Eleven representative stratigraphic sections were logged in the upper Devonian sedimentary sequence (Fig. 1) and over 620 samples were collected for analysis (Fig. 2). The position of samples in stratigrafic sections are provided in the electronic supplementary material accompanying this report (named Stratigraphical Profies). These samples were studied using combined OM/SEM/AAS/XRD analysis.

Over 424 samples were analyzed to study their provenance and diagenesis, including those of the Rodanas Fm. (132 samples), the Bolloncillos Fm. (69 samples), the Hoya Fm. (218 samples) and the Huechaseca Fm. (5 samples). A Zeiss Jena 30-G0060 Jenapol polarizing microscope with 25x, 50x and 100x magnification was used for petrographic analysis. Standard point counting techniques were applied, using the integrated Gazzi-Zuffa point counting method (Zuffa, 1985), as recommended by Ingersool et al. (1984) and González-Acebrón (2017). 300 points were counted per thin section, distinguishing thirteen different components. This data was applied for sandstone classification and for estimating the amount of porosity lost by compaction, cementation and matrix/pseudomatrix, assuming 45% original porosity (Torrijo, 2003; Bernet et al., 2007).

SEM analyses were carried out using ZEISS DSM 940A and JSM 6400 microscopes provided with with a Thechnosym 8200 MKII. Mineral identifications were evaluated by chemical spot analyses using an eXL-10 Link Analytical X-ray EDS analysis. Digital SEM images were taken at 150 to 200 µA beam current and 10-13 kV acceleration voltage at an average working distance of 20 mm. Images of 30x, 60x and 100x magnification were taken at 8000-pixel average. The samples studied are rock fragments included in resin.

The content of various chemical elements were determined with atomic absorption spectroscopy and X-ray fluorescence. AAS analysis was done with a Perkin-Elmer 3030 and the elements analysed and detection limits were the following: Ca (1000 ppm), Mg (20 ppm), Fe (100 ppm), Mn (6,5 ppm), Na (10 ppm) and K (50 ppm).

On the other hand, XRF was done in X-Assay Laboratory (XRAL) of Toronto and the elements analysed and detection limits were the following: SiO₂ (0,01%), Al₂O₃ (0,01%), CaO (0,01%), MgO (0,01%), Na₂O (0,01%), K₂O (0,01%), Fe₂O₃ (0,01%), MnO (0,01%), TiO₂ (0,01%), P₂O₅ (0,01%), Rb (2 ppm), Sr (2 ppm), Y (2 ppm), Zr (2 ppm), Nb (2 ppm) and Ba (20 ppm).

A Pananalytical Xpert with Detector XCeleretor and a Bruker D8 Advance with SOL-X were used for X-ray diffraction analysis. The determination of the clay’s crystalline phases was made as recommended by Galán & Martín Vivaldi (1973).

The arenites from the Rodanas Fm. are quartz arenites (Pettijohn et al., 1987) composed of detrital quartz grains, mainly monocrystalline quartz, although some polycrystalline quartz grains with undulating extinction are observed. Silicate minerals (muscovite, tourmaline, zircon, potassium feldspar), apatite grains and lithic fragments are scarce, as well as no plagioclase grains were observed. Grain contacts in arenites are concavo-convex to sutured. The phyllosilicate matrix is very rare and is associated with the diagenetic alteration of the labile components (epimatrix) and the deformation of the ductile grains (mica) during the first phase of the compaction processes. The scarce interparticle porosity is sealed by siliceous cement of a syntaxial type and ferruginous cements. Limolites are a quartz wackes and lithic wackes (Pettijohn et al., 1987), formed by phyllosilicate matrix of quartz grains, lithic fragments and micas (muscovite), in variable proportion.

In the Bolloncillos Fm., the arenites, similar to those of the Rodanas Fm., are also quartz wackes to lithic wackes (Pettijohn et al., 1987), or quartz arenites to sublitharenites (Pettijohn et al., 1987), although the latter in smaller proportion. The wackes are constituted, mostly, by quartz clasts and by lithic fragments and micas (muscovite) in minor proportion, and also, phyllosilicate and quartz matrix (15-20 %). The quartz arenites and sublitharenites are mainly by quartz clasts basically monocrystalline, although some polycrystalline quartz grains with undulating extinction are observed, and in minor proportion, sedimentary rock fragments, zircon, mica and apatite grains.

