INTRODUCTION

Lower Cretaceous Urgonian-type shallow-water limestones are widespread in the North Cantabrian Basin of northern Spain (Najarro, 2015, and references therein). As in other regions, e.g. southern France (Arnaud- Vanneau, 1980), these north Iberian platform carbonates contain rich assemblages of benthic foraminifera including taxa that have their type-locality in this basin (Delmas and Deloffre, 1961; Ramírez del Pozo, 1971) or in neighboring basins (Ciry and Rat, 1952; Deloffre, 1961; Schroeder and Poignant, 1964; Moullade and Peybernès, 1978). Thin-section analysis of Aptian–Albian limestones have yielded a new benthic foraminifer, Glomospirella cantabrica n. sp., identfied in the upper Aptian Reocín Formation and in one locality of the lower Albian Las Peñosas Formation. The paper furthermore focuses on the implications of other benthic foraminifera, e.g. orbitolinids, in the biostratigraphy of the Cantabrian Urgo–Aptian, and Albian pro parte. Last but not least, the poorly diversi ed dasycladalean algal assemblage in these deposits is stressed and documented. The resulting stratigraphic and biostratigraphic scheme allows establishing correlations with coeval carbonate systems of the Basque-Cantabrian Basin and the Iberian Chain, as well as with the global sea-level changes.

GEOLOGICAL SETTING

The studied Aptian–Albian sections are located in the North Cantabrian Basin (NCB) (Fig. 1), which constitutes the northwestern margin of the Basque-Cantabrian Basin. The NCB was generated by rifting tectonics linked to the opening of the Bay of Biscay and North Atlantic during the Late Jurassic and Early Cretaceous (e.g.Le Pichon and Sibuet, 1971; Malod and Mauffret, 1990). During the Early Cretaceous the NCB underwent strong structural segmentation in a series of horsts and tilted blocks, mainly outlined by N017, N060 and E−W oriented faults (Najarro, 2015). These faults controlled differential subsidence and variations in facies, thicknesses and stratigraphy over short distances at least during Hauterivian–Albian times (Figs. 2; 3).

The Aptian–Albian succession of the NCB was initially studied by Mengaud (1920) who established a rst stratigraphic and biostratigraphic scheme of the Aptian. Later, Rat (1959), Ramírez del Pozo (1972), Collignon et al. (1979), García-Mondéjar (1982), Pascal (1985), Hines (1985) and Wilmsen (2000, 2005) contributed to clarify the general lithostratigraphic framework of the Aptian to Cenomanian. Recently, the depositional sequences of this time interval have been reviewed, new lithostratigraphic units have been established and previous stratigraphic schemes and biostratigraphic data have been updated (Najarro et al., 2011; Najarro, 2015; Rosales and Schlagintweit, 2015).

The Aptian–Albian succession of the NCB is composed of nine formations (Hines, 1985; Najarro et al., 2011; Najarro, 2015). From oldest to youngest, they are (Figs. 2A, 3): i) Rábago Formation (0–36m thick, lowermost lower Aptian), which consists of heterolithic sediments deposited in a mixed shallow platform; ii) Umbrera Formation (0–25m thick, lowermost Aptian), which consists of skeletal-oolitic grainstones deposited in shoal complexes in a high- energy carbonate ramp; iii) Patrocinio Formation (0–80m thick, lower Aptian Deshayesites forbesi zone, Najarro et al., 2011), which consists of marls, lutites and minor sandstones deposited in offshore to delta front environments; iv) San Esteban Formation (0–55m thick; upper lower Aptian), which consists of rudist limestones deposited in a shallow inner platform; v) Rodezas Formation (0–105m thick, lowermost upper Aptian), which consists of coral limestones, marly limestones, marls, sandstones and siltstones deposited in environments ranging from open sea to shoreface; vi) Reocín Formation (9–300m thick, upper Aptian), which consists of rudist limestones and skeletal-foraminiferal packstone and grainstones deposited in shallow inner platform to platform margin environments; vii) Las Peñosas Formation (0–200m thick, lower–middle Albian), which consists of coal shales, siltstones and sandstones deposited in deltaic to estuarine environments; viii) Barcenaciones Formation (13–65m thick, middle–upper Albian), which consists mainly of grainstones and Caprina limestones deposited in middle to outer platform environments; and finally ix) Bielba Formation p.p. (Somocuevas Member, ca. 128m thick, uppermost Albian, Rosales and Schlagintweit, 2015), which consists of siltstones and sandstones deposited in environments ranging from deltaic-estuarine to shoreface and offshore marine.

The Reocín Formation was formally named by García-Mondéjar (1982), and is equivalent to the “barre urgonienne supérieure” of Collignon et al. (1979), the “seconde masse urgonienne” of Rat (1959) and the level C₁₅²³ of the Magna series of the Spanish Geological Map (Ramírez del Pozo et al., 1974; Portero- García et al., 1976). Recent detailed stratigraphic information on depositional facies and sequences of the Reocín Formation was provided by Najarro et al. (2007), Blázquez-Fernández et al. (2014), Fernández- Mendiola et al. (2015) and Najarro (2015). A summary of the general vertical and lateral facies distribution and lateral changes of sedimentary thicknesses of the Reocín Formation (and other units) is represented in Figure 3. This figure provides a basin-wide cross-section based on the correlation of the sections that yielded Glomospirella cantabrica n. sp., selected from 12 measured sections located in Figure 1. Depositional environments of the Reocín Formation range from outer platform, transition between the outer and the inner platform, marginal shoals and tidal bars, inner open platform, and inner restricted platform (Najarro et al., 2007; Blázquez-Fernández et al., 2014). The Reocín Formation can be divided into two main depositional sequences separated by an unconformity with local subaerial exposure, followed by a widespread transgressive marly bed (Najarro et al., 2007; Blázquez-Fernández et al., 2014; Najarro, 2015).

This transgressive bed can be correlated over tens of kilometres across the basin (Fig. 3). The rst sequence ranges from 8m (Cuchía coast section, Fig. 3) to 100m thick (Novales section, Fig. 3), and it is characterized by the stacking of rudist-bearing lithofacies. It is accompanied by boundstone- oatstone-rudstone of bacinellid fabrics forming thrombolithic masses and oncoids, and by cross- bedded grainstones. These were deposited mainly in inner restricted platform to lagoonal environments with local development of sand shoals and tidal channels/bars. This sequence is commonly dolomitized (López-Cilla et al., 2012). The second sequence ranges from 3m (Cuchía coast section, Fig. 3) to ca. 114m thick (e.g. Novales section, Fig. 3) and it is characterized by the development of coral-bearing lithofacies, foraminiferal limestones and bacinellid fabrics with lumps and oncoids. These are interpreted to be deposited in open platform environments with poor development of rudist-bearing lithofacies. A major sea-level fall on top of the Reocín Formation exposed the platform subaerially. The sedimentation continued during the early Albian with a deltaic-estuarine system (Las Peñosas Formation) in lling a kilometric- wide incised valley (Najarro, 2015) (Fig. 3).

MATERIAL AND METHODS

In this study more than 250 thin sections from 12 stratigraphic sections logged along the NCB have been investigated. The geographic location, stratigraphy, thicknesses and previous studies of each section are summarized in Figure 1 and Table I. This study is focussed on the Reocín Formation but limestone samples from the Rábago, San Esteban, Rodezas and Las Peñosas formations were studied in addition.

The thin sections are housed in the Museo Geominero of the Instituto Geológico y Minero de España, Madrid, under the numbers MGM-10847C-1 to -10888C-1. Each figure is assigned an individual number, and the original sample designation is added in brackets after the official museum number. For the sample localities were used the following acronyms (in alphabetical order): BU (Bustriguado section), CCU (Cantera de Cuchía section), CU and PH (Cuchía coast section), CL (Cantera de Las Lastrías section), SOP (El Soplao section), No- and NO (Novales section), LA (Rábago section), PN (Río Nansa section), Ru (Ruilobuca section), SV (San Vicente de la Barquera section), SE2 (Santa Eulalia section), SU (Suances section).

In the present paper, we refer to the Aptian including the Bedoulian as a substage (=lower Aptian, e.g. Reboulet et al., 2014). We note that there is also a new concept retaining the Bedoulian sensu nuovo as an individual stage between the Barremian and the Aptian sensu stricto (Moullade et al., 2011). In the latter concept, the Aptian sensu nuovo is de ned at its base (Bedoulian-Aptian boundary) with the First Appearance Datum (FAD) of the ammonoid genus Dufrenoya (D. furcata zone) and at its top (Aptian-Albian boundary) with the FAD of Hypacanthoplites (H. jacobi zone).

DESCRIPTION OF THE STRATIGRAPHIC SECTIONS

The samples that have yielded Glomospirella cantabrica n. sp., and associated foraminifera, are from six stratigraphic sections (Fig. 3, see location in Table I and Fig. 1):

1. i) Río Nansa section. It is exposed ca. 0.7km northwest of the Rábago village, at the cut of the road CA-181 from Muñorrodero to Puentenansa, along the Nansa River. Its stratigraphy and micropaleontological content have been investigated by Ramírez del Pozo (1972), Najarro et al. (2011) and Rosales et al. (2013). In this section the Rábago Formation rests unconformably on Triassic red beds (Buntsandstein facies). The section comprises successively (Fig. 3): the Rábago Formation (ca. 16m), the Patrocinio Formation (ca. 30m), the Reocín Formation (ca. 70m, the rst 20m are dolomitized), the Las Peñosas Formation (ca. 60m), the Barcenaciones Formation (ca. 55m) and the base of the Bielba Formation. There are major unconformities on top of the Rábago and Patrocinio formations, with absence of the Umbrera, San Esteban and Rodezas formations (Figs. 2A; 3).

2. ii) El Soplao section. The section is exposed ca. 4.8km east of the Rábago village. The base is exposed around the entry to the El Soplao cave and the section continues along the road of access to the El Soplao cave from the Rábago village. The ca. 220-m-thick section comprises the Rábago Formation (ca. 8m) resting unconformably on a few meters of lowermost Cretaceous continental red beds (Wealden facies), followed by the Umbrera Formation (ca. 6m), the Patrocinio Formation (ca. 27m), and a limestone-dolostone lithosome ca. 115m thick. The first 15m of this lithosome are constituted by nodular and decimetric-bedded wackestone with requieniids and Orbitolinopsis? simplex (henson) (Rosales et al., 2013), indicating that in this section the basal portion of the lithosome is still lower Aptian (Bedoulian) in age and coeval with the San Esteban Formation (Fig. 3). These basal limestones rapidly pinch-out to the west, being absent in the Rábago section, located 2km to the west. The overlaying ca. 100m correspond to the Reocín Formation, with the rst ca. 35m dolomitized and with silty marls, marly limestones, grainstones and coral-rudist limestones in the upper part. Here, the Rodezas Formation is also absent (Figs. 2A; 3). Finally, the section culminates with ca. 60m of marly limestones with oysters, siltstones and sandstones of the lower part of the Las Peñosas Formation.

3. iii) Novales section. The section is exposed ca. 11 km west of the Comillas town, in the cut of the road CA-353 from Novales to Barrio Cerrazo. The ca. 300-m-thick section comprises the Reocín Formation (ca. 230m thick) and the lower part of the Las Peñosas Formation (ca. 70m thick). The rst 160m of the Reocín Formation exhibit pervasive dolomitization hosting Pb-Zn ore mines. The upper 70m of the section has yielded abundant specimens of Glomospirella cantabrica n. sp., and the holotype specimen is from sample No-14, located in the midpart of the upper undolomitized interval.

