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Eustatic versus tectonic control in an intraplate rift basin (Leza Fm, Cameros Basin). Chronostratigraphic and paleogeographic implications for the Aptian of Iberia/ Control eustatico versus control tectonico en una cuenca de rift intraplaca (Fm Leza, Cuenca de Cameros). Implicaciones cronoestratigraficas y paleogeograficas para el Aptiense de Iberia.

1. Introduction

Tectonics and eustasy are the main allocyclic factors controlling the creation of accommodation space in sedimentary basins (e.g. Ingersoll and Busby, 1995; Bosence, 1998; Miall and Miall, 2001; Leeder, 2011). In general, tectonics can be regarded as the most important factor, especially in rift basins, because in them, crustal extension is typically expressed in surface as faults on the basin substrate, which generate accommodation space that will be filled by sediments (Leeder and Gawthorpe, 1987; Leeder, 1995; Gawthorpe and Leeder, 2000). But if a rift basin is close to the marine realm, rising and falling of sea-level will be an additional factor controlling accommodation space (Pietman, 1978; Lambeck et al., 1987; Leeder and Gawthorpe, 1987; Ravnas and Steel, 1998). When both factors are actively found together, as in coastal/marine rifts and proto-oceanic rift troughs (Leeder, 1995; Ravnas and Steel, 1998; Gawthorpe and Leeder, 2000), they create a complex combination which has proved to be difficult to untangle (Lambeck et al., 1987; Miall and Miall, 2001; De Benedictis et al., 2007). In these cases, detailed tectonic and sedimentological studies are necessary to discriminate their relative roles on the generation of accommodation space (Pietman, 1978; Lambeck et al., 1987; Collier, 1990; Gawthorpe et al., 1997; Cross et al., 1998; Perrin et al., 1998; Plaziat et al., 1998; Ravnas and Steel, 1998; Miall and Miall, 2001). Here we present the case study of a coastal carbonate unit (Leza Formation) deposited on the active margin of an intraplate rift basin (Cameros Basin), during a period of significant eustatic rise.

In this work, detailed geological mapping and outcrop analysis are used to interpret the tectonic control of the Leza Fm, which was deposited in a series of small fault-bounded depressions along the northern margin of the Cameros rift basin. In addition, sedimentological analysis is carried out in order to accurately describe the marine influence in the Leza Fm deposits. The aim of this study is to compare this marine influence with the tectonic setting of the Leza Fm, which would allow differentiation between the relative roles of eustasy and tectonics as factors controlling the generation of accommodation space and the sedimentation of the unit.

Furthermore, this study provides new data on the controversial age of the Leza Fm. These data, together with the new evidences of marine influence, are an interesting source of paleogeographic information, and they lead to a reinterpretation of the sources of marine influence on the Leza Fm, as well as a revision of the early Aptian paleogeography of NE Iberia.

2. Geological setting

The Cameros Basin is the northwesternmost basin of the Mesozoic Iberian Rift System (Fig. 1). It was formed during Late Jurassic to Early Cretaceous times, and it was inverted during the Cenozoic Alpine Orogeny (Casas-Sainz and Simon-Gomez, 1992; Mas et al., 1993; Guimera et al., 1995). The sedimentary infill of the basin was deposited on top of a Triassic-Jurassic substrate during Tithonian to early Albian times, and it is composed of sedimentary rocks deposited in continental and transitional environments (Tischer, 1966; Salomon, 1982; Guiraud & Seguret, 1985; Alonso and Mas, 1993; Mas et al., 1993; 2011; Quijada et al., 2010; 2013; 2014; Suarez-Gonzalez et al., 2010; 2012). This sedimentary infill has a vertical thickness of up to 6000 m and it was originally divided by Tischer (1966) in five lithostratigraphic groups (Tera Gr, Oncala Gr, Urbion Gr, Enciso Gr, and Olivan Gr). These denominations are still in use, but were adapted to sequence stratigraphy (Mas et al., 1993) and are currently divided in eight depositional sequences (Mas et al., 2002a; 2004; 2011;Fig. 2).

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The Leza Fm is a carbonate unit with strongly variable thickness (from less than 20 m to almost 280 m), because it crops out in a discontinuous series of small lithosomes along the northern margin of the basin (Diaz Martinez, 1988;Alonso and Mas, 1993; Suarez-Gonzalez et al., 2010; 2011) (Figs. 1, 3, 4). These lithosomes include the Leza Fm and the underlying Jubera Fm, and they are limited by faults that fracture the Mesozoic substrate of the Cameros Basin. The Jubera Fm, which also shows a strongly variable thickness (Fig. 3, 4), consists of conglomerates, sandstones and shales. Deposits of the Jubera Fm are interpreted as formed in alluvial fans related to the erosion of the faulted substrate (Alonso and Mas, 1993). The Leza Fm is mainly composed of limestones, dolomites and marls but it also contains variable siliciclastic influence (conglomerates and sandstones). It was attributed to lacustrine and palustrine environments with levels of marine influence (Guiraud, 1983; Alonso and Mas, 1993). The lithosomes of the Jubera and Leza units are overlaid by mixed siliciclastic-carbonate facies of the Enciso Group (Figs. 2, 3, 4).

Outcrops of the Leza Fm can be divided in two main sectors, which are separated by an extensive outcrop of Tertiary rocks (Figs. 1, 3, 4). The Western sector is located between the valleys of the Leza River and the Jubera River (La Rioja, Spain) and contains three lithosomes: San Vicente, San Martin and Leza lithosomes (Figs. 1,3). The Eastern sector is located around the Cidacos River valley between the towns of Arnedillo and Prejano (La Rioja, Spain) and contains five lithosomes of the Jubera and Leza Fms: Prejano, Penalmonte, Arnedillo, Canteras and Castellar lithosomes (Figs. 1, 4).

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2.1. Ages previously attributed to the Leza Fm