The Hoya Fm. has been subdivided into three members (Gozalo, 1994) that from base to up are Filluelo Mb., Valdeinglés Mb. and Coscojar Mb. The Filluelo Mb. is a detrital alternance constituted by arenites and lutites-limolites. The Valdeinglés Mb. consists of an arenite-lutite alternance. Its limit with the underlain Filluelo Mb. is based on the augment of lutitic material and in a colour change (white to green and brown colours). The Coscojar Mb. consists of lutites with narrow intecalations of arenites. Generally, the arenites are sublitharenites to lithic wackes (Pettijohn et al., 1987) formed by quartz clasts, basically monocrystalline, and in minor proportion, lithic fragments, very altered potassium feldspar, tourmaline (partially silicified) and mica grains. Grain contacts in arenites are concave-convex to sutured, and the phyllosilicate and quartz matrix (2-16 %) is associated with the diagenetic alteration of the labile components (epimatrix) and the deformation of the ductile grains (mica) in the first phase of the compaction processes.

In Huechaseca Fm., the arenites are quartz arenites (Pettijohn et al., 1987) formed by quartz clasts, mainly monocrystalline quartz, although some polycrystalline quartz grains with undulating extinction are observed. Silicate mineral (muscovite, tourmaline, zircon, apatite), and lithic fragments grains are scarce, as well as no plagioclase grains were observed; and the phyllosilicate matrix is very rare (<1 %). Grain contacts are concave-convex to sutured (Fig. 3).

Analyses done using combined SEM and OM on individual quartz grains showed that the majority of the sand grains in the studied samples were identified as of plutonic origin, thanks to the presence of spider-web microcracks within the grains (Sprunt & Nur, 1979; Berner et al., 2007). Grains of potential volcanic affinity are almost exclusively restricted to the finest sand-sized fraction of the samples (Fig. 4).

The most pronounced compositional differences between the analysed samples are in the in SiO₂ and Al₂O₃ content, which would reflect the different proportions of phyllosilicates and quartz present in each type of rock. In addition, there are noticeable differences in the average content in Fe₂O₃ due to synsedimentary and diagenetic processes. The proportion of TiO₂ is also higher in the lutites than the other lithologies. The high correlation presented by Al₂O₃ with K₂O and TiO₂ would indicate that they are being provided primarily by phyllosilicates, while those with lower Fe₂O₃, would indicate they are also found in other mineral phases such as Fe-oxyhydroxides. In the case of CaO and MgO, no significant correlations are observed with Al₂O₃, suggesting they should be present in other mineral phases, possibly carbonates, especially in the Rodanas Fm. The samples analyzed by X-ray fluorescence, except the carbonated samples of the Rodanas Fm., were geochemically classified (Fig. 5) according to Herron (1988), as suggested by Rollinson (1998).

In addition, it has been observed that the Rb, Cs, Ba, Sr, Th and U contents significant correlations with the amount of Al₂O₃. This would suggest that, in different proportions, the distribution of all of them is controlled by the presence of phyllosilicates (Dumitru et al., 2015). However, Sr presents a behavior lightly erratic, probably due to its presence in several mineral phases (i.e., carbonates, phyllosilicates...). Besides, the good linear interrelations that the Rb and the Cs present with the K₂O, might indicate that, possibly, they are being controlled by the micaceous phases (Fig. 6). Zr exhibits a geochemical behavior similar to Hf (Bauluz, 1997), reflected in the high correlation between both (Zr/Hf = 30-40). This would indicate that they are being contributed mainly by zircons (Murali et al., 1983).

Finally, with regard to rare-earth elements (REE), they are provided with the information contributed by Bauluz (1997). It show that both light and heavy rare earth elements (LREE and HREE) have a similar geochemical behavior. That is, they tend to concentrate on the same type of mineral phases. However, LREE and HREE tend to have slightly different geochemical behaviors.

Detailed cuantitative tables containing the results derived from the complete geochemical analyses are provided in the electronic supplementary material accompanying this paper (named Geochemical Data).

The sand-sized grains from the Hoya Fm. samples are mostly angular to sub-rounded in shape. Most of the sand-sized grains in the Rodanas, Bolloncillos and Huechaseca formations’ samples have a higher textural maturity, being mainly sub-rounded to rounded. Grain contacts in all these formations range from concave-convex to sutured. Additional petrographic information of arenites in upper Devonian Formations are provided in Table 2.

