Potential Foraminiferal Markers for the Visean–Serpukhovian and Serpukhovian–Bashkirian...

POTENTIAL FORAMINIFERAL MARKERS FOR THE VISEAN–SERPUKHOVIAN AND SERPUKHOVIAN–BASHKIRIAN BOUNDARIES—

A CASE-STUDY FROM CENTRAL MOROCCO

PEDRO COZAR,1 ISMAIL SAID,1 IAN D. SOMERVILLE,2 DANIEL VACHARD,3 PAULA MEDINA-VAREA,1

SERGIO RODRIGUEZ,1 AND MOSTAFA BERKHLI4

1UEI y Depto. de Paleontologıa, Instituto de Geologıa Economica/Instituto de Geociencias CSIC-UCM, c/Jose Antonio Novais 2,28040-Madrid, Spain, ,[email protected]., ,[email protected]., ,[email protected]., ,[email protected].; 2UCD School of Geological

Sciences, University College Dublin, Belfield, Dublin 4, Ireland, ,[email protected].; 3Universite de Lille 1, UFR Sciences de la Terre,UMR 8157 du CNRS, Batiment SN 5, Villeneuve d’Ascq 59655, France, ,[email protected].; and 4Universite Moulay Ismaıl, Faculte des

Sciences, Departement de Geologie, UFR analyse et prospection des bassins sedimentaires,BP. 11201 Zitanne, Meknes, Morocco, ,[email protected].

ABSTRACT—The Carboniferous succession in Adarouch (Central Morocco, north of the Atlas Transform Fault)contains thick carbonate beds including upper Visean, Serpukhovian and basal Bashkirian rocks. Foraminifersenable precise recognition of the Visean/Serpukhovian (V/S), early/late Serpukhovian (eS/lS) and Serpukhovian/Bashkirian (S/B) boundaries. Insolentitheca horrida, Loeblichia ukrainica, ‘‘Millerella’’ spp. and Endostaffella? sp. 2are regarded as regionally useful indices to the V/S boundary, whereas Eostaffellina spp., Eostaffella pseudostruveiand some evolved species of Archaediscus exhibit greater reliability for worldwide correlation of this level. Similarly,the eS/lS boundary is marked locally by Brenckleina rugosa, Eosigmoilina sp., and Monotaxinoides spp.and globally by Loeblichia minima, Bradyina cribrostomata, Plectostaffella spp., Eostaffellina ‘‘protvae’’ and‘‘Turrispiroides’’, and the S/B boundary is marked locally by Globivalulina bulloides and globally by Seminovellaelegantula, and Novella?. Occurrences of these taxa in Morocco allow correlations with the Moscow Basin, theUrals, the Donetz Basin and North America. The Moroccan assemblages share few taxa in common with Saharanbasins south of the Atlas Transform Fault. Correlations with western European basins are difficult because of thepaucity in the latter of foraminiferal-bearing carbonate strata.

INTRODUCTION

RESEARCH ON the Visean–Serpukhovian (V/S) boundarydeals with several potential stratotypes, involves many

different fossil groups, and includes work in both deep-waterfacies and shallow-water facies. The base of the Serpukhovianwas equated to the base of the Namurian, which is defined bythe first appearance of Cravenoceras leion, a datum wellestablished in the British Isles (Bisat, 1930).

Ammonoids, in particular C. leion, are not free ofcontroversy and their identification depends on well-preservedspecimens. Furthermore, their usefulness for intercontinentalcorrelations has been questioned (Nikolaeva and Kullmann,2001). A third inconvenience is the strong facies control on theammonoid faunas but this is a similar problem observed inother Carboniferous fossil groups. Nevertheless, ammonoidzonal schemes similar to the British one have been usedsuccessfully in Morocco and Algeria (e.g., Pareyn, 1961;Lemosquet et al., 1985; Korn et al., 2007; Korn andEbbighausen, 2008; Wendt et al., 2009), and the Britishammonoid succession has been correlated with Germany (e.g.,Korn, 1996, 2006; Korn and Horn, 1997), the Urals(Nikolaeva et al., 2009a) and North America (Ramsbottomand Saunders, 1985; Richards and Task Group, 2009).