Due to the scarcity of high resolution biostratigraphic data, the sedimentary record of the Cameros Basin is difficult to date accurately (Martin-Closas and Alonso, 1998) and, in particular, the Leza Fm has been given many different ages, ranging from Berriasian to Aptian (Fig. 5). The Leza Fm was defined as a formal lithostratigraphic unit by Mas et al. (1990), but its deposits were mentioned in previous studies. Tischer (1966) briefly described the carbonates of the Leza Fm throughout the northern margin of the basin, and he stated that they change laterally to the Enciso Gr. Based on ostracod biostratigraphy, Kneuper-Haack (1966) assigned a Berriasian age to the Enciso Gr, and Brenner & Wiedmann (1975) dated the Enciso Gr as Hauterivian-Barremian. Salomon (1982) redefined the age of the Enciso Gr as early Valanginian, based on mapping and stratigraphic relationships. However, Salomon (1982) did not consider the deposits of the Leza Fm as a uniform unit: in the Leza River area (Fig. 3) they are mapped as equivalent to the Enciso Gr of Tischer (1966), but in the Jubera River (Fig. 3) and Arnedillo (Fig. 4) areas they are considered as equivalent to the Tera Gr of Tischer (1966). Guiraud (1983) was the first to recognize the Leza Fm deposits as a lithostratigraphic unit, which he informally named serie Soto. He also named the Jubera Fm as serie Leza. He considered the Jubera Fm as part of the Urbion Gr and the Leza Fm as part of the Enciso Gr, both early Valanginian in age, following the chronostratigraphy of Salomon (1982). Guiraud (1983) found dasycladales in the Arnedillo section, interpreting for the first time marine influence in the deposits of the Leza Fm. Schudack (1987) further refined the age of the Enciso Gr, using ostracods and charophytes, as Barremian. Diaz Martinez (1988) recognized that the Jubera and the Leza Fms are tectonically controlled, also describing a lateral relationship between both units. Hernandez Samaniego et al. (1990) used regional lithologic correlations and scarce charophyte data to assign the deposits of the Jubera Fm and Leza Fm as Kimmeridgian-Berriasian (Tera Gr ofTischer, 1966) and Berriasian (Oncala Gr), respectively. In contrast, Mas et al. (1990) used previous data to assign a Valanginian-Barremian age to both units. Alonso and Mas (1993) described lateral relationship between the Leza Fm and the Enciso Gr. They mentioned sporadic occurrence of dasycladales and foraminifers in the Leza Fm and, given the age of the overlying units and the chronostratigraphic range of the dasycladales, they considered the Enciso Gr as Barremian-Aptian in age. Mas et al. (1993) refined this age as upper Barremian-lower Aptian. Casas-Sainz and Gil-Imaz (1994) did not discuss chronostratigraphy of the Cameros Basin, and they did not mention the Leza Fm as a unit, but in their Figura 3 presented an outcrop sketch of the Prejano area (Fig. 4) where the Leza Fm deposits are classified as part of the Enciso Gr. In addition, their Figura 8 showed a geological map of the Arnedillo area (Fig. 4) where outcrops of the Leza Fm are attributed to the Oncala Gr. Martin-Closas and Alonso (1998) conducted a thorough chronostratigraphic study of the Cameros Basin, including data from ostracods, charophytes, palynomorphs and dasycladales, as well as data from geological mapping and regional stratigraphic correlations. For them, the Leza Fm is part of the Enciso Gr, which is upper Barremian-lower Aptian in age. Mas et al. (2002a; 2004) updated the sequence stratigraphic framework of the basin, including the Jubera and Leza Fms in the seventh depositional sequence (DS7, Fig. 2), upper Barremian-lower Aptian in age. Doublet (2004) studied the Enciso Gr and considered that the Leza Fm belongs to the Oncala Gr. Schudack and Schudack (2009) changed the previous ostracod biostratigraphy of the Cameros Basin, considering the Enciso Gr as upper Valanginian-Barremian in age. Casas et al. (2009) did not discuss chronostratigraphy of the Cameros Basin, but in their Figure 8 they showed outcrop photographs of the Jubera Fm and the Leza Fm deposits in the Leza River area (Fig. 3), in which they are considered as part of the Oncala Gr and Enciso Gr, respectively. Suarez-Gonzalez et al. (2010) presented new occurrences of dasycladales (Salpingoporella urladanasi) and foraminifers in the Leza Fm, suggesting that marine influence was more important than previously thought and confirming this unit as part of the Enciso Gr, Barremian-Aptian in age, based on the stratigraphic range of that species (Carras et al., 2006). Clemente (2010) considered the Leza Fm as part of the Oncala Gr, lower-middle Berriasian in age, using the criteria ofHernandez Samaniego et al. (1990).

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In this study we present new stratigraphic, sedimentological and paleontological data, as well as a new detailed geological mapping that will shed some light on the controversial chronostratigraphy of the Leza Fm and the Cameros Basin.

3. Methods

This work is based on detailed geological mapping and sedimentological and paleontological analysis of the Leza Fm, as well as on a thorough revision of the literature concerning the chronostratigraphic and paleogeographic context of the Leza Fm.

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For the work on the Leza Fm, an approximate area of 240 [km.sup.2] was mapped at 1:5000 scale using field observations, aerial photographs and satellite images. ArcGIS software was used to integrate all the cartographic data and to elaborate the final simplified synthetic maps (Fig. 3, 4). Twelve complete stratigraphic sections of the Leza Fm have been measured (Fig. 6) with a decimetre resolution and logged at 1:100 scale. The base of the sections corresponds to the contact between Jubera Fm and Leza Fm, which is gradational and, in this work, it is located at the first meter-scale carbonate bed found in the upper part of the Jubera Fm. The contact between the Leza Fm and the overlying Enciso Gr is also gradational and, in this work, the base of the Enciso Gr is considered to be marked by the first occurrence of decimetre-scale alternation of marls, sandstones and sandy ostracod-rich limestones, which are characteristic facies of the Enciso Gr (Mas et al., 1993; Alonso-Azcarate, 1997; Doublet et al., 2003). 750 rock samples were collected from the stratigraphic sections, as well as from other outcrops. A polished and uncovered thin section (30 [micro]m thick) was prepared for each sample, in order to conduct petrographic analysis. Thin sections were partially stained with Alizarin Red S and potassium ferricyanide (Dickson, 1966), for accurate distinction between calcite and dolomite. The petrographic and sedimentological description of this work will follow the classification of carbonate rocks of Dunham (1962).

For the interpretation of the paleogeographic context of the Leza Fm, we have elaborated a comprehensive compilation of information regarding the early Aptian in Northern and Eastern Spain. The main source of data for this compilation was the 1:50000 geological map of Spain (MAGNA series, available from the Geological Survey of Spain, IGME, and the Geological Survey of Catalunya, IGC). 212 maps of this series (see Appendix) have been carefully examined looking for lower Aptian outcrops. Additional information has been obtained from works of regional geology (Peybernes, 1976; Mas, 1982; Melendez, 1983; Salas, 1987; Alonso and Mas, 1988; Garcia-Mondejar, 1990; Berastegui et al., 2002; GarciaSenz 2002; Rosales et al., 2002; Mas et al., 2002b; 2004; Garcia-Mondejar et al., 2004; Robador and Garcia-Senz, 2004; Gonzalez Fernadez et al., 2004). Borehole data have also been used for the paleogeographic reconstruction. A compilation of data from exploration wells edited by IGME (1987) has been used. Several previous paleogeographic reconstructions have been also used in order to complete our reconstruction of areas where data were not available (Ziegler, 1988; Hay et al., 1999, Masse et al., 2000; Berastegui et al., 2002; Rosales et al., 2002; Mas et al., 2002b; 2004; Garcia-Mondejar et al., 2004; Robador and Garcia-Senz, 2004; as well as the paleogeographic maps of Ronald Blakey, available at http:// www2.nau.edu/rcb7).

4. Results

4.1. Geological mapping, tectonic framework and relationships with adjacent units

Geological maps of the northern margin of the Cameros Basin (Figs. 3, 4) show that the Leza Fm and the underlying Jubera Fm crop out discontinuously, on a series of lithosomes limited by faults that fracture the Mesozoic (Jurassic and Triassic) substrate of the basin. These lithosomes are arranged in a NW-SE direction, parallel to the northern thrust of the Cameros Basin, and they are overlain by the Enciso Gr. Furthermore, smaller-scale faults are observed inside the lithosomes, which control the thickness of the Jubera Fm and the Leza Fm (Figs. 3, 4). Both units are typically thicker in the middle part of the lithosomes and they thin towards the limits, disappearing laterally in many cases, which locally allows the Enciso Gr to be directly on top of the Jurassic substrate (Fig. 4). The faults that limit the lithosomes and those which control the thickness of the Jubera and Leza Fms do not seem to significantly affect the overlying Enciso Gr.

