Sedimentary evolution of a shallow carbonate ramp (Kimmeridgian, NE Spain): Unravelling controlling factors for facies heterogeneities at reservoir scale

Abstract

The facies evolution of a Late Jurassic (latest Kimmeridgian) shallow carbonate ramp was reconstructed after the analysis and correlation of 21 logs in a 20 × 30 km outcrop area located south of Zaragoza (northeast Spain). The studied succession belongs to the Higueruelas Formation, which is of potential use as an analogue for understanding facies heterogeneities in certain hydrocarbon carbonate reservoirs (e.g. the Arab Formation, Persian Gulf). The studied succession is arranged in nine sedimentary units bounded by discontinuity surfaces that can be traced over kilometres. Facies analysis permitted the reconstruction of two sedimentary models showing the transition from inner ramp subenvironments (i.e. intertidal, lagoon, backshoal/washover, shoal-sand blanket) to the mid-ramp foreshoal and offshore domains: an oncolitic-peloidal-oolitic and an oolitic-peloidal-dominated ramp. The oncolitic-peloidal-oolitic-dominated ramp is characterized by peloidal-oolitic and oncolitic-dominated shoal-sand blankets that developed in higher-energy inner areas, protecting peloidal-oolitic backshoal and oncolitic lagoon domains including a mosaic of stromatoporoid carpets. Peloidal facies with fenestral porosity accumulated in an intertidal belt or as patches on top of the shoal-sand blankets and washover deposits. Offshore from the shoal-sand blankets, chaetetid/stromatoporoid/coral-rich buildups grew on the more proximal mid-ramp, surrounded by peloidal and peloidal-bioclastic grain- to mud-supported facies. An oolitic-peloidal-dominated ramp developed in a second stage of the evolution of the platform, characterized by the presence of a wide restricted peloidal-bioclastic-oolitic lagoon on the inner ramp grading into a backshoal area dominated by storm-related intraclastic-peloidal deposits. Stromatoporoid carpets disappeared and oncolitic-dominated deposits were constrained to the foreshoal and backshoal domains, and locally to local ponds that developed in the intertidal belt or the restricted lagoon. Internal and external factors controlling facies heterogeneity and the sedimentary evolution of the carbonate ramp include resedimentation, topographic relief, and long- to short-term sea-level fluctuations.