The Visean/Serpukhovian boundary is currently under inten-sive study worldwide in connection with efforts to select a GSSP(see Richards and Task Group, 2009, 2010). During 2009–2010,the task group chair intended to submit a proposal that the baseof the Serpukhovian will be defined by the first appearancedatum (FAD) of the conodont Lochriea ziegleri within thelineage L. nodosa–L. ziegleri, but the scarce knowledge of thegeographic distribution of the lineage and the degree ofdiachroneity of the FAD of L. ziegleri warrant a vote to beaccepted or rejected. However, in areas where conodonts are rare

or absent, such as in shallow-water platform interiors (e.g.,Central Morocco), the V/S boundary can be recognized byforaminifers which provide a highly useful auxillary tool.

The Serpukhovian/Bashkirian boundary is well establishedas it also coincides with the mid-Carboniferous Mississippian/Pennsylvanian boundary (e.g., Heckel and Clayton, 2006).The GSSP is located at Arrow Canyon (Nevada, U.S.A.) andis defined by the first appearance of the conodont Declinog-nathodus noduliferus (Brenckle et al., 1997a, 1997b; Lane et al.,1999). Diagnostic Bashkirian foraminifers occur some distanceabove the boundary in the stratotype section in the Urals(Groves, 1988; Groves et al., 1999; Kulagina et al., 2009).

The Carboniferous succession in Adarouch (central Mo-rocco) ranges in age from the middle Visean up to theBashkirian, with excellent preservation and exposure of thelatest Visean and Serpukhovian carbonates. The successionoccurs in several faulted blocks or thrust sheets (e.g., Berkhli,1999; Vachard et al., 2006; Fig. 1). It is characterized by cyclicsequences, hundreds of meters thick, comprising shallow-water platform carbonates in the lower part and deep-wateropen platform to slope carbonates and shales in the upper part(Berkhli, 1999; Berkhli and Vachard, 2001; Cozar et al.,2008a), foraminiferal assemblages in the carbonates areabundant and of high diversity.

The aims for this study are to 1) document the foraminiferalsuccession from the latest Visean to Bashkirian in a relativelyunknown area in central Morocco (western Paleotethys); 2)analyze those problems related to the Visean/Serpukhovianboundary, as well as the Serpukhovian/Bashkirian boundary;and 3) to propose foraminiferal taxa which might bepotentially used as markers for these boundaries, which inthe case of the Visean/Serpukhovian boundary, in the absenceof the Lochriea lineage, may provide important localalternatives in biostratigraphy.

Journal of Paleontology, 85(6), 2011, p. 1105–1127

Copyright ’ 2011, The Paleontological Society

0022-3360/11/0085-1105$03.00

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1106 JOURNAL OF PALEONTOLOGY, V. 85, NO. 6, 2011

GEOLOGIC AND BIOSTRATIGRAPHIC SETTINGS

The Carboniferous formations described in the Adarouchregion (Fig. 1D) are included in the northern part of theAzrou-Khenifra Basin which was interpreted as a forelandbasin (Beauchamp and Izart, 1987; Fig. 1B). The oldestsediments in the area are situated in Agouraı (Berkhli et al.,2000; Fig. 1C), dated as V2a, mid Visean. In Adarouch,sedimentation spans only the late Asbian–Bashkirian interval.Upper Asbian–Brigantian rocks are represented by the Tizraand Mouarhaz formations. The best known Serpukhovianformation is the carbonate-dominated Akerchi Formation(Fig. 1D). This formation was originally assigned to the lateVisean by Termier and Termier (1951), Termier et al. (1975),and Conil and Verset (1979). However, Dedok and Hollard(1980) attributed the upper part of the formation to the earlyNamurian on the basis of brachiopods. Vachard and Tahiri(1991), Vachard and Fadli (1991) and Vachard and Berkhli(1992) considered the Akerchi Formation as entirely lowerSerpukhovian.

Berkhli (1999), Berkhli et al. (2001) and Berkhli and Vachard(2001) subdivided the Akerchi Formation (,100 m thick) intotwo members. They considered the lower AK1 member(predominantly limestone and shales) as uppermost Visean(Brigantian), and the upper AK2 member (predominantly sandylimestones and sandstones) as mostly lower Serpukhovian.

