Upper Viséan Saccamminopsis-sponge microbial mud mounds, Sierra de la Estrella, Southwestern Spain

Abstract

Dome-shaped mud mounds ranging in size from 2 m to 25 m thick and from 2 m to 100 m in diameter are present in the Upper Viséan of Sierra de la Estrella, Guadiato Valley, in the Sierra Morena region of SW Iberian Peninsula. The mounds are composed of up to 70% peloidal matrix and contain a varied but sparse assemblage including bryozoans, crinoids, brachiopods, calcareous algae, foraminifers, and gastropods. A three-stage biotic succession is recognizable in the mounds. The first stage consists of crinoid–sponge spicule packstones. The second stage is represented by a low-diversity, autochthonous assemblage of scattered sponges and up to 40–60% by volume of the microproblematical taxon Saccamminopsis fusulinaeformis (McCoy). The third stage consists of peloidal framework and cementstone with abundant primary growth cavities. These rocks are interpreted to be microbial boundstone-cementstone. The three stages of mound growth developed below storm wave base, and the probable coeval, level-bottom beds consisting of marls are interpreted to have been deposited in a dysphotic environment.