4. iv) Cantera de Las Lastrías section. The section is exposed ca. 11km west of Torrelavega, in the quarry of Las Lastrías in the San Esteban town (Fig. 2B). The section exhibits in its base ( rst 7m) the transition between the Rodezas and Reocín formations, followed by 130m of limestones of the Reocín Formation. The upper part of the section shows an unconformity on top of the Reocín Formation, followed by red-green claystones with paleosoils of the Las Peñosas Formation (Fig. 2B).

5. v) Cantera de Cuchía section. The section is exposed ca. 17km to the North of Torrelavega along the cuts of the Cuchía quarry (Fig. 2C). Limestones cropping out in this section were previously investigated for the foraminiferal content by Collignon et al. (1979), who already attributed them to the Upper Aptian. The stratigraphy of the section has been later described by Najarro (2015) and Fernández- Mendiola et al. (2015). The ca. 120-m-thick succession exposed in the Cuchía quarry commences with the Reocín Formation (ca. 80m thick) that is directly overlain by the Barcenaciones Formation (ca. 26m thick). In this section, both, the base of the Reocín Formation and the Rodezas Formation (if present) are covered. In addition, the Las Peñosas Formation is absent (Fig. 2A, C), and the contact between the Reocín Formation (upper Aptian) and the Barcenaciones Formation (middle–upper Albian) is represented by an unconformity (Fig. 2C) with features of subaerial exposure and paleokarst development (Najarro, 2015). The overlying Barcenaciones Formation consists of cross-bedded grainstones rich in Involutina hugarica (sido) and packstone-wackestone with rudist-coral bioherms rich in Caprina choffatidouvillé toward the upper part (Najarro, 2015). In this section, the Barcenaciones Formation shows in its lower part two internal unconformities with features of subaerial exposure, brecciation and/or dissolution, and a nal subaerial exposure surface with truncation of strata, paleokarst and bioturbation at the top of the unit, in the contact between the Barcenaciones and the Bielba formations (Fig. 3).

6. vi) Cuchía coast section. This section is located ca. 17km to the north of Torrelavega and 1km to the north of the Cantera de Cuchía section. It was previously studied by Mengaud (1920) and Collignon et al. (1979). Recently, the ammonite fauna of the Patrocinio Formation of this section has been re-studied by Najarro et al. (2011) and García-Mondéjar et al. (2015), and the stratigraphy has been described in Wilmsen (2005), Najarro (2015) and García-Mondéjar et al. (2015). The ca. 160-m-thick section shows an almost continuous exposure of the Hauterivian- Barremian (Wealden) to upper Albian succession (Fig. 3) along the coastal cliffs from Punta del Cuerno to Playa de Cuchía or Playa de Marzán, only interrupted by several normal faults of some few meters of displacement. The base of the section (Punta del Cuerno) shows an erosive unconformity at the contact between the Wealden deposits and the lowermost Aptian Umbrera Formation (ca. 22m thick). In this section the Rábago Formation is missing (Fig. 3). The succession continues with marls, siltstones and sandstones of the Patrocinio Formation (ca. 80m thick) cropping out along the cliff of Playa de los Caballos beach. It is overlain by limestones of the San Esteban Formation, which crop out along the cliff from Playa de los Caballos to Punta de Afuera. The top of the San Esteban Formation at the Punta de Afuera site displays a major unconformity of subaerial exposure with paleokarst depressions lled with limestone breccias containing black pebbles. It is overlain by ca. 1.5m of silty marls and marly limestones with brachiopods and branching corals, which correspond to a reduced equivalent to the Rodezas Formation (Fig. 3). The succession follows with an also very-reduced (ca. 11m thick) Reocín Formation. The contact between the reduced Rodezas Formation and the Reocín Formation is disrupted by a local fault. The Reocín Formation crops out along the cliffs from Punta de Afuera to Playa del Huevo. It consists mainly of rudstone of oncoidal bacinellid fabrics and is capped by a paleokarst surface (Fig. 3) (Najarro, 2015). The succession follows with the Barcenaciones Formation cropping out from Playa del Huevo to Playa de Cuchía or Playa de Marzán. The Barcenaciones Formation (ca. 18m) consists successively of nodular-bioturbated limestones, minor sandstones, cross-bedded grainstones with Involutina hungarica (sido), and nally rudist-coral limestones with abundant sections of the upper Albian rudist Caprina choffatidouvillé, already reported by Rat (1959). The upper contact of the Barcenaciones Formation with the Bielba Formation, cropping out at Playa de Marzán, is truncated by fault.

SYSTEMATIC PALAEONTOLOGY

The high-rank classi cation follows Pawlowski et al. (2013), the low-rank classi cation Kaminski (2014).

Phylum: Foraminiferida d’orbigny, 1826

Class: Tubothalamea pawlowskiet al., 2013

Order: Ammodiscida mikhalevich, 1980

Family: Ammodiscidae reuss, 1862

GENUS Glomospirella plummer, 1945

Type-species: Glomospirella umbilicata cushman and waters, 1927

Glomospirella cantabrica n. sp. (Fig. 4A–R)

?1961 Glomospirella sp. – deloffre: p. 107, not figured.

?1982 Glomospirella sp. – cherchi and schroeder: p. 155, not figured.

1987 Glomospirella sp. – reitnner: Pl. 2, g. 6.

Origin of the name. The species is named after the autonomous community of Cantabria in northern Spain.

Type material. The holotype specimen is a partly broken equatorial section with repository number MGM-10847C-1 (No 14) (Fig. 4K), coming from the Novales section (Fig. 3). Seventeen paratypes are designed with the repository numbers: MGM-10853C-1 (Fig. 4A), -10863C-1 (Fig. 4B), -10848C-1 (Fig. 4C), -10855C-1 (Fig. 4D), -10853C-2 (Fig. 4E), -10847C-1 (Fig. 4F), -10847C-2 (Fig. 4G), -10847C-3 (Fig. 4H), -10862C-1 (Fig. 4I), -10862C-2 (Fig. 4J), -10880C-1 (Fig. 4L), -10865C-1 (Fig. 4M), -10887C-1 (Fig. 4N), -10881C-1 (Fig. 4O), -10866C-1 (Fig. 4P), -10854C-1 (Fig. 4Q), -10854C-2 (Fig. 4R).

Diagnosis. Medium-sized discoidal representative of Glomospirella. Early part tightly twisted in a glomospiral manner upon a plane with intercalated planispiral whorls. The adult part is irregularly planispiral, composed of up to eight whorls, the rst two of them sometimes with coiling planes perpendicular to the next whorls. The diameter of the tubular chamber is increasing slightly in the early part, becoming larger in the planispiral part where its diameter remains more or less constant. Chamber wall dark, homogeneous, nely agglutinated. Aperture simple and terminal.

Description. Test discoidal (diameter up to 0.65mm) with a globular central elevation corresponding to the irregularly coiled early part. The type of coiling of the earliest part (directly following the proloculus) is unknown. Later the undivided tubular second chamber is tightly twisted in a glomospiral manner upon a plane, occasionally with intercalated individual planspiral whorls (Fig. 4J). This early stage may be composed of up to ve whorls. In the holotype specimen there are up to ten twisting folds within a glomospirally coiled whorl (Fig. 4K, highlighted in colour). In this part, the diameter of the tubular chamber increases slowly but continuously.

The final part eventually becomes completely planispirally coiled, although slightly oscillating with up to eight whorls. In some specimens, the rst two planispiral whorls exhibit a varying coiling plane, perpendicular to the nal ones. In the holotype specimen the planispiral nal part amounts for more than 2/3 of the total test diameter. The diameter of the tubular chamber is larger than in the early growth part and remains almost constant in width (about 40μm). The wall appears dark, micritic, homogeneous, nely agglutinated. Aperture simple and terminal.

Remarks.Glomospira has been a basket for all tubular, irregularly coiled, subglobular, finely agglutinating foraminifera. Refining differences in the coiling mode, some species were taxonomically revised. For example, Glomospira glomeratahöglund, which was choosen as the type-species of Arenomeandrospira by Jones and Wonders (2000), is characterized by a meandrospiral coiling of the tubular chamber in tight folds displaying subparallel axes. The genus Glomospira itself has been emended by Kaminski and Gradstein (2005), defining the coiling initially as a high trochospire about a common axis, later becoming glomospirally coiled. In contrast, Glomospirella was defined as a Glomospira with a final planispirally coiled part (e.g.Loeblich and Tappan, 1987, p. 51). The specimens studied, however, do not allow specifying the coiling mode previous to the glomospiral part.

It is worth mentioning that Glomospirella was regarded as a junior synonym of Glomospira by Charnock and Jones (1990; p. 156), more precisely as a Glomospira species that “tend to become planispiral in later stages”. However, this view was not followed by most workers and Glomospirella plummer was kept as valid genus in the new classi cation of agglutinated foraminifera provided by Kaminski (2014) and in the World Foraminifera Database (Hayward and Pignatti, 2015).

Glomospirella cantabrica was most likely observed by Deloffre (1961) and Cherchi and Schroeder (1982) in upper Aptian strata containing Pseudochoffatella cuvillieri from the Pyrenean area. Both authors indicate the presence of Glomospirella sp. in their material (see synonymy).

Comparisons. The widespread Glomospirella gaultiana (berthelin) is a typical outer-shelf to abyssal plain dwelling “flysch-type” taxon occurring in marly lithologies yielding isolated specimens (e.g. Kaminski et al., 1992; Koutsoukos, 2000; Galeotti et al., 2004; Moullade et al., 2008). Accordingly, this species has a long stratigraphic range from the late Aptian to at least the Paleocene-Eocene transition (see Galeotti et al., 2004). Apart from different specific paleoenvironmental requirements, G. gaultiana differs from G. cantabrica by its smaller size (~0.3mm in the Albian and up to 0.73mm in the lower Maastrichtian according to Koutsoukos, 2000), greater diameter of tubular chamber and its prominent streptospiral stage with only one to two planispiral whorls (see Fig. 4T). Moreover, G. gaultiana does not display individual planispiral coiled whorls intercalated in the early glomospiral stage as in Glomospirella cantabrica.

General morphological similarities exist also with Glomospirella sp. illustrated by Setoyama et al. (2011: pl. 2, g. 18) from the Late Cretaceous Kveite Formation of the Barents Sea (Fig. 4S), are typically deep-water forms like other Cretaceous representatives of Glomospirella (e.g. Grzybowski, 1898; Setoyama et al., 2011).

Microfacies and associated microfauna and microflora.Glomospirella cantabrica occurs generally in foraminifer-rich wackestones to packstones that can be referred to as an internal platform lagoonal facies (Reocín Formation). One ocurrence is found in a packstone bed interbedded with siliciclastic materials referred to as estuarine facies of the Las Peñosas Formation. The foraminifera associated with G. cantabrica will be discussed in the next chapter. Additionally, G. cantabrica is occasionally associated with dasycladalean green algae in the Reocín Formation such as Terquemella sp. (rare spicules), Cylindroporella? pedunculata (jaffrezo, poisson and akbulut) (Fig. 5C), Salpingoporella hasi conrad, radoiČIĆ and rey (Fig. 5D), and Genotella pfenderae (konishi and epis) (Fig. 5E). The occurrence of Salpingoporella melitae radoiČIĆ in the Novales section is worth mentioning (Fig. 5F), since it was so far reported only from the upper Hauterivian to the lower Aptian (Carras et al., 2006, Table 1). In consequence, the chronostratigraphic range of this species should be extended until the late Gargasian or even the Clansayesian.