During the late Brigantian two main contrasting succession-types are recognized. The first one is a deepening-upwardsequence into open platform to slope sediments in the upperpart (e.g., Tizra and Mouarhaz formations; Figs. 1, 2). Thesecond one is a shallowing-upward trend, passing intoshallow-water, nearshore siliciclastic-rich shelf facies (AkerchiFormation). The carbonate-rich lower member of the Mouar-haz Formation (MZ1) and the lower part of the AkerchiFormation (AK1) contain shallow-water facies foraminifers oflate Brigantian age (Figs. 3–5; Cozar et al., 2008a).

Said (2005) described a typical Brigantian rugose coralassemblage from the biostrome at the base of the AK2member (Figs. 4, 5) and assigned a Brigantian age for thelower part of the AK2 member. Subsequently, Cozar et al.(2008a) documented Brigantian foraminifers from the bio-strome but relatively poor assemblages in higher levels up tothe stromatolitic band (,35 m above the base of the section,see Fig. 5). However, further sampling of the sandstones andpebbly limestone beds between the stromatolite and thebiostrome revealed the presence of Serpukhovian foraminifers.Thus, the base of the Serpukhovian is situated in the bed fromwhich sample 3230 in Akerchi 1 section was collected andfrom sample 3232 in Akerchi 2 (see Figs. 4 and 5). The base ofthe late Serpukhovian is located immediately above thestromatolite in sample 2772 (see Fig. 5). A Bashkirian age inthe upper part of the Akerchi Formation was proposed byDedok and Hollard (1980) based on the presence of thebrachiopod Titanaria. An unpublished re-examination of thematerial (Legrand-Blain, personal commun., 2000), consid-ered that the specimen is not the typical species found inAlgerian Sahara. This, together with its earliest occurrence in

North America (Carter, 1990), led Berkhli (1999), Berkhli andVachard (2001), and Berkhli et al. (2001) to assign the topof the Akerchi Formation to a probable E2 Zone (lateSerpukhovian age). The foraminiferal assemblages from theupper beds, although sparse, do contain significant taxa,supporting a probable Bashkirian age (see below). Unfortu-nately, conodonts have not been found in these youngestsiliciclastic-rich beds at Akerchi.

The Idmarrach Formation to the northeast of Akerchi(Fig. 1D) was described by Berkhli and Vachard (2002) anddated as Serpukhovian. Those authors only studied theIdmarrach 1 section. According to the coral assemblages, Said(2005) considered the formation as Brigantian. However, recentconodont sampling has established a late Serpukhovian age forlower levels in Idmarrach 1 section, with the discovery ofGnathodus bilineatus bollandensis (Fig. 2). The occurrence of theconodont Declinognathodus noduliferus in the youngest limestonebeds (,40 m above the base of the Idmarrach 2 section), confirmsa Bashkirian age for the upper 10 m of the section (Fig. 2), whichshows pebbly reddish siliciclastic beds at the top (Fig. 7).

Finally, the Tirhela Formation is exposed to the north ofIdmarrach (Figs. 1D, 8). This unit was first described byBerkhli and Vachard (2002) and dated by them as late Viseanto Serpukhovian. The Tirhela Formation (,90 m thick)comprises marine limestones with abundant gigantoproduc-toid brachiopods in the lower part and is attributed mostly tothe late Serpukhovian. However, foraminifers from theuppermost limestone beds are assigned to the Bashkirianand are comparable with those limestones from near the top ofIdmarrach 2 section (Fig. 2). The upper part of the TirhelaFormation marks a thick transition into reddish marginalmarine and deltaic conglomerates, sandstones and shales, whichare compared to the upper red pebbly beds in Idmarrach 2.

FORAMINIFERAL MARKERS OF THE UPPERMOST VISEAN TO

BASHKIRIAN IN ADAROUCH

A summary of the stratigraphic range of the most significantforaminiferal taxa illustrated in Figures 10 to 13 is given inFigure 9. Details of their ranges displayed in Figures 3–8 isbased on examination of 1,050 thin-sections, prepared fromthe samples highlighted in the stratigraphic logs. Thin-sectionsare housed in the Palaeontological collection of the Uni-versidad Complutense de Madrid (Faculty of GeologicalSciences).

