Bollettino della Società Paleontologica Italiana, 59 (3), 2020, 247-259. Modena ISSN 0375-7633 doi:10.4435/BSPI.2020.19 Donezella-chaetetid mounds in the Valdeteja Formation (Bashkirian, Pennsylvanian) at Truébano, Cantabrian Mountains, northern Spain Isabel Rodríguez-Castro*, Sergio Rodríguez & Marián Fregenal-Martínez I. Rodríguez-Castro, Departamento de Geodinámica, Estratigrafía y Paleontología, Facultad de Ciencias Geológicas, Universidad Complutense de Madrid, c/ José Antonio Novais 2, E-28040 Madrid, Spain; isrodr01@ucm.es *corresponding author S. Rodríguez, Departamento de Geodinámica, Estratigrafía y Paleontología, Facultad de Ciencias Geológicas, Universidad Complutense de Madrid, c/ José Antonio Novais 2, E-28040 Madrid, Spain; Departamento de Geología Sedimentaria y Cambio Medioambiental, Instituto de Geociencias, CSIC, UCM, c/ José Antonio Novais 2, E-28040 Madrid, Spain; sergrodr@ucm.es M. Fregenal-Martínez, Departamento de Geodinámica, Estratigrafía y Paleontología, Facultad de Ciencias Geológicas, Universidad Complutense de Madrid, c/ José Antonio Novais 2, E-28040 Madrid, Spain; mariana@ucm.es KEY WORDS - Carboniferous, algospongia, León, limestone, palaeontology. ABSTRACT - The Bashkirian-lower Moscovian Valdeteja Formation crops out in the Cantabrian Zone (NW Spain). It is composed of pale grey limestone with a diverse fossil content, calcareous breccias and massive limestone composed of algal and microbial mounds accumulated in a high relief carbonate platform. Outstanding outcrops of that formation appear near the village of Truébano (León Province, North Spain) at the old coal mine “Mina Rosario.” The mine is a peculiarity in the formation as it shows interbedded siltstones and coal beds containing coal balls. The studied succession above the coal seam is lower Bashkirian and 20.2 m thick. Dark grey, massive to well- bedded limestones interbedded with thin marly beds are dominant in that interval. The main component of the limestones is the algospongia Donezella that is found in two different facies: packstone of resedimented Donezella, which appears in the lower beds of the section, and boundstone of Donezella, Girvanella and chaetetids, in the upper beds. Additional components are highly diverse including foraminifera, other calcified microbes, rhodophyta, sponges, echinoderms, arthropods, brachiopods, bryozoans and scarce corals and molluscs. Organic matter is abundant in the marly beds, but palynomorphs are poorly preserved. An interbedded layer of quartz sandstones lacking fossil content occurs in the upper part of the sequence. The depositional environment of the facies is part of a carbonate platform top near the fair-weather wave base, within subtidal zone, with development of “algal” mounds and sedimentation of debris from the same buildups. The composition and components distribution of both microfacies fit well with the mounds previously described in other outcrops of the Valdeteja Formation, with the exception of the participation of chaetetids as a main building component in some beds. INTRODUCTION Algal mounds are common in the Pennsylvanian and have been described in locations such as the American Midcontinent China, the Carnic Alps and the Cantabrian Mountains, in Spain (Samankassou, 2001, 2003; Gong et al., 2007). The main builders of these mounds are phylloid algae, but there are reports of mounds built by other organisms. For instance, Dasycladales (Samankassou, 2001) and algospongia such as donezellids, formerly considered algae (Vachard & Cozar, 2010). “Algospongia” is a Class proposed by Vachard & Cózar (2010). It includes problematic organisms, traditionally assigned to Porifera, Chlorophyta and Rhodophyta, and regroups them in two orders: Moravamiinida and Aoujgaliida. Algal mounds are common in the Carboniferous limestones from the Cantabrian Mountains (northern Spain), mainly in the Valdeteja, Picos de Europa and San Emiliano formations. The algospongia Donezella is the main builder of many of these mounds, which have been reported and studied in different locations by authors such as Bowman (1979), Riding (1979), Eichmuller (1985), Samankassou (2001), Della Porta et al. (2002a) and Chesnel et al. (2016, 2017). All the Donezella mounds