New insights into the Barremian – lower Aptian calcareous nannofossils of the Mediterranean Tethys: Chronostratigraphic and paleobiogeographic implications

A detailed study of calcareous nannofossil assemblages from twelve uppermost lower Barremian – lower Aptian sections in the Subbetic Domain of the Betic Cordillera was performed. Seven new nannofossil species ( Cruci-biscutum bastetanum , Crucibiscutum gracile , Chiastozygus lamprostauros , Cyclagelosphaera platyaspis , Lithraphidites aichmoides , Lithraphidites pugio , and Rhagodiscus sicutclipeus ) are described, one species is emended ( Lithraphidites magnus ) and the taxonomic concept of the marker species Hayesites irregularis is discussed and clarified. The detailed stratigraphic ranges of the new species, together with those of other relevant taxa, are determined and correlated to standard ammonite biostratigraphy. Age estimates of biostratigraphically relevant calcareous nannofossil biohorizons are calculated using astrochronologically tuned cyclostratigraphic data. Five new calcareous nannofossil subzones are proposed which enhance upper Barremian biostratigraphic resolution at a regional scale and are directly correlated with respect to the standard Tethyan ammonite zonation. Two of the new species described here are used as biostratigraphic markers for the newly proposed subzones. The duration of each subzone is provided through astrochronological calibration. This study allows the refinement of the calcareous nannofossil zonation for the Mediterranean – Atlantic province of the Tethyan Realm. The implications of these new results are discussed regarding the extant definition and use of the Barremian/Aptian boundary. The morpho-evolutionary trends of selected nannofossil groups are reviewed in relation to the latest Barre-mian – Aptian paleogeographic changes, showing these were a prominent factor controlling calcareous nanno-plankton evolution and biogeographical distribution in the west European-Atlantic region.

One of the most convenient ways to identify these episodes is through their C-isotope imprints, as their lithological expression in different basins may vary depending on the local depositional and environmental conditions (e.g., Jenkyns, 2010).The calibration of the resulting C-isotope curves to biostratigraphy, chronostratigraphy, magnetostratigraphy and to geochronology will greatly impact global correlations (e.g., Ogg et al., 2016;Olierook et al., 2019;Gradstein et al., 2020;Martinez et al., 2020;Castro et al., 2021;Zhang et al., 2021).Tethyan ammonite biostratigraphy (e.g., Reboulet et al., 2018) represents, in the Barremian, a high-precision reference scale to which Cisotope data could be tied.In the absence of ammonites, biostratigraphic scales based on calcareous nannofossils, planktonic foraminifera and/or radiolarians) may be used (e.g., Thierstein, 1971Thierstein, , 1973Thierstein, , 1976;;Sissingh, 1977;Roth, 1978;Perch-Nielsen, 1985;Coccioni and Premoli-Silva, 1994;Jud, 1994;O'Dogherty, 1994;Bralower et al., 1995;Premoli Silva et al., 2018).However, the biostratigraphic resolution of these microfossil groups is currently much lower compared to that obtained using ammonites.In addition, the calcareous nannofossil zonations have a low resolution with regard to counterpart schemes developed for the West European Province of the Boreal Realm (e.g., Jakubowski, 1987;Bown et al., 1998;Jeremiah, 2001).This may be due, in part, to the spread of sedimentary facies unfavorable for a good preservation of the taxa (i.e., limestones) in the Tethyan Realm, leading to a poor investigation in land sections where nannofossils can be correlated to other reference groups such as ammonites.
The Barremian successions of argillaceous limestones and marlstones of the Subbetic Domain in the Betic Cordillera are well dated by ammonites (e.g., Company et al., 1992Company et al., , 1995Company et al., , 2003;;Aguado et al., 1992Aguado et al., , 1997)), and proved to contain abundant and moderately to wellpreserved calcareous nannofossil assemblages (e.g., Aguado et al., 1997Aguado et al., , 2014a)).Some of these successions were also studied for C-isotope stratigraphy, both MBE and TE were identified in them (e.g., Aguado et al., 2014a;Martinez et al., 2020), and they have been recently calibrated by astrochronology (Martinez et al., 2020).These successions represent good candidates to improve Tethyan calcareous nannofossil biostratigraphy by providing adequate chronostratigraphical and geochronological frameworks to tie all the biostratigraphic events.
The aim of this paper is to improve the resolution of the Barremian calcareous nannofossil biozonation for the Mediterranean so it can be used as an alternative to ammonite zones.The stratigraphic range of the calcareous nannofossil species with biostratigraphic potential, together with that of other relevant taxa, will be directly correlated to standard ammonite biostratigraphy and to the geochronologic scale.Finally, as the Barremian/Aptian boundary is included within the interval studied, it will be discussed in the light of new findings.