Not associated with G. cantabrica, we note the occurrence of Neomeris cf. cretaceasteinmann in the Rábago Formation (Bustriguado section) (Fig. 5A), and Montiella elitzae (bakalova) in the San Esteban Formation (Ruilobuca section) (Fig. 5B).

Chronostratigraphy. The stratigraphic range of Glomospirella is indicated by Kaminski et al. (2008) as Lower Silurian (Llandovery) to Miocene obviously excluding the Recent Glomospirella fijiensis reported from very shallow environments of brackish mangrove-mudflats (Brönnimann et al., 1992; Berkeley et al., 2009). Glomospirella cantabrica, of Aptian to lower Albian age, does not show a definite distribution within the Reocín Formation. Details on the biostratigraphy of the Reocín Formation based on benthic foraminifera are discussed in the following chapter.

Biostratigraphic remarks on some other benthic foraminifera

Some of the benthic foraminifera co-occurring with Glomospirella cantabrica in the studied sections of the Reocín Formation are of biostratigraphic relevance; some are reported for the rst time from the late Aptian, and others for the rst time from this region. These taxa and some others are commented in the following subsection, supplemented also with some species observed in the underlying Rodezas and San Esteban and overlying Las Peñosas formations (Figs. 6–8). For the occurrences of individual taxa in the different formations see Table 1. A taxonomical revision of some of the taxa is beyond the scope of the present contribution.

Order: Lituolida lankester, 1885

Family: Nautiloculinidae loeblich and tappan, 1985

GENUS Nautiloculinamohler, 1938

Nautiloculina cretaceapeybernès, 1976 (Fig. 6A–B)

N. cretacea was described by Peybernès (1976) from the Hauterivian Organyà section of the Spanish Pyrenees. The genus Nautiloculina with its two Lower Cretaceous representatives N. cretacea and N. broennimanni, was revised by Arnaud-Vanneau and Peybernès (1978). Concerning N. cretacea they concluded (op. cit., p. 67) that “it does not seem to exist beyond the upper Bedoulian”, referring to its occurrence in southern France. The last occurrence of the genus in the Bedoulian was also included in the monograph of Loeblich and Tappan (1987). However, shallow-water conditions ended in the Urgonian type-region in the upper part of the Desayesites forbesi ammonite zone (=D. weissi, early Bedoulian) (Clavel et al., 2013) so that the last appearance of this species in France is not necessarily coeval with the latest appearances of certain benthic foraminifera such as N. cretacea, Glomospira urgonianaarnaud-vanneau or Dobrogelina? carthusiana arnaud-vanneau, which were all observed in the upper Aptian Reocín Formation. Accordingly, the ranges of these taxa should be extended to the late Aptian. N. cretacea was already reported by Granier (1987) from the upper Aptian to lower Albian of the Prebetic zone.

Order: Loftusiida kaminski et mikhalevich in Kaminski, 2004

Family: Cuneolinidae saidova, 1981

GENUS Cuneolinad’orbigny, 1839

Cuneolina cf. parvahenson, 1948a (Fig. 6C–D)

According to Arnaud-Vanneau and Sliter (1995) the chronostratigraphic range of C. parva is Albian to Cenomanian, ?Santonian. Besides its occurrence in the Reocín Formation (and the overlying lower Albian Las Peñosas Formation), there are also other records of Cuneolina parva henson from upper Aptian strata (e.g. Kuss and Schlagintweit, 1988: Egypt; Luperto Sinni and Masse, 1992: Italy).

GENUS Akcayaözdikmen, 2009

Akcaya minuta (hofker, 1965) (Fig. 6G, J pars)

The species was originally described by Hofker (1965) as Textulariella minuta from the Aptian-Albian transition of the Santander area, northern Spain. It became the type-species of Sabaudia as revised later in the same year by Charollais and Brönnimann (1965). The name Sabaudia however was already occupied by the ctenophore (“comb jelly”) Sabaudia liguriaeghigi, 1909 as compiled by Özdikmen (2009), who established the new combination Akcaya minuta, adopted in the recent classi cation of Kaminski (2014). The specimen illustrated in Figure 6G displays a juvenarium composed of four subglobular chambers. Note that quadrilocular embryos are more seldom than trilocular ones (see Arnaud-Vanneau and Chiocchini, 1985). A. minuta is one of the most frequently observed taxa in the Reocín Formation.

Akcaya capitata (arnaud-vanneau, 1980) (Fig. 6J pars)

S. capitata was described by Arnaud-Vanneau (1980) from the Urgonian of southern France. Its chronostratigraphic range is Barremian to lowermost Albian (Arnaud-Vanneau and Chiocchini, 1985). In the Reocín Formation both A. minuta and A. capitata are rather common.

Family: Charentiidae loeblich and tappan, 1985

GENUS Charentia neumann, 1965

Charentia cuvillierineumann, 1965 (Fig. 6E–F)

Charentia cuvillieri was described by Neumann (1965) from the Cenomanian of France. It is a geographically widespread taxon reported from the Hauterivian to the Cenomanian (Arnaud-Vanneau, 1985). From the Aptian- Albian transition of the Santander area, northern Spain, it was described by Hofker (1965) as Haplophragmoides greigi (henson).

Family: Cyclamminidae marie, 1941

GENUS Pseudochoffatelladeloffre, 1961

Pseudochoffatella cuvillierideloffre, 1961 (Fig. 6I)

The species was both poorly illustrated and described by Deloffre (1961) from the upper Aptian of the French- Basque Pyrenees. For a detailed description and illustration of the species see Gušic (1975) and Cherchi and Schroeder (1982).

Later, the chronostratigraphic distribution was re ned to the late Gargasian (“biozone à P. cuvillieri”) for the area of the Pyrenees below the rst appearance of Simplorbitolina manasi (Fourcade, 1970; Moullade and Peybernès, 1975; Peybernès, 1976). In the studied sections of the Reocín Formation, P. cuvillieri appears in the same levels as Coskinolinella daguini and coexists with S. manasi. Whereas the latter two persist into the lower Albian Las Peñosas Formation, P. cuvillieri disappears in the uppermost part of the Reocín Formation concluding its presence also in the uppermost Aptian. In other areas, however, P. cuvillieri is recorded also throughout the lower Albian (Granier, 1987; Betic Cordillera, Spain). These varying ranges are due to differences in facies evolution, as P. cuvillieri has a preference for internal platform facies and is therefore missing in the estuarine Las Peñosas Formation of Cantabria.

Family: Pfenderinidae smout and sudgen, 1962

GENUS Dobrogelinaneagu, 1979

Dobrogelina? cartusiana arnaud-vanneau, 1980 (Fig. 6H, K–L)

The species D.? cartusiana was described by Arnaud- Vanneau (1980) from the upper Barremian-lower Aptian of SW France. The stratigraphic range can be extended into the upper Aptian. D.? cartusiana represents a common taxon in the Reocín Formation (e.g. Ramírez del Pozo, 1971; Pl. 6, g. 3, as Valvulammina).

Family: unclear (see remarks below)

GENUS Coskinolinella delmas and deloffre, 1961

Coskinolinella daguini delmas and deloffre, 1961 (Fig. 6M)

C. daguini was described by Delmas and Deloffre (1961) from the upper Aptian to lower early Albian of Aquitaine, SW France. Later, it was documented by Hofker (1965) from the Aptian-Albian transition in the Santander area, northern Spain. A detailed description and revision was provided by Cherchi (1985) con rming the given range. Cherchi (1985, p. 53) indicated test diameters from 1.4 to 1.6mm (max. 2.0mm), but up to 1.5mm according to Hofker (1965). The specimen illustrated here from the El Soplao section attains an unusual large size of 3.2mm, and possibly represents a microspheric specimen. It is worth mentioning that in all studied sections, the higher evolved Coskinolinella santanderensisramírez del pozo (with rafters) has not been observed. This species has an upper lower Albian to lower middle Albian chronostratigraphic range (Cherchi, 1985). Both C. daguini and C. santanderensis were reported by Arnaud-Vanneau and Premoli Silva (1995) from Paci c guyots near Japan. However, in our opinion, the illustrations supplied do not allow con rming these determinations. The presumed paleobiogeographic belonging of C. daguini to the northwestern-Tethyan margin is supported by the absence of Coskinolinella in the Aptian–Albian of the Prebetic zone, belonging to the former southern Tethyan margin (Masse et al., 1992). The genus Coskinolinella was treated by Cherchi (1985) as an orbitolinid taxon showing a lineage with increasing test complexity. As a matter of fact, C. daguini has no septules at all, C. santanderensis displays only rafters (vertical septules), and C. navarrensis has both rafters and beams (vertical and horizontal septules). However, Hofker (1965) refuted its attribution to the Orbitolinidae, and assigned it instead to the Lituolidae. Loeblich and Tappan (1987, p. 697) considered Coskinolinella as a genus of uncertain status, whereas in the new classi cation of agglutinated foraminifera provided by Kaminski (2014), it has not been included. Its test architecture (see details in Cherchi, 1985), however, accounts for its attribution to the suborder Orbitolinina as de ned by Kaminski (2004, 2014).

Family: Orbitolinidae martin, 1890

GENUS Palorbitolinaschroeder, 1963a

Palorbitolina lenticularis (blumenbach, 1805) (Fig. 7A–B)

Specimens of P. lenticularis (blumenbach) were observed in the Rábago Formation (sample PN 4, Río Nansa section; sample SOP 1, El Soplao section) and in the San Esteban Formation (sample CU 10, Cuchía coast section). The sample SOP 1 containing P. lenticularis and Choffatella decipiens was taken about 1m above the non-marine siliciclastic Wealden facies. It is worth mentioning here that, Neagu and Cîrnaru (2004) consider Choffatella cruciensis (pictet and renevier) as the type-species of Choffatella with C. decipiens as a junior synonym of the former. The embryonic apparatus of P. lenticularis includes a well-developed peri-embryonic ring (or chamber) surrounding the protoconch in its upper part. The sizes of the protoconchs (inner diameters 0. 145/0.15/0.14/0.21/0.2/0.16mm) and the statistically insuf cient number of measured specimens do not allow an assignment to either typical upper Barremian or lower Aptian assemblages (see Gušic, 1981, for details). Note that the rst appearance of the species is from the lower Barremian (pulchella ammonite zone) as recently evidenced by Granier et al. (2013), who showed (plates 1 and 11) that these lower Barremian specimens display a simple embryo, with a subspherical protoconch, only rudimentary septules and no distinct (if ever present) periembryonic ring.

GENUS Praeorbitolina schroeder, 1964a

Praeorbitolina cormyischroeder, 1964a (Fig. 7C)

Rare specimens of Praeorbitolina cormyi were observed in the lower Aptian (Bedoulian) San Esteban Formation, from where many other specimens of at to low-conical orbitolinids could not be determined to the speci c rank due to the lacking of embryo sections.

GENUS Mesorbitolinaschroeder, 1962

Mesorbitolina texana (roemer, 1849) (Fig. 8H, J)

The first occurrence of M. texana is at the base of the upper Gargasian (Schroeder et al., 2010). In this study, the rst specimens of M. texana were observed in the upper part of the Rodezas Formation persisting into the Reocín Formation.

