Sedimentary evolution of an Upper Jurassic epeiric carbonate ramp, Iberian Basin, NE Spain

Abstract

AbstractA synthesis of the sedimentary evolution of the Upper Jurassic carbonate epeiric ramps that developed in the northern part of the Iberian Basin (NE Spain) is presented. The facies distributions reconstructed from the analysis of a 200 km-long transect, show a transition from shallow to relatively deep sedimentation sites. The studied carbonate ramps record major long-term transgression, from mid-Oxfordian to mid-Kimmeridgian followed by progressive basinwards coastal shift until the major regressive event around the mid-Berriasian. Subsidence was relatively homogeneous across the northern Iberian Basin during most of the studied interval. Major episodes of differential subsidence occurred around the Oxfordian–Kimmeridgian transition and onwards from the mid-Tithonian.The sedimentary evolution and particular facies types of the successive Iberian carbonate ramps is described, considering five depositional sequences that have a long-term transgressive-regressive evolution. The Oxfordian sequence shows a sharp transition from shallow to deep ramp areas: from mixed siliciclastic-carbonate (ooidal, skeletal, peloidal) facies to condensed (i.e. spongiolithic, peloidal, glauconitic) facies in the open platform domain. In the two Kimmeridgian sequences (Kim1 and Kim2), the transition between shallow and deep areas is more gradual and thickness distribution across the ramp is more homogeneous. Coral-microbial reefs and oolitic-peloidal-skeletal shoals characterized the shallow areas. Towards the offshore domain, these facies grade rapidly to a tempestite-dominated lithofacies and then into thick lime mudstone successions (i.e. rhythmic marls-mudstone alternations). Shallow oncolitic-peloidal and skeletal facies covered wide areas of the carbonate ramp during the early Tithonian (Ti1 sequence) and graded basinwards to thick successions of well-bedded micrites. The middle Tithonian to lower Berriasian platform (Ti2 sequence) is only partly exposed and formed during a stage of more heterogeneous subsidence. It is characterized by a thick succession with metre-scale shallowing-upward sequences with local development of peritidal, algal-laminated caps. The factors that controlled the sedimentary evolution and major facies changes across the successive epeiric carbonate ramps are discussed by comparison to other Upper Jurassic platforms developed in the western Tethyan realm.