Geological setting
All sections studied belong to the Subbetic Domain (Fig. 1), a complex tectonostratigraphic unit that paleogeographically corresponds to Fig. 1.Geologic sketch of the central and eastern sectors of the Betic Cordillera, showing the present-day location of the sections included in this study.A: X.Cp 2 section; B: X.V 1 section; C: X.Kv and X.Kv 2 sections; D: X.Ag 6 section; E: RA03 section; F: X.CT and X.HA sections; G: X.Z section; H: X.F and X.F1 sections; I: X. CO 2 section.
Except for X.Cp 2 section (see Chapter 3), all sections studied belong to the widely extended Lower Cretaceous Carretero Formation (Figs. 3,4).Roughly, the lithologic succession of this formation (e.g., de Gea, 2004) consists of a rhythmic alternation of yellowish to gray argillaceous limestone beds (5-90 cm thick) and gray marlstone interbeds (3-760 cm thick).The lime fraction is partially made up of calcareous nannofossil remains and carbonate particles of micritic size (micarbs) which probably originated from the adjacent platforms.Clay minerals are, by far, the main components of the detrital fraction (e.g., Aguado et al., 2008).Overlying the Carretero Formation, some sections include parts of the Argos, Fardes, or Carbonero formations (Figs. 3,4; see also Supplementary Material 1 (SM1) for details on lithostratigraphy and biostratigraphy).
Although sections X.Cp 2 , RA03, X.CT, X.HA, X.F, X.F1 and X.CO have been studied previously (see SM1), new smear-slides were prepared and studied for all samples.Samples from X.V 1 , X.Kv, X.Kv 2 , X. Ag6 and X.Z sections (370) are new.The number of samples studied in each section and their respective positions are stated in Figs. 3, 4, and in Supplementary Material 2 (SM2).The sampling intervals were highly variable (Figs. 3 and 4), from 6 to 7 cm (e.g., sections X.V 1 and X.Kv 2 ) to several meters (e.g., lower part of X.F section).Except for samples from the RA03 section and those from the uppermost Barremian to lower Aptian parts of the X.F and X.F1 sections, the remainder of them are directly correlated to ammonite zones/subzones (Aguado, 1994;Aguado et al., 1992, 1997, Aguado et al., 2017;Company et al., 1995, and this paper).In the present work, the standard ammonite zonation for the Mediterranean Province (Reboulet et al., 2018) is followed, and used as a reference to calibrate the calcareous nannofossil bioevents.In the absence of magnetostratigraphical data, the base of the Deshayesites oglanlensis ammonite Zone (AZ) is used here to determine the base of the Aptian (Reboulet et al., 2011(Reboulet et al., , 2018)).
Preservation in the assemblages was evaluated in each sample (see SM2) based on the visual criteria established by Roth and Thierstein (1972) and Roth (1983).Limestone beds were avoided for sampling, as they contain impoverished (poorly to moderately preserved) assemblages with moderate to heavily overgrown taxa.Overall abundance per sample was estimated by counting the total number of nannofossils in 20 random fields of view.
Photomicrographs of calcareous nannofossils were acquired with an Olympus Camedia C5050 camera attached to the Olympus BHSP microscope, using cross-polarized light (XPL).A wide variability of size was observed for some taxa recorded throughout the studied interval.To test whether size of specific taxa fluctuates throughout the studied interval, specimens of Lithraphidites spp.(120), Hayesites irregularis group (140) and Flabellites oblongus (120) were photographed and measured.In addition, some specimens (6-22) of the new species described were also photographed and measured.The results are documented in the SM2.Measurements were taken using ImageJ software, with an accuracy of ±0.03 μm.Regarding precision, in a set of 10 repetitive measurements of 10 specimens, the error was lower than ±0.14 μm with a 95% confidence level.The lengths (L) and widths (W) of Lithraphidites spp., H. irregularis gr. and F. oblongus specimens were later used to test whether these three groups consist of several taxa.
To test the supposed multimodality in the populations of the measured taxa, mixture analyses were applied to the whole data sets, (i.e., all specimens of each group pooled together) using the free PAST v4.05 software package (Hammer et al., 2001).This statistical analysis is a maximum-likelihood method for estimating the descriptive parameters (mean, standard deviation and proportion) of two or more distinct distributions, based on an initially pooled univariate sample (Hammer and Harper, 2006).The minimum values of the Akaike Information Criterion (AIC, Akaike, 1974) helped to identify the groups obtained by mixture analysis with the lowest overfitting (Hammer et al., 2001).The number of bins for histograms in mixture analyses follows the Sturges' rule (k = (log 2 n) + 1), where k is the number of bins and n the number of observations).

Nannofossil abundance and preservation
Calcareous nannofossil abundance usually fluctuates between >5 and 30 specimens per field of view (SFOV), with only discrete samples showing abundances below 5 SFOV, while 22 samples were barren (see SM2).Nannofossil assemblages are rich and moderately to well preserved, showing slight to moderate overgrowth except for those from the organic-rich beds of X.Ag6 and X.Z sections, which showed moderate to strong etching (see SM2).

Mixture analyses
Fluctuations observed in length (L) and width (W) in the pool of the measured specimens of Lithraphidites spp.(Fig. 5A-D) suggest that several species can be differentiated.The results of a mixture analysis performed on the W values (Fig. 5E) reveal three different-sized groups.The first group corresponds to L. carniolensis (Fig. 5A), while the second and third group correspond to L. aichmoides (Fig. 5B; Chapter 6) and to the L. pugio/L.magnus plexus respectively (Fig. 5C, D).The same statistical analysis was applied to the length (L) of all specimens with W greater than 4.5 μm (L.pugio/L.magnus plexus).The frequency histogram (Fig. 5G) reveals the existence of two different-sized groups, which represent the new species L. pugio and L. magnus (Fig. 5C, D; Chapter 6).Fig. 5H shows the descriptive parameters resulting from the mixture analysis performed on W in the whole data set and on L in those specimens having a W greater than 4.5 μm.However, total length (L) proved not to be an outright criterion to separate the latter two species, instead the L/W ratio was more effective (Fig. 6; see also Chapter 6).
Hayesites irregularis is an important marker species in the Tethyan Realm (e.g., Thierstein, 1973;Perch-Nielsen, 1985;Bralower et al., 1995).Its taxonomic clarification can increase the biostratigraphic precision of stratigraphic correlations.Variations observed in the length (L) and width (W) of the specimens measured in this study (Fig. 7A, B) suggest the presence of two morphotypes in the H. irregularis group (gr.).This was corroborated by the results of a mixture analysis on the L/W ratio of the complete pool of measurements (Fig. 7C).Forms with a nearly circular outline (L/W smaller or equal to 1.12), being younger in time, were assigned to H. irregularis sensu stricto (s.str.).Specimens having a more elongated outline (L/W > 1.12) and poorly defined elements, being slightly older, were assigned to H. irregularis morphotype E (H. irregularis E; Chapter 6).
Mixture analyses performed on size measurements (L and W) of specimens of Flabellites oblongus sensu lato (s.l.) spread across the uppermost lower Barremian-lower Aptian of the study sections (see SM2 and Fig. 8) provided non-conclusive results.These showed similar AIC values for unimodal/bimodal solutions suggesting a rather continuous increase in size through the complete data pool (Fig. 8) thereby hindering a clear separation of different populations (see Chapter 6).

Sequence of nannofossil bioevents
One hundred and four taxa were identified through the complete interval studied, including 7 new species (see SM2 and Chapter 6).The following sequence of bioevents (from bottom to top) has been observed: A summary of the main bioevents recorded and their stratigraphic context is shown in Fig. 9.

Biostratigraphic remarks
Although most of the taxa shown in Fig. 9 have stratigraphic value, several of them (e.g., Chiastozygus lamprostauros, Crucibiscutum gracile, Lithraphidites magnus, Nannoconus sp.cf.N. truittii, Phosterolithus prossii, Rhagodiscus sicutclipeus and Stoverius acutus) are rare and/or have a spotty and discontinuous record (drawn in dashed line in Fig. 9) throughout a substantial part of their respective stratigraphic ranges.
Other taxa have unclear LOs due to the presence of transitional morphologies in the stratigraphic record.Such is the case of the LOs of Rhagodiscus gallagheri (obscured by the presence of transitional forms from small Rhagodiscus asper) and Lithraphidites magnus (difficult to differentiate from transitional specimens from Lithraphidites pugio in the upper part of the Hemihoplites feraudianus ASz).The LO of Nannoconus truittii (upper part of Deshayesites oglanlensis AZ) is masked by the record of forms similar to this species reported here as Nannoconus sp.cf.N. truittii (see Chapter 6: Figs. 3, 4, and range charts of SM2).Finally, specimens of Rhagodiscus gallagheri transitional to Rhagodiscus angustus were observed from the upper part of the Martelites sarasini AZ.The oldest forms assignable to R. angustus were recorded from the uppermost part of the Deshayesites oglanlensis/lowermost Deshayesites forbesi AZs upwards, which agrees with the observations of Rutledge and Bown (1996).
Other bioevents, such as the LOs of Flabellites oblongus and Hayesites irregularis have been used as biostratigraphic markers (e.g., Thierstein, 1973Thierstein, , 1976;;Bralower et al., 1995), but they were never adequately correlated to ammonite biostratigraphy.The LO of F. oblongus was recently identified in the lower part of the Moutoniceras moutonianum AZ (Aguado et al., 2014a;Martinez et al., 2020).Here we report the LO of F. oblongus from the Holcodiscus caillaudianus ASz in the X.Kv and X.V 1  sections.This species is very rare and shows a spotty record throughout the H. caillaudianus ASz and lowermost part of the M. moutonianum AZ.Its consistent record (Figs. 3, 9) correlates with the level where Aguado et al. (2014a) and Martinez et al. (2020) reported the LO of this species.
Hayesites irregularis E is rather rare near its LO and is more abundant from the upper part of the Hemihoplites feraudianus ASz.The LO of H. irregularis s.str.(Chapter 4.3 and Fig. 9) was not recorded until the mid part of the Imerites giraudi AZ (Figs. 3,4;SM2).