Only 63 samples (14.8 % of total samples) presented secondary porosity, ranging between 0.1 and 1.2 %, and no primary porosity was found in any of the samples because it was occluded by compaction, post depositional cementation and by the formation of matrix/epimatrix. Compaction is, in general, the most important factor of loss of primary porosity and resulted in an increase in contact strength, with more concave-convex and sutured contacts than long or point contacts, brittle deformation and deformation of ductile grains (e.g. muscovite). Quartz cementation is the second important factor for porosity reduction. Quartz cement appears in most samples with various grey shades in panchromatic SEM images. Samples with a relatively high matrix content were less affected by compaction.

Compaction is the most important diagenetic process along the first 2 km of burial, whereas cementation increases at higher depths, especially when temperatures reach 85ºC or more (Worden & Morad, 2000; Torrijo, 2003; Bernet et al., 2007; Surpless, 2015). In the Iberian Chains at present approximately 2 km thickness of the stratigraphically overlying Carboniferous, Permian and Triassic deposits exist (Torrijo, 2003). Therefore, upper Devonian quartz arenite samples from the Iberian Chains are characterized by post-depositional compaction and quartz cementation.

Several diagenetic processes have been distinguished in the samples studied. The development of the diagenetic structures (nodules and concretions) that appear in the Rodanas and Hoya formations, took place within the early diagenetic processes (Torrijo et al., 1998, 2000, 2001, 2004a, 2004b, 2005; Torrijo, 2003). As final processes, the presence of concave-convex and sutured contacts between the skeleton constituents can be noted. The presence of iron oxides in these materials is both synsedimentary (indicated by the presence of banding) and properly diagenetic or hydrothermal (presence of hematites associated with crack fillers and epidiagenetic (genesis of Fe and Mn oxides and oxyhydroxides).

The post-depositional quartz cementation produced syntaxial overgrowths. These cements have diverse chemical compositions, indicating that these cements are not genetically linked. Silica sources for cementation in these formations were controlled by the lack of lithic fragments in the rocks and feldspars (e.g. Worden & Morad, 2000; Caja et al., 2010). Therefore, the dissolution of the quartz grains by pressure-dissolution during compaction, or the infiltration of silica-bearing pore fluids from adjacent areas, may be the most likely silica source (Torrijo, 2003; Bernet et al., 2007). Evidences for this process were found in the studied samples.

Aparicio et al. (1991) indicate, for the Paleozoic of the Iberian Chains, a progressive decrease in the diagenetic degree reached by the materials from the Precambrian (with values of illite crystallinity index of 3.25) and Cambrian materials (with an crystallinity average value of 3.6) to the Ordovician (with increasing values ranging from 3.8 at the base to 5.2 at the top of the sequence). These cristallinity indexes place the Precambrian rocks in conditions of the epizone; the Cambrian rocks in the Epizone-Anchizone boundary, and the Ordovician rocks in the anchizone conditions.

Similar conclusions are obtained for by Bauluz et al. (1998) in Cambrian-Ordovician rocks of the Iberian Chains. They indicate a gradual evolution from the Epizone-Anchizone limit for Cambrian rocks or to the Anchizone - Diagenesis-Anchizone for the Ordovician rocks. These data would be consistent with a simple model of progrant evolution of the phyllosilicates, being the progressive increase of temperature during the burial the main controlling factor: the oldest materials reach higher depths of burial (i.e. higher temperatures) and are those achieve a more advanced stage in the mineralogical transformation sequence of the phyllosilicates.

The results presented by Aparicio et al. (1991) and Gimeno (1999) for the Silurian of the Iberian Chains would also be consistent with this model: the recorded illite crystallinity indexes and the observed diagenetic processes are typical for an advanced diagenetic environment (Fig. 7). Bescós (1988) for Silurian-Devonian deposits from the Iberian Chain also indicates an evolutionary stage proper to the diagenetic environment and far away from the conditions of the anchizone.

Therefore, only to be explained the cause of the abnormally high values of the crystallinity of the illite for Lower-Medium Devonian rocks (Aparicio et al., 1991). However, according to their mineralogy (Fig. 7), they would fall within the general pattern of simple burial models. It is therefore reasonable to think that the crystallinity values recorded in the Upper Devonian from Tabuenca area would fall within the ranges defined by the materials placed immediately under and by the overlying materials, always within the diagenetic environment. According to Aparicio et al. (1991), the appearance of prograde or retrograde effects on the degree of crystallinity of the illite from the Devonian rocks is due to the effect of the hydrothermal activity of igneous intrusions (Gimeno, 1999).

