Drive to Stop 1. Buses leave Guadalupe driving north following a winding stretch of road EX-118 (see Fig. 2). Outcrops along the road belong to the Lower Alcudian-Domo Extremeño Supergroup and are dominated by thick-bedded greywacke and shale strata. Detrital zircon dating in nearby regions to the west has given an age of about 582 Ma for the youngest concordant population of zircon grains (Orejana et al., 2015). No macroscopic fossils are known from this succession and organic-walled microfossils are restricted to Sphaerocongregus. After some 3 km we will turn left, onto a narrow paved road. This road is known as military pathway (“pista militar”), because it leads to a military plant at the summit of Las Villuercas hill (1601 m), the highest point within the Geopark. At the crossroad, a small whitish building stands on the right side: this is the “Ermita del Humilladero” or “Ermita de la Santa Cruz”, a hermitage constructed in the 15th century as a place for pilgrims to pray upon seeing the Guadalupe Monastery.

Location and geological context. Stop 1 is reached after driving 2.1 km on “Pista Militar” climbing toward the Villuercas summit (WGS 84) at 39°28’02”N, 05°22’06”W (Point 1 on Fig. 2). This outcrop of the Ibor Group lies on the southern limb of the Ibor Anticline, in the north-central part of Geological/Topographic Map 707 (14–28) of Logrosán. The exact stratigraphic position of the outcrop within the Ibor Group can only be approximately placed, due to large covered intervening areas. This is part of García Hidalgo’s (1985: p. 78–79) “pista militar” section, who located it at the transitional levels between subunits AS.2 and AS.3, which would place it stratigraphically below the Cloudina-bearing carbonates (lower member of the Villarta Formation), close to the Castañar/Villarta formations contact. Two nearby sections will be looked at:

Discussion. Filamentous fossils from the Ibor Group are relatively abundant in this stop. Despite ubiquitous cleavage, neither weathering nor tectonic deformation is significant. These organic filaments have been traditionally assigned to Vendotaenia. They do indeed show close similarities to vendotaenids reported from the East European Platform and Namibia. Features showing that these are filamentous fossils, and not trace fossils, include evidence of kinking and abrupt terminations (Fig. 3A). A characteristic feature of this log is that relatively flat filamentous fossils are associated with elevated ridges of comparable dimensions, forming similar general trajectories, which raises the question if the two have the same origin but display different modes of preservation. Some specimens were figured by Jensen et al. (2006: fig. 1e) and Jensen et al. (2007: fig. 4b) as case studies to differentiate between organic filaments and trace fossils. Where up-down orientations are available, specimens are preserved as raised convex up ridges. This has been found to be the case or this outcrop and several other locations from the Ibor Group. A possible stepwise taphonomic succession leading to the preservation of an originally tubular fossil is illustrated in Figure 4. This somewhat unusual style of preservation raises questions similar to those of Ediacara-type fossils preserved as negative hyporeliefs and corresponding counterpart casts. That is, if preservation was aided by some form of early mineralization by pyrite crusts, possibly mediated by microbial mats (“death masks”; Gehling, 1999; MacGabhann et al., 2019), silica precipitation (Tarhan et al., 2016), or if sediment properties alone would be sufficient (Bobrovskiy et al., 2019) to account for this type of preservation. Alternatively, there could be a case of co-occurring filamentous fossils and trace fossils. This question has some stratigraphic implications as simple filamentous organisms have deeper stratigraphic ranges than do trace fossils.

The bus continues along the “pista militar” to stop at a point that provides good views of the Appalachian-type orography (see point 2 on Fig. 2), where many of the typical geomorphological features that characterize the Geopark can be observed. The road leads to the highest peak of the Geopark, 1601 m above sea level and nearly 1 km higher than Guadalupe town. The view to the north shows a succession of synclines and anticlines. The weathering resistant Ordovician Armorican Quartzite forms the pronounced crests. Fracturation of the Armorican Quartzite has led to the accumulation of abundant large blocks on scree slopes. Toward the southeast, the strikingly horizontal landscape form of the “rañas” (piedmont infills) is observed.

Drive to Stop 3. Bus returns to road EX-118 and drives north towards Castañar de Ibor village. During this drive, the road parallels the Ibor river cutting the strata of the Lower Alcudian-Domo Extremeño Supergroup, composed of thick-bedded greywacke and claystone sediments. After Navalvillar de Ibor, some carbonates of the Villarta Formation occur on the right side. As all carbonates in this area, they have undergone dolomitization and magnesitization processes (Herrero et al., 2011). Cloudina has not been identified in the carbonates of the Navalvillar de Ibor area, but these carbonates are believed to represent the lower member of the Villarta Formation. The bus will then cross a bridge over “Garganta de Salóbriga” (Salobriga gorge), which has given its name to one fossil described by Hufnagel (2008) –Salobrigia– from the lower parts of the Ibor Group further down the gorge. After the bridge, both sides of the road exhibit weathered siliciclastic strata of the middle member of the Villarta Formation, rich in vendotaenids. In Castañar de Ibor, exit onto EX-386.