Proposed biozones
Here we document a detailed zonation of the upper Barremian-lower Aptian interval of the Mediterranean area.The zonation uses the scheme of Bralower et al. (1995) by adding new subzones as digits.The proposed subzones are useful on a regional scale (e.g., Martinez et al., 2020), but they could be applied to the Mediterranean-Atlantic area, as some of the marker species were also recorded from outside of the Betic Cordillera (chapters 5.4, 6).
Base: LO of Flabellites oblongus.Calibrated here to 124.72 Ma, slightly earlier than in Martinez et al. (2020).This bioevent also corresponds to the base of the NC5E Subzone (Bralower et al., 1995).
Age and stratigraphic range: Latest early Barremian-earliest late Barremian (upper part of the Holcodiscus caillaudianus ASz-lower part of the Gassendiceras alpinum ASz).This subzone has a duration of 1.15 myr following the chronostratigraphy of Martinez et al. (2020) Age and stratigraphic range: Latest Barremian-early Aptian (lower part of the M. sarasini AZ-Deshayesites forbesi AZ/Hedbergella excelsa Zone of planktonic foraminifera).This subzone has a duration much greater than 0.97 myr following Martinez et al. (2020).

Calcareous nannofossil bioevents, C-isotope stratigraphy and the Barremian/Aptian boundary: an update
Currently, the boundary between the Barremian and Aptian Stages is provisionally located at the base of the CM0r magnetochron, and the Gorgo a Cerbara section is its possible Global Stratotype Section and Point (Erba et al., 1996).This designation was made based on the supposed proximity of the lower boundary of CM0r to the LO of deshayesitid ammonites (=base of the Aptian used by ammonite specialists; e.g., Reboulet et al., 2018).However, magnetostratigraphic record is very poorly preserved in hemipelagic sections where ammonite zonations are established and, to date, no direct calibration of magnetic polarity and ammonite zones is so far available for the upper Barremian-lowermost Aptian interval.
The LO of Hayesites irregularis has been reported in Gorgo a Cerbara from ~6 m below the base of CM0r (Patruno et al., 2015).New findings (Martinez et al., 2020, and present paper) indicate that the LO of H. irregularis gr.occurs in the lower part of the Hemihoplites feraudianus ASz (see chapters 4.3 and 5.1), below that reported by Aguado et al. (1997).This is consistent with the stratigraphy of Gorgo a Cerbara proposed by Frau et al. (2018), and indicates that the LO of H. irregularis showing the distribution curves resulting from a mixture analysis applied to the L/W ratio of all measured specimens.The small table shows the descriptive statistical parameters (proportion, mean, and standard deviation) resulting from the mixture analysis.Two populations are revealed based on the L/W ratio.The forms with L/ W > 1.12 were assigned to H. irregularis E. See text for details.
R. Aguado et al. is far below the base of the Aptian as defined by the first appearance of deshayesitids.
The wc > nc Event (e.g., Erba et al., 1999;Larson and Erba, 1999;Channell et al., 2000;Bellanca et al., 2002;Tremolada et al., 2006;Erba et al., 2019) was recorded in the Gorgo a Cerbara section within CM0r (Channell et al., 2000;Patruno et al., 2015).This horizon has been here correlated to the lower part of the Martelites sarasini AZ (Figs. 3,4,9 and SM2).This change in the proportions of narrow/wide canal nannoconids requires time-consuming analyses to be determined, and probably is not a good alternative as a primary marker to be used in the definition of the base of the Aptian, but it could be used as a secondary indicator at least in the Tethyan Realm.
The HO of the new coccolith species Crucibiscutum bastetanum follows the wc > nc Event and slightly predates the onset of the C-isotope Intra-Sarasini Negative Excursion (ISNE) linked to the Taxy Episode (Föllmi, 2012;Frau, 2020;Martinez et al., 2020).According to the chronology of Martinez et al. (2020), this bioevent predates the Barremian/Aptian boundary by 0.57 myr, being a moderately good approximation to it.However, this new species has been identified only in the Subbetic Domain as yet.
The LOs of Nannoconus truittii and Rhagodiscus angustus (upper part of Deshayesites oglanlensis-lower part of Deshayesites forbesi AZs) do not provide reliable events because they are masked by the presence of specimens with transitional morphologies (see chapters 5.1 and 6).No other reliable calcareous nannofossil event has been recorded from the Betic Cordillera, until the 'nannoconid crisis', which has been correlated to the upper part of the D. forbesi AZ (Aguado et al., 1999;Moreno-Bedmar et al., 2009, 2012).
The C-isotope ISNE, has been identified in several sections within the mid-upper part of the Martelites sarasini AZ (Kuhnt et al., 1998;  Moullade et al., 1998aMoullade et al., , 1998b;;Godet et al., 2006;Frau, 2020;Martinez et al., 2020).Its top is close to the base of the Aptian as defined by ammonite biostratigraphy.In sections from SE France and Spain (see also Sanchez-Hernandez and Maurrasse, 2016), the ISNE is made of two spikes with lower C-isotope values separated by a short excursion with slightly higher values (Fig. 10).In the Gorgo a Cerbara section the ISNE consists of only one spike in the δ 13 C curve, which is located at the top of CM0r and correlates with the change from the 'Maiolica' to the 'Marne a Fucoidi' formations (e.g., Godet et al., 2006;Stein et al., 2011;Frau et al., 2018).
Fig. 10 summarizes the findings of the current study around the Barremian-Aptian interval and correlates the X.Kv 2 section and some relevant French and Italian sections by using bio-and chemostratigraphy.Given the proximity of the ISNE (especially its top) to the base of D. oglanlensis AZ, we think this negative excursion of the δ 13 C carb is an alternative for defining the base of the Aptian.