[FIGURE 5 OMITTED]

This general tectonic framework of the northern margin of the Cameros Basin shows that the siliciclastic Jubera Fm and the carbonate Leza Fm are tectonically related. Furthermore, transition between both units is gradational: the top of the Jubera Fm contains progressively more abundant calcareous sandstones and thin limestone levels (Ochoa, 2006); the base of the Leza Fm is rich in clastic facies (mainly conglomerates and sandstones with fragments of Jurassic limestone, similar to those of the Jubera Fm), which gradually disappear towards the top of the unit (Fig.6). This gradual transition between both units suggests a lateral relationship of facies. Figure 7A shows a panoramic view of "Penas de Leza" seen from the town of RibafTecha to the North (see exact location in Fig. 3). In this view it can be observed that the upper strata of the Jubera Fm are westward changing to the lower strata of the Leza Fm, producing a progressive eastward thinning of the Leza Fm (Fig. 7B). This lateral relationship can also be observed at a smaller scale (Fig. 7C).

Geological maps (Figs. 3, 4) show that the Leza Fm is always overlain by part of the Enciso Gr, which is a thick unit (up to 1100 m in its depocentre) formed by a wellbedded alternation of sandstones, siliciclastic mudstones, marls, limestones and dolomites (Mas et al., 1993; Alonso-Azcarate, 1997; Alonso-Azcarate et al., 1999; Doublet et al., 2003), worldwide-known for the abundance of dinosaur footprints (Moratalla and Sanz, 1997; PerezLorente, 2002; Moratalla and Hernan, 2010). Transition from the Leza to the Enciso deposits is also typically gradual, which causes interbedding of thin-bedded marls and sandy limestones of the Enciso Gr with thicker-bedded carbonates of the Leza Fm at the contact of both units (Fig. 8). The relationship between the Leza Fm and the Enciso Gr is clearly seen in the Leza River valley. Figure 9 shows N-S panoramic photographs of the eastern side of the valley, taken from the West (see Fig. 3 for exact location). These panoramic views show that levels of the Leza Fm (seen in the field as hard carbonate packages producing marked topographic relief) gradually pass to the south to Enciso Gr levels (seen in the field as more erodible and vegetated alternations of marls, carbonates and sandstones). This transition creates a southwards facies change from the Leza Fm to the Enciso Gr (Fig. 3). The southern limit of this lateral facies change is located around the village of Soto en Cameros (Fig. 9C), where the Enciso Gr deposits predominate, displaying its characteristic lithologies and facies (Tischer, 1966, Salomon, 1982; Guiraud, 1983; Mas et al., 1993; 2011), as well as its characteristic paleoichnological content (Casanovas et al., 1990; 1992; Moratalla and Hernan, 2010).

4.2 Sedimentology of the Leza Fm

The detailed sedimentological analysis of all the measured sections of the Leza Fm (Fig. 6) has led to the recognition of many different facies that can be grouped and summarized in five facies associations

a) The clastic facies association is very abundant in the lower part of most of the studied sections of the Leza Fm and its abundance decreases upwards (Fig. 6). It includes conglomerates, cross-bedded sandstones, and less common marls. Conglomerates are poorly sorted and generally matrix-supported. They are composed of lithoclasts of Jurassic limestones, quartz and quartzite pebbles, and carbonate intraclasts, within a sandy matrix (Fig. 10A). Sandstones are coarse- to fine-grained and commonly contain fragments of Jurassic limestone. The sandstone bodies typically show irregular bases, fining-upward trends, and trough cross-bedding. This facies association is interpreted as formed in an alluvial system whose main source area was the marine Jurassic limestones from the substrate of the Cameros Basin, which was faulted (Fig. 3, 4) and, therefore, exposed and being actively eroded during the sedimentation of the Leza Fm (Suarez-Gonzalez et al., 2010; 2014).

b) The black limestones facies association comprises the most characteristic facies of the Leza Fm. It occurs both in the lower and upper part of all the studied sections (Fig. 6). This facies association is typically arranged in thickening-upwards sequences, 1-4 m thick (Fig. 10B), formed by black bioclastic limestones and less abundant marls. Limestones generally have mudstone-wackestone textures in the lower part of the sequences and wackestone-packstone textures in the upper part of the sequences. The top of these sequences is marked by features such as mud cracks, abundant bioturbation, root traces, brecciated horizons, nodular and mottled horizons, vertebrate footprints, and ferruginous surfaces (Fig. 10C). Black limestones of the lower part of the Leza Fm are generally sandy, whereas quartz grains are rarer in limestones of the upper part. They contain bioclasts, intraclasts and very abundant oncoids. The bioclasts are ostracods, charophytes, gastropods, dasycladales, filamentous microbial colonies, and fragments of vertebrate bones and egg-shells (Fig. 10D). These bioclasts lack any signs of reworking (Fig. 10D) and, therefore, they are considered as in situ remains valid for paleoenvironmental interpretations. Some sequences of the western outcrops of the Leza Fm (Trevijano and Leza sections, Fig. 6) contain skeletal stromatolites (Suarez-Gonzalez et al., 2014). The sequences of this facies association are interpreted as shallowing-upward sequences of shallow bodies of water (Suarez-Gonzalez et al., 2010; 2014). The common presence of in situ microfossils of both continental and marine affinities (charophytes and dasycladales, respectively) suggests that these bodies of water were coastal-lakes with influence of both fresh-water and marine water (Suarez-Gonzalez et al, 2010; in press). Areas between coastal-lakes were probably covered by vegetation, since the top of the shallowing-upward sequences contain characteristic features of edaphic alteration and development of paleosoils in carbonates (e.g. Platt and Wright, 1992; Freytet and Verrechia, 2002; Alonso-Zarza and Wright, 2010, and references therein).

c) The oolite-stromatolite facies association has only been observed in the eastern outcrops of the Leza Fm (Fig. 6), and it occurs in the middle and upper parts of the sections. This facies association contains cross-bedded oolitic grainstones that alternate with less abundant grey mudstones creating flaser, wavy and lenticular beddings (Fig. 10E). Flat-pebble breccias are common. These facies are laterally and vertically related with domal agglutinated oolitic stromatolites (Fig. 10F). Mud-cracks and vertebrate footprints are also observed in this facies association. Grainstones are composed of ooids, peloids, micritic intraclasts and bioclasts (mainly ostracods and benthic miliolid foraminifers, Fig. 10G). Ostracods and foraminifers are also found as trapped particles within the stromatolites. These bioclasts lack any signs of reworking (Fig. 10G) and, therefore, they are considered as in situ remains valid for paleoenvironmental interpretations. This facies association is interpreted to be formed in shallow coastal-lakes, and its characteristic sedimentary structures (flaser, wavy and lenticular beddings) point to tidal influence during its deposition (Suarez-Gonzalez et al., in press). In addition, the fact that the fossil content is almost restricted to ostracods and foraminifers suggests a somehow anomalous salinity in these coastal-lakes, probably due to a stronger sea-water input than in the black limestones facies association.