Uppermost Visean–lower Serpukhovian.—The shallow-wateroolitic limestones (MZ 1 member) of the Mouarhaz Forma-tion contain Globivalvulina parva, Asteroarchaediscus ex gr.baschkiricus, Janischewskina, Endothyranopsis sphaerica andcommon Euxinita efremovi (Fig. 3). All are consideredlate Brigantian markers elsewhere in Europe (Cozar andSomerville, 2004; Cozar et al., 2005, 2008a, 2008b, 2010).Noteworthy, is Pseudocornuspira (Fig. 10.1–10.3) (or Recto-cornuspira of other authors), which was commonly recorded inthe late Brigantian from the Donetz Basin by Vdovenko(2001) and Kazakhstan (Brenckle and Milkina, 2003).Another interesting new taxon is Globivalvulina sp. 1(Fig. 10.6, 10.7), which can be readily included within the

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FIGURE 1—A, location of the main Carboniferous Basins in Morocco, Algeria and Tunisia: 1, Central Massif; 2, Rehamna; 3, Djebilet; 4, Tafilalt; 5,Bechar; 6, Jerada; 7, Tindouf; 8, Reggane; 9, Ahnet; 10, Mouydir; 11, subsurface Carboniferous; AA5Anti-Atlas, ATF5Atlas Transform Fault,EM5Eastern Meseta, HA5High Atlas, MA5Middle Atlas, WM5Western Meseta; B, detail of the Variscides in Morocco, pale gray areas areCarboniferous outcrops, dark grey is the Azrou-Khenifra Basin; C, location of the Adarouch area (encased box) in the northern part of the Azrou-Khenifra Basin, see also arrow in B; D, photogeological map showing the location of the measured stratigraphic sections in the Carboniferousformations (modified from Weyant, 1985; Hoepffner et al., 2005; Simancas et al., 2005).

COZAR ET AL.—LATE VISEAN TO BASAL BASHKIRIAN FORAMINIFERS FROM MOROCCO 1107

Globivalvulina granulosa group but seems to be endemic tocentral Morocco.

The first appearance of Neoarchaediscus postrugosus(Fig. 11.9) is recorded in the lower part of the AkerchiFormation of latest Brigantian age. The first appearancedatum (FAD) of this species elsewhere is in the latestBrigantian, in England, Scotland (Cozar and Somerville,2004; Cozar et al., 2008b), Ireland (Somerville and Cozar,2005; Cozar et al., 2005), Spain (Cozar et al. 2006), and theUrals (Kossovaya et al., 2001; Reitlinger et al. in Einor, 1996).Noteworthy is the first occurrence of Euxinita pendleiensis(Fig. 11.12–11.14) in the upper part of the calcareoussuccession (AK1). This species was described from Pendleianrocks from the Midland Valley of Scotland (Cozar et al.,2008b). Also highlighted is the first occurrence of the Miliolatacalcivertellids (including Calcitornella, Calcivertella, Trepei-lopsis and Ammovertella; Fig. 10.4, 10.5).

One of the most significant occurrences in the AkerchiFormation is the genus ‘‘Millerella’’ and some species ofEndostaffella, which is included by some authors within thesynonymous genus, Zellerinella. The type species of Zellerinellaselected by Mamet and Skipp (1970) was Endothyra discoideaGirty, 1915, and they also included most of the primitive Millerelladescribed in the Chesterian of the midcontinent, U.S.A. However,Girty (1915) did not select a holotype and neither did Mamet andSkipp, 1970 (as already noted by Brenckle, 2005), and the twoaxial sections illustrated within the types are morphologicallydistinct. They could be identified here as morphotype 1 (Girty,1915, pl. 10, fig. 11), with more embracing and elongated whorlsthan in morphotype 2 (Girty, 1915, pl. 10, fig. 12), although thissecond morphotype was not included in the species by Mamet andSkipp (1970). Reitlinger (1975, 1981) highlighted the similarity ofthe species with Endostaffella shamordini (Rauser-Chernoussova,1948) and both species have been commonly considered assynonyms (e.g., Brenckle, 2005; van Ginkel, 2010). The generaZellerinella and Endostaffella have been also considered assynonymous by Brenckle and Groves (1981), Baxter andBrenkle (1982), and Rich (1986). However, Loeblich andTappan (1988), Rauser-Chernoussova et al. (1996) and Pinardand Mamet (1998) kept both genera as independent taxa. Asclaimed by Pinard and Mamet (1998), the lectotype selected byLoeblich and Tappan (1988) is an equatorial section which isnot representative enough. The single axial section considered asthe lectotype by the former authors is more representative, butas Brenckle (2005) remarked, it was not written in the originaldiagnosis of the genus. The latter author published numeroustopotypes and paralectotypes, which readily correspond to themorphotype 2, which might be considered also as Endostaffella?.The problem may arise with specimens similar to morphotype 1,as well as with those others species included by Mamet andSkipp (1970) in the genus, such as Endothyra tortula Zeller, 1953and E. designata Zeller, 1953. Those specimens can be foundreferred to in the literature as Millerella, ‘‘primitive Millerella’’,‘‘Millerella’’ and Paramillerella. Although none of the previousgenus names satisfies completely the taxonomic characters ofthe specimens, for pragmatic purposes we prefer to retain theuse of ‘‘Millerella’’ here.