reported by those researchers are upper Bashkirian and Moscovian, except for the lower Bashkirian mounds studied by Eichmüller (1985) near the Valdeteja village. This study focuses on the “Mina Rosario”, an abandoned coal mine that provides an excellent outcrop of the Valdeteja Formation. The mine is in the place known as “Cuesta del Sol” next to Truébano, a village in the San Emiliano municipality in the León Province, northern Spain (Fig. 1). Here we report the first description and analysis of the Donezella-bearing limestones strata overlying the carbonaceous marls of the coal mine. The aim of the palaeontological and sedimentological analyses herein presented is to establish the sedimentary environment and the age of the Donezella mounds. This analysis is part of a larger study about the palaeontology and microfacies in the “Mina Rosario” outcrop, part of which is published by Rodríguez-Castro et al. (2019). GEOLOGICAL SETTING The Valdeteja Formation (Bashkirian) crops out in Northwest Spain in the Cantabrian Zone of the Iberian Massif. The Cantabrian Zone consists in a thick succession of Palaeozoic deposits that was deformed into a set of imbricated thrusts during the Variscan Orogeny (Bahamonde et al., 2000; Alonso et al., 2009). It is characterised by a low-degree or null metamorphism, low deformation and thin-skinned tectonic structure (Julivert, 1971; Bastida, 2004). The thrust sheets divide the zone S. P. I. SO C IE TA ' P A LEON TO L OGICA I T A L IA NA Bollettino della Società Paleontologica Italiana, 59 (3), 2020248 in multiple tectonic units (Bastida, 2004), such as the Sobia-Bodón Unit, where the study area is located. The sedimentary record of the Cantabrian Zone can be divided in two thick sedimentary sequences: the pre-orogenic sequence (Precambrian-Devonian) and the syn-orogenic sequence (Carboniferous) (Julivert, 1978; Marcos & Pulgar, 1982), which records the sedimentation in carbonate platforms developed in the foreland basin of the Variscan orogen currently located in the north of the Iberian Massif. The studied succession belongs to this sequence. Winkler Prins (1968) originally defined as “Valdeteja” the Valdeteja Member of the Caliza de Montaña Formation. This member is now a formation of its own, and “Caliza de Montaña” has turned into an informal term for both the Barcaliente Formation (Serpukhovian- Bashkirian) and the Valdeteja Formation (Bashkirian). The former appears in all the tectonic units of the Cantabrian Zone, while the latter is limited to the Sobia- Bodon, Áramo and Picos de Europa units, and to the Central Carboniferous Basin (Bastida, 2004). Bastida (2004) described the Valdeteja Formation as an ensemble of light-coloured limestones with diverse fossil content, calcareous breccias and massive microbial and algal boundstones. Although it is a well-known formation, detailed sedimentological and microfacies studies of the Valdeteja Formation are scarce in the León Province. The facies of the Carboniferous carbonate platform have been studied in higher detail in several outcrops in Asturias, especially in the Sierra de Cuera, where it is hard to distinguish the Valdeteja Formation from the overlying Picos de Europa Formation (Moscovian) (Bahamonde et al., 1997). Moreover, most of those studies focus on the later formation and substage (Bahamonde et al., 2004, 2008), and when they also address the Bashkirian they usually just include a few samples or a small section of the stratigraphic logs from the upper Bashkirian (Della Porta et al., 2002a, b, 2003, 2004; Verwer et al., 2004). The main exceptions are Bahamonde et al. (1997, 2007), which analyse more in detail the facies of Valdeteja. Most studies in the León Province focus on its palaeontological content and biostratigraphy based on foraminifera and macroflora (Wagner et al., 1971; Villa, 1982; Ginkel & Villa, 1991; Villa et al., 2001). The main sedimentological study of the Valdeteja Formation in the province is that of Eichmüller (1985), who established the depositional environment of the formation as a high relief carbonate platform surrounded by a deep siliciclastic basin. This interpretation is confirmed by Bahamonde et al. (2000), Della Porta et al. (2002b), Kenter et al. (2002) and