Abstract Lower Carboniferous (Upper Viséan and Pendleian) rocks from the Guadiato Area, in the southwestern part of Spain, comprise mixed carbonate-siliciclastic platform facies, with siliciclastics predominant. The calcareous intervals contain a highly diversified foraminiferal fauna, composed mainly of endothyroids, although some primitive fusulinids are also present. Fourteen families, 9 subfamilies, 67 genera, and 134 species or species groups of foraminifera have been identified. These allow the identification of zones 14 to 18 of Mamet’s classification. Within this zonal framework the appearance, disappearance, and maximum abundance of selected taxa in the Guadiato Area are described and discussed. The first appearance of foraminiferal species and genera in the Guadiato Area is compared to that in other European (Montagne Noire, northern France and Belgium; Britain; and Ireland) and North African (Algéria and Morocco) basins. It shows that some foraminifera occurred earlier in Spain whereas other taxa occurred later than in these regions. These early or late appearances of taxa are grouped in two trends, which are probably related to tectonic movements coeval with sedimentation in the Guadiato Area. Moreover, cluster analysis comparing the foraminifera of the twelve neighboring Carboniferous basins or regions establishes the paleobiogeographical relationship between the Guadiato Area and these other regions.

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.