d) The evaporite-dolomite facies association only occurs in the upper part of the eastern sections of the Leza Fm (Fig. 6). It is formed by well-bedded to laminated grey dolomites with abundant pseudomorphs after evaporitic minerals (Figs. 11A, B). Dolomites have dense micritic or peloidal textures. They are poor in fossils, containing scarce ostracods and benthic miliolid foraminifers. The pseudomorphs can be scattered in the matrix (Figs. 11A) or grouped in centimetre-scale laterally-continuous layers (Figs. 11B). Pseudomorphs are variable in size and shape and they grow both displacing and replacing the dolomitic matrix. Morphology of original gypsum and anhydrite are typically observed in the pseudomorphs. Ferruginous surfaces, nodular horizons, mud-cracks and rare teppees structures occur at the top of some beds. This facies association is interpreted as deposited in relatively restricted coastal areas with common influence of sea-water (Suarez-Gonzalez et al., 2010; in press) due to the abundance of pseudomorphs after evaporite minerals and to the scarcity and nature of the fossil content, which suggests that salinity of the original environment was anomalous and/or rapidly changing.

e) The well-bedded grey limestones facies association has been observed in the middle and upper parts of the sections measured on the western outcrops of the Leza Fm (Fig. 6). It is formed by 10-30 cm thick beds of grey limestones, which typically present mud-cracks and/or vertebrate footprints at their top surfaces. Three different textures are observed in these grey limestones: mudstonewackestones of ostracods and benthic miliolid foraminifers (Fig. 11C, D); packstone-grainstones of peloids, ostracods and foraminifers; and laminated fenestral limestones with micritic, clotted-peloidal and agglutinated microfabrics, as well as relicts of microbial filaments. Small vertical cracks are common in these fenestral limestones, and their fossil content is very low: scattered ostracods and foraminifers, and rare charophytes and dasycladales. Fossils of this facies association lack signs of reworking (Figs. 11C, D). Beds of this facies association are very abundant in the upper part of the unit. They also occur in the middle part (Fig. 6), generally showing a scarcer fossil content. This facies association can be interpreted as being deposited in shallow coastal-lakes with influence of marine water, as indicated by the fossil content. The common mud-cracks and the small vertical cracks preserved in fenestral limestones indicate that desiccation of the coastal-lakes was common.

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4.3. Evidences of marine influence

Deposits of the Leza Fm contain sedimentological and paleontological evidences of marine influence during their sedimentation. The main sedimentological evidence is the heterolithic alternation of grainy and muddy facies observed in the oolite-stromatolite facies association, which creates sedimentary structures such as flaser, wavy and lenticular beddings (Fig. 10E). These sedimentary structures are characteristic of modern and ancient carbonate tidal environments (see many examples in Ginsburg, 1977; Hardie, 1977; Demicco, 1983; Laseim et al., 2012).

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The presence of in situ dasycladales and foraminifers in the Leza Fm deposits (Figs. 10D, 10G, 11C, D) is a clear paleontological indicator of very common marine influence throughout most part of the sedimentation of the unit, since they occur in many successive levels, often alternating with levels only containing fresh-water fossils (Fig. 6). Dasycladales occur in sequences of the black limestones facies association but only in sequences from the middle and upper parts of the studied sections (Fig. 6). A single species of dasycladales has been found in these deposits: Salpingoporella urladanasi (Marc Conrad, Nicolaos Carras and loan Bucur, pers. com.). This green alga has a Barremian-Albian stratigraphic range (Carras et al., 2006), and it is usually found in restricted marine, brackish facies, associated with foraminifers, ostracods and charophytes, but also in facies of normal marine salinity (Carras et al., 2006). The paleobiogeography of this species corresponds to the northern Tethyan realm (Fig. 12). In the context of the Iberian Peninsula, S. urladanasi has been confidently described in the Barremian-Aptian of the South-Pyrenean Basin (Peybernes, 1976; Conrad et al., 1977), and in the Albian of Portugal (Rey et al., 1977). According to Carras et al. (2006) it is uncertainly cited in the Basque-Cantabrian Basin (Pascal, 1984). It is cited but not figured in the Asturias area (Dragastan, 1982), and it has been cited as S. cf. urladanasi and not figured in the Maestrazgo Basin (Canerot et al., 1982).

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Foraminifers are also commonly found in situ in the middle and upper parts of the studied sections of the Leza Fm (Fig. 6), but they occur in facies associations different from those of the dasycladales. In fact, samples where dasycladales and foraminifers occur together are extremely rare. This mutual exclusion of dasycladales and foraminifers is further evidence that the Leza Fm was deposited in a complex system with many different paleoenvironments with varying salinities and different degrees of marine influence: facies with dasycladales also commonly include charophytes (Fig. 10D), suggesting fresh-water influence, but facies with foraminifers almost never contain charophytes (Figs. 10G, 11C, D), and many of them show tidal influence (Fig. 10E). Samples with foraminifers occur in the middle and upper parts of the unit, but those found in the middle part typically contain scarce foraminifers. All the foraminifers observed in thin-sections of the Leza Fm belong to the same morphotype of miliolids (Figs. 10G, 11C, D), which presents the characteristic features of the genus Istriloculina (Esmeralda Caus, pers. com.). This genus is Early Cretaceous in age (Loeblich and Tappan, 1988) and it has been described in localities such as the Southern Pyrenees (Bernaus et al., 2002; 2003), Portugal (Lezin et al., 2010), SE France (Arnaud-Vanneau, 1980; Masse et al., 2003), Croatia (Marton et al., 2010), Romania (Neagu, 1984), Bulgaria (Iovcheva, 1962), and Turkey (Masse et al., 2009). Istriloculina is typically found in shallow, restricted environments with anomalous salinities, and commonly associated with ostracods, dasycladales and charophytes.

Charophytes of the black limestones facies association are also an important source of paleoenvironmental information. They belong to the families Clavatoraceae and Porocharaceae (Carles Martin-Closas, pers. com.). Specimens of both families can be found together in the same sample but some sequences of the lower and middle parts of the studied sections contain charophytes assemblages mostly dominated by porocharacean gyrogonites. The presence of homogeneous populations of porocharacean remains in Lower Cretaceous deposits is an indicator of brackish paleoenvironments (Martin-Closas and Grambast-Fessard, 1986; Mojon, 1989; Schudack, 1993), and they have been found associated with dasycladales and benthic foraminifers (Climent-Domenech et al., 2009). Therefore, these porocharacean assemblages of the Leza Fm can be considered as further evidence of the influence of marine water during the deposition of this unit.

For this study, we have also re-examined the microfossil content of the Enciso Gr facies in the area surrounding Soto en Cameros, where these facies are laterally changing to those of the Leza Fm (Fig. 3, 8C), and we have found previously unrecorded marine microfossils (dasycladales and foraminifers) in two levels of the Enciso Gr close to Soto en Cameros (Fig. 8C). These microfossils (Fig. 11E, F) are identical to those of the Leza Fm (Figs. 10C, 10G, 11C, D) and, interestingly, they have been found in levels stratigraphically correlatable with the uppermost part of the Leza River section of the Leza Fm (Fig. 9), where marine microfossils are most abundant (Fig. 6).

5. Discussion

5.1. Tectonic control of the Leza Fm and relationships with adjacent units

Sedimentation of the Jubera Fm and the Leza Fm was tectonically controlled, since these units crop out in a series of independent fault-bounded lithosomes with smaller-scale faults that control the thickness of the units (Figs. 3, 4). When the geographic distribution of these lithosomes and the measured thicknesses of the Jubera and Leza Fms are represented together in a correlation panel (Fig. 13) the influence of synsedimentary faults in the distribution and thickness ofboth units is clearly noticeable.