Description. The base of the Castañar Formation (Ibor Group) is unconformable and currently recognized as an angular discordance. Along the road EX-386 (point 3 on Fig. 5), the base of the formation is covered, but its lower part is dominated by shales and fine-grained greywackes, locally interrupted by the presence of breccia and conglomerate interbeds (Fig. 6A-C), up to 2.4 m thick, and dolostone nodules and concretions, up to 0.8 m in size. Conglomerates and breccias, distinguished by the rounding vs. angular shape of their clasts, comprise erosive bases and display normal grading and local imbrication. Breccia interbeds are both clast- and matrix-supported (the latter also named diamictites, a descriptive –non genetic– term), whereas conglomerate beds are clast-supported. Clasts are dominated by mono- and polycrystalline quartz, the latter related to contemporaneous hydrothermal activity (Fig. 6C), and intraformational shale, sandstone, greywacke and conglomerate clasts, up to 10 cm in size, and commonly polyphasic. Intraformational shale clasts are commonly distorted and contorted, linking to local slumping fabrics. This mosaic of facies points to high-energy, slope-related events interrupting background greywacke-to-shale sedimentation. High-energy events were controlled by the orogenic uplift pulsations recorded by the neighbouring Cadomian Arc, located to the SW of the area.

Along the road EX 386 (point 4 on Fig 5), some outcrops of partly dolomitized limestones allow the recognition of a superposition of Cloudina-microbial biostromes and bioherms. Here, the lower member of the Villarta Formation, about 14 m thick, consists of four shale-to-carbonate cycles topped with amalgamated biostromes flanked by patch-reefs with poorly developed intraclastic flanks. These beds are fringed and sandwiched by claystone. Laminated carbonates show parallel lamination, ripple-cross, lenticular and flaser beddings and flat-pebble breccia at their tops. Boundstone and floatstone microfacies are strongly recrystallized into pseudospar, whereas a secondary porosity through dolomitization is conspicuous (Fig. 6D) Secondary porosity has increased the final permeability by connecting primary laminoid fenestral pores. Cloudina shells can be recognized by the replacement of their walls and occlusion of their intraparticle pores, leading to conical mosaics of sparry calcite floating in recrystallized thromboid masses. Cloudina is preserved both uplift (in life position) and lying on the surface (as parautochthonous assemblages).

Dolostone and magnesite packages crosscutting stratification display both massive and laminated features. Massive dolostones consist of a coarse mosaic of impure dolomite including scattered silt-sized quartz grains, ghosts of Cloudina and successive dolomitization and magnesitization phases (see Herrero et al., 2011). Within Castañar de Ibor, the upper member of the Villarta Formation hosts a hydrothermally induced giant karstic cave famous for aragonite, calcite, dolomite and magnesite speleothems (Martín-Pérez et al., 2012, 2015).

Climbing the road to Castañar de Ibor, the disappearance of carbonate interbeds marks the top of the lower member. The middle member of the Villarta Formation consists of shales and greywacke sandstones, several hundred metres thick, exposed along a now abandoned stretch of road (point 5 in Fig. 5). This represents, in part, García Hidalgo’s (1985, p. 59–61) Castañar de Ibor III log. Depositional sedimentary structures are well preserved, such as erosive bed bases and slumping and contorted interlaminae. The eastern continuation of the section contains packages of sandstone beds, a feature typical of this part of the Ibor Group. Rare poorly preserved filamentous fossils have been found in this section.

Following the road EX 386 (point 6 in Fig. 5), we will cross the above mentioned sandstone package marking the middle member of the Villarta Formation, and a succession of dolostone/shale alternations (upper member) along EX-118 north of Castañar de Ibor. Following the latter, we will recognize, to the right side, the shales of the Arrocampo Formation, conformably overlain by an alternation of variegated shales and sandstones that belong to the San Lorenzo Formation. Yellowish silty interbeds display a typical Fortunian ichnofabric of small sandstone-filled burrows associated with thin sandstone/shale couplets (Fig. 7), mimicking the ichnofabrics that characterize the Chapel Island Formation of SE Newfoundland. Millimetric I- and J-shaped burrows are seen. Larger centrimetre-wide trace fossils are present on some sandstone bed soles, although poorly preserved.

Drive to stop 7. This stop is located west of La Calera village (Calera means lime kiln or lime pit) at (WGS 84) 39°30’45”N, 05°15’31”W, within the northern flank of the Ibor-Guadalupe Anticlinorium. From Guadalupe this location can be reached by a narrow but paved road or by a more circuitous route through Alía. Stratigraphic logs of the area were illustrated by García Hidalgo (1985: p. 71–72 “La Calera I”).

Description. Carbonates of the Ibor Group were exploited in several open quarries as source for lime and other products. The carbonate was burnt for several days at temperatures of 700–900 ºC transforming the carbonate to calcium oxide (quicklime, burnt lime). Mixed with sand this was used as a binding agent for walls and to chalk building walls.