Chesnel et al. (2016, 2017). These authors described accurately the geometry and stratigraphic architecture of the carbonate platform in the Picos de Europa unit based on exceptional outcrop conditions at Las Llacerias, Sierra de Cuera and Valdorria. The “Mina Rosario” outcrop is a peculiarity inside the Valdeteja Formation, because of the presence of carbonaceous marls with coal balls. It was first studied while the mine was still active (Gómez-de-Llarena & Rodríguez-Arango, 1946). Those authors described the coal balls, called “Tacañas” by the miners, and their fossil content (Calamites, other vegetal remains, corals, crinoids, brachiopods and small gastropods). They also established the age of the carbonaceous marls as early Westfalian (Moscovian). Other authors that studied the mine have also focused on the coal balls, analysing their depositional environment, formation processes and their fossil content, specifically the foraminifera and algae (Vachard & Beckary, 1988, 1991). Despite the interest that the carbonaceous bed has awakened among the researchers, the rest of the outcrop and its unique features have been ignored until now. Fig. 1 - Location of the Mina Rosario outcrops. Modified from google maps (image property of TerraMetrics) and WikimediaCommons (author HansenBCN). 249I. Rodríguez-Castro et alii - Donezella-chaetetid mounds in the Carboniferous of Spain METHODS Field work includes measurement of stratigraphical log (Fig. 2), observation and description of rock structures and textures and sedimentological and palaeontological sampling of each bed. The carbonaceous marls serve as the base of the log, while the top is the first bed that could not be measured due to the difficult access. The palaeontological samples include palynomorphs, microfossil and macrofossil samples, which are stored in the Facultad de Ciencias Geológicas (Universidad Complutense de Madrid). The palynological samples have been treated with acids for extraction of palynomorphs in the laboratory of the Huelva University by F. González, who also analysed them. Horizontal and vertical thin sections have been prepared from each sedimentological and palaeontological sample. They have been studied with optical microscope. The thin sections from bed 9 have been stained for checking the presence of carbonate cements (Lindholm & Finkelman, 1972). The carbonate rocks have been described using the Dunham (1962) and Embry & Klovan (1971) classifications, while for sandstones we apply Pettijohn (1954). For the environmental reconstruction we employed the method described by Said et al. (2010). It consists in the identification of environmental factors (such as hydrodynamic energy, salinity, depth and oxygenation), which then are used to deduce the sedimentary environment. DESCRIPTION OF THE “MINA ROSARIO” OUTCROP The studied succession crops out in two open pit mines at the Mina Rosario (Fig. 3). In the biggest open pit, the bedding planes strike roughly east-west and dip almost vertical due to its location next to the overthrust of the Sobia-Bodón Unit by the Somiedo Unit, which in this area is E-W directed. In the western open pit, of smaller size, the bedding planes’ strike and dip are conditioned by a local fault (Fig. 3). The carbonaceous marls are lenticular and present lateral thickness changes. The measured and studied succession is 20.2 metres thick. It is mainly composed of decimetric to metric grey limestones and marl beds. The limestones are laterally continuous in thickness along the mine, while the marl beds are thinner, and some of them disappear laterally. Stratification is irregular because of the amalgamation of the mounds, already reported in other areas of the Cantabrian mountains (Bahamonde et al., 2000; Corrochano et al., 2011). Bioturbation is common in all the carbonate beds. The packstones that occur in the 13.5 m thick lower part of the succession (beds 1-6 in Fig. 2) are fine-grained, bioclastic, and do not contain any fossil identifiable at field scale. Beds 2 and 6 are well bedded in decimetric layers, and bed 6 even contains interbedded thin marl layers, but most of the limestone levels are massive. Petrographic Fig. 2 - (color online) Stratigraphic log of the studied