Given the facies associations described in Section 4.2, the Leza Fm can be interpreted as deposited in a system of coastal wetlands mainly formed by shallow carbonate water-bodies separated by flat palustrine areas (Suarez-Gonzalez et al., 2010; 2012; in press). These coastal wetlands were laterally related to the clastic deposits of the Jubera Fm (Fig. 7), attributed to alluvial fans with their main source areas located on the Jurassic carbonate substrate of the basin (Alonso and Mas, 1993). This stratigraphic relationship between alluvial fans and more distal lacustrine, coastal or marine deposits is characteristic of small tectonic depressions (i.e. grabens or halfgrabens) from the active margins of modern and fossil rift basins (Leeder and Gawthorpe, 1987; Gawthorpe et al., 1997; Gawthorpe and Leeder, 2000).

The coastal wetlands of the Leza Fm were related to the south (central area of the Cameros Basin) with deposits of the Enciso Gr (Fig. 8), which have been interpreted as wide fluvial and shallow lacustrine areas with carbonate precipitation and strong siliciclastic influence (AlonzoAzcarate, 1997; Alonso-Azcarate et al., 1999; Doublet et al., 2003; Doublet, 2004), with main paleocurrent directions to the NE (Mas et al., 1993). Thus, the lateral facies change between the Enciso Gr facies and the Leza Fm (Fig. 8) indicates a progradation of the fluvio-lacustrine Enciso Gr over the more distal Leza Fm coastal wetlands.

All these tectonic and stratigraphic data show that the Jubera Fm, the Leza Fm and the Enciso Gr belong to the same depositional sequence. During this sequence, extensional stresses produced fracturing of the Cameros Basin substrate on its northern margin, creating small depressions arranged in a NW-SE distribution. In these depressions, fault-scarps and associated erosion of the fractured substrate generated alluvial fan deposits (Jubera Fm) laterally related with distal coastal wetlands (Leza Fm). In turn, these coastal wetlands passed gradually towards the centre of the basin to a broad fluvio-lacustrine system (Enciso Gr) (Fig. 14).

5.2. Eustatic control of the Leza Fm

Our detailed stratigraphic and sedimentological study of the Leza Fm shows that marine influence during sedimentation of the unit is stronger than previously suggested (Guiraud, 1983; Guiraud and Seguret, 1985; Alonso and Mas, 1993). In fact, the common occurrence of levels with evidences of marine influence and their interfingering with levels that do not contain any of those evidences (Fig. 6) suggests that, during the sedimentation of the Leza Fm, water-bodies with sea-water input coexisted laterally with water-bodies mainly filled with freshwater, as it is typically observed in present-day coastal systems (Gebelein, 1977; Hardie, 1977; Platt and Wright, 1992; Reed, 2002). Furthermore, the main paleontological evidences of marine influence in the Leza Fm carbonates are assemblages of dasycladales and foraminifers with extremely low diversity but high abundance, which is a common situation in stressful environments (Brenchley and Harper, 1998). In the context of the Leza Fm, this biotic stress could have been easily produced by changes in salinity, as it occurs in modern coastal systems, either due to decreasing salinity by mixture of waters, or to increasing salinity by restriction and evaporation (Hardie, 1977; Waterkeyn et al., 2008). These changes in salinity in the Leza Fm are supported by the presence of brackish-water charophytes and pseudomorphs after evaporite minerals.

[FIGURE 10 OMITTED]

Evidences of marine influence are not randomly distributed in the stratigraphic sections of the Leza Fm (Fig. 6). Although some of the sections present different distribution of facies, evidences of marine influence show the same trend in most of them (Fig. 6):

a) The lower part of the sections is dominated by clastic deposits with very little marine influence: some samples rich in porocharaceans, and scattered samples with few foraminifers in the western area.

b) In the middle part of the section, samples with dasycladales start to be very common, alternating with samples containing porocharaceans, samples without marine influence, and less common samples with foraminifers. In the eastern outcrops, facies with tidal influence also start to be abundant at the middle part of the sections.

c) Towards the upper part of the sections, samples with foraminifers start to be more abundant. In the eastern outcrops, facies with tidal influence occur, but evaporitic facies, also containing foraminifers, predominate. Evaporitic facies have not been found in the western outcrops. Moreover, samples without any evidence of marine influence are especially rare in the upper part of the Leza Fm.

This general vertical trend is found in most of the measured stratigraphic sections of the Leza Fm (Fig. 6), which suggests that sedimentation of the unit was somehow controlled by eustasy, showing a transgressive evolution, from: a) a system dominated by alluvial environments and freshwater to brackish carbonate lakes; to b) a system of coastal-lakes and wetlands with clear marine influence (abundance of dasycladales) but with fresh-water influence still noticeable (common presence of charophyterich facies); ending with c) a similar system of coastal wetlands, in which coastal-lakes containing ostracods and foraminifers were more common. In the eastern sector, many of these coastal-lakes were influenced by tides, and others were relatively restricted, allowing precipitation of evaporite minerals, such as gypsum and anhydrite.

5.3. Age of theLezaFm and correlation with marine basins

The new data presented here, concerning marine influence in the Leza Fm and its relationship with Jubera Fm and Enciso Gr can shed light on the controversial age of these units (see Section 2.1). Geological mapping and stratigraphic data show that the Leza Fm is genetically related with the Jubera Fm (Fig. 3, 4, 7), and that it changes laterally to the Enciso Gr (Fig. 8), thus being part of it, as it was originally described by Tischer (1966) and has subsequently been recognized by different authors (see Section 2.1 and Fig. 5). Furthermore, the paleontological data presented here support the assignment of an upper Barremian-lower Aptian age for the Enciso Gr, as proposed by Mas et al. (1993) and Martin-Closas and Alonso (1998), since the dasycladales (Salpingoporella urladansi) found in the Leza Fm and in the Enciso Gr facies have a Barremian-Albian distribution (Carras et al., 2006), and the foraminifers found in both units (cf. Istriloculina) have a Berriasian-Aptian distribution, but are most commonly cited in Barremian-Aptian deposits (Iovcheva, 1962; Neagu, 1984; Bernaus et al., 2002; Masse et al., 2003; 2009). The alternative dating that has been proposed for the Leza Fm considers it as part of the Oncala Gr, Berriasian in age (see Section 2.1 and Fig. 5), but this attribution is not supported by stratigraphic, sedimentological and paleontological results presented herein. Furthermore, detailed sedimentological studies of the Oncala Gr (Quijada et al., 2010; 2013; in press; this volume) clearly show that its facies and sedimentary evolution differ significantly from those observed in the Leza Fm. Therefore, both the Jubera and Leza Fms are part of Depositional Sequence 7 (DS7) of Mas et al. (2002a), upper Barremian-lower Aptian in age (Fig. 2). Given this age and given the transgressive trend described in the Leza Fm (see section 5.2), a higher chronostratigraphic resolution might be obtained for this unit by comparison with eustatic trends of neighbouring marine basins and with global eustatic curves.

