Facies mosaic in the inner areas of a shallow carbonate ramp (Upper Jurassic, Higueruelas Fm, NE Spain)

Abstract

The internal facies and sedimentary architecture of an Upper Jurassic inner carbonate ramp were reconstructed after the analysis and correlation of 14 logs in a 1 × 2 km outcrop area around the Mezalocha locality (south of Zaragoza, NE Spain). The studied interval is 10–16 m thick and belongs to the upper part of the uppermost Kimmeridgian–lower Tithonian Higueruelas Fm. On the basis of texture and relative proportion of the main skeletal and non-skeletal components, 6 facies and 12 subfacies were differentiated, which record subtidal (backshoal/washover, sheltered lagoon and pond/restricted lagoon) to intertidal subenvironments. The backshoal/washover subenvironment is characterized by peloidal wackestone–packstone and grainstone. The lagoon subenvironment includes oncolitic, stromatoporoid, and oncolitic-stromatoporoid (wackestone and packstone) facies. The intertidal subenvironment is represented by peloidal mudstone and packstone–grainstone with fenestral porosity. Gastropod-oncolitic (wackestone–packstone and grainstone) facies with intercalated marl may reflect local ponds in the intertidal or restricted lagoon subenvironments. Detailed facies mapping allowed us to document 7 sedimentary units within a general shallowing-upward trend, which reflect a mosaic distribution, especially for stromatoporoid and fenestral facies, with facies patches locally more than 500 m in lateral extent. External and internal factors controlled this heterogeneity, including resedimentation, topographic relief and substrate stability, combined with variations in sea-level. This mosaic facies distribution provides useful tools for more precise reconstructions of depositional heterogeneities, and this variability must be taken into account in order to obtain a solid sedimentary framework at the kilometer scale.