Mesorbitolina parva (douglass, 1960) (Fig. 8K–L)

Rare specimens of M. parva were observed in the Rodezas Formation and the lowermost parts of the Reocín Formation. Thin sections that do not cut the megalospheric embryo, such as those found in sandy wackestones below the rst de nite occurrence of M. texana, could either belong to M. parva or M. texana. M. parva has its rst appearance in the latest Bedoulian ranging up into the late Gargasian, where it co-occurs with M. texana (see Fig.1 in Cherchi and Schroeder, 2013).

Mesorbitolina birmanica (sahni, 1937) (Fig. 8I, M–N)

For a recent revision of this poorly known taxon see Schlagintweit and Wilmsen (2014). Ramírez del Pozo (1971) found M. birmanica, identi ed as Orbitolina (Mesorbitolina)texana melendezi nov. subsp., exclusively in upper Gargasian carbonates of Escoriaza, which are equivalents of the Reocín Formation. This subspecies was de ned by the concave lower side of the subembryonic zone, a feature that can be observed only in some specimens of M. birmanica. In the Reocín Formation, M. birmanica appears higher up in the sections than M. texana, as observed in other areas (e.g. Fourcade and Raoult, 1973: reported as Mesorbitolina sp. A).

GENUS Dictyoconusblanckenhorn, 1900

Dictyoconus? pachymarginalisschroeder, 1965a

(Fig. 7D, E, H)

Schroeder (1965a) described Dictyoconus pachymarginalis from upper Bedoulian-Gargasian strata of the Alborz Mountains, northern Iran. In the Prebetic zone of Spain, Masse et al. (1992) considered that it characterizes a comparatively short interval, i.e. the middle part of the lower Gargasian (their biozone of Dictyoconus pachymarginalis). Recent studies in Central Iran have shown that D.? pachymarginalis is present throughout the whole Praeorbitolina cormyi zone of Schroeder et al. 2010, (fig. 10: Deshayesites deshayesi and D. furcata ammonite zones) and co-occurs with M. texana in its upper range (Schlagintweit et al., 2013). Rare specimens of D.? pachymarginalis, previously not reported from the North Cantabrian Basin, have been observed in the lower part of the Reocín Formation, in beds directly overlying the dolomitic unit (Río Nansa section, samples PN-13, -14) and in samples CCU 1 of the Cantera de Cuchía section, LA 17 of the Rábago section, and CL 14 of the Cantera de Las Lastrías section, where it occurs along with Mesorbitolina parva. The whole vertical range might be masked by the dolomitic portion of the sections, where identi cation of taxa was not possible.

GENUS Orbitolinopsis henson, 1948b

Orbitolinopsis? simplex (henson, 1948b) (Fig. 7F, G, I)

Originally described as Iraqia simplex by Henson (1948b) from the Lower Cretaceous of Iraq, the species has been reported repeatedly from different regions in Spain (e.g. Schroeder, 1964b; Ramírez del Pozo, 1971; Masse et al., 1992; Ullastre et al., 2002). According to Ramírez del Pozo (1971) it characterizes the upper Bedoulian (see also Moullade et al., 1985; Masse, 2003). While most authors consider Iraqia as a valid genus (Douglass, 1960; Billiard and Moullade, 1964; Loeblich and Tappan, 1987; Masse, 2003; Kaminski, 2004, 2014), it is regarded a junior synonym of Orbitolinopsis by others (Schroeder et al., 1968; Schroeder, 1972; Ramírez del Pozo, 1971; Ullastre et al., 2002). In the studied sections, O.? simplex is restricted to the San Esteban Formation, where it is a common taxon, reaching the top of the formation (see also Najarro et al., 2011; García-Mondejar et al., 2015). In conclusion, the occurrence of O.? simplex is restricted to the rst “système biosédimentaire Urgonien” (=Bedoulian) sensu Pascal (1985).

Orbitolinopsis reticulata moullade and peybernès, 1978 (Fig. 7J–K)

O. reticulata was described by Moullade and Peybernès (1978) from the Pyreneanupper Aptian (middle-upper Gargasian). In the French type- locality, it occurs in the “calcaires à Pseudochoffatella cuvillieri”, a taxon also reported from the Reocín Formation. O. reticulata was mentioned by Collignon et al. (1979) from the Gargasian of the Reocín Formation of the Cuchía section. In the Prebetic zone O. reticulata and Simplorbitolina aquitanica occur in a small range in the lower upper Gargasian (Masse et al., 1992). In contradiction to all existing data in the literature, Millán et al. (2014; p. 170) reported the occurrence of O. reticulata and Simplorbitolina aquitanica (without illustrations) in their Unit 4 of the Artxueta Formation (southeastern part of the Basque- Cantabrian Basin), ascribed to the lower Albian (op. cit., fig. 3). An early Albian age was recently erroneously assigned to the Reocín Formation based on the occurrence of O. reticulata and Mesorbitolina gr. texana-minuta (Fernández-Mendiola et al., 2015).

In the Reocín Formation O. reticulata was observed in the strata overlying the dolomitic complex (e.g. Río Nansa section, sample PN 13; El Soplao section, sample SOP 14). The whole range might be masked by the dolomitic portion of the sections, where identi cation of taxa was not possible.

GENUS Simplorbitolina ciry and rat, 1952

Simplorbitolina aquitanica (schroeder in Schroeder and Poignant, 1964) (Fig. 8A)

The species Orbitolinopsis aquitanica was described by Schroeder in Schroeder and Poignant (1964) from the upper Aptian (Gargasian) of Aquitaine (Basque Pyrenees, SW France). Later the new combination Simplorbitolina aquitanica was introduced by Moullade and Peybernès (1979) based on material from the upper Gargasian of the Pyrenees. Both S. aquitanica and O. reticulata were assigned to the lower Gargasian interval by Moullade et al. (1985, fig. 1).

In the Prebetic zone of the Murcia area, Masse et al. (1992) indicated the co-occurrence of O. reticulata and S. aquitanica, de ned as a biozone of short duration within the early upper Gargasian. Later Fenerci-Masse et al. (2006; p. 770), con rmed that both species “identify the upper Gargasian”. S. aquitanica is reported here for the rst time from the Reocín Formation.

Simplorbitolina manasi ciry and rat, 1952 (Fig. 8B–E)

The species Simplorbitolina manasi was described by Ciry and Rat (1952) from the area near Pamplona, autonomous community of Navarra, northern Spain. The cartographically isolated outcrop was tentatively assigned to the Aptian-Albian transition. S. manasi appears in the upper part of the Reocín Formation after the rst occurrences of P. cuvillieri and C. daguini. Youngest specimens were observed in the lower part of the Las Peñosas Formation. For a detailed description and compilation on occurrences and chronostratigraphy of this species see Schroeder (1985). The specimen from the Reocín Formation shown in Figure 8C is directly comparable to the specimen of Schroeder (1985: pl. 20, g. 15), who showed that the initial spire (following the embryo) is composed of 4-6 chambers. In addition we observed specimens with a more pronounced initial spire consisting of up to 12 (?13) chambers (Fig. 8D).

Simplorbitolina conulusschroeder, 1965b (Fig. 8F–G)

Simplorbitolina conulus was described by Schroeder (1965b) from Navarra, northern Spain. Its chronostratigraphic range is upper lower to middle Albian (Berthou and Schroeder, 1979; Schroeder and Neumann, 1985; Table 1). S. conulus was observed in the upper part of the Las Peñosas Formation of the San Vicente de la Barquera section (sample SV 31). The species was recently illustrated by Bodego et al. (2015; Fig. 8G) from the Buruntza Formation of the eastern Basque-Cantabrian Basin.

DISCUSSION

Biochronostratigraphic attribution of the Reocín Formation: a historical overview

Different biostratigraphic subdivisions of the upper Aptian shallow-water carbonates in Spain were proposed mainly based on orbitolinids (see Schroeder, 1963b, 1964b; Ramírez del Pozo, 1971, 1972; García-Hernández, 1981; Masse et al., 1992; Castro et al., 2001). Differences in the datation of the Reocín Formation are due to varying ranges and taxonomic attributions of taxa, different understanding of lithostratigraphic units in the study area, variable lithostratigraphic evolution leading to differing ranges of units, and last but not least the problematic subdivision of the upper Aptian (Gargasian, Clansayesian) in the Tethyan domain. This resulted in a lack of consensus for the chronostratigraphy of the Reocín Formation. Based on the orbitolinids Simplorbitolina manasi and Mesorbitolina texana, Ramírez del Pozo (1972) indicated an upper Aptian age for this formation (see also Najarro et al., 2011). However, as both of the mentioned orbitolinids range into the middle Albian (see Schroeder and Neumann, 1985), their occurrence is not necessarily a proof for a late Aptian age. An upper Gargasian – lower Albian or lowermost Albian age was indicated for the Reocín Formation by García-Mondéjar (1982) and García-Mondéjar et al. (1985). Recently, a lower-middle Albian range (upper Aptian not excluded for the lowermost part) was assigned to the Reocín Formation of the Cuchía section (García- Mondéjar et al., 2015). Finally, a lower Albian age was attributed to the Reocín Formation based on orbitolinids that are typically upper Aptian such as Orbitolinopsis reticulata (Férnandez-Mendiola et al., 2015).

The only data based on ammonites to establish the minimum age of the Reocín Formation are available from the upper part of the Rodezas Formation, which is referred to the Epicheloniceras gracile subzone of the Epicheloniceras martini zone (Mengaud, 1920; Moreno- Bedmar et al., 2011), belonging to the middle part of the lower Gargasian (see Reboulet et al., 2014) (Fig. 9).

New biochronostratigraphic data of the Reocín Formation and discussion

The biochronostratigraphic data for the Reocín Formation presented herein were obtained from the analysis of several stratigraphic sections with varying thicknesses including also under- and overlying formations. In the San Esteban Formation of the Cuchía and Ruilobuca sections we observed Palorbitolina lenticularis (blumenbach), rare Praeorbitolina cormyi schroeder, and the most common Orbitolinopsis? simplex (henson). These taxa were also reported by Pascal (1985) and García-Mondéjar et al. (2015) from the San Esteban Formation. In marly limestones of the lower part of the San Esteban Formation, O.? simplex is typically associated with Choffatella decipiens schlumberger, also referred to as Choffatella cruciensis (pictet and renevier) by Neagu and Cîrnaru (2004). In the Rodezas Formation we observed Mesorbitolina parva and, in its upper part, the first specimens of Mesorbitolina texana (roemer).

Based on orbitolinids, an upper Gargasian-Clansayesian age is assigned to the Reocín Formation (Fig. 9). Its extension into the lower Albian can neither be proven nor excluded. In continuous sections (i.e. without a stratigraphic gap), the Reocín Formation is followed by the lower Albian Las Peñosas Formation (García-Mondéjar, 1982; Hines, 1985) thar in turn is overlain by the middle-late Albian Barcenaciones Formation. In several sections the latter directly follows the Reocín Formation with a gap, e.g. Suances, Cantera de Cuchía, and Cuchía coast sections (Figs. 2; 3). In the Reocín Formation of the Cuchía section, García-Mondéjar et al. (2015, p. 13) did not mention any orbitolinid but only Hensonina lenticularis (henson). These specimens, referred to as Involutina hungarica (sido) (see Schlagintweit and Piller, 1990; Rigaud et al., 2015), were not observed in the Reocín Formation but in the middle-upper parts of the Las Peñosas Formation (e.g. Fonfría section) and in all the studied sections of the Barcenaciones Formation (Rosales et al., 2013; Najarro, 2015). Together with debris of the udoteacean alga Boueina camenitzae (dragastan and bucur), Involutina hungarica typically occurs in high-energy open marine carbonates in the middle-late Albian Barcenaciones Formation (e.g. Río Nansa, Cantera de Cuchía, Cuchía coast, Bustriguado sections) (see e.g. fig. 3F in Rosales et al., 2013). The lower part of the Las Peñosas Formation includes instead sandy, marly limestones with oysters. Therefore it can be concluded that the report of Hensonina lenticularis henson [=Involutina hungarica (sido)] from the Reocín Formation by García-Mondéjar et al. (2015) in fact refers to samples from the Barcenaciones Formation that unconformably overlies the Reocín Formation, e.g. Cantera de Cuchía section (Figs. 2C; 3) and Cuchía coast section (Fig. 3).