This genus Zellerinella and thus, the species included in‘‘Millerella’’, is considered as mostly endemic to the NorthAmerican Realm, although rare specimens have been recordedin eastern Europe and the Far East (see Armstrong and Mamet,1977). More recently, ‘‘Millerella’’ tortula was recorded in theTarusskian and Steshevskian in the Moscow Basin (Gibshman,2001, 2003; Gibshman and Baranova, 2007), ‘‘Millerella’’designata and ‘‘Millerella’’ cooperi (5Eostaffella advena) from

the Serpukhovian and Bashkirian of Kazakhstan (Brenckle andMilkina, 2003), Zellerinella spp. from Ireland and Scotland(Somerville and Cozar, 2005, pl. 3, figs. 19–21; Cozar et al.,2010, fig. 7g), and Zellerinella sp. 1, Zellerinella sp. 2, Z.designata and Z. pressula from China (Wu et al., 2009). Mostspecimens recorded in Adarouch are determined as Endostaf-fella? discoidea (Fig. 12.14, 12.15).

Specimens identified as ‘‘Millerella’’ aff. tortula are rarelyrecorded (Fig. 12.19, 12.20). Although they do not present thesame number of whorls and size as in the original material, theevolute arrangement of the whorls and depressed umbilicalareas are rather similar. ‘‘Millerella’’ aff. tortula is exclusivelyrecorded in Serpukhovian rocks in Adarouch, together withsome uncommon specimens identified as ‘‘Millerella’’ sp.(Fig. 12.16). The presence of these assemblages of ‘‘Millerella’’highlight a local influence of the North American fauna onCentral Morocco for this period, and its paleobiogeographicimplications should be analyzed in detail.

An unusual taxon is recorded from the basal Serpukhovianbeds in Adarouch, referred to here as Endostaffella? sp. 2(Fig. 11.21–11.25). This taxon shows characters of that genus(skew-coiled inner whorls and final planispiral whorls), butdiffers in two aspects: 1) a differentiated wall with markedbright clear grains, which in some cases developed a well-defined diaphanotheca and 2) secondary basal deposits in theform of pseudochomata, better developed than in the genusEndostaffella. In fact, this species might be derived from anevolved form of Euxinita, which developed more planispiralfinal whorls. Some conspecific specimens might occur in theMidland Valley of Scotland (Cozar et al., 2008b, 2010). Amuch more common species of the genus and restricted also tothe Serpukhovian in Adarouch is identified as Endostaffella?sp. 1 (Fig. 12.12, 12.13), which is distinctly wider and withslightly more involute whorls than the former species, and it isconsidered close to E.? discoidea, but the latter first occurs inthe latest Brigantian, as do other species of the genus. Thesefeatures, together with the plectogyroid inner whorls, givegenerally, a weaker development of the depressed umbilicalareas.

Eostaffella pseudostruvei (Fig. 12.2, 12.3) first occurs fromthe Serpukhovian in Adarouch, although it first occurs earlier,in the Brigantian, in some European basins, such as theMidland Valley of Scotland (Cozar et al., 2008b, 2010), and theUrals (Kossovaya et al., 2001; Reitlinger et al. in Einor, 1996).