succession. The carbonaceous marls serve as a base for the log, while the top (T) marks the start of beds that could not be reached. Intervals 1 to 10 based on lithological features. Colors in the log represent the actual colors of the rocks on the field. Bollettino della Società Paleontologica Italiana, 59 (3), 2020250 analysis shows a diverse fossil assemblage, composed mainly of broken Donezella thalli and other algospongia genera such as Ungdarella, Petschoria, Faciella, Beresella and Uraloporella. Other components are crinoids and undetermined echinoderm plates, foraminifera (mainly fusulinids and endothyrids), broken brachiopod shells, ostracods, bryozoans and Girvanella. Scarce trilobites, mollusc fragments, rugose corals and sponge spicules are found in some samples. The limestones of the upper part of the succession (beds 7 to top in Fig. 2) are boundstones, and their main components are chaetetids, algospongia (mainly Fig. 3 - Sketch diagram of the outcrop over aerial photograph. Satellite image from google maps (image property of TerraMetrics). Fig. 4 - Field photograph of base of bed 6. The dome-shaped chaetetids form a framestone that serves as a base for the mound. Geological hammer (30 cm) as size reference. 251I. Rodríguez-Castro et alii - Donezella-chaetetid mounds in the Carboniferous of Spain Donezella) and Girvanella. The mounds range from 40 centimetres to two metres in thickness. The base of some of the buildups is a continuous framestone of chaetetids (Fig. 4), which become less common towards the upper part of the stratum. The spaces between the chaetetids are filled with a bafflestone composed of Donezella and Girvanella, and with bioclasts. The grain size decreases upwards, and bed 7 passes gradually upwards to a marl layer. The beds overlying the studied succession appear to be similar buildups, with different thickness of the individual beds. The marl beds are laminated and do not contain macrofossils. They vary from black and dark brown marls in bed 4 to brown in bed 6 and to light brown in bed 8. The darker levels contain abundant organic matter and degraded phytoclasts. An ochre quartz sandstone appears near the top of the succession (bed 9). It is composed of two fining- upwards sequences with irregular bases. The sandstone completely lacks fossil content or carbonate components, as it is only composed of well sorted quartz grains. Until now, this is the only sandstone bed described for the Valdeteja Formation in the León Province. FOSSIL CONTENT The thin sections show a high-diversity assemblage, where at least seven animal Phyla are represented: Porifera, Cnidaria, Arthropoda, Echinodermata, Mollusca, Brachiopoda, Bryozoa (Fig. 5). There are also members of the Phyla Foraminifera, Cyanobacteria, Rhodophyta and the Class Algospongia (undetermined Phylum and Kingdom) (Fig. 6). The palinomorph samples just yielded scarce and unidentifiable spores and continental amorphous organic matter (degraded phytoclasts). Most fossil remains are broken and/or disarticulated. It was possible to identify foraminifera, algospongia, cyanobacteria, rhodophyta, rugose corals and sponges on the genus level. The abundance and diversity of foraminifera and algospongia made possible to identify even some species. Porifera - Chaetetids are one of the main components of the boundstones in beds 7 and 10. They range from 10 to 20 centimeters and are dome-shaped (Fig. 4). Moreover, scarce sponge spicules appear in bed 1. Cnidaria - Scarce tabulated and rugose corals appeared in scree from the section. The only identifiable specimen was the rugose coral Semenophyllum sp., which was found in scree probably from bed 7. Arthropoda - Ostracods occur as a secondary component in all units, and scarce broken trilobite fragments appear in beds 1 and 5. Echinodermata - Echinoderm plates are frequent in every bed. Most of them are crinoid and undetermined plates, but Echinoidea spines appear in some thin sections too. Brachiopoda - They occur in the whole outcrop as a secondary component of the fossil assemblage. All of them are broken shells that cannot be assigned to any Class. Mollusca - Molluscs are scarce and mainly found in the first bed. Most of them are broken unidentifiable shells, but