[FIGURE 11 OMITTED]

A general trend of rising sea-level is widely recognized from the late Barremian to the early Aptian, resulting in the established view that the early Aptian is an essentially transgressive period (Tyson and Funnell, 1987; Ruffell, 1991; Sahagian et al., 1996; Mutterlose, 1998; Huang et al., 2010). This transgressive trend is also apparent in the marine basins closest to the Cameros Basin: the Basque-Cantabrian Basin (Garcia-Mondejar, 1990; Wilmsen, 2005; Garcia-Mondejar et al., 2009;Najarro et al., 2011); the Iberian Basin (Canerot et al, 1982; Vilas et al, 1983; Soria et al., 1992; Salas and Martin-Closas, 1995; BoverArnal et al., 2003; Moreno-Bedmar et al, 2009; Peropadre, 2012); and the Pyrenean Basin (Peybernes, 1976; Rosell and Llompart, 1982; Garcia-Senz, 2002; Bernaus et al., 2003). The exact chronostratigraphic position of the transgressive-regressive cycles defined in these basins depends on the location, methodology and resolution of the study and, therefore, the age of the maximum peak of late Barremian-early Aptian sea-level differs slightly in some of the aforementioned works on marine basins from northern and eastern Iberia. However, the transgressive peak is, in general, placed at some point of the two middle ammonite biozones of the early Aptian, Deshayesites forbesi (also referred to as D. weissi) and Deshayesites deshayesi biozones (Garcia-Senz, 2002; Bernaus et al., 2003; Bover-Arnal et al., 2003; Willmsen, 2005; Garcia-Mondejar et al., 2009; Moreno-Bedmar et al, 2009; Najarro et al., 2011; Peropadre, 2012). This is consistent with most of the age data for the maximum sea-level during the same period in other Tethyan and North Atlantic basins (Arnaud-Vanneau and Arnaud, 1990; Jacquin et al., 1998 and references therein; Haq and Al-Qahtani, 2005; Bachmann and Hirsch, 2006; Masse and Fenerci Masse, 2011). Therefore, the transgressive peak of the middle-upper part of the early Aptian can be regarded as a widespread eustatic maximum.

[FIGURE 12 OMITTED]

5.4. Eustatic vs. Tectonic control

Rift basins located in coastal or marine settings challenge recognition of the relative roles of tectonics and eustasy in the generation of accommodation space (Lambeck et al., 1987; Ravnas and Steel, 1998; Miall and Miall, 2001; De Benedictis et al., 2007). In the case of the Leza Fm, the role of tectonics is shown by its deposition in a series of small fault-controlled depressions (Figs. 3, 4,13). The amount of accommodation space generated by tectonics was different in each depression, as shown by changes of maximum thicknesses, facies and vertical distribution of facies from one lithosome to the other (Figs. 6, 13). In spite of these changes, the same transgressive trend is observed in sections of all tectonic depressions (Fig. 6, see section 5.2), which points to an additional eustatic control on the sedimentation of the unit.

Faults on the Jurassic substrate of the Cameros Basin created accommodation space, in which a proximal system of alluvial fans and a distal system of coastal wetlands were deposited (Fig. 14). During sedimentation of the lower part of the Leza Fm, clastic facies, dominated by lithoclasts of the Jurassic substrate, were very abundant, indicating that this substrate was being eroded, probably due to active creation of relief by fault movement. In addition, the lower part of the Leza Fm contains very rare evidences of marine influence, which suggests that the wetlands were dominated by fresh-water input. Towards the upper part of the Leza Fm clastic facies are less abundant (Fig. 6). One possible explanation for this is that fault movement was attenuated. However, sections of the Leza Fm located in marginal areas of the lithosomes, such as Clavijo and Luezas sections (Fig. 6), contain very abundant clastic facies even in upper parts of the unit, suggesting that fault-scarps were also being generated and eroded in late stages of sedimentation of the Leza Fm. In addition, evidences of marine influence are progressively more abundant upwards, and Figure 7 shows that while lower levels of the Leza Fm are rapidly changing laterally to the Jubera Fm, the upper levels (those with maximum marine influence, Fig. 6) are much more extensive, reaching even the fluvio-lacustrine sediments of the Enciso Gr (Fig. 8). These data suggest that a rising sea-level during the middle-upper part of the early Aptian created additional accommodation space for the sedimentation of the upper part of the Leza Fm. This allowed the deposits of the unit to spread extensively towards the borders of the tectonic depressions, and even towards the South, to more proximal areas of the Cameros Basin. This provides a suitable hypothesis to the progressive reduction of clastic facies generally observed in the upper part of the Leza.

Therefore, we interpret that the upper part of the Leza Fm, where the strongest marine influence is recorded, might be correlated with the two middle biozones of the early Aptian, in which the transgressive peak is generally found (see section 5.3 above).

5.5. Paleogeographic context of the Leza Fm: the early Aptian of NE Iberia

During the early Aptian, the eastern Cameros Basin had a clear Southwest-Northeast paleogeographical distribution of sedimentary environments (Mas et al., 2011): from siliciclastic fluvial systems on the Southwest (upper-most Urbion Gr, Fig. 2), to mixed siliciclastic-carbonate fluvio-lacustrine plains (Enciso Gr, Fig. 2), and finally to carbonate marine-influenced coastal-wetlands on the Northeast (Leza Fm, Figs. 2, 8). The northeastern-most margin of the basin was marked by fault-scarps on the Jurassic substrate, which was the main source area of a system of alluvial fans (Jubera Fm, Fig. 2) that were laterally related to the coastal-wetlands of the Leza Fm (Fig. 7). Further to the north, outside the Cameros Basin, there was an area of none to very low subsidence, part of the Ebro Massif, with small subsiding depressions interpreted to be associated with the extension of the Cameros Basin (Mas et al., 2002b; 2004). In order to establish the paleogeographic context of the Cameros Basin during this period, Figure 15A presents a new detailed compilation of outcrop and borehole data (see section 3 for bibliographical details) concerning the early Aptian record of sedimentary basins from Northern and Eastern Iberia.

[FIGURE 13 OMITTED]

[FIGURE 14 OMITTED]

The marine influence observed in the Leza Fm has been typically considered as coming from the Iberian Basin, to the SE of the Cameros Basin (Alonso and Mas, 1993; Mas et al, 2004; Suarez-Gonzalez et al., 2010; Mas et al., 2011), due to the Tethyan affinity of Salpingoporella. urladanasi (Carras et al., 2006) and to the fact that the Cameros Basin is part of the Iberian tectonosedimentary rift system (Mas et al., 1993; Guimera et al., 1995; Salas et al., 2001). The northernmost limit of the early Aptian transgression for the Iberian Basin is located just to the Southeast of the Cameros Basin (Fig. 15A), close to the town of Ciria (Soria), in an outcrop of ostreid-rich coastal siliciclastic sediments (Alonso and Mas, 1988; Mas et al., 2011; Sacristan-Horcajada et al., 2012). However, the marine Aptian outcrop closest to the Leza Fm is located at the northeastern margin of the Cameros Basin (Fig. 15A), close to the town of Gravalos (La Rioja), and it is part of the strongly thinned footwall succession of the basin (Mas et al., 2011). This outcrop contains bioclastic limestones with abundant rudists, foraminifers, green and red algae, and echinoderms (Munoz et al., 1997; Arribas et al., 2009; Rodriguez Quiroga, 2011). An early Albian age has been assigned to this Gravalos ouctrop (Munoz et al., 1997) but, according to other interpretations, it is more likely to be early Aptian in age, since it is overlaid by sediments of the upper Aptian-lower Albian depositional sequence (Arribas et al, 2009; Mas et al, 2011; Rodriguez Quiroga, 2011). Therefore, this early Aptian shallow marine area was very likely to be connected to the coastal-wetlands of the Leza Fm (Fig. 15A). The Gravalos ouctrop has been paleogeographically assigned to the northern Basque-Cantabrian Basin (Munoz et al., 1997), but also to the southeastern Iberian Basin (Arribas et al, 2009; Mas et al, 2011; Rodriguez Quiroga, 2011). It is clearly established that the early Aptian transgression coming from the Iberian Basin reached areas located on the SE of the Cameros Basin, such as the Ciria outcrop (Alonso and Mas, 1988) but, since the Gravalos outcrop is approximately equidistant from the Ciria outcrop and from abundant marine facies of the Basque-Cantabrian Basin, a northern source of marine influence should not be ruled out.

