Facies architecture of a microbial–siliceous sponge-dominated carbonate platform: the Bajocian of Moscardón (Middle Jurassic, Spain)

Abstract

AbstractExtensive facies analysis of the outcrops located near Moscardón (Iberian basin, NE Spain) resulted in a precise reconstruction of the facies architecture of a Bajocian (Middle Jurassic) carbonate platform. Different types of microbialites occurred in the transitional area between the shallow and relatively deep carbonate platform domains, located above and below wave base level, respectively. The most significant volume of the micorbialites is found in the platform slope, located below wave base level, in a depth range of around 30–50 m. In the lower slope, during stages of rapid accommodation gain, the vertical aggradation of individual stratiform building blocks results in the formation of up to 25 m-thick microbial–siliceous sponge buildups. During stages of sea-level highstand the individual building blocks are dominated by lateral (down-slope) progradational accretion, resulting in flatter, lens-shaped buildups. The transition between the upper slope and the shallow platform area is characterized by microbial-encrusted intraclastic–bioclastic packstones. Microbial crust development helped to stabilize the seafloor, allowing the eventual accumulation and preservation of the sand-sized grains above wave base.