Due to differences in facies evolution, the vertical distribution of taxa presented here for the North- Cantabrian Basin cannot be applied directly to other regions. The vertical distribution of orbitolinids and other foraminifera and the resulting biozonation established by Masse et al. (1992) for the Prebetic zone of southern Spain is different from the Cantabrian distribution in details, since in the former area, Orbitolinopsis? simplex-Praeorbitolina cormyi, and Pseudochoffatella cuvillieri-Simplorbitolina manasi are distinctly separated from each other. Coskinolinella daguini is missing presumably due to its palaeobiogeographic restriction to the northern Tethyan domain.

Implications in sequence stratigraphy

The biostratigraphic results obtained in this paper provide new data to help in the datation and correlation of the sequence stratigraphy scheme of the basin (Fig. 9). The unconformity at the transition Reocín to Las Peñosas formations possibly relates to the sea level event KAp7 (~ 113.3Ma) sensu Haq (2014) that occurred around the Aptian-Albian boundary. On the other hand, the transition between the San Esteban and Rodezas formations possibly is coincident with the KAp2 event (~123Ma) at the top of the Dufrenoyia furcata ammonite zone, the base of the Gargasian (sensuReboulet et al., 2014). This boundary might then be coeval to the Gargasian tectonic event of Pascal (1985) (see also Wilmsen, 2005).

Based on the identification of regional unconformities and facies stacking patterns, eight depositional sequences (transgressive-regressive sequences compiled from Najarro, 2015, and Rosales and Schlagintweit, 2015) can be recognized in the Aptian–lower Cenomanian succession of the NCB (Fig. 10). The biostratigraphic results of this study based on benthic foraminifers improve the chronostratigraphy of the depositional sequences and allow their comparison with the main depositional sequences recognized in other areas of the Basque-Cantabrian Basin and the Iberian Chain (García-Mondéjar et al., 2004; Bover-Arnal et al., 2009; Martín-Martín et al., 2013) and the recently revised global sea level falls of Haq (2014).

The first depositional sequence of the North-Cantabrian Basin is a short cycle that occurred at the lowermost Aptian (sequence I, Fig. 10). The base of the sequence corresponds to the widespread marine transgression at the base of the Aptian. The upper sequence boundary is marked by a subaerial exposure surface between the Rábago and Umbrera formations. In the Iberian Chain, this cycle correlates with a coeval initial short cycle identi ed in both the Galve and Benicàssim areas of the Maestrat Basin (Bover-Arnal et al., 2009; Martín-Martín et al., 2013), whereas in other areas of the Basque-Cantabrian Basin it has not yet been distinguished (García-Mondéjar et al., 2004). This depositional sequence may be correlated to the global sea-level fall KAp1 (~125.6Ma).

The sequence II (Fig. 10) is lower to upper Bedoulian and comprises the Umbrera, Patrocinio and San Esteban formations. The Maximum Flooding Zone (MFZ, Fig. 10) of this sequence, represented by the Patrocino Formation, is coeval with the oceanic anoxic event 1a (Najarro et al., 2011; García-Mondéjar et al., 2015). The top of the sequence is a subaerial exposure surface with paleokarst development and brecciation on top of the San Esteban Formation. In the Maestrat Basin, this sequence correlates well with the sequence II of the Galve and Benicàssim areas (Fig. 10) identi ed respectively by Bover-Arnal et al. (2009) and Martín-Martín et al. (2013). In other areas of the Basque-Cantabrian Basin, the sequences I and II of this study correspond to the main depositional sequence I of García-Mondéjar et al. (2004). There are some discrepancies regarding the age of the upper boundary of sequence II between the different areas (Fig. 10). In the Galve area, Bover-Arnal et al. (2009) located the boundary on top of the last ammonite biozone of the Bedoulian (D. furcata ammonite zone). Later the same authors (Moreno- Bedmar et al., 2012; Bover-Arnal et al., 2014) relocated the boundary within the D. furcata ammonite zone on the basis of the occurrence of Dufrenoyia ammonites in the transgressive deposits just above the sequence boundary, adopting the same stratigraphic position for this boundary as in the Benicàssim area (Martín-Martín et al., 2013). In other areas of the Basque-Cantabrian Basin, García- Mondéjar et al. (2004) located the sequence boundary in a lower position (Fig. 10), below the Tropaeum bowerbanki ammonite zone, which is equivalent to the D. furcata ammonite zone of the Mediterranean region. In the present study, the boundary has been located at the Bedoulian- Gargasian transition (sensu Reboulet et al., 2014) in agreement with the global sea-level fall KAp2 (~123Ma), although a lower position below the Bedoulian-Gargasian transition cannot be excluded.

The transgressive deposits of the sequence III correspond to the Rodezas Formation (Fig. 10). The MFZ (Fig. 10) is recognized in the argillaceous-marly interval with ammonites of the E. gracile ammonites sub-zone (Mengaud, 1920; Moreno-Bedmar et al., 2011) of the middle part of the lower Gargasian (Fig. 10), approximately in the same stratigraphic position than in the Maestrat Basin (Moreno-Bedmar et al., 2012). The upper sequence boundary of sequence III is related to facies regression and local subaerial exposure that occurred within the Reocín Formation (Najarro et al., 2007). In the North- Cantabrian Basin, the age of this sequence boundary falls in an uncertain position within the Gargasian (dashed red lines in Fig. 10). In the Maestrat Basin a likely equivalent sequence boundary has been recognized on top of the E. martini ammonite zone (Bover-Arnal et al., 2009; Moreno-Bedmar et al., 2012), which can be approximately equivalent to the global event KAp4 (~118.2Ma) of Haq (2014) (Fig. 10).

Sequence IV, late Gargasian to Clansayesian in age, corresponds with the upper part of the Reocín Formation. The upper sequence boundary is placed around the Aptian to Albian transition (Fig. 10). A nearly equivalent sequence boundary has been recognized in the Galve and Benicàssim areas of the Maestrat Basin (Bover-Arnal et al., 2009; Martín-Martín et al., 2013). In other areas of the Basque- Cantabrian Basin, the sequences III and IV documented in the North-Cantabrian Basin and the Iberian Chain correspond to the main depositional sequence II of García- Mondéjar et al. (2004), with its upper boundary located as well around the Aptian to Albian transition (Fig. 10). This sequence boundary, which is nearly coeval in the different areas, most likely corresponds with the global event KAp7 (~113.3Ma) sensuHaq (2014).

Sequences V and VI, lower to late Albian in age, corresponds with the Las Peñosas and Barcenaciones formations (Fig. 10). The precise age of their upper sequence boundaries is still uncertain but they fall within the early Albian and late Albian, respectively (Fig. 10). Depositional sequences roughly equivalent to sequence V have been recognized in other areas of the Basque- Cantabrian Basin (sequence III of García-Mondéjar et al., 2004) and in the Benicàssim area of the southern Maestrat Basin, with their upper boundary at the top of the Leymeriella tardefurcata ammonite zone of the early Albian (García-Mondéjar et al., 2004; Martín-Martín et al., 2013). This boundary could be coincident with the global event KAl1 (~111.4Ma) of Haq (2014). The sequence VI of the North-Cantabrian Basin (upper Las Peñosas and Barcenaciones formations, Fig. 10), comprises the sequences IV to VI of García-Mondéjar et al. (2004) for other areas of the Basque-Cantabrian Basin. Their correspondence with the global sequences of Haq (2014) is unsure. Finally, the depositional sequences VII and VIII correspond respectively to the Somocuevas and Cóbreces members of the Bielba Formation (Fig. 10). The boundary between these two sequences is located around the Albian– Cenomanian transition (Rosales and Schlagintweit, 2015), and is coincident with the major global cycle boundary KAl8 (~100.6Ma) sensu Haq (2014).

Therefore, it could be concluded that despite the evidence of syn-rift tectonic activity in all these basins, the main depositional sequences can be correlated between the different basins of Iberia and with some of the global sequences of Haq (2014), suggesting a strong eustatic control in their origin. A more precise dating of the sequences and their boundaries is needed to improve the intra- and inter-regional correlation and their precise correspondence with global events.

CONCLUSIONS

1. i) Despite recent studies focused on lithofacies and depositional sequences of the Aptian platform carbonates of the North-Cantabrian Basin, there is still a lack of knowledge on the composition of their benthic assemblages. The biostratigraphic results provided here allows filling this gap and provide relevant information for regional stratigraphical and sequential correlations. In addition, the new benthic foraminifer Glomospirella cantabrica n. sp. is described from the upper Aptian Reocín and Lower Albian Las Peñosas formations.

2. ii) Microfacies analysis of the Aptian platform limestones of Cantabria reveals a scarceness of dasycladalean green algae and a proliferation of benthic foraminifera. Based on the assemblage of benthic foraminifera of the Reocín Formation, an upper Aptian age is proposed for this unit.

3. iii) Owing to their presence in the upper Aptian Reocín Formation, the chronostratigraphic ranges of Salpingoporella melitaeradoicic, Nautiloculina cretacea peybernès, Glomospira urgonianaarnaud-vanneau and Dobrogelina? carthusianaarnaud-vanneau have to be extended to the upper Aptian.

4. iv) Major unconformities related to sea-level falls with subaerial platform exposure occurred on top of the Rábago (lowermost Aptian), San Esteban (lower Aptian), Reocín (upper Aptian) and Barcenaciones (middle-late Albian) formations. They could be related respectively to the sea level global events KAp1 (~125.6Ma), KAp2 (~123Ma), KAp 7 (~113.3Ma) and KAl7 (~103Ma) sensuHaq (2014). Other two sequence boundaries related to facies regression and local subaerial exposure occurred within the Reocín and Las Peñosas formations. The precise age of these two sequence boundaries is still uncertain but falls within the Gargasian and lower Albian, respectively. They could be related tentatively to the sea-level global events KAp4 (~118.2Ma) and KAl1 (~111.4Ma), respectively. The correlation of the identi ed sequences with the global events of Haq (2014), and with other areas of the Basque- Cantabrian Basin and of the Iberian Chain, indicates a strong eustatic control in the origin of the sequences.

ELECTRONIC APPENDIX I

Acknowledgements

This study is a contribution to the research project CGL2014-53548-P, funded by the Ministerio de Economía y Competitividad (MINECO) of Spain. We kindly acknowledge the helpful comments of the reviewers Michel Moullade and Esmeralda Caus as well as the careful editing by Carles Martín Closas.