a few gastropods are present in thin sections. Bryozoa - They occur in every bed of the outcrop, but they are not abundant. Most of them are broken and cannot be identified, but a few of them belong to the Order Fenestrata. Algospongia, algae and cyanobacteria - Those are some of the most diverse groups in the studied section. The most abundant fossils in the studied outcrop belong to Algospongia, such as Donezella, the main mound- builder (along with chaetetids and some cyanobacteria). Ungdarella is also abundant, along with the red algae Archaeolithophyllum and the cyanobacteria Girvanella. Foraminifera - Foraminifera are the most diverse Phylum in the outcrop. At least twenty species and genera have been identified. They are frequent in every bed, and most of them belong to Fusulinida and Endothyrida, while Archeodiscida are scarcer. There is just one genera (Tuberitina) of Afusulinina, but it is abundant in all the samples. The list of all the identified taxa and their distribution is shown in Fig. 7. MICROFACIES Two carbonate microfacies, characterised by distinct depositional textures, fossil assemblages and taphonomic preservation states, can be differentiated in the studied section. Microfacies 1: resedimented algospongia packstone It is the most frequent microfacies in the studied levels and appears in samples in all limestone beds (Fig. 2). This packstone is defined by the presence of broken and resedimented Donezella as the main component (Fig. 8). Grain size varies between samples and even between different areas of the same sample, but most samples are fine-grained. The secondary components are other algospongia such as Beresella, Petschoria and Fasciella, broken brachiopod shells, crinoid plates, sea urchin spines and foraminifera. There are abundant fusulinids, endothyrids and Tuberitina, and scarce or even absent archaeodiscids. There are also ostracods, abundant red algae (Archaeolithophyllum), mollusc remains, some bryozoans, trilobite fragments, cyanobacteria (Girvanella and Renalcis) and isolated rugose corals. This assemblage is relatively diverse, with seven animal Phyla and more than twenty-five genera of Foraminifera, Algospongia, Cyanobacteria and Rhodophyta (Fig. 7). The equitability is low, as Donezella absolutely dominates the assemblage. Bollettino della Società Paleontologica Italiana, 59 (3), 2020252 253I. Rodríguez-Castro et alii - Donezella-chaetetid mounds in the Carboniferous of Spain Bollettino della Società Paleontologica Italiana, 59 (3), 2020254 Fossil remains are disorganised, with some areas composed almost exclusively of Donezella remains, while others are more diverse. Most fossils appear to be oriented roughly horizontally, and most remains are broken and disarticulated, specially the bigger ones. These features suggest the fossils are resedimented (sensu Fernández-López, 1991), but there are no signs of prolonged transport. Microfacies 2: Donezella, Girvanella and chaetetids boundstone It occurs in the limestone beds in the upper part of the succession, specifically in some areas of samples TRU 15 and TRU T (Fig. 2). It is defined by the presence of chaetetids and Donezella in growth position, creating an organic framewortk with gaps inhabited by cyanobacteria like Girvanella and burrowers, like the Thartarella producers (Fig. 9). Besides Donezella and Girvanella, which are the absolute main components of the assemblage, there are fusulinids, Endothyrida (specially paleotextularids), archaeodiscids, Tuberitina, red algae, some disperse echinoderm plates and broken brachiopods shells. This boundstone presents a fossil assemblage very similar to the “algal” mounds described in other outcrops of the Valdeteja Formation, which have been thoroughly studied by Eichmüller (1985), Samankassou (2001), Della Porta et al. (2002a), and Chesnel et al. (2016, 2017). The main difference between the boundstone from the Mina Rosario and those described by these researchers is the higher abundance of Girvanella and chaetetids occurring in the mine. This fossil assemblage is less diverse than the assemblage of the microfacies 1, but the equitability is higher, since chaetetids and cyanobacteria are also main components of the limestone, along with