Barremian-Aptian calcareous nannofossil morpho-evolutionary trends and paleobiogeography
Although the driving factors for size changes of calcareous nannofossils have been discussed in the last decades, both for living assemblages and for fossil species, these still remain unclear.In living assemblages, some link was found between coccolith morphology and environmental factors such as sea-water temperature and salinity (e.g., Bollmann and Klaas, 2008;Bollmann et al., 2009;Triantaphyllou et al., 2010).In deeper time, studies are more problematic due to difficulties in the reconstruction of the paleoenvironmental conditions and the effects of preservation in the fossil assemblages.Despite this, factors such as sea-water temperature (e.g., Bornemann and Mutterlose, 2006;Linnert and Mutterlose, 2013;Wulff et al., 2020), nutrient (e.g., Erba et al., 1995;Giraud et al., 2006;Linnert and Mutterlose, 2013;Lübke et al., 2015;Wulff et al., 2020) and light availability (e.g., Lübke et al., 2015;Lübke and Mutterlose, 2016), acidification (e.g., Erba et al., 2010), or trace metal-and CO 2 water concentrations (e.g., Faucher et al., 2017) are thought to have influenced coccolith growth and calcification.Coccolith size change in the fossil record has been also attributed to evolutionary processes (López-Otálvaro et al., 2012;Gollain et al., 2019).Changes toward decreasing size are usually claimed to represent a response to stressful and unstable environmental conditions (eutrophication, lower temperature and light availability, increased CO 2 concentrations and acidification) in some fossil coccolith species, while other taxa do not show size alterations.Long-term size increases are however claimed to be related to evolutionary processes.Since most of the observed biometric changes in this study (e.g., in Flabellites oblongus, in the new Lithraphidites morphospecies and in the Hayesites irregularis gr.) represent mainly long-term size increases, they are interpreted as related to evolutionary processes.
The biometric studies cited above were all performed on coccolith species.However, most of the biometric data presented in this study correspond to nannoliths whose possible relationship with coccoliths is uncertain and whose ecological preferences are mostly unknown.
However, our data suggest that some link existed between morphologic change/evolutionary patterns and paleogeography.Here we review the morpho-evolutionary trends of selected nannofossil groups in relation to the latest Barremian-Aptian paleogeographic changes.
The genus Lithraphidites first appeared in the Berriasian (e.g., Perch-Nielsen, 1985) and consists of bladed rod-shaped nannoliths that taper Fig. 9. Geochronostratigraphic sketch showing a compilation of the main biostratigraphic events recorded in this study.Geochronology and ammonite stratigraphy after Martinez et al. (2020).Positions of the MBE (Mid-Barremian Episode) TE (Taxy Episode) and C-isotope Intra-Sarasini Negative Excursion (ISNE) are based on data from Martinez et al. (2020).Calcareous nannofossil subzones are those proposed here.The stratigraphic ranges of all new species described in present study and the newly described calcareous nannofossil subzones are calibrated to ammonite zones and to geochronology.Ranges with black lines correspond to marker species.Intervals of the species ranges with very rare/spotty record are marked with dashed line.Numbers in parentheses refer to the numerical ages (in Ma) of the bioevents associated to zonal markers using the chronology of Martinez et al. (2020).The wc > nc horizon indicates the stratigraphic position where the wide-canal nannoconids outnumber the narrow canal nannoconids (wc > nc Event).Fig. 10.Correlation of the uppermost Barremian-lowermost Aptian interval of the sections of Barranco de Cavila (X.Kv 2 ), Angles, Casis-La Bédoule and Gorgo a Cerbara using ammonite and C-isotope data.Light green shaded band correspond to the ISNE associated to the Taxy Episode.Light blue shaded band correspond to the OAE 1a.Lines of correlation: dashed lines based on ammonite biostratigraphy, dotted-dashed lines are based on calcareous nannofossils, and dotted line is based on C-isotope curves.Data for X.Kv 2 section after Martinez et al. (2020) and this paper; data for Cassis-La Bédoule after Kuhnt et al. (1998) and Moullade et al. (1998a); data for Angles after Delanoy (1995), Wissler et al. (2002) and Godet et al. (2006); data for Gorgo a Cerbara after Stein et al. (2011Stein et al. ( , 2012) ) and Frau et al. (2018).In Angles section, the boundary between Martelites sarasini and Deshayesites oglanlensis AZs marked with a star is after Godet et al. (2006), the boundary marked with two stars (bed 197b) is after Delanoy (1995), and reinterpreted here following Reboulet et al. (2011).(For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)toward both ends, have a cruciform cross-section and may have a minute basal murolith coccolith.Janin (1998) suggested affinities of these nannoliths with Actinozoa that most authors do not find compelling, and it is currently thought that they may represent disarticulated spines of a heterococcolith (https://www.mikrotax.org/system/index.php?taxo n=Lithraphidites&module=ntax_mesozoic).
A common evolutionary trend within the genus Lithraphidites consists of a widening of the longitudinal blades in a symmetrical or asymmetrical way.This trend episodically originated in several species across the Cretaceous (e.g., L. houghtonii and L. moray-firthensis in the Aptian; L. alatus, L. acutus and L. eccentricus in the Albian-Cenomanian; L. praequadratus, L. quadratus and L. kennethii in the Campanian-Maastrichtian).The current work shows this trend also operated on the Tethyan-Atlantic Lithraphidites across the latest early Barremian-late Barremian (Figs. 11,12,13), leading to the differentiation of three species (L.aichmoides, L. pugio and L. magnus; Chapter 6).These constitute the earlier known record of this evolutionary trend within the genus Lithraphidites.
Besides the Subbetic Domain, L. magnus was recorded in the North American Basin (Covington and Wise Jr., 1987), West Iberian Continental Margin (Bralower et al., 1994) and northern Gargano (Cobianchi et al., 1997).This suggests a westernmost Tethys-North Atlantic paleogeographic record for this species (Fig. 2).The records of L. aichmoides and L. pugio are so far limited to the Subbetic as both are new species described in the current work and remain undifferentiated from L. magnus in the previous papers.
The marker species Flabellites oblongus and Hayesites irregularis gr. also underwent morphologic changes across the late Barremian-early Aptian here interpreted as the result of long-term evolutionary processes.The early coccoliths of F. oblongus are small, progressively increasing to medium size from the Gerhardtia provincialis ASz upwards (Figs. 8, 9; see Aguado et al., 1997;Bown, 2005).Regarding the H. irregularis gr., aside from the two morphotypes identified by mixture analyses (Chapter 4.2, 6; Fig. 7), a gradual increase in size has been observed in the specimens of H. irregularis s.str.across the Martelites sarasini AZ (SM2).The LOs of F. oblongus and H. irregularis are often recorded, as rare species, from the lower Aptian interval (Prodeshayesites fissicostatus/tenuicostatus-Deshayesites forbesi AZs) in the WEP of the Boreal Realm (e.g., Erba et al., 1996;Bown et al., 1998;Mutterlose and Böckel, 1998;Jeremiah, 2001).However, these records correspond to the entry of the species in the Boreal Realm, which is concomitant with the homogenization of floras and faunas and Tethyan influx described above, and do not correspond to the true (evolutionary) LOs of these species.
During the late Barremian, the WEP of the Boreal Realm and the Tethyan Realm were nearly isolated from each other (e.g., Ziegler, 1990;Mutterlose, 1992b;Barrier et al., 2018).However, Jeremiah (2001) recorded short influxes of Micrantholithus stellatus in rocks equivalent to the uppermost Barremian Parancyloceras bidentatum AZ in the North Sea Basin (Fig. 2).The LO of M. stellatus in the Subbetic Domain has been recorded in the upper part of the Gerhardtia provincialis ASz (see chapters 4.3 and 5.1, Fig. 9), that is, much earlier that its occurrence in the North Sea Basin.Based on its morphological similarities with the extant species Braarudosphaera bigelowii, the genus Micrantholithus is commonly interpreted as a marginal/neritic taxon (e.g., Roth, 1994; Applegate et al., 1989; Street and Bown, 2000;Bown, 2005;Bottini and Mutterlose, 2012;Quijano et al., 2012;Aguado et al., 2014aAguado et al., , 2014b)).The short influxes of M. stellatus in the North Sea Basin suggest that shallow seaways intermittently connected the WEP of the Boreal Realm and the Tethyan Realm already during the late Barremian, favoring the expansion of Tethyan neritic nannofloras into the Boreal Realm.As no Boreal taxa were recorded in our sections during this interval, we suggest this influx of neritic Tethyan taxa (M.stellatus) into the Boreal Realm was probably favored by increasing temperatures related to the Taxy Episode.Late Barremian episodes of sea isolation, coincident with regressive periods, favored the allopatric speciation of calcareous nannoplankton and the apparition of endemic taxa under restricted conditions, (e.g., in the WEP of the Boreal Realm; Jakubowski, 1987;Crux, 1989;Bown et al., 1998;Jeremiah, 2001).During moderate to extensive high stands, seaways opened improving the communication between the Tethyan Realm and the WEP of the Boreal Realm, and nannofloral exchange (e.g., Mutterlose, 1992aMutterlose, , 1992bMutterlose, , 1996)).All the described biogeographic data suggest that paleogeography played a fundamental role in the evolution and spatial distribution of calcareous nannoplankton in the west European-Atlantic region during the late Barremian-early Aptian interval.