[FIGURE 15 OMITTED]

The Basque-Cantabrian Basin shows a very similar distribution of paleoenvironments to that of the Cameros Basin, with continental facies on the Southwest passing to marine facies to the Northeast (Fig. 15A). For the early Aptian, the Cameros Basin and the Basque-Cantabrian Basin were separated by La Demanda Massif (Fig. 15B), which was an emerged land since Kimmeridgian times (Alonso et al., 1986-1987; Benito and Mas, 2006), and by the Ebro Massif, an area with very little subsidence. However, borehole (Fig. 15A) and seismic data show that in this area some scattered tectonic depressions contain Lower Cretaceous sediments (Mas et al., 2002a; 2004), which indicates that rifting activity was not totally absent in the area between both basins. Given these paleogeographic context, and the fact that the NW outcrops of the Leza Fm are very close to abundant early Aptian marine deposits of the Basque-Cantabrian Basin, (Fig. 15A), we propose that, in addition to the clear Iberian affinity of the Cameros Basin, influence of the Basque-Cantabrian marine realm should also be considered for the early Aptian, since the small subsident depressions of the Ebro Massif between both basins might have acted as seaways connecting the Basque-Cantabrian Basin with the Cameros Basin during moments of especially high sea-level, such as the early Aptian (Fig. 15B). This double marine affinity from the northwestern Boreal marine realm and the southwestern Tethyan marine realm is supported by paleontological data, such as the probable presence of Salpingoporella urladanasi in the Basque-Cantabrian Basin (Dragastan, 1982; Pascal, 1984) and in the Iberian Basin (Canerot et al., 1982), and the similarity of shark populations found in the early Aptian of the Cameros Basin with those found in the basins of the Boreal and the Tethyan realms (Bermudez-Rochas, 2009; 2012).

During late Barremian-early Aptian times sedimentation in the northern and eastern margins of the Iberian plate was eminently marine, with reefal carbonate platforms ("Urgonian" platforms) being the most characteristic feature of this period in the Basque-Cantabrian, Pyrenean and Iberian basins. The early Aptian transgressive pulse is marked in these basins by a drowning of the carbonate platforms and the onset of facies of deeper environments, such as dark, ammonite-rich marls (see Berastegui et al., 2002; Mas et al., 2002b; 2004; Rosales et al., 2002; Garcia-Mondejar et al., 2004; Robador and Garcia-Senz, 2004; and references in them). This fact indicates that the early Aptian transgression produced a landwards displacement of the facies belts, allowing that inland areas characterized by broad fluvio-lacustrine plains, such as the Cameros Basin (Enciso Gr), could be locally invaded by seawater, developing coastal-wetlands (Leza Fm). Facies similar to those of the Leza Fm, with coexistence of charophytes and poorly diverse dasycladales and foraminifers (including the two genera found in the Leza Fm, Salpingoporella and Istriloculina) have also been described in the upper Barremian of the Pyrenean Basin (Bernaus et al., 2003) and the Iberian Basin (Albrich et al., 2006; Climent-Domenech et al., 2009), supporting the idea of a landwards migration of facies due to the early Aptian transgression.

The Pyrenean and Iberian basins are separated by the Tertiary Ebro Basin, which is an area interpreted to be a paleogeographic high (the Ebro Massif) during Early Cretaceous times (e.g. Martin-Chivelet, et al., 2002 and references therein). However, three boreholes show Lower Cretaceous rocks below the Tertiary Ebro Basin (Fig. 15A), suggesting that, at least small areas of the Ebro Massif were subsident during periods of the Early Cretaceous. Since emerged areas of the Lower Cretaceous of NE Iberia are believed to have had a low topography, easily flooded during moments of high sea-level (Martin-Chivelet et al., 2002), these small depressions might point to an additional seaway that eventually connected areas of the Pyrenean and the Iberian Basin. This promising hypothesis deserves further research.

Although the Cameros Basin is tectonically related to the Iberian Basin, various facts suggest that a paleogeographic connection with the Basque-Cantabrian Basin, at least ephemeral or instable, should not be discarded for the transgressive peak of the middle-upper part of the early Aptian (Fig. 15B). Therefore, here we propose that during that period the northern margin of the Cameros Basin was configured as a coastal rift basin gulf (sensu Gawthorpe and Leeder, 2000) because sedimentation in it was controlled by rifting fractures but also by rising sea level. This area had a probable paleogeography similar to a narrow seaway partially connecting the Tethys realm (Iberian Basin) to the Boreal realm (Basque-Cantabrian Basin) during the early Aptian (Fig. 15B), as it did during other periods of very high sea-level, such as the Aalenian (Garcia-Frank et al., 2008), the Kimmeridgian (Benito et al., 2005), or the Cenomanian-Turonian (Alonso et al., 1993; Segura et al., 2004).

6. Conclusions

The Leza Fm is a carbonate unit from the northern Cameros Basin. This unit was deposited in a series of fault-bounded tectonic depressions distributed along the northern margin of the basin. The Leza Fm changes laterally to the underlying Jubera Fm, mainly composed by conglomerates formed in alluvial fans. The thickness of both units is also controlled by faults. These facts point to tectonics as the main factor generating accommodation space for both units. To the South, towards the centre of the Cameros Basin, the Leza Fm changes laterally to mixed carbonate-siliciclastic deposits of the Enciso Gr deposited in fluvio-lacustrine environments.

Detailed sedimentological analysis shows that the Leza Fm had significant marine influence during its sedimentation, especially in the middle and upper part of the unit. This is indicated by sedimentary structures of tidal origin, and very common marine microfossils, such as dasycladales (Salpingoporella urladanasi) and miliolid foraminifers (cf. Istriloculina), as well as homogeneous populations of porocharacean charophytes, which indicate brackish conditions. Thus, the Leza Fm is interpreted as deposited in a carbonate system of coastal-wetlands, with variable influence of alluvial clastic deposits.

New biostratigraphic and sedimentological data confirm that the Leza Fm, the Jubera Fm and the Enciso Gr belong to the same depositional sequence, upper Barremian --lower Aptian in age. This dating is further refined by comparison of the sedimentological evolution of the Leza Fm with the eustatic evolution of neighbouring marine basins. A transgressive trend is observed in all the lithosomes of the Leza Fm, towards the upper part of the unit. Therefore, the upper part of the Leza Fm can be correlated with the highest sea-level peak of the late Barremian-early Aptian period, which is widely observed in the middle-upper part of the early Aptian. When this early Aptian transgression reached the northern margin of the Cameros Basin, eustatic accommodation space was generated, in addition to the accomodation space created by tectonics.

An extensive compilation of paleogeographic data shows that this early Aptian transgression probably reached the northern Cameros Basin both from the Iberian Basin to the SE and from the Basque-Cantabrian Basin on the NW. The early Aptian paleogeography of NE Iberian plate was therefore dominated by low and flat areas with some subsiding zones that allowed the transgression to reach the Cameros Basin, located in a central part of the plate. During this period the northern Cameros Basin was similar to a coastal rift basin gulf that probably linked the Boreal and the Tethyan realms.

