Microbial mud mounds between inner and outer ramp setting.
Asbian-Brigantian

Abstract ref. 2010:
     In the Guadiato Area sedimentation occurred during the upper Viséan to form the Sierra de la Estrella outcrops which belong to the Sierra del Castillo Unit The
Guadiato Area is located on the boundary between the Ossa-Morena and Central-Iberian zones, in the south-western Iberian Peninsula, where Lower
Carboniferous outcrops are numerous. Buildups development has been recognised in most outcrops of the Sierra del Castillo Unit, and they are located at La Casa
de la Calera, Peñarroya, Sierra Boyera and Sierra de la Estrella. Although the stratigraphical setting of the first three sections has been previously described, their
buildup development and morphologies are different to those of Sierra de la Estrella, whose buildups are thicker and more abundant. 
     The stratigraphic succession from Sierra de la Estrella is dated precisely as upper Viséan by means of foraminifers (Zone 15 of Mamet). The main guide taxa are:
Palaeotextularia (bilaminar), Cribrostomum, Vissariotaxis compressa, Howchinia, 'Monotaxinoides' sp., Endothyranopsis crassa, and the Microproblematicum
Saccamminopsis fusulinaeformis. Sediments at Sierra de la Estrella show characteristics of a storm-dominated transitional zone between outer and inner ramp. The
outstanding feature of this ramp is the development of microbial buildups. They may be called mud-dominated buildups or mud-mounds because they are
mud-dominated (they show more than 50% of mud). They are regarded as microbial mounds because they are mainly composed of organomicrite and show
common stromatactoid cavities. 
     Two main morphologies have been identified: 

     1. Tabular mud-banks; they extend laterally for 1000 m to 1300 m, and are 35-60 m in thickness. 
     2. Domal mud-mounds; they have variable size; they are 2-25 m in thickness and 4- 40 m in diameter.

Buildup types were related to sedimentological conditions; domical mud-mounds were developed in transitional facies between the inner and outer ramp, with
variations in the environmental conditions, while tabular mud-banks were developed in more stable conditions in an outer ramp setting. 
     Microbial buildups are interbedded with tempestites and marls. Some siliciclastic beds showing erosion surfaces and hummocky cross-bedding also occur 
     The sedimentological and paleontological characteristics of the Sierra de la Estrella section allow us to recognise two deepening-upward sequences (probably of
4th order), which are integrated into a major transgressive sequence (belonging to a 3rd order cycle). This glacio-eustatic cycle is recognised in upper Viséan
throughout the Guadiato Area, so it could be envisaged that it will influence all outcrops from this epoch within the Ossa-Morena and Central Iberian zones. 