Donezella. Some remains are broken and may have undergone resedimentation, but most of them are in growth position. ENVIRONMENTAL RECONSTRUCTION The previous observations allow the identification of some environmental factors for the limestone sedimentary environment. The presence of Donezella and chaetetids in growth position suggests a low to moderate hydrodynamic energy, while the abundance of broken and disarticulated remains appears to indicate the opposite. Moreover, the presence of abundant micrite implies periods of low energy. These features suggest an environment with moderated and discontinuous sea swell influence. The cyanobacteria and chaetetids in the mounds provide a stronger framework that allows the Donezella to resist the waves, but some specimens are still broken and deposited around the mounds. The limestones in the lower half of the section represent the sedimentation of the debris and broken fossils from the mounds, while the buildups form beds 7 and 10. The diversity of the fossil assemblages and the presence of stenohaline organisms, such as brachiopods, echinoderms and chaetetids, indicate a normal marine salinity, about 36-40 ppm (Fürsich, 1993). Moreover, the abundant bioturbation and the biodiversity both suggest a well-oxygenated environment. All these features are characteristic of an open sea and imply that the mounds did not form a barrier that isolated the inner platform, but they represent patches widely developed in a shallow platform, in a situation similar to that of the Donezella buildups described in Della Porta (2002a). The presence of autochthonous inferred photosynthetic organisms, such as cyanobacteria (Girvanella) and algae, indicates that the mounds were in the photic zone. The influence of the sea swell also rules out a high depth. This implies that the mound organisms inhabited a relatively shallow environment, but with no evidences of subaerial exposure. Presence of beds in the lower part of the succession with abundant Donezella shingle indicates periodical erosion by waves and resedimentation of the mounds. The marl beds are the result of the sedimentation in periods with less hydrodynamic energy and higher influx of sediment from the continent, which includes fine clastic sediment and organic matter. Therefore, the sedimentary environment would have been a carbonate platform close to the fair-weather wave base, in the subtidal zone. The rocks that crop out in the Mina Rosario are the result of the development of “algal” mounds in that platform (microfacies 2), and the detrital sedimentation of thalli between and around them (microfacies 1). In the previous pages: Fig. 5 - (pag. 252) Mound builders and dwellers. a) Rugose corals, Semenophyllum sp. incrusted by a chaetetid, scree, DPM 12066 TRU 0. b) Bryozoans, fenestrate bryozoan, DPM 12066 TRU 13. c) Calcified microbes, Girvanella sp., DPM 12066 TRU 14. d-g) Algospongia, Ungdarella sp. (d), DPM 12066 TRU 9; Fasciella sp. (Aoujgaliida) (e), DPM 12066 TRU 13b, Donezella lutugini Maslov, 1929 (Moravamminida) (f), DPM 12066 TRU 10; Uraloporella sp. (Moravamminida) (g), DPM 12066 TRU 10. h) Ichnofossil, Thartarella sp. (worm tubes), DPM 12066 TRU 14. Scale bars: a, 1 cm; b-h, 1 mm. Fig. 6 - (pag. 253) Foraminifera. a) Ozawainella umbonata, DPM 12066 TRU 15. b) Eostaffella postmosquensis, DPM 12066 TRU 15. c) Pseudostaffella sp., DPM 12066 TRU 15. d) Tetrataxis sp., DPM 12066 TRU 13b. e) Bradyina nautiliformis Möller, 1878, DPM 12066 TRU 10. f) Climacammina sp., DPM 12066 TRU 18. g) Monotaxinoides sp., DPM 12066 TRU 11. h) Insolethiteca sp., DPM 12066 TRU 9. i) Hemiegordierina sp., DPM 12066 TRU 10. Scale bars: 1 mm for all specimens, except g = 0.25 mm. Fig. 7 - Stratigraphical distribution of the identified fossils. Patterns according to the legend in Fig. 2. 