Massive conglomerate layers, 1–2 m thick and with lateral continuity of more than 100 m, are found at the base of both the Can Camps and Faig sections (Fig. 2 and Fig. 3). The fabric is supported by the coarse sandstone matrix. Clasts of variable size, up to 20 cm in diameter, are mostly angular and formed by Tournaisian–Visean black cherts. Other lithologies include quartz pebbles, microconglomerate clasts from the Lower Carboniferous Culm Formation, and clasts from Devonian Limestone. In the Can Camps mine, these layers are intercalated with microconglomerates, rippled sandstone and laminated siltstone organised in 50-cm- to 1-m-thick, fining-upwards sequences.The massive, matrix-supported conglomerates are interpreted as debris-flow deposits formed in proximal areas of alluvial fans that fed into the pre-Hercynian rocks bordering the Stephanian basin. The fining-upwards cycles intercalated with the former facies may indicate the occurrence of traction deposits in relatively more distal areas of these alluvial fans. Another type of conglomerate, which contains volcanoclastic blocks, occurs on top of the Faig succession (Fig. 3). This layer is attributed to debris flow deposits of an alluvial fan feeding in the uplifted basin margins.

Dark grey, even-laminated siltstones and shale form the thickest deposits in both sections studied and contain abundant plant remains (Fig. 2 and Fig. 3). In the Faig mine, these deposits bear abundant siderite nodules. The monotonous siltstone succession is interrupted by rare, 10- to 50-cm-thick and a few metres long bodies of coarse sandstone showing planar cross bedding and ripple-marks. These sand bodies generally have a concave base and a flat top, but one of them, observed in the Faig mine, has a flat base and a convex top.

Laminated siltstones are attributed to the deposition of overbank, suspension-load sediment in floodplains. The dark colour and preservation of lamination indicate high organic matter content and show that they were deposited under standing, anoxic water, generally without bioturbation. The abundance of siderite nodules in the floodplain deposits of the Faig mine is attributed to high Eh and low pH conditions during early burial. Cross-bedded, sandstone bodies with concave base correspond to small channels that provided some drainage to the floodplain. The lens with a convex top observed in Faig is interpreted as an isolated hydraulic dune within the floodplain.

Up to 6-m-thick, medium- to coarse-grained, rippled sandstone constitutes the top of the succession at Can Camps (Fig. 2). The base of this body is planar on underlying laminated siltstone and is internally organised in sets of megaripples, about 30 cm thick, with planar base and undulating top. Amalgamated sets are separated from each other by 30–40-cm layers of siltstone to fine sandstone with abundant plant remains including rooting structures. The intercalation of relatively thin layers of fine-grained deposits and thick, rippled sandstone is attributed to deposition of suspended load in quiet-water conditions after a flooding event. The river channel was transformed during these stages into a low-regime or sluggish channel that allowed helophytic vegetation to develop.

In the Faig mine, the upper part of the succession shows 7 m of medium- to coarse-grained sandstone with irregular bedding that contains towards the top a thin intercalation of floodplain shale and coal (Fig. 3). The base of the sandstone is planar, but clearly erosive on underlying beds.

These sandstone bodies are attributed to the infilling of fluvial channels based on their basal and internal features. The topmost channel at Can Camps displays features of a high sinuosity river, whilst the main channel at Faig may be of low sinuosity. However, the limited lateral continuity of the outcrops hinders a fuller comprehension of their detailed sedimentology.

The main coal-seams were exploited in gallery, especially during the period 1880–1890, when the mines provided an average of 3500–4500 Tm (up to 6600 Tm) of coal per year and were the third most productive in Spain. It appears that most of the coal seams were 1–2 m thick. However, in particular places, the accumulated thickness of superposed seams reached 14 m. Analyses carried out by Closas-Miralles [7], when the main coal seams were still accessible, indicated a carbon content of 66–83% and a caloric power of 6.3–8.1 kcal.

In the Can Camps opencast mine, there were two main coal seams, the Tallobert and the Can Camps. Only the second is still available for sampling (Fig. 2). In the Faig mine, there are a number of thin (up to a few decimetres thick) coal layers accessible, especially to the top of the section (Fig. 3).

