) caida significativa en el nivel de base, de posible origen climatico y tambien involucrando una importante entrada de siliciclasticos en las areas del norte de la subcuenca, alrededor de la parte media del Barremiense superior. Palabras clave Barremiense * Iberia * Tectonica extensional * Facies transicionales * Fosiles de vertebrados