255I. Rodríguez-Castro et alii - Donezella-chaetetid mounds in the Carboniferous of Spain Bollettino della Società Paleontologica Italiana, 59 (3), 2020256 Further data are required to understand the spatial distribution, extension and morphology of the mounds, since this analysis comprises just one stratigraphic succession, which is not enough to completely characterise the carbonate platform. AGE There are few previous biostratigraphic studies conducted in the Mina Rosario. Vachard & Béckary (1991) studied the foraminifera from the coal bed and determined a Prikamian (Askinbasian) age, which is the highest horizon of the lower Bashkirian, according to the chronostratigraphic scale defined in the Russian platform. Vachard & Béckary (1991) also studied the macroflora they found in the coal balls, which belongs to the Namurian C regional substage (Yealdonian). However, they state that it is hard to distinguish between Namurian C and Westphalian A (Langsetian) regional substages with the findings from the mine. Other authors that have studied the macroflora from the Mina Rosario in the past (Gómez de Llarena & Rodríguez Arango, 1946, 1948) also maintain this ambivalent situation between upper Namurian and lower Westphalian. The new results are consistent with previous studies. Since there were more identifiable species in the lower beds, the Fusulinoidea recorded in the whole outcrop were used, instead of relying on the specimens from the beds over the coal level. Eostaffella postmosquensis Kireeva in Rauzer-Chernousova,1951, Millerella concinna Potievskaya, 1964, Ozawainella umbonata Brazhnikova & Potievskaya, 1948 and Pseudostaffella variabilis Reitlinger, 1961 were also found by Vachard & Béckary (1991). These species only overlap in Severokeltmenian (Akavasian) and Prikamian horizons (lower Bashkirian). Vachard & Béckary (1991) were able to narrow the age down to the Prikamian horizon because of the presence of Pseudostaffella praegorskyi Rauzer-Chernousova, 1949, which has not been found in our thin sections. However, we have no reason to argue their findings, so it is most likely that the outcrop belongs to the Prikamian and not the Severokeltmenian with no doubt that it is lower Bashkirian. Moreover, the overall assemblage matches the one described by Vachard & Béckary (1991) as the usual assemblage in both Spain and the Donetz basin: the firsts Ozawainella and abundant Monotaxinoides transitorius Brazhnikova & Yartseva, 1956, Archaediscida and Ozawainelloidea, like Eostaffella, Millerella and Plectostafella. The Rugosa genus Semenophyllum is reported exclusively in the Bashkirian (Rodríguez-García, 1984; Coronado & Rodríguez, 2009), which further supports the age based on the foraminifera. Most Donezella mounds in the Valdeteja Formation are upper Bashkirian and/or Moscovian (Bahamonde et al., 2004; Chesnel et al., 2016). This means that these results imply that these are some of the oldest mounds described in the Valdeteja Formation, along with the mounds from the type section, described by Eichmüller (1985). CONCLUSIONS The Mina Rosario outcrop is unique in the Valdeteja Formation because of the carbonaceous marls with coal Fig. 8 - Microfacies 1. a) Resedimented algospongia packstone, vertical thin section (bed 2). Very small bioclasts, mostly algospongia fragments with homogeneous distribution. Fu: Fusulinina, Tu: Tuberitina sp. Scale bar: 5 mm. b) Horizontal thin section (bed 1) showing some larger bioclasts. Eq: echinoderm plates, Br: brachiopod shell, Dz: Donezella fragments of branches. Scale bar: 1 cm. c) Horizontal thin section (bed 3) showing intense bioturbation (upper left). Scale bar: 1 cm. 257I. Rodríguez-Castro et alii - Donezella-chaetetid mounds in the Carboniferous of Spain balls that were mined in the 1940s. The strata above the coal bed are composed of marl and limestone beds, formed mainly by resedimented Donezella or by chaetetids, Donezella and Girvanella in growth position, building mounds. These beds have a relatively high diversity and contain abundant Foraminifera, crinoids and undetermined echinoderm plates, brachiopods, ostracods, bryozoans and corals. We have differentiated two carbonate microfacies: resedimented algospongia packstone limestones (microfacies 1) and chaetetids, Donezella and Girvanella boundstone (microfacies 2). The latter is very similar to the typical “algal” mounds in the Valdeteja Formation. The sedimentary environment is part of an open carbonate platform. The limestones were deposited near the fair-weather wave base. The fossils identified in this study support the previous dating by other authors. 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