Systematic paleontology (by R. Aguado)
The taxonomic descriptions below follow the terminology guidelines of Young et al. (1997) and the higher taxonomy follows Bown and Young (1997).Only taxonomic references that do not appear in Bown (1998) or cannot be found in the Nannotax website (http://www.mikrotax.org/Nannotax3/) are provided in the reference list.In the following descriptions, L = length, W = width, XPL = cross-polarized light, CNZ /CNSz = calcareous nannofossil Zone/Subzone.
Images and smear slides of type material are stored in the Department of Geology of the University of Jaén (DG image numbers bracketed in the descriptions below).All species names are registered at the Plant Fossil Names Registry (PFNR; https://plantfossilnames.org) of the National Museum Prague.The corresponding PFNR nomenclatural act number is indicated for each new species.The reference calcareous nannofossil biozonation used is that of Bralower et al. (1995), with the modifications introduced in this paper.The reference planktonic foraminifera biozonation is that of Coccioni et al. (2007).
Diagnosis: Small to medium-sized (3.4-5.5 μm) broadly elliptical to normally elliptical Crucibiscutum coccoliths with a relatively narrow central area spanned by off-axial (slightly rotated) cross bars.The rim is bicyclic, with the bright inner cycle being wider (~1 μm width) than the outer dark cycle.
Description: Under XPL, the bright inner cycle of the rim has equal or greater width than the outer dark cycle.The central area is nearly filled by a relatively thick cross slightly rotated with respect to the axes of the ellipse defined by the rim.The cross is bright (although not as bright as the inner cycle of the rim) under XPL when oriented at 45 • , and dark when oriented to 0 • .The long and short arms of the central cross usually have slightly different rotation.
Type locality: X.HA section, Province of Granada, southeastern Spain.
Occurrence: This species has a short range.Its LO was found near the top of the Gerhardtia sartousiana AZ, (upper part of the Hemihoplites feraudianus ASz), which is equivalent to the lowermost part of the NC6A1 CNSz, and is shortly preceded by the LO of the primitive forms (elongated) of Hayesites irregularis E. Its HO was recorded in the lower part of the Martelites sarasini AZ (upper boundary of the NC6A1 CNSz), shortly following the nc > wc Event (Chapter 4.3, Fig. 9).Usually this species is a rare component of the assemblages, being more abundant from the upper part of the Imerites giraudi AZ to its HO, but shows a rather consistent record.It was recorded in sections X.Ag 6 , X.F, X.F1, X. HA, X.Kv, X.Kv 2 , and RA03 from the Subbetic Domain in the Betic Cordillera (southern Spain).Its HO is used here to define the upper boundary of the NC6A1 CNSz.2020), the range of P. giraudii is early Hauterivian-late Barremian (HO in T. vandenheckii AZ), being earlier in time than C. bastetanum and there is a stratigraphical displacement between these two species.
Diagnosis: Small (3.4-4.7 μm) sub-circular to broadly elliptical (axial ratio ~ 1.1) Crucibiscutum coccoliths with a wide central area spanned by slim axial cross bars.The rim is narrow, bicyclic, with the bright inner cycle being usually slightly narrower (~0.5 μm width) than the outer dark cycle.
Description: The central area is wide (around twice as wide as the rim width) and partially covered by a slim bright cross with arms aligned with respect to the axes of the ellipse defined by the rim.The central cross is slightly brighter under XPL when oriented at 45 Type level: Uppermost Barremian, sample X.HA-2 [DGF001] (NC6A1) nannofossil Subzone; upper part of the Imerites giraudi AZ.
Type locality: X.HA section, Province of Granada, southeastern Spain.
Occurrence: Found throughout the upper Barremian to lower Aptian (uppermost part of the NC5E1 to NC6A2 CNSzs; lower part of the Gassendiceras alpinum ASz to Hedbergella excelsa Zone of planktonic foraminifera) in sections X.Cp 2, X.F, XF1, X.HA, X.Kv, X.Kv 2 , and RA03 from the Subbetic Domain in the Betic Cordillera (southern Spain).This species was also recorded, as Cruciplacolithus hayi, in DSDP Site 603 off Cape Hatteras by Covington and Wise Jr. (1987)   Site 641 by Bralower et al. (1994).
Remarks: Crucibiscutum gracile differs from all previously described Neocomian Crucibiscutum species (C. giraudii, C. neuquenensis, C. pinnatus, C. ryazanicum, C. salebrosum, C. trilensis) including C. bastetanum (above) by having a wider central area and a narrower rim with a lower axial ratio (~ 1.1), usually showing a sub-circular outline.Crucibiscutum gracile also differs from C. bastetanum, C. trilensis, and C. ryazanicum in having an axial slim cross spanning the central area.Crucibiscutum gracile has lower axial ratio and a wider and open central area than C. pinnatus.Crucibiscutum hayi, from the Upper Albian, has a greater axial ratio, a wider rim and a central area slightly narrow than that of C. gracile.
Family Cretarhabdaceae Thierstein, 1973. Genus Flabellites Thierstein, 1973.Flabellites oblongus (Bukry, 1969) Crux in Crux, 1989.Remarks: A known morphological trend for the specimens of Flabellites oblongus along the upper Barremian-Albian (e.g., Aguado et al., 1997;Bown, 2005) is the increase in coccolith size.Recently, de Kaenel et al. ( 2020) erected a new species (Flabellites eclepensensis) for those small (3 to <5 μm) specimens previously assigned to F. oblongus (e.g., Aguado et al., 2014a).However, the mixture analysis performed in the present study (Chapter 4.1 and Fig. 8) suggest a rather continuous increase in size of the measured population.The selected size of 5 μm by de Kaenel et al. (2020) to separate the specimens assigned to F. eclepensensis within the complete pool of F. oblongus s.l.seems arbitrary.In the absence of any other distinctive biometric (e.g., ellipticity) or morphological character that could help in a net separation of both species, we opted here to retain the wide concept (F.oblongus s.l., or simply F. oblongus) of the species.
Diagnosis: Small to medium-sized (4.3-7.2 μm) normally elliptical Chiastozygus coccoliths with a narrow (~1.2 μm) rim.The relatively wide central area is covered by a diagonal cross whose arms are seen simple and brighter than the rim when the longitudinal direction is oriented at 45 • under XPL.
Description: This species has an axial ratio ~ 1.4 and a relatively narrow rim, which is dark and diffusely bicyclic under XPL.The diagonal cross spanning the central area have narrow (~0.5 μm) arms that show median lines and remain dark when the longitudinal direction is oriented at 0 • .These arms are seen simple (without median lines) and bright under XPL when the longitudinal direction is oriented at 45 • .The angle between the arms of the cross is greater (~105 • ) in the longitudinal direction than in the transverse direction (~75 • ).The arms of the diagonal cross are asymmetrical (slightly rotated) with respect to the axes of the ellipse.In some specimens, the diagonal cross supports the base of a distal stem.
Remarks: Chiastozygus lamprostauros is rather similar to Chiastozygus amphipons (Santonian-Maastrichtian) in rim construction and optical behavior from which is differentiated by having the arms of the diagonal cross slightly rotated with respect to the axes of the ellipse (asymmetric).It differs from Chiastozygus bifarius (Albian-Maastrichtian) and Chiastozygus platyrhethus (Aptian-Coniacian) by having a narrower, simple (with no median lines when oriented at 45 • ) diagonal cross with slightly asymmetrical (rotated) arms with respect to the axes of the ellipse.Chiastozygus litterarius (Aptian-Maastrichtian) is a rather poorly documented taxon originally described from the upper Maastrichtian sedimentary successions of Poland, and is characterized by having a weakly birefringent diagonal cross instead of the bright cross when oriented at 45