REFERENCES

Arnaud-Vanneau, A., 1980. L’Urgonien du Vercors septentrional et de la Chartreuse. Géologie Alpine, 11(3, Mémoire), 1-874. Arnaud-Vanneau, A., 1985. Genre Charentia Neumann, 1965. In: Schroeder, R., Neumann, M., (coords.). Les Grands Foraminifères du Crétacé Moyen de la région Méditerranénne. Géobios, mémoire special 7, 17-18.

Arnaud-Vanneau, A., Peybernès, B., 1978. Les représentants éocrétacés du genre NautiloculinaMohler, 1938 (Foraminifera, Fam. Lituolidae?) dans les Chaînes Subalpines Septentrionales (Vercors) et les Pyrénées Franco-Espagnoles. Géobios, 11(1), 67-81.

Arnaud-Vanneau, A., Chiocchini, M., 1985. Le genre Sabaudia Charollais et Brönimman, 1965 (Foraminifère benthique Crétacé) et ses différentes especès. Revue de Micropaléontologie, 28(1), 3-22.

Arnaud-Vanneau, A., Premoli Silva, I., 1995. Biostratigraphy and systematic description of benthic foraminifers from Mid-Cretaceous shallow-water carbonate platform sediments at Sites 878 and 879 (MIT and Takuyo-Daisan Guyots). In: Haggerty, J.A.A. Premoli Silva, I., Rack, F.R., McNutt, M.K.. (eds.). Procceddings of the Ocean Drilling Program, Scientific Results, 144, 199-219.

Arnaud-Vanneau, A., Sliter, W.V., 1995. Early Cretaceous shallow-water benthic foraminifers and fecal pellets from Leg 143 compared with coeval faunas from the Pacific Basin, Central America, and the Tethys. Proceedings Ocean Drilling Program, Scientific Results, 143, 537-564.

Berkeley, A., Perry, C.T., Smithers, S.G., Horton, B.P., Cundy, A.B., 2009. Foraminiferal biofacies across mangrove-mudflat environments at Cocoa Creek, north Queensland, Australia. Marine Geology, 263, 64-86.

Berthelin, G., 1880. Mémoire sur les foraminifères fossils de l’étage Albien de Moncley (Doubs). Mémoires de la Société Géologique de France, série 3, 1(5), 1-84.

Berthou, P.Y., Schroeder, R., 1979. Découverte d’un niveau à Simplorbitolina Ciry et Rat dans l’Albien de Guincho (region de Lisbonne, Portugal). Comptes Rendus de l’Académie des Sciences Paris, 288, Série D, 591-594.

Billiard, J., Moullade, M., 1964. Étude de quelques représentants du genre Iraqia (Orbitolinidae) dans l’Aptien des contreforts Pyrénéens Français et Espagnols. Revue de Micropaléontologie, 6(4), 237-242.

Blanckenhorn, M., 1900. Neues zur Geologie und Paläontologie Ägyptens. Zeitschrift der Deutschen Geologischen Gesellschaft, 52, 403-479.

Blázquez-Fernández, S., López-Cilla, I., Gasparrini, M., Rosales, I., Lerat, O., Doligez, B., Martín-Chivelet, J., 2014. Geostatistical workflows for modeling the facies-texture- porosity interdependence in a partially dolomitized platform (Lower Cretaceous, Basque Cantabrian basin, Spain). IFP Énergies Nouvelles, Report 63256, 115pp.

Blumenbach, J.F., 1805. Abbildungen naturhistorischer Gegenstände. Göttingen, Heft 8 (80), H. Dieterich, 1-2.

Bodego, A., Iriarte, E., Agirrezabala, L.M., García-Mondéjar, J., 2015. Synextensional mid-Cretaceous stratigraphic architecture of the eastern Basque-Cantabrian basin margin (western Pyrenees). Cretaceous Research, 55, 229-261.

Bover-Arnal, T., Salas, R., Moreno-Bedmar, J.A., Bitzer, K., 2009. Sequence stratigraphy and architecture of a late Early- Middle Aptian carbonate platform succession from the western Maestrat Basin (Iberian Chain, Spain). Sedimentary Geology, 219, 280-301.

Bover-Arnal, T., Salas, R., Guimerà, J., Moreno-Bedmar, J.A., 2014. Deep incision in an Aptian carbonate sucession indicates major sea-level fall in the Cretaceous. Sedimentology, 61, 1558-1593.

Brönnimann, P., Whittaker, J.F., Zaninetti, L., 1992. Brackish water foraminifera from mangrove sediments of southwestern Viti Levu, Fiji Island, southwest Pacific. Revue de Paléobiologie, 11, 13-65.

Carras, N., Conrad, M.A., Radoicic, R., 2006. Salpingoporella, a common genus of Mesozoic Dasycladales (calcareous green algae). Revue de Paléobiologie, 25(2), 457-517.

Castro, J.M., Company, M., De Gea, G.A., Aguado, R., 2001. Biostratigraphy of the Aptian-Middle Cenomanian platform to basin domain in the Prebetic Zone of Alicante, SE Spain: calibration between shallow water benthonic and pelagic scales. Cretaceous Research, 22, 145-156.

Charnock, M.A., Jones, R.W., 1990. Agglutinated foraminifera from the Palaeogene of the North Sea. In: Hemleben, C., Kaminski, M.A., Kuhnt, W., Scott, D.B. (eds.). Paleoecology, Biostratigraphy, Paleoceanography and Taxonomy of Agglutinated Foraminifera. NATO ASI Series, Dordrecht, Kluwer Academic Publishers, 139-244.

Charollais, J., Brönnimann, P., 1965. Premiére note sur les foraminifères du Crétacé inférieur de la région genevoise. Sabaudia C_{HAROLLAIS ET .RÖNNIMANN}, n. gen. Archives des Sciences, 18(3), 615-624.

Cherchi, A., 1985. Genre Coskinolinella DELMAS & _DELOFFRE, 1961. In: Schroeder, R., Neumann, M., (coords.). Les Grands Foraminifères du Crétacé Moyen de la région Méditerranénne. Géobios, mémoire special 7, 52-56.

Cherchi, A., Schroeder, R., 1982. Précisions sur Pseudochoffatella DELOFFRE et remarques sur Balkhania balkhanica MAMONTOVA (Foraminifères). Revue de Micropaléontologie, 25(3), 154-162.

Cherchi, A., Schroeder, R., 2013. The Praeorbitolina/ Palorbitolinoides association: an Aptian biostratigraphic key-interval at the southern margin of the Neo-Tethys. Cretaceous Research, 39, 70-77.

Ciry, R., Rat, P., 1952. Déscription d’un nouveau genre de Foraminifère: Simplorbitolina manasi nov. gen., nov. sp. Bulletin Scientifique de Bourgogne, 14, 85-100.

Clavel, B., Conrad, M.A., Busnardo, R., Charollais, J., Granier, B., 2013. Mapping the rise and demise of Urgonian platforms (Late Hauterivian – Early Aptian) in southeastern France and the Swiss Jura. Cretaceous Research, 39, 29-46.

Collignon, M., Pascal, A., Peybernès, B., Rey, J., 1979. Faunes d’Ammonites de l’Aptien de la région de Santander (Espagne). Annales de Paléontologie (Invertébrés), 65(2), 139-156.

Cushman, J.A., Waters, 1927. Arenaceous Paleozoic foraminifera from Texas. Contributions from the Cushman Laboratory for Foraminiferal Research, 3, 146-153.

Delmas, M., Deloffre, R., 1961. Découverte d’un nouveau genre d’Orbitolinidae dans la base de l’Albien en Aquitaine. Revue de Micropaléontologie, 4(3), 167-172.

Deloffre, R., 1961. Sur la découverte d’un nouveau lituolidé du Crétacé inférieur des Basses-Pyrénées: Pseudochoffatella cuvillieri n. gen., n. sp. Revue de Micropaléontologie, 4, 105-107.

Douglass, R.C., 1960. The foraminiferal genus Orbitolina in North America. Geological Survey Professional Papers, SSS, 1-52.

Fernández-Mendiola, P.A., Pérez-Malo, J., García-Mondéjar, J., 2015. Facies analysis and correlation in an Albian carbonate platform (Cuchía quarry, Cantabria, Spain). Geogaceta, 57, 99-102.

Fenerci-Masse, M., Masse, J.-P., Arias, C., Vilas, L., 2006. Archaeoradiolites, a new genus from the Upper Aptian of the Mediterranean region and the origin of the rudist family Radiolitidae. Palaeontology, 49(4), 769-794.

Fourcade, E., 1970. Le Jurassique et le Crétacé aux confins des chaînes bétiques et ibériques (Sud-Est de l´Espagne). PhD Thesis. University Pierre and Marie Curie, Paris, 427pp.

Fourcade, E., Raoult, J.F., 1973. Crétacé du Kef Hahouner et position stratigraphique de “Ovalveolina. reicheli P. De Castro (série septentrionale du mole néritique du Constantinois, Algérie). Revue de Micropaléontologie, 15(4), 227-246.

Galeotti, S., Kaminski, M.A., Coccioni, R., Speijer, R.P., 2004. High-resolution deep-water agglutinated foraminiferal record across the Paleocene/Eocene transition in the Contessa Road Section (Central Italy). In: Bubík, M., Kaminski, M.A. (eds.). Proceedings of the Sixth International Workshop on Agglutinated Foraminifera. Grzybowski Foundation Special Publication, 8, 83-103.

García-Hernández, M., 1981. Biozonation du Crétacé inférieur à l’aide des foraminifères benthiques et des algues Dasycladacées dans le Prébetique occidental (Cordillères Bétiques, Esp.). Géobios, 14, 261-267.

García-Mondéjar, J., 1982. Aptiense y Albiense. El Cretácico de España. Universidad Complutense Madrid, 63-84.

García-Mondéjar, J., Hines, F.M., Pujalte, V., Reading, H.G., 1985. Sedimentation and tectonics in the western Basque- Cantabrian area (northern Spain) during Cretaceous and Tertiary times. In: Milá, M.D., Rosell, J. (eds.). Excursion Guidebook. 6th European Regional Meeting, International Association of Sedimentologists, 308-392.

García-Mondéjar, J., Fernández-Mendiola, P.A., Agirrezabala, L.M., Aranburu, A., López-Horgue, M.A., Iriarte, E., Martínez-Rituerto, S., 2004. El Aptiense-Albiense de la Cuenca Vasco-Cantábrica. In: Vera, J.A. (ed.). Geología de España. Madrid, Sociedad Geológica de España-Instituto Geológico y Minero de España, 291-296.

García-Mondéjar, J., Owen, H.G., Fernández-Mendiola, P.A., 2015. Early Aptian sedimentary record and OAE1a in Cuchía (northern Spain): new data on facies and ammonite dating. Neues Jahrbuch für Geologie und Paläontologie Abhandlungen, 276(1), 1-26.

Ghigi, A., 1909. New Zealand Ctenophores. Raccolte planctoniche, fatte dalla R. nave Liguria. Ctenofori, 2 (19).

Granier, B., 1987. Le Crétacé inférieur de la Costa Blanca entre Busot et Altea, Alicante (Espagne). Biostratigraphie, Sédimentologie, Evolution tectono- sédimentaire. Thèse, Docteur de l’Université Paris VI (nouveau régime), 23 Novembre1987; Mémoires des Sciences de la Terre, Université Pierre et Marie Curie, Paris, 87-49, vol. I (texte): 281 pp., 63 fig. ; vol. II- (planches): 54 pl.