APPENDIX

Sheets of the Geological Map of Spain (MAGNA series) used for the compilation of paleogeographic data of the early Aptian.

013 - Aviles

014 - Gijon

015 - Lastres

028 - Grado

029 - Oviedo

030 - Villaviciosa

031 - Ribadesella

032 - Llanes

033 - Comillas

034 - Torrelavega

035 - Santander

036 - Castro Urdiales

037 - Algorta

038 - Bermeo

039 - Lequeitio

052 - Proaza

053 - Mieres

056 - Carrena-Cabrales

057 - Cabezon de la Sal

058 - Los Corrales de Buelna

059 - Villacarriedo

060 - Valmaseda

061 - Bilbao

062 - Durango

063 - Eibar

064 - San Sebastian

065 - Vera de Bidasoa

082 - Tudanca

083 - Reinosa

084 - Espinosa de los Monteros

085 - Villasana de Mena

086 - Landaco

087 - Elorrio

088 - Vergara

089 - Tolosa

090 - Sumbilla

107 - Barruelo de Santullan

108 - Las Rozas

109 - Villarcayo

110 - Medina de Pomar

111 - Orduna

112 - Vitoria

113 - Salvatierra

114 - Alsasua

115 - Gulina

133 - Pradanos de Ojeda

134 - Polientes

135 - Sedano

136 - Ona

137 - Miranda de Ebro

138 - La Puebla de Arganzon

139 - Eulate

140 - Estella

144 - Anso

166 - Villadiego

167 - Montorio

169 - Casalarreina

170 - Haro

200 - Burgos

201 - Belorado

202 - Santo Domingo de la Calzada

203 - Najera

204 - Logrono

213 - Pont de Suert

238 - Villagonzalo-Pedernales

239 - Pradoluengo

241 - Anguiano

242 - Munilla

243 - Calahorra

252 - Tremp

255 - La Pobla de Lillet

258 - Figueres

276 - Lerma

277 - Salas de los Infantes

278 - Canales de la Sierra

279 - Villoslada de Cameros

280 - Enciso

281 - Cervera del Rio Alhama

296 - Torroella de Montgri

297 - L'Estartit

314 - Cilleruelo de Abajo

315 - Santo Domingo de Silos

316 - Quintanar de la Sierra

317 - Vinuesa

318 - Almarza

319 - Agreda

320 - Tarazona

348 - San Leonardo de Yague

349 - Cabrejas del Pinar

350 - Soria

351 - Olvega

353 - Pedrola

380 - Borobia

381 - Illueca

382 - Epila

383 - Zaragoza

409 - Calatayud

410 - La Almunia de Da Godina

411 - Longares

412 - Pina de Ebro

419 - Villafranca del Panades

420 - Hospitalet de Llobregat

439 - Azuara

440 - Belchite

446 - Valls

447 - Villanueva y Geltru

448 - Prat de Llobregat

466 - Moyuela

467 - Muniesa

468 - Albalate del Arzobispo

470 - Gandesa

471 - Mora de Ebro

472 - Reus

473 - Tarragona

492 - Segura de los Banos

493 - Oliete

494 - Calanda

495 - Castelseras

496 - Horta de San Juan

497 - Perrello

498 - Hospitalet del Infante

515 - El Pobo de Duenas

516 - Monreal del Campo

517 - Argente

518 - Montalban

519 - Aguaviva

520 - Penarroya de Tastavins

521 - Beceite

522 - Tortosa

541 - Santa Eulalia

542 - Alfambra

543 - Villarluengo

544 - Forcall

545 - Morella

546 - Ulldecona

547 - Alcanar

564 - Fuertescusa

565 - Tragacete

566 - Cella

567 - Teruel

568 - Alcala de la Selva

569 - Mosqueruela

570 - Albocacer

571 - Vinaroz

587 - Las Majadas

588 - Zafrilla

589 - Terriente

590 - La Puebla de Valverde

591 - Mora de Rubielos

592 - Villahermosa del Rio

593 - Cuevas de Vinroma

594 - Alcala de Chivert

610 - Cuenca

611 - Canete

612 - Ademuz

613 - Camarena de la Sierra

614 - Manzanera

615 - Alcora

616 - Villafames

617 - Faro de Oropesa

634 - San Lorenzo de la Parrilla

635 - Fuentes

636 - Villar del Humo

637 - Landete

638 - Alpuente

640 - Segorbe

641 - Castellon de la Plana

664 - Enguidanos

663 - Valera de Abajo

665 - Mira

666 - Chelva

667 - Villar del Arzobispo

691 - Motilla del Palancar

692 - Campillo Altobuey

693 - Utiel

694 - Chulilla

695 - Liria

719 - Venta del Moro

720 - Requena

721 - Cheste

722 - Valencia

745 - Jalance

746 - Llombay (ojo, repetido)

747 - Sueca

766 - Valdeganga

767 - Carcelen

768 - Ayora

769 - Navarres

770 - Alcira-Lavisa

791 - Chinchilla de Monte Aragon

792 - Alpera

793 - Almansa

794 - Canals

795 - Jativa

796 - Gandia

817 - Pozo Canada

818 - Montealegre del Castillo

819 - Caudete

820 - Onteniente

821 - Alcoy

822 - Benissa

823 - Javea

844 - Ontur

845 - Yecla

846 - Castalla

847 - Villajoyosa

848 - Altea

870 - Pinoso

871 - Elda

872 - Alicante

892 - Fortuna

893 - Elche

http://dx.doi.org/10.5209/rev_JIGE.2013.v39.n2.42502

Acknowledgements

This study was funded by the Spanish DIGICYT Project CGL2011-22709, by the research group "Sedimentary Basin Analysis" UCM-CM 910429 of the Complutense University of Madrid and by a FPU scholarship of the Spanish Department of Education. Esmeralda Caus, Marc Conrad, Nicolaos Carras and Ioan Bucur provided paleontological classifications and advices that have been extremely useful for our study. We thank Beatriz Moral, Gilberto Herrero and Juan Carlos Salamanca for preparing the thin sections; Modesto Escudero for his constant help with the computer, the printer and the scanner; Laura Donadeo for providing many of the references used; and Valle Lopez for support with ArcGIS. The manuscript was improved by comments of reviewers Gilbert Camoin and Carles Martin-Closas, who was also very helpful with the study of charophytes. We are also grateful to Jose Lopez-Gomez and Javier Martin-Chivelet for their support during the editorial process. We thank Andrea Baza for helping to stain the thin sections, Silvia Omodeo for field-work support, and Belen Galan for field-work support and crucial help with the figures and references of the manuscript.

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P. Suarez-Gonzalez (1,2) *, I. E. Quijada (1,2), M. I. Benito (1,2), R. Mas (1,2)

(1) Departamento de Estratigrafia, Fac. Ciencias Geologicas, Universidad Complutense de Madrid, 28040 Madrid, Spain

(2) Instituto de Geociencias IGEO (CSIC, UCM), C/ Jose Antonio Novais 12, 28040 Madrid, Spain pablosuarez@geo.ucm.es; equijada@geo.ucm.es; maribel@geo.ucm.es; ramonmas@geo.ucm.es

* corresponding author

Received: 20/04/2013 / Accepted: 10/07/2013
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Title Annotation:texto en ingles
Author:Suarez-Gonzalez, P.; Quijada, I.E.; Benito, M.I.; Mas, R.
Publication:Journal of Iberian Geology
Date:Jul 1, 2013
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