Derivation of name:
From the Latin words sicut meaning 'as', 'such as', and clipeus, the elliptical war shield used by the ancient Greeks and Romans which resembles the XPL image of this species.
Diagnosis: Small to medium-sized (4.6-5.9 μm) normally elliptical Rhagodiscus coccoliths with a relatively wide central area bearing a small spine base, which is bright in XPL.The rim and central area images are distinctly dark in XPL.
Description: This species has an elliptic rim (axial ratio ~ 1.4) and central area that remain relatively dark under XPL.The central area bears a small spine base, which is seen as a bright, solid (not hollow) circle traversed by four sharp extinction gyres.The spine base is relatively small (~1.3 μm in diameter), remains isolated in the middle of the central area and does not reach the internal margin of the rim.
Remarks: Rhagodiscus sicutclipeus is rather similar to Rhagodiscus achlyostaurion (upper Aptian-Coniacian) but differs by its noticeably smaller central spine base, which does not seem hollow and does not reach the internal margin of the rim.Rhagodiscus pancostii (Lower Turonian) is smaller in size (holotype length = 3.96 μm) and lacks the distinctly optical features present in the rim and central area of R. sicutclipeus.Rhagodiscus hamptonii (upper Aptian-Upper Albian) is greater in size and has a less clearly defined (usually absent) bright spine base.Rhagodiscus buisensis lacks the solid birefringent spine base (de Kaenel et al., 2020) present in R. sicutclipeus.Probably most of the Barremian-lower Aptian occurrences of R. achlyostaurion cited in the literature correspond to R. sicutclipeus.
Description: Circular placoliths with proximal and distal shield elements composed by R-units.In distal view, the V-unit forms a narrow distal cycle around the central area and is seen as a thin, dark line under XPL.The central area is very small (1.1-1.4 μm) compared to the distal shield (7.0-8.4 μm), and is completely closed.
Occurrence: Sporadically recorded throughout the upper Barremian to lowermost Aptian (uppermost part of the Gassendiceras alpinum ASz to the Deshayesites oglanlensis AZ).This interval is equivalent to the uppermost part of the NC5E1-NC6A2 CNSzs.This species is a very rare component of the assemblages.It has been recorded from sections X.Kv, X.Kv 2 and X.Ag 6 in the Subbetic Domain of the Betic Cordillera (southern Spain).
Remarks Diagnosis: Very large (15.3-25.3μm) Lithraphidites nannolith having an outline similar to a bladed dagger.In the direction opposite to the 'handle', the outline is slightly convex and decreases its width slowly before tapering toward the point.The maximum width oscillates between 2.7 and 4.1 μm.
Description: Calcareous rods with cruciform cross-section built of long blades of identical optical orientation.The outline is similar to a bladed dagger in which the 'handle' (~1.1 μm width and frequently missing by breakage) is followed by a wider expansion (2.7-4.1 μm width) which slowly decreases its width before tapering toward the point.
Occurrence: Recorded from the uppermost lower Barremian (upper part of the Moutoniceras moutonianum AZ) to the upper Barremian (uppermost part of the Hemihoplites feraudianus ASz), within NC5E1-NC6A1 CNSzs.This species is a rare component of the assemblages, but has a consistent and continuous record until the uppermost part of the Gerhardtia provincialis ASz.It has been recorded from sections X.CO 2 , X.CT, X.F, X.Kv, X.Kv 2 , and X.V 1 from the Subbetic Domain in the Betic Cordillera (southern Spain).The LO of L. aichmoides has been recorded 467 cm above that of Flabellites oblongus (base of NC5E1 CNSz) in section X.V 1 .
Remarks: Lithraphidites aichmoides differs from L. magnus (emend.)and L. pugio by having a more stylized outline, with a maximum width smaller than 4.5 μm.This width appears as the more appropriate to separate both species according to the measurements made in the present study (Fig. 5).Lithraphidites aichmoides differs from Lithraphidites alatus (Upper Albian-Lower Cenomanian) by having an outline similar to a bladed dagger instead of a 'closed umbrella', the latter decreasing quickly in width from the end close to the 'handle' toward the point.It differs from Lithraphidites houghtonii (Boreal lower-upper Aptian) by having a greater length and a smaller width.
Lithraphidites magnus (Covington and Wise Jr., 1987)  μm width and sometimes missing by breakage) is followed by a wider expansion (4.5-7.0 μm width) which nearly maintains its width a long distance (around three fifths of the nannolith length) before tapering toward the point.The maximum width is greater than 4.5 μm and the L/ W ratio is greater than 3.5 (average 4.1).
Remarks: Covington and Wise (Covington and Wise Jr., 1987, p. 631) originally described this taxon, but as a subspecies of Lithraphidites alatus (L.alatus ssp.magnus).Lithraphidites magnus is here erected to the category of species because the lack of stratigraphic connection with L. alatus and the existence of morphologic differences between both taxa.While L. magnus is restricted to the uppermost Barremian-lowermost Aptian, L. alatus ranges from Upper Albian to Lower Cenomanian.The original description of L. magnus was based on two SEM micrographs in which specimens are foreshortened due to tilting or partially covered.
The estimated holotype dimensions were 5.7 μm wide and ~ 20 μm long.
However, the holotype appears to be a broken specimen, its true length probably being ~25 μm.The length in the population measured in the present paper oscillates between 21.2 and 26.2 μm (average 23.8 μm).
After a biometric study (Fig. 6), all specimens with L/W ratio smaller than 3.7 (usually with L < 21 μm) were here assigned to Lithraphidites pugio n. sp., which is characterized by a wider and shorter outline (see below).It seems a width greater than 4.5 μm is also a good value to characterize these forms differentiating them from Lithraphidites aichmoides n. sp.(Fig. 5).
Occurrence: Covington and Wise Jr. (1987) recorded this taxon in sediments from core 44 of DSDP Hole 603B (North American Basin of North Atlantic).These were dated as lower Aptian, although no convincing evidence supporting this age was provided from calcareous nannofossil assemblages.Bralower et al. (1994) reported this species from upper Barremian-lower Aptian sediments of DSDP Site 398 (West Iberian continental margin).Cobianchi et al. (1997) recorded this species throughout upper Barremian-lower Aptian (M.hoschulzii to H. irregularis CNZs) in northern Gargano (Apulia, Italy).However, the species concept of these authors probably includes L. magnus and L. pugio as differentiated here, which would have extended its range.In the Subbetic Domain of the Betic Cordillera, L. magnus has been recorded from the uppermost Barremian (uppermost part of the Hemihoplites feraudianus ASz) to the lower Aptian (lower part of the Deshayesites forbesi AZ), throughout most of the lowermost part of NC6A CNSz.This species is a rare component of the assemblages, but has a consistent and continuous record until the upper part of the Martelites sarasini AZ, from which it becomes rare.It has been recorded from sections X.Cp 2 , X.F, X. F1, X.HA, X.Kv, X.Kv 2 , and RA03, in the Subbetic Domain of the Betic Cordillera (southern Spain).Diagnosis: Very large (13.4-23.5 μm) Lithraphidites nannolith having an outline similar to a short bladed dagger.In the direction opposite to the 'handle', the outline is convex and quickly decreases its width before tapering toward the point.The maximum width oscillates between 4.5 and 8.1 μm.