The carbonate package visited here belongs to the lower member of the Villarta Formation and exhibits metre-scale muddy plano-convex geometries underlain, overlain and flanked by bedded carbonates with trough cross-laminated sets (Fig. 8A). These are commonly lined with pale-coloured angular intraclasts reflecting reworking of mudstone chips probably derived from polygonal desiccation cracks (Fig. 8B).

Location. Continuing the dirt road from Stop 7, some 1.5 km in a westerly direction, a shale-dominate outcrop is found at (WGS 84) 39°31’18”N, 05°16’11”W.

Description. This is one of the scattered outcrops of the Ibor Group with sabelliditids. The material is weathered and tectonically deformed, but the characteristic transverse wrinkling or divisions of the sabelliditids can be observed (Jensen et al., 2007: fig. 6) (Fig. 8C). The sabelliditids of the Ibor Group have not yet been studied in detail, but Contreras Sánchez et al. (2006) identified Sabellidites cambriensis and Saarina sp. from this section. In a nearby section, Vidal et al. (1994) identified Sabellidites sp. (as S. cambriensis in Vidal et al., 1999). Saarina is characterized by widely spaced divisions, in some species with a distinct distal flarings in each division. A morphological similarity between Saarina and Cloudina has been repeatedly noted, most recently by Selly et al. (2019). Sabellidites cambriensis has a stratigraphic range largely restricted to the basal Fortunian, which suggests a Cambrian age for the upper part of the Ibor Group, as supported by trace fossils (see Álvaro et al., 2019). The base of the San Lorenzo Formation is recognized, a short distance to the west, by the occurrence of pinkish conglomerates (Fig. 8D) and sandstones. As a result, we interpret the base of the San Lorenzo Formation eroding, at least, the Arrocampo Formation and the upper member of the Villarta Formation in this area.

Location. From Stop 8 return to Alía, drive east on EX-102 for about 8 km to enter a pass through “Sierra de Guadalupe”. Two areas for parking and observations are present on the left hand side.

Description. The “Strait of the Yellow Rock” provides impressive views of a landscape strongly shaped by the weathering-resistant Armorican Quartzite. Across the gorge formed by the Jariguela river, Griffon vultures, nesting in the area, are generally seen circling the higher pinnacles. The yellow colour of many rock surfaces is caused by lichens. Toward the northeast, a fine view is offered of the Guadarranque Syncline with the distant mountain range consisting of Amorican Quartzite of the north-east flank of the syncline. The syncline allows observation of Ordovician and Silurian siliciclastic rocks with sandstone-rich units marking gently raised areas. Sedimentary rocks showing influence of the Hirnantian glaciation have been described and this syncline has been the source for the description of a wide range of fossils.

The arthropod trace fossil Cruziana can be observed on bed soles in outcrop along the road, with examples of Cruziana furcifera and C. goldfussi,. Some surfaces are impressive by delicate preservation, both in vertical and horizontal views, of Cruziana loops crosscutting other trace fossils (Fig. 9A). This kind of surface brings home how deeply within the sediment were formed some Cruziana.

Location.- This stop at (WGS 84) 39°23’01”N, 05°18’48”W represents a key geological touristic site of the Armorican Quartzite, surrounded by alluvial material close to a major divide which cuts the Santa Lucía Syncline to the north from an extensive development of “rañas” to the south.

Description. Daedalus is a highly characteristic trace fossil of the Armorican Quartzite, where it often occurs in great densities to totally dominate the aspect of the strata. It was formed by the gradual displacement of a straight or curved formative vertical elements in a straight or spiralling motion. Among many impressive localities with Daedalus in the Central Iberian Zone can be -mentioned the “Daedalus mega-ichnosite” in the Naturtejo UNESCO Global Geopark in central Portugal (Neto de Carvalho et al., 2016) and Fontanarejo, Ciudad Real (Gutiérrez Marco et al., 2017). In the Villuercas-Ibores-Jara Geopark localities with well-preserved material of Daedalus include that of Risco Carbonero, a location that cannot be accessed by bus. The Las Amoladeras site exhibits numerous specimens of Daedalus desglandi, an ichnospecies with relatively broad causative elements forming conical to toroid systems. D. desglandi is typically found in the lower but not lowest part of the Armorican Quartzite. Although the outcrop at Las Amoladeras is of relatively limited extension, it has the merit of exposing lateral views and gives a good impression of the density of Daedalus (Fig. 9B). The extent of sediment disturbance is particularly impressive when contrasted to the weak bioturbation seen in the pre-Ordovician stops visited during these fieldtrips.

A visitor centre with information on the Villuercas-Ibores-Jara Geopark is located in Cañamero village. In addition to information on the Geopark, it contains rock samples and fossils from the area. Of special interest to the IMECT congress is that it hosts a large carbonate block containing the type material of Cloudina carinata described in Cortijo et al. (2010) (Fig. 10A–C). This block originated from the Membrillar megabreccia, the most impressive of the several megabreccias within the Valdelacasa Anticline.