Granier, B., Clavel, B., Moullade, M., Busnardo, R., Charollais, J., Tronchetti, G., Desjacques, P., 2013. L’Estellon (Baronnies, France), a “Rosetta Stone” for the Urgonian biostratigraphy. Carnets de Géologie (Notebooks on Geology), Article 2013/04 (CG2013_A04).

Grzybowski, J., 1898. The Foraminifera of the oil-bearing deposits of the Krosno region. Rozprawy Wydziału Matematyczno- Przyrodniczego, Akademia Umiej9tnosci w Krakowie, serya 2, 41, 219-286.

Gušic, I., 1975. Lower Cretaceous imperforate Foraminiferida of Mt. Medvednica, northern Croatia. Palaeontologia Jugoslavica, 14, 1-51.

Gušic, I., 1981. Variation range, evolution, and biostratigraphy of Palorbitolina lenticularis (BLUMENBACH) (Foraminiferida, Lituolacea) in the Lower Cretaceous of the Dinaric Mountains in Yugoslavia. Paläontologische Zeitschrift, 55(3-4), 191-208.

Haq, B.U., 2014. Cretaceous eustasy revisited. Global and Planetary Change, 113, 44-58.

Hayward, B., Pignatti, J., 2015. Glomospirella P_LUMMER, 1945. In: Hayward, B.W., Cedhagen, T., Kaminski, M., Gross, O. (eds.). World Foraminifera Database. Last accessed: January 2016. Website: www.marinespecies.org/foraminifera

Henson, F.R.S., 1948a. New Trochamminidae and Verneuilinidae from the Middle East. Annals and Magazine of Natural History, Series 11, 14 (117), 605-630.

Henson, F.R.S., 1948b. Larger imperforate Foraminifera of south-western Asia. Families Lituolidae, Orbitolinidae and Meandropsinidae. London, Monograph British Museum (Natural History), 127pp.

Hines, F.M., 1985. Sedimentation and tectonics in north-west Santander. In: Milá, M.D., Rosell, J. (eds.). Excursion Guidebook. 6th European Regional Meeting, International Association of Sedimentologists, 371-398.

Hofker, J., 1965. Some foraminifera from the Aptian-Albian passage of northern Spain. Leidse Geologische Mendelingen, 33, 183-189.

Jones, R.W., Wonders, A.A.H., 2000. On Arenomeandrospira gen. nov. (Foraminiferida, Ammodiscidae), and its association with Natural Gas Seepage. In: Hart, M.B., Kaminski, M.A., Smart, C.W. (eds.). Proceedings of the Fifth International Workshop on Agglutinated Foraminifera. Gryzbowski Foundation Special Publication, 7, 179-184.

Kaminski, M.A., 2004. The year 2000 classification of the agglutinated foraminifera. In: Bubík, M., Kaminski, M.A. (eds). Proceedings of the Sixth International Workshop on Agglutinated Foraminifera. Grzybowski Foundation Special Publication, 8, 237-255.

Kaminski, M.A., 2014. The year 2010 classification of the agglutinated foraminifera. Micropaleontology, 60 (1), 89-108.

Kaminski, M.A., Gradstein, F.M., 2005. Atlas of Palaeogene cosmopolitan deep-water agglutinated foraminifera. Grzybowski Foundation Special Publication, 10, 1-548.

Kaminski, M.A., Gradstein, F.M., Geroch, S., 1992. Uppermost Jurassic to Lower Cretaceous deep-water benthic foraminiferal assemblages from Site 765 on the Argo abyssal plain. In: Gradstein, F.M., Adamson, A.C., Ludden, J.N., Poag, W (eds.). Proceedings of the Ocean Drilling Program, Scientific Results, 123, 239-269.

Kaminski, M.A., Setoyama, E., Cetean, C.G., 2008. Revised stratigraphic ranges and the Phanerozoic diversity of agglutinated foraminiferal genera. In: Kaminski, M.A., Coccioni, R., (eds). Proceedings of the Seventh International Workshop on Agglutinated Foraminifera. Grzybowski Foundation Special Publication, 13, 79-106.

Koutsoukos, E., 2000. “Flysch-type” foraminiferal assemblages in the Cretaceous of northeastern Brazil. In: Hart, M.B., Kaminski, M.A., Smart, C.W. (eds.). Proccedings of the Fifth International Workshop on Agglutinated Foraminifera. Grzybowski Foundation Special Publication, 7, 243-260.

Kuss, J., Schlagintweit, F., 1988. Facies and stratigraphy of Early to Middle Cretaceous (Late Aptian-Early Cenomanian) strata from the northern rim of the African craton (Gebel Maghara- Sinai, Egypt). Facies, 19, 77-96.

Lankester, E.R., 1885. Protozoa. Encyclopedia Brittanica, 19 (9th Edition), 830-866.

Le Pichon, X., Sibuet, J.C., 1971. Western extension of the boundary between European and Iberian plates during the Pyrenean orogeny. Earth and Planetary Science Letters, 12, 83-88.

Loeblich, A.R.Jr., Tappan, H., 1985. Some new and redefined genera and families of agglutinated foraminifera I. Journal of Foraminiferal Research, 15, 91-104.

Loeblich, A.R.Jr., Tappan, H., 1987. Foraminiferal genera and their classification, Van Nostrand Reinhold. New York, 2, 970pp, 847pls.

López-Cilla, I., Rosales, I., Najarro, M., 2012. Diagenesis in lower Cretaceous platform carbonates of northern Spain (NW Cantabria): an example of multistage dolomitization and calcite cementation. Geofluids VII International conference, IFP Énergies Nouvelles, Proceedings, 205-208.

Luperto Sinni, E., Masse, J.P., 1992. Biostratigrafia dell’Aptiano in facies di piattaforma carbonatica delle Murge baresi (Puglia– Italia medridionale). Rivista Italiana di Paleontologia e Stratigrafia, 98(4), 403-424.

Malod, J.A., Mauffret, A., 1990. Iberian plate motions during the Mesozoic. Tectonophysics, 184, 261-278.

Marie, P., 1941. Les foraminifères de la Craie à Belemnitella mucronata du Bassin de Paris. Mémoires du Museum Nationale d’Histoire Naturelle, 12(1), 1-296.

Martin, K., 1890. Untersuchungen über den Bau von Orbitolina (Patellina auct.) von Borneo. Sammlungen des Geologischen Reichs-Museums in Leiden, 1(4), 209-231.

Martín-Martín, J.D., Gomez-Rivas, E., Bover-Arnal, T., Travé, A., Salas, R., Moreno-Bedmar, J.A., Tomás, S., Corbella, M., Teixell, A., Vergés, J., Stafford, S.L., 2013. The Upper Aptian to Lower Albian syn-rift carbonate succession of the southern Maestrat Basin (Spain): Facies architecture and fault-controlled stratabound dolostones. Cretaceous Research, 41, 217-2S6.

Masse, J.P., 2003. Integrated stratigraphy of the Lower Aptian and applications to carbonate platforms: a state of the art. In: Gili, E., Negra, M.E.H., Skelton. P.W. (eds.). North African Cretaceous Carbonate Platform Systems, Nato Science Series 203-214.

Masse, J.P., Arias, C., Vilas, L., 1992. Stratigraphy and biozonation of a reference Aptian–Albian, p.p. Tethyan carbonate platform succession: The Sierra del Carche series (oriental Prebetic zone – Murcia, Spain). In: Kollmann, H.A., Zapfe, H. (eds.). New aspects on Tethyan Cretaceous fossil assemblages. Schriftenreihe der Erdwissenschaftlichen Kommissionen der Österreichischen Akademie der Wissenschaften, 9, 201-221.

Mengaud, L., 1920. Recherches géologiques dans la région Cantabrique. Bulletin de la Société d’Histoire naturelle de Toulouse, 48, 73-272.

Mikhalevich, V., 1980. Systematics and evolution of foraminifera in the light of new data on their cytology and ultrastructure. Trudy Zoologicheskogo Instituta, Akademiya Nauk SSSR., 94, 42-61.

Millán, M.I., Weissert, H.J., López-Horgue, M.A., 2014. Expression of the late Aptian cold snaps and the OAE1b in a highly subsiding carbonate platform (Aralar, northern Spain). Palaeogeography, Palaeoclimatology, Palaeoecology, 411, 167-179.

Mohler, W., 1938. Mikropaläontologische Untersuchungen in der nordschweizerischen Juraformation. Abhandlungen der Schweizerischen Paläontologischen Gesellschaft, 60, 1-53.

Moreno-Bedmar, J.A., Grauges, A., Matínez, R., Barragán- Manzo, R., 2011. Revisión sistemática de las amonitas del Aptiano Tardío de Reocín (Cuenca Vasco-Cantábrica; Norte de España) de la colección Mengaud (Univ. Paul Sabatier, Toulouse). Mexico, XII Congreso Nacional de Paleontología, Puebla de los Ángeles, Abstract, 99.

Moreno-Bedmar, J.A., Bover-Arnal, T., Barragán, R., Salas, R., 2012. Uppermost Lower Aptian transgressive records in Mexico and Spain: chronostratigraphic implications for the Tethyan sequences. Terra Nova, 24, 333-338.

Moullade, M., Peybernès, B., 1975. Biozonation par Orbitolinidés du Clansayesien et de l´Albien calcaires des Pyrénées franco- espagnoles. Comptes Rendus de l’Académie des Sciences, D, 280, 2529-2532.

Moullade, M., Peybernès, B., 1978. Un nouvel Orbitolinidé du Gargasien Supérieur (Aptien Supérieur) des Pyrénées, Orbitolinopsis reticulata n. sp. Géobios, 11(4), 493-503.

Moullade, M., Peybernès, B., 1979. Révision d’“Orbitolinopsis. aquitanica S_CHROEDER, 1964, Orbitolinidé du Gargasien (= Aptien Supérieur) Pyrénéen. Archives des Sciences, 32(3), 261-166.

Moullade, M., Peybernès, B., Rey, J., Saint-Marc, P., 1985. Biostratigraphic interest and paleobiogeographic distribution of early and mid-Cretaceous Mesogean orbitolinids (Foraminiferida). Journal of Foraminiferal Research, 15(3), 149-158.

Moullade, M., Tronchetti, G., Bellier, J.B., 2008. Associations et biostratigraphie des Foraminifères benthiques et planctoniques du Bédoulien sommitale et du Gargasien inférieur de La Tuilière – St-Saturnin-lès-Apt (aire stratotypique de l’Aptien, Vaucluse, SE France). Carnets de Géologie-Notebooks on Geology, Article 2008/01, CG2008_A01.

Moullade, M., Granier, B., Tronchetti, G., 2011. The Aptian stage: back to fundamentals. Episodes, 34(3), 148-156.

Najarro, M., 2015. Las plataformas carbonatadas y sistemas deltaicos del Aptiense-Albiense inferior del noroeste de Cantabria: registro de cambios paleoambientales y eventos anóxicos. PhD Thesis. Madrid, Universidad Complutense de Madrid, 450pp.

Najarro, M., Rosales, I., Martín-Chivelet, J., 2007. Evolución de la plataforma carbonatada de la Florida durante el rifting del Cretácico Inferior (Aptiense, NO de Cantabria). In: Bermúdez, D.D., Najarro, M., Quesada, C. (eds.). Volumen Monográfico de la II Semana de Jóvenes Investigadores del Instituto Geológico y Minero de España. Publicaciones del Instituto Geológico y Minero de España, 123-128.