Lithraphidites pugio
Description: Calcareous rods with cruciform cross-section built of long blades of identical optical orientation.The outline is similar to a bladed dagger in which the 'handle' (~1.1 μm wide and frequently missing by breakage) is followed by a wider expansion (4.5-8.1 μm) which nearly maintains its width a short distance (around a half of the nannolith length) before quickly tapering toward the point.The L/W ratio is smaller than 3.5 (average 2.9).
Occurrence: In the Subbetic Domain of the Betic Cordillera, L. pugio has been recorded throughout part of the upper Barremian (from the middle part of the Gassendiceras alpinum ASz to the uppermost part of the Hemihoplites feraudianus ASz; base of NC5E2 to basal part of NC6A1 CNSzs).This species is scarce, but has a consistent record in the assemblages from the X.F, X.HA, X.Kv, X.Kv 2 and X.V 1 sections.Martinez et al. (2020) used the LO of this species to correlate the uppermost part of the X.V 1 and the lowermost part of the X.Kv 2 sections.This bioevent has shown biostratigraphic potential to be used in correlation, at least at a regional scale (chapters 5.1 and 5.2).
Remarks: Lithraphidites pugio differs from L. magnus (emend.)by having a shorter (usually <21 μm) and wider outline, with an average L/ W ratio ~ 2.9.The expansion of the blades decreases more quickly in L. pugio than in L. magnus.It differs from L. aichmoides by having a greater width (>4.5 μm) and nearly parallel sides (by around the half of its length) in side view, before tapering at the end.Lithraphidites pugio differs from Lithraphidites alatus (Upper Albian-Lower Cenomanian) by having an outline similar to a short bladed dagger instead of a 'closed umbrella', the latter having a straight to slightly concave outline quickly decreasing in width from the end close to the 'handle' toward the point.Jeremiah (2001) Covington and Wise Jr., 1987 with an elongated outline (L/W > 1.12) usually showing poorly defined radial elements under cross-polarized light microscopy (XPL).See Section 4.2 for details.
Description: A mixture analysis performed on the L/W ratio of 140 specimens of the H. irregularis gr.(Fig. 7C and SM2) indicates that two populations are present within this pool.Those forms with nearly circular outline, (L/W smaller or equal to 1.12), being younger in time, were assigned to Hayesites irregularis s.str.Those specimens having a more elongated outline (L/W > 1.12), generally showing poorly defined radial elements and being slightly older, were assigned to H. irregularis morphotype E (H. irregularis E).
Occurrence: Hayesites irregularis E was recorded from the lower part of the Hemihoplites feraudianus ASz in the Subbetic Domain of the Betic Cordillera (sections RA03, X.Ag 6 , X.F, X.HA, X.Kv, X.Kv 2 ) and extends throughout the Imerites giraudi-Deshayesites oglanlensis AZs of the upper Barremian-lowermost Aptian.The LO of this species has been used here to define the base of the NC6A1 CNSz.The LO of H. irregularis s. str.was recorded from the middle part of I. giraudi AZ. Nannoliths.