Two taxa which first occur in the Serpukhovian of Adarouch,Insolentitheca horrida (Fig. 10.15) and Loeblichia ukrainica(Fig. 11.17–11.20), both from the Idmarrach Formation couldbe potentially useful as regional markers. They have beendocumented from the Serpukhovian (Aisenverg et al., 1979a;Lys, 1985; Charlot-Prat and Vachard, 1989), but also arerecorded in the Brigantian (late Visean). Loeblichia ukrainica iswell known in the late Visean in the Donetz Basin (Vdovenko,2001), northern Bulgaria (PC, unpublished data) and in theTindouf Basin (Sebbar et al., 2000). Insolentitheca is also rare,but it was documented in upper Visean rocks by Mamet (1970),Ivanova (1973a, 1973b), Conil (1980), Brazhnikova andVdovenko in Aizenverg et al. (1983), Laloux (1988) andVdovenko (2001), although they might belong to its ancestralform, Protoinsolentitheca Vachard and Cozar, 2004. The speciesL. ukrainica is characterized by the skew-coiled inner whorls.However, this character is variable within specimens and someare almost planispiral (Fig. 11.18, 11.19), in which case it mightbe confused with other species of the genus (e.g., L. ammonoidesor L. paraammonoides). On the other hand, the roundedperiphery of the lumen is characteristic, also for those slightly


biumbilicate specimens (Fig. 11.17), which might be confusedwith L. minima (with a marked acute periphery of the whorls,Fig. 11.15–11.16). Most of the Moroccan specimens belong toL. ukrainica.

The Archaediscus at tenuis stage (Fig. 11.2, 11.4–11.6) sensuConil et al. (1980) are also considered important for thedefinition of the Serpukhovian, although not without someproblems. This group is characterized by the evolutearrangement of the whorls, loose coiling and the virtualabsence of the microgranular layer. The subfamily Aster-oarchaediscinae sensu stricto, and the evolution between theNeoarchaediscus and Asteroarchaediscus species might beparticularly useful, because the late Brigantian–Serpukhovianinterval is the acme of those forms, with many new species.

Eostaffellina spp. (Fig. 13.1–13.4) is also recorded in theearly Serpukhovian in Adarouch. This compressed species isalso recorded in the early Serpukhovian of Kazakhstan(Brenckle and Milkina, 2003, as Eostaffellina? sp.). In theMoscow Basin, Aisenverg et al. (1979a) documented Eostaf-fellina with a rounded periphery from the Tarusskian, but nospecies determinations were documented, that might be thecase for those Eostaffellina spp. These specimens can becharacterized by low length/diameter ratios, around theminimum proposed by Reitlinger (1963) in the diagnosis ofthe genus (0.60), and close to the parameters described for E.schartimiensis (Malakhova, 1956). In Tian Shan and Pamirsareas, unsually, the rounded and subspherical species of thegenus are listed from a lower horizon of the Serpukhovian (e.g.,E. ‘‘protvae’’, E. schartimiensis), whereas compressed forms,attributed to E. ‘‘paraprotvae’’ are only recorded in the upperpart of the late Serpukhovian (Bensh et al. in Einor, 1996).

The last taxon that first occurs in the early Serpukhovian ofAdarouch is Endothyranopsis plana (Fig. 10.13, 10.14). Thisspecies is also potentially a global marker, and it has beendocumented in Europe and Africa, although in some cases, inthe late Serpukhovian (Poletaev et al., 1991; Krainer andVachard, 2002; Cozar et al., 2008b). In Adarouch, its FAD issituated in the upper part of the early Serpukhovian in theIdmarrach 3 section.

In summary, the early Serpukhovian of Adarouch allows usto propose 1) four regional foraminiferal markers for the baseof the Serpukhovian (Fig. 9): Endostaffella? sp. 1, Eostaffellapseudostruvei, Insolentitheca horrida, and Loeblichia ukrainica,and 2) four more taxa or groups of taxa which potentially,might be tested as global markers: Endostaffella? sp. 2,Archaediscus at tenuis stage, Eostaffellina spp., and Endothyr-anopsis plana. In addition, there are other groups, with theiracmes or abundance that also can be used for recognizing thebase of the Serpukhovian: Asteroarchaediscinae s.s., Globi-valvulina and calcivertellids.