As a summary, it can be inferred that the materials constituting the Upper Devonian of the Iberian Chains in the area of Tabuenca did not reached an advanced diagenetic stage. They would be placed in the proper diagenetic environment, reaching maximum temperatures of 125-150ºC (Torrijo, 2003).

The abundance of trace elements in detritic sedimentary rocks has been commonly used to trace the source area composition (e.g. McLennan et al., 1983; Bhatia, 1985; Taylor & McLennan, 1989; Wronkiewicz & Condie, 1990; Shukla et al., 2020; George & Ray, 2021). In this sense, for the case of the rocks studied, the triangular diagrams La-Th-Sc and Th-Hf-Co have been chosen. And besides, to calculate the approximate percentage of felsic and maphic volcanic rocks in the source area, a Co/Th vs. La/Sc diagram has been used (McLennan et al., 1983; McLennan, 1989).

The results suggest that the lutites are similar to the PAAS-type slates, which would indicate that their composition would be similar to that of the upper continental crust. Therefore, the primitive source area would be predominantly of a felsic type. Besides, the lutites of the Fm. Rodanas could come from source areas where the maphic material represented about the 15% of the constituents, while in the more recent formations (Bolloncillos Fm. and Hoya Fm.) the proportion increases up to the 25% (Fig. 8).

The arenites of the Rodanas and the Huechaseca formations are composed of mono- and rare polycrystalline quartz (total quartz > 90%). Silicate minerals (muscovite, tourmaline, zircon, potassium feldspar), apatite grains and rock fragments grains are scarce, as well as no plagioclase grains were observed. This composition corresponds that of sediments derived from recycled orogenic or craton interior sources according to Dickinson et al. (1983). On the other hand, the arenites of Bolloncillos and the Hoya Formations have a sand-sized framework composed of mono- and polycrystalline quartz (total > 75%). Feldspar grains are scarce, and no plagioclase grains were observed. However, muscovite, tourmaline, zircon and apatite are more abundant than in the Rodanas and in the Huechaseca formations. These compositions (Fig. 9) are typical from craton interior or recycled orogenic sources (Dickinson et al., 1983).

In this way, primary source areas of the siliciclastic materials from the upper Devonian formations are located to the Northeast (Oliveira et al., 1986) and are part of a crystalline basement and quartz-rich sedimentary cover units (the Ebro Massif, see Carls, 1983, 1999). Given that no plutonic rocks were exposed in this area during the Devonian (Gozalo & Liñan, 1988; Carls, 1999), it seems probable that the quartz grains were second-cycle grains derived from sedimentary rocks which could have lost their inherited quartz overgrowths by abrasion during transport. The few available lithic fragments found in these sediments also reflect a combination of crystalline basement and sedimentary sources (Arribas et al., 2014; Konstantinou et al., 2014). Sediment recycling in upper Devonian materials of the Iberian Chains was also suggested by Bauluz (1997) and Torrijo (2003).

All the arenites of these above-mentioned formations are coastal sediments (Fig. 10) derived from quartz-rich sources. The most likely candidate to explain the high maturity of the studied arenites is a climatic influence (Torrijo, 2003). Currently, it is considered that, from Cambrian to Devonian ages, with the exception of the South Portuguese Zone that probably belonged to Avalonia, the whole Iberian Peninsula was part of the North Gondwana Province that extended along the northern margin of the African part of the Gondwana landmass (Gutiérrez-Marco et al., 2001, and references therein). Thereby, the latitudinal position of the present Iberian can thus be estimated only roughly as intermediate between the rather warm or cold temperature of high latitudes (ca. 50ºS) of the latest Ordovician times, and the warmer temperatures of the subtropical latitudes (ca. 35ºS) of the Devonian succession (Robardet & Gutiérrez-Marco, 2002), with a high rainfall regime and high mean-annual temperatures. So, these climatic conditions may have led to a rapid weathering and breakdown of unstable rock fragments during transport, deposition and along the early diagenesis, enriching the sediments in quartz grains (Basu, 1985a, b).