The coal layers were always intercalated in floodplain siltstones. Most coal seams preserve compressed rooting systems on bedding planes at the base of the coal bed, indicating that they were initiated by in situ accumulation of organic remains in peat mires, rather than being formed by allochthonous accumulation of organic debris. In the siltstone underlying the soil at the base of the Tallobert seam, there are abundant cylindrical and contorted burrows, preserved in siderite. These biogenic structures indicate that, before the beginning of the peat accumulation under anoxic conditions, there was a period of stabilisation under oxygenated water in the permanently inundated floodplain. This allowed the aquatic burrower fauna to thrive.

Roof shale was only available for study at the Faig mine since the whole Tallobert seam and the roof shales of the Can Camps seam were extracted during coal mining (Fig. 2 and Fig. 3). The top of the available coals in the Faig mine is planar and may contain a number of clastic partitions that pass gradually to the overlying floodplain siltstones and shale. Gradual development of roof shales from underlying coal indicates that they constituted a natural extension of peat mires during their late infilling stages (Type B roof shale of Gastaldo et al. [14]: Fig. 3).

Two types of volcano-sedimentary deposits were recognized in the studied sections: (Fig. 2 and Fig. 3). (1) Cinerites attributed to ashfalls are abundant at the base of the Faig mine. They are generally 2–3-m massive layers of dark-red fine-grained tonsteins with a granular texture. They have 50-cm-large, concentric figures of alteration. (2) Cinerites attributed to pyroclastic flows are 50–70 cm thick, greyish; they consist of compact layers containing abundant, elongated debris of charred wood. They may show internal horizons rich in porosity attributed to degasification. These layers were exclusively found in the central part of the Can Camps section. The top of the layers shows large lycopsid logs.

Alluvial fan conglomerates are generally devoid of plant remains in the basin. However, in Can Camps, the top of some layers is finer in grain size and contains 2–3-m-long and 30-cm-wide logs, associated with abundant cordaitalean leaves (Pachycordaites type) and seeds (Cardiocarpus sp.). In the absence of structures, characteristic of other Stephanian tree-forming plant groups, the logs are also attributed to cordaitaleans (Figs. 4.1 and 4.2). Other plant remains (pteridosperm foliage debris) are scarce and extremely fragmentary. The abundance of cordaitalean remains, the relatively good preservation of leaves, and the association of a number of different organs of the same plant group suggest that the assemblage of cordaitalean remains is parautochthonous in distal alluvial fan facies.

Laminated siltstones and shale contain the largest diversity of plant remains in the section studied. In the Can Camps mine, the most abundant remains correspond to Pecopteris foliage with subsidiary and smaller fragments of pteridosperm foliage (Odontopteris, Linopteris…) and cordaitalean remains (Pachycordaites, Cardiocarpus). In the Faig mine, the most abundant remains in floodplain facies belong to large specimens of Alethopteris pennsylvanica pyrenaica, sometimes associated with large Pachytesta seeds. Other abundant taxa include well-preserved pecopterid foliage (Pecopteris polymorpha = Polymorphopteris polymorpha, Pecopteris feminaeformis = Nemejcopteris feminaeformis) and Odontopteris foliage. In both outcrops, some floodplain horizons are very rich in compressed sphenopsid remains including abundant Calamites suckowii and well-articulated Annularia stellata (Fig. 4). More rarely these remains are associated with Asterophyllites, Sphenophyllum oblongifolium, Calamostachys, and Macrostachya. Calamites pith casts were found in erect position crossing the cross-laminations of hydraulic dunes in the Faig mine. Lateral rooting structures were emitted by this axis, indicating growth within the dune.

With the exception of this Calamites axis, plant remains in floodplain deposits were all parautochthonous or allochthonous since no rooting structures were observed. Medullosan pteridosperms and marattialean tree ferns appear to be the plants that grew closest to the floodplain, especially in Faig, since their foliage is preserved as large and well-articulated specimens, associated with seeds in the case of pteridosperms.

