The systematic study of a brachiopod fauna collected from a Brigantian, uppermost Visean, Mississippian, mud mound complex on the Derbyshire Carbonate Platform (England, United Kingdom) recognises 45 species, representing 36 genera and seven orders (Productida, Orthotetida, Orthida, Rhynchonellida, Spiriferida, Spiriferinida, and Terebratulida). The mound complex is a decametre-scale lens-shaped buildup composed of three facies associations: the basal tabular unit made of skeletal packstone beds and tabular mounds, the complex core formed by metre-scale lens-shaped massive mounds and the surrounding inclined skeletal packstone flank beds. Brachiopods are widespread and very abundant in all three facies associations. Spinose, concavo-convex productides are dominant in the mud mound fauna, both in terms of the number of specimens, species, and biovolume. Productide success is related to scattered and scarce food resources, which they better exploited using their simple, unsupported feeding apparatus in comparison with that of the spiriferides. Spiriferides with a wide interarea are common and large in the basal tabular unit, but are rare and small in the complex core, probably due to greater availability of food resources during the deposition of the basal unit. Substrate type also played a role in controlling brachiopod diversity: varied substrates in the mound complex core allowed small-sized pedicle-attached rhynchonellides, spiriferides, and terebratulides to extensively colonise the seafloor, whereas they are rare in the basal unit.

Several brachiopod-rich mud mounds occur in the upper Visean (Brigantian) of the Derbyshire Carbonate Platform succession in UK. The re-evaluation of the lithofacies architecture of a Derbyshire mud mound complex, developed in an intraplatform middle-ramp environment, led to the recognition of three lithofacies associations: (a) a 10 m thick basal unit of automicrite boundstone with siliceous sponge spicules and brachiopod–bryozoan packstone to wackestone beds; (b) a 10 m thick, 250 m wide, lens-shaped, convex-up massive core of clotted peloidal micrite and fenestellid bryozoan boundstone with sponge spicules; (c) inclined brachiopod–bryozoan–crinoid packstone flank beds. In the mud mound complex core, most of the carbonate mud with clotted peloidal and structureless micrite fabric is the result of biologically induced and influenced in-situ precipitation processes (automicrite). Brachiopods are not, as previously thought, limited to storm-scoured “pockets” in the mud mound complex core but are abundant and diverse in all lithofacies and lived on the irregular mud mound complex surface concentrating in depressions sustained by automicrite boundstone and the growth of bryozoans and sponges. The upper Visean Derbyshire mud mounds are, thus, representatives of a newly defined fenestellid bryozoan–brachiopod–siliceous sponge mud mound category, occurring in various middle–upper Visean Western European sites, a sub-type of the fenestellid bryozoan–crinoid–brachiopod Type 3 buildups of Bridges et al. (1995). These mud mounds, and other types of brachiopod-rich buildups, developed in carbonate platform settings between fair-weather and storm wave base, in dysphotic environments with dispersed food resources during the Visean. Brachiopod mud mound colonisation was favoured by moderate water depth, availability of food resources, and diverse substrates.