The palaeoecological distribution of the endothyroids (foraminifera) in the Guadiato area (SW Spain, Mississippian)

This paper focusses on the distribution and methodological problems that are observed in the palaeoecological analyses of the endothyroids from the Guadiato area, in the southwestern part of the Iberian Peninsula. In spite of a long history of taxonomical and biostratigraphical studies on endothyroids, there have been few investigations of their palaeoecology and taphonomy. The Guadiato area contains a sequence of upper Viséan to Pendleian marine carbonates. The upper Viséan units were deposited in a storm-dominated ramp. The Pendleian strata were deposited in a tectonically controlled shelf, with narrow platform facies (supra-, inter- and subtidal) and a wide area of slope deposits. Some of the foraminiferal assemblages of this succession typify intertidal facies and incipient shoals, and are regarded as para-autochthonous. Other assemblages, such as the endothyroids in the higher part of the Pendleian slope, are of doubtful allochthony. It is likely that endothyroids did not live in slope facies (it was too deep), but the extent of their transportation cannot be determined since their tests do not show signs of abrasion. Several factors controlled the endothyroid distribution, such as salinity and depth. Deposits formed in high-energy environments such as shoals and tidal flats were not favourable for the endothyroids. Particular palaeoecological factors also determine the distribution of certain families, subfamilies or genera. One of these factors is relative environmental stability; for example, some endothyroids that lack secondary deposits (the Archaediscinae and ‘Endothyra’=Priscella) were more abundant in stable environments. In contrast, other genera with secondary deposits (the Asteroarchaediscinae, Omphalotis and the evolved Endothyra) were more abundant in unstable or fluctuating microfacies. This factor, however, did not control the distribution of every genus, because this difference is not observed in some species of genera with or without secondary deposits (e.g. Globoendothyra).