Fluvial sand dunes are crossed by abundant erect pith casts of Calamites suckowii in both the Faig and the Can Camps mines (Figs. 5.1–5.3). Some of them show features considered by Gastaldo [13] to be indicative of regenerative growth after burial such as vertical increase in the pith-cast diameter. Compressed Calamites suckowii axes were found radiating from a central point in a bedding surface of siltstone to fine-grained sandstone intercalated between sets of rippled coarse sandstone (Fig. 5.6). They may correspond to the branching of erect buried axes after regeneration. These data indicate that Calamites suckowii grew isolated within the active sandy channels and eventually colonized the ground during the deposition of channel low-regime deposits.

Rooting structures occurred in the same channel low-regime facies. A large structure, 100 cm across, shows a large number of radial impressions of axes, 5 mm to 2 cm thick, with superficial striation (Fig. 4.4). The same bedding plane around this structure is covered by large and well-articulated specimens of Pecopteris foliage (Pecopteris polymorpha = Polymorphopteris polymorpha for authors) (Fig. 5.5). Other smaller rooting impressions, about 50 cm across and without clearly associated foliage, occur in another bedding plane of the same shale facies.

The large rooting structure is attributed to a marattialean tree fern that presumably grew during a low-regime period of the fluvial channel. Other smaller plants, ferns or pteridosperms and the already-mentioned Calamites suckowii could have grown along with it in the same deposits.

The taphonomic information available about peat mires in the Surroca-Ogassa coalfield is relatively scarce, due to the mining out of most of the available coal seams, especially in the Can Camps mine. In the Faig mine, some additional information can be obtained from the study of roof shales of thin coal layers with abundant clastic partitions at the top of the section (Faig-2 seam in Fig. 3). The coal bases of the main coal seams show abundant and well-articulated Stigmaria ficoides compressed rooting structures (Fig. 4.3), usually associated with Cyperites foliage. Some of these structures radiate from a central rounded depression, which may correspond to the tree stump. This stump was probably compressed within the overlaying coal, which indicates continuity between the Stigmaria soil and the overlaying original peat. Roof shales of the Faig mine, analysed by point-quadrat counting (Fig. 6), show a clear succession of lycopsid remains (extremely decorticated lycopsid bark attributed to Sigillaria, along with Stigmaria ficoides and Cyperites), followed in floodplain facies by sphenopsids and pteridosperm remains. This succession was the rule in similar depositional and palaeogeographic contexts, especially in the Graissessac Basin, Montagne Noire (Martín-Closas and Galtier [19]). These authors showed that the presence of Stigmaria ficoides in the coal base and abundant Sigillaria brardii remains in type-B roof shale might indicate that the peat itself was formed by the growth and accumulation of the remains of this species. In Ogassa-Surroca the evidence does not allow such a conclusive interpretation, especially because the lycopsid bark in roof-shale does not bear definite characters and also because the coal contains a number of spores belonging to other lycopsids [2]. Especially significant is the presence of ca 10% of Densosporites, a spore that could be related to Omphalophloios according to Wagner [26].

Two cineritic layers with associated lycopsid logs found in the Can Camps section provide significant information for taphonomic purposes. These deposits lie on thin coal layers and show, on top, abundant compressed logs of Sigillaria brardii ranging between 30 cm and 1 m in width (Fig. 4.4 and 4.5). These trunks show a marked NW–SE orientation for the lower layer and a less clear north–south to NE–SW orientation for the upper one. Charred plant remains are found within the cinerite.

The accumulation and orientation of large lycopsid logs on top of the cineritic layers suggest that the assemblage was produced as a consequence of the pyroclastic flow. The difference of more than 45° in the orientation of logs between the two cinerites at Can Camps Mine indicates that the volcanic flux had a different direction in each event. The thin coal layer visible at the cinerite base suggests that the burning cloud swept away peat mire. The monospecific accumulation of trunks suggests that the original forest, swept away by the burning cloud, consisted only of Sigillaria brardii. This is significant for our study since it sheds light on the uncertain results obtained from the taphonomic analysis of coal layers. In addition, the different sizes of logs indicate that the forest was not pioneering, but included different stages of growth, which are more characteristic of mature communities.