Najarro, M., Rosales, I., Moreno-Bedmar, J.A., de Gea, G.A., Barrón, E., Company, E., Delanoy, G., 2011. High- resolution chemo- and biostratigraphic records of the Early Aptian oceanic anoxic event in Cantabria (N Spain): Palaeoceanographic and palaeoclimatic implications. Palaeogeography, Palaeoclimatology, Palaeoecology, 299, 137-158.

Neagu, T., 1979. Données nouvelles concernant les répresentants de la famille des Pfenderinidae de l’Eocrétacé de la Dobrogea Méridionale (Roumanie). Revista Española de Micropaleontología, 11, 479-504.

Neagu, T., Cîrnaru, P., 2004. Genus Choffatella (SCHLUMBERGER), 1904 (Foraminifera) in the lower Aptian (Bedoulian) from Southern Dobrogea and SE part of the Romanian plain. Acta Palaeontologica Romaniae, 4, 269-275.

Neumann, M., 1965. Contribution á l’étude de quelques Lituolidés du Cénomanien de l’île Madame (Charente-Maritime). Revue de Micropaléontologie, 8(2), 90-95.

Orbigny, A., d’, 1826. Tableau méthodique de la classe des Céphalopodes. Annales des Sciences Naturelles, 7, 245-314. Orbigny, A., d’, 1839. Foraminifères. In: de la Sagra, R. (ed.). Histoire physique, politique et naturelle de l’île de Cuba.

Özdikmen, H., 2009. Substitute names for some unicellular animal taxa (Protozoa). Munis Entomology & Zoology, 4(1), 233-256.

Pascal, A., 1985. Les Systems biosédimentaires urgoniens (Aptien–Albien) sur la marge Nord Ibérique. Mémoires Géologiques de l’Université de Dijon, 10, 1-569.

Pawlowski, J., Holzmann, M., Tyszka, J., 2013. New supraordinal classification of Foraminifera: Molecules meet morphology. Marine Micropaleontology, 100, 1-10.

Peybernès, B., 1976. Le Jurassique et le Crétacé inférieur des Pyrénées franco-espagnoles entre la Garonne et la Méditerranée. PhD Thesis. University Paul Sabatier, Toulouse, 459pp.

Plummer, H.L., 1945. Smaller foraminifera in the Marble Falls, Smithwick, and lower Strawn strata around the Llano uplift in Texas. Bulletin University of Texas, Bureau of Economic Geology and Technology, 4401, 209-271.

Portero-García, J.M., Ramírez del Pozo, J., Olivé-Davó, A., Martín-Alafont, J.M., 1976. Mapa Geológico de España a escala 1:50.000, Hoja nº 33, Comillas, Serie Magna. Instituto Geológico y Minero de España.

Ramírez del Pozo, J., 1971. Bioestratigrafía y microfacies del Jurásico y Cretácico del Norte de España (región cantábrica). Memoria del Instituto Geológico y Minero de España, 78, 1-357.

Ramírez del Pozo, J., 1972. Algunos datos sobre la Estratigrafía y Micropaleontología del Aptense y Albense al oeste de Santander. Revista Española de Micropaleontología, num. Extraord, 30, 59-97.

Ramírez del Pozo, J., Portero-García, J.M., Olivé-Davó, A., Martín-Alafont, J.M., Aguilar-Tomás, M.J, 1974. Mapa Geológico de España a escala 1:50.000, Hoja nº 35, Santander. Serie Magna. Instituto Geológico y Minero de España.

Rat, P., 1959. Les pays crétacés basco-cantabriques (Espagne). Publications de l’Université de Dijon, 18, 1-525.

Reboulet, S., Szives, O., Aguirre-Urreta, B., Barragán, R., Company, M., Idakieva, V., Ivanov, M., Kakabadze, M.V., Moreno-Bedmar, J.A., Sandoval, J., Baraboshkin, E.J., Çaglar, M.K., Főzy, .I, González-Arreola, C., Kenjo, S., Lukeneder, A., Raisossadat, S.N., Rawson, P.F., Tavera, J.M., 2014. Report on the 5th International Meeting of the IUGS Lower Cretaceous Ammonite Working Group, the Kilian Group (Ankara, Turkey, 31st August 2013). Cretaceous Research, 50, 126-137.

Reitner, J., 1987. Mikrofazielle, palökologische und paläogeographische Analyse ausgewählter Vorkommen flachmariner Karbonate im Basko-Kantabrischen Strike Slip Fault-Becken-System (Nordspanien) an der Wende von der Unterkreide zur Oberkreide. Documenta naturae, 40, 1-2S9.

Reuss, A.E., 1862. Entwurf einer systematischen Zusammenstellung der Foraminiferen. Sitzungsberichte der Kaiserlichen Akademie der Wissenschaften in Wien, Mathematisch-Naturwissenschaftliche Classe (1861), 44(1), 355-396.

Rigaud, S., Blau, J., Martini, R., Rettori, R., 2015. Taxonomy, phylogeny, and functional morphology of the foraminiferal genus Involutina. Acta Palaeontologica Polonica, 60(1), 235-244.

Roemer, F., 1849. Texas: mit besonderer Rücksicht auf deutsche Auswanderung. Adolph Marcus: Bonn. 379pp.

Rosales, I., Schlagintweit, F., 2015. The uppermost Albian–lower Cenomanian Bielba Formation of the type-area (Cantabria, northern Spain): facies, biostratigraphy, and benthic Foraminifera. Facies, 61(3), 16, 30pp. DOI: https://doi.org/10.1007/s10347-015-0441-9

Rosales, I., Barrón, E., de Gea, G.A., Najarro, M., Castro, J.M., 2013. Nuevas aportaciones al conocimiento bioestratigráfico del Aptiense–Albiense del entorno de El Soplao. In: Rosales, I. (ed.). Avances en la investigación geológica de la Cueva El Soplao y su entorno. Publicaciones del Instituto Geológico y Minero de España, Serie Informes Técnicos, 7, 53-66.

Sahni, M.R., 1937. Discovery of Orbitolina-bearing rocks in Burma, with a description of Orbitolina birmanica sp. nov. Records of the Geological Survey of India, 71(4), 360-375.

Saidova, Kh.M, 1981. On an up-to-date system of supraspecific taxonomy of Cenozoic benthonic foraminifera (in Russian). Institut Okeanoligi P.P. Shirshova, Moscow, Akademija Nauk SSSR, 73pp.

Schlagintweit, F., Piller, W., 1990. Involutina hungarica (SIDO) from allochtonous Urgonian limestones of the Northern Calcareous Alps and remarks on the genus Hensonina Moullade and Peybernès, 1974. Beiträge zur Paläontologie, 16, 145-153.

Schlagintweit, F., Wilmsen, M., 2014. Orbitolinid biostratigraphy of the top Taft Formation (Lower Cretaceous of the Yazd Block, Central Iran). Cretaceous Research. 49, 125-133.

Schlagintweit, F., Bucur, I.I., Rashidi, K., Saberzadeh, B., 2013. Praeorbitolina claveli n. sp. (benthic foraminifera) from the Lower Aptian (Bedoulian) of Central Iran. Carnets de Géologie-Notebooks on Geology, Letter 2013/04, 255-272.

Schroeder, R., 1962. Orbitolinen des Cenomans Südwesteuropas. Paläontologische Zeitschrift, 36(3-4), 171-202.

Schroeder, R., 1963a. Palorbitolina, ein neues Subgenus der Gattung Orbitolina (FORAM.). Neues Jahrbuch für Geologie und Paläontologie Abhandlungen, 117, 346-359.

Schroeder, R., 1963b. Grundlagen einer Orbitoliniden- Biostratigraphie des tieferen Urgons im pyrenäisch- kantabrischen Grenzgebiet (Nordspanien). Neues Jahrbuch für Geologie und Paläontologie Monatshefte, 3, 320-326.

Schroeder, R., 1964a. Communication préalable sur l’origine des Orbitolines. Compte Rendu sommaire des séances de la Société géologique de France, 10, 411-41S.

Schroeder, R., 1964b. Orbitoliniden-Biostratigraphie des Urgons nordöstlich von Teruel (Spanien). Neues Jahrbuch für Geologie und Paläontologie Monatshefte, 1964, 462-472.

Schroeder, R., 1965a. Dictyoconus pachymarginalis n. sp. aus dem Apt des Elburz-Gebirges (Nord-Iran) (Studien über primitive Orbitolinidae III). Eclogae Geologicae Helvetiae, 58(2), 976-979.

Schroeder, R., 1965b. Neorbitolinopsis n. gen. und ihre systematische Position innerhalb der Orbitoliniden. Eclogae Geologicae Helvetiae, 58(1), 579-589.

Schroeder, R., 1972. Zwei neue Orbitolinidae (Foram.) der spanischen Kreide. Neues Jahrbuch für Geologie und Paläontologie Monatshefte, 2, 108-119.

Schroeder, R., 1985. Genre Simplorbitolina Ciry & Rat, 1953. In: Schroeder, R., Neumann, M., (coords.). Les Grands Foraminifères du Crétacé Moyen de la région Méditerranénne. Géobios mémoire special, 7, 46-50.

Schroeder, R., Poignant, A.F., 1964. Orbitolinopsis aquitanica, eine neue Foraminifere der Unterkreide der Aquitaine (SW- Frankreich) (Studien über primitive Orbitolinidae I). Eclogae Geologicae Helvetiae, 57(2), 553-558.

Schroeder, R., Neumann, M. (coords.), 1985. Les grands Foraminifères du Crétacé Moyen de la région Méditerranénne. Geobios, Mémoire Spécial, 7, 1-160.

Schroeder, R., Conrad, M.A., Charollais, J., 1968. Sixième note sur les Foraminifères du Crétacé inférieur de la region genevoise. Contribution à l’etude des Orbitolinidae: Valserina brönnimanni SCHOEDER & _CONRAD, n. gen., n. sp.; Paleodictyoconus barremianus (MOULLADE) et Paleodictyoconus cuvillieri (FOURY). Archives des Sciences, 20(2), 199-222.

Schroeder, R., Van Buchem, F.S.P., Cherchi, A., Baghbani, D., Vincent, B., Immenhauser, A., Granier, B., 2010. Revised orbitolinid biostratigraphic zonation for the Barremian– Aptian of the eastern Arabian Plate and implications for regional stratigraphic correlations. GeoArabia Special Publication, 4, 49-96.

Setoyama, E., Kaminski, M.A., Tyszka, J., 2011. Late Cretaceous agglutinated foraminifera and implications for the biostratigraphy and palaeobiogeography of the southwestern Barents Sea. In: Kaminski, M.A., Filipescu, S. (eds). Proceedings of the Eight International Workshop on Agglutinated Foraminifera. Grzybowski Foundation Special Publication, 16, 251-309.

Smout, A.H., Sudgen, W., 1962. New information on the foraminiferal genus Pfenderina. Palaeontology, 4, 581-591.

Ullastre, J., Schroeder, R., Masriera, A., 2002. Sobre la estratigrafía del singular corte de la Roca de Narieda (parte S de la serie del Cretácico inferior de Organyà). Pirineo catalán. España. Treballs del Museu de Geologia de Barcelona, 11, 67-95.

Wilmsen, M., 2000. Evolution and demise of a Mid-Cretaceous carbonate shelf: the Altamira Limestones (Cenomanian) of northern Cantabria (Spain). Sedimentary Geology, 133, 195-226.

Wilmsen, M., 2005. Stratigraphy and biofacies of the Lower Aptian of Cuchía (Cantabria, northern Spain). Journal of Iberian Geology, 31(2), 253-275.