Conclusions
A detailed study of the calcareous nannofossil assemblages from twelve uppermost lower Barremian-lowermost Aptian sections in the Subbetic Domain of the Betic Cordillera, well dated by ammonite biostratigraphy, has allowed to the identification of seven new species.
The stratigraphic ranges of each new species, together with those of other relevant markers, are directly correlated to standard ammonite biostratigraphy and tied to the geochronological scale using a previous astrochronological calibration of the complete interval studied.
Five new calcareous nannofossil subzones are proposed (NC5E1, NC5E2, NC5E3, NC6A1, and NC6A2) which allow the refinement of the zonation for the Mediterranean-Atlantic Province of the Tethyan Realm and are directly correlated with respect to the standard Tethyan ammonite zonation.Two of the new species described here are used as biostratigraphic markers for the new proposed subzones.The duration of each one of these subzones is also provided through a previous astrochronological calibration.
The implications of these results on the extant definition of the Barremian/Aptian boundary are discussed.In the absence of magnetostratigraphic data, we chose the definition of the Barremian/Aptian boundary in coincidence with the LO of the ammonite species Deshayesites oglanlensis.Regarding calcareous nannofossils, none of the biostratigraphic reliable markers coincides with this boundary.The recorded bioevent closer to the Barremian/Aptian boundary was the HO of the new species Crucibiscutum bastetanum, which correlates to the lower part of the Martelites sarasini AZ.Based on its proximity to the base of the D. oglanlensis AZ, the ISNE of the δ 13 C curve may be an alternative for the definition of the base of the Aptian, if it is identified in additional locations.
The morpho-evolutionary trends and paleogeographic distribution of some selected nannofossil taxa (mainly from genera Flabellites, Lithraphidites and Micrantholithus) across the interval studied were analyzed.This analysis suggests that paleogeography played a fundamental role as a factor controlling the evolution of the calcareous nannoplankton in the west European-Atlantic region during the late Barremian-early Aptian interval.

Declaration of Competing Interest
None.

Fig. 3 .
Fig. 3. Lithologic sketches of sections X.V 1 , X.Kv, X.Kv 2 and RA03, with indication of formations, stage, ammonite/calcareous nannofossil biostratigraphy, thickness, position and number (in parentheses) of samples studied and main calcareous nannofossil bioevents recorded.Marker species names are in bold typeface.

Fig. 5 .
Fig. 5. Cross-plot of width (W) vs. length (L) for 120 upper Barremian Lithraphidites spp.specimens.A-D: Cross-plots of width vs. length for the different taxa and sketches of the side and top views of each one (upper right), with indication of measured parameters.E, F: Frequency histograms of the width (E) and length (F) of the complete data set.The distribution curves in E result from a mixture analysis applied to the whole data set using the widths of all measured Lithraphidites spp.specimens.G: Frequency histogram showing the distribution curves resulting from a mixture analysis applied to the length of all measured specimens having a width greater than 4.5 μm.H: Table showing the descriptive statistical parameters (proportion, mean, and standard deviation) of the mixture analyses performed on the width and length of the measured specimens.Dashed vertical lines on the cross-plot are the widths suggested to separate Lithraphidites carniolensis from the new species L. aichmoides (2.5 μm) and L. aichmoides from the L. magnus/L.pugio plexus (4.5 μm).Circles with cross on the graph indicate the calculated mean values for each species/group of taxa.W was measured in the area with the maximum expansion of the blades of Lithaphidites spp.

Fig. 6 .
Fig. 6.Cross-plot of length/width (L/W) ratio vs. length (L) for 69 Lithraphidites specimens of the L. pugio/L.magnus plexus.Note as all specimens assigned to L. magnus have L > 24 μm and L/W ratio > 3.5, being located within the upper right quadrant of the graph.

Fig. 7 .
Fig. 7. A. Parameters measured in 140 specimens of the Hayesites irregularis group.B) Cross-plot of L vs. W. Shaded dots indicate initially assumed H. irregularis E. Regression lines considering all specimens (solid) and the separated populations of H. irregularis s.str.and H. irregularis E (dashed) are shown.C) Frequency histogramshowing the distribution curves resulting from a mixture analysis applied to the L/W ratio of all measured specimens.The small table shows the descriptive statistical parameters (proportion, mean, and standard deviation) resulting from the mixture analysis.Two populations are revealed based on the L/W ratio.The forms with L/ W > 1.12 were assigned to H. irregularis E. See text for details.

Fig. 8 .
Fig. 8. X. Cross-plot of coccolith length (L) vs. width (W) for 120 specimens of Flabellites oblongus s.l., referred to ammonite zones (different symbols for data points), with frequency histograms of the complete data set.The distribution curves on the histograms result from applying mixture analyses.Dashed-line curves (A) result from the discrimination of two populations within the whole data set.Solid continuum line curves (B) result from the discrimination of only one population in the complete data set.Y. Table showing the descriptive statistical parameters resulting from the mixture analyses, where the two options (A and B) are considered.Mout = Holcodiscus caillaudianus ASz + Moutoniceras moutonianum AZ; Vand = Toxancyloceras vandenheckii AZ; Sart = Gerhardtia sartousiana ASz; Prov = Gerhardtia provincialis ASz; Fera = Hemihoplites feraudianus ASz; Gira = Imerites giraudi AZ; Sara = Martelites sarasini AZ; Ogla = Deshayesites oglanlensis AZ; Forb = Deshayesites forbesi AZ.Numbers in parentheses represent the specimens measured in each interval.Note the nearly continuous distribution of the coccolith size, where two populations can not be clearly differentiated and the close AIC values for cases A and B.

Fig. 12 .
Fig. 12. Cross-polarized light micrographs of several specimens of some of the new species described here.Holotypes/paratypes are indicated.Species name and section -sample of provenance are shown for each one.

Fig. 13 .
Fig. 13.Cross-polarized light micrographs of several specimens of some of the new species described here.Holotypes/paratypes are indicated.Species name and section -sample of provenance are shown for each one.

Fig. 14 .
Fig. 14.Cross-polarized light micrographs of several specimens of some of the new species described here.Holotypes/paratypes are indicated.Species name and section -sample of provenance are shown for each one.

Fig. 15 .
Fig. 15.Cross-polarized light micrographs of several specimens of the Hayesites irregularis group, with differentiation of the two morphotypes described in the text and Nannoconus sp.cf.N. truittii.Species name and section -sample of provenance are shown for each one.
and as Corollithion cf. C. achylosum across the upper Barremian-lowermost Aptian of the ODP R.Aguado et al.
• which is present in C. lamprostauros.Chiastozygus tenuis (another poorly documented species) has a slim diagonal cross symmetrical with respect of the axes of the ellipse instead of a broader, slightly rotated one as present in C. lamprostauros.Chiastozygus lamprostauros differs from other species of this genus (C.antiquus, C. garrisoni, C. stylesii and C. trabalis) by having a dark diffusely bicyclic rim.Probably most of the late Barremian-early Aptian C. litterarius specimens from the literature should be assigned to C. lamprostauros.
: Cyclagelosphaera platyaspis differs from Cyclagelosphaera margerelii by having a noticeably larger size (7.0-8.4 μm instead of 4-6 μm), although both species have a very small central area closed by calcite elements.Cyclagelosphaera platyaspis differs from Cyclagelosphaera brezae by having a distinct V-unit cycle around the central area, and from C. argoensis, C. jiangii, C. lacuna and C. wiedmannii by the lack of central opening or open central area.Cyclagelosphaera rotaclypeata and C. deflandrei both have central areas wider than that of C. platyaspis, which also lacks the raised central plugs present in C. reinhardtii and C. shenleyensis.