Upper Serpukhovian.—Monotaxinoides species (Fig. 10.16,10.18–10.21) first occur consistently in the late Serpukhovianin Central Morocco, and hence, the genus can be used a localmarker. Their first occurrence is established by some authorsas latest Visean (without illustrations: Conil et al., 1980, 1991;Kossovaya et al., 2001; Poty et al., 2006), but Monotaxinoidesis illustrated in the Brigantian from the Donetz Basin(Vdovenko, 2001, pl. 4, fig. 41) and late Brigantian inNorthern Ireland (Cozar et al., 2005, fig. 8.16, 8.17), andcommonly documented from the base of the Serpukhovian in

FIGURE 2—Stratigraphic correlation of the sections in the Adaroucharea with first occurrence datum (FAD) of key conodont taxa: D.

noduliferus5Declinognathodus noduliferus and G. bollandensis5Gnathodusbilineatus bollandensis. PE5Pendleian, MZ5Mouarhaz, AK5Akerchi.

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the Urals (Nikolaeva et al., 2009a, as Monotaxinoides? sp. orEolasiodiscus muradynus), Tunisia (Lys, 1988, as M. priscus),England (Stephenson et al., 2010), Bechar Basin (Lys, 1975,1985; Sebbar and Lys, 1989; as M. priscus) and Kazakhstan(Brenckle and Milkina, 2003). Nevertheless, a primitive speciesof the genus might be present from late Visean rocks(Vachard, 1977, as M.? capriensis). In general, it is observedthat the planispiral forms, such as M. priscus, are usuallydocumented in older rocks than those more helicospiral forms.It might be interpreted that forms such as M. subconica or M.subplana are the ancestral species of the genus, and in thatcase, they might be derived from Howchinia gibba. Otherrelated forms are assigned to ‘‘Turrispiroides’’ (Fig. 10.17,10.22), because of the lack of a fibrous layer, but the validityof the genus and its use is controversial, since the name wasoriginally used to describe a Miliolata (see discussion inVachard and Beckary, 1991). However, its FAD wasconsistently assigned to the late Serpukhovian in Europeand North America (e.g., Brenckle et al., 1982, 1997a; Conilet al., 1991; Krainer and Vachard, 2002; Brenckle andMilkina, 2003).

In Adarouch Eosigmoilina (Fig. 11.10, 11.11) and Brenck-leina (Fig. 11.7, 11.8) are recorded in the late Serpukhovianof Idmarrach 1 and Tirhela sections, with both generaoccurring in the same sample (3338) at the base of the lateSerpukhovian in Akerchi 1 section (Fig. 4). In general, thereis agreement that both genera show the same stratigraphicrange. However, in the Urals (see Kulagina et al., 2001, 2009;Nikolaeva et al., 2009a) and in Tunisia (Lys, 1988) neithertaxa has been documented. In some cases only one genus isdocumented (e.g., Conil et al., 1991; Gibshman, 2001). In

general, the FAD of both genera is at the base of the lateSerpukhovian (Mamet and Skipp, 1970; Mamet, 1974;Laloux, 1988; Conil et al., 1991; Perret, 1993; Mamet et al.,1994; Sebbar, 1998; Sebbar et al., 2000; Gibshman, 2001;Poty et al., 2006; Pille, 2008).

Rare specimens of Eosigmoilina were illustrated from theTarusskian–Steshevskian horizons by Rozovskaya in Aisen-verg et al. (1979a), but later the same specimens were revisedby Vdovenko (2001) to the base of the ProkhorovskianHorizon (C5 Limestone) (Fig. 14), laterally equivalent to theProtvinskian Horizon. Eosigmoilina is considered a lateSerpukhovian marker in the Donetz Basin (Brazhnikova andVdovenko in Aizenverg et al., 1983; Poletaev et al., 1991;Vdovenko, 2001), although some specimens of Brenckleinawere documented in C4 Limestone by Brazhnikova andVdovenko in Aizenverg et al. (1983). The earliest occurrenceof Brenckleina might be related to the distinction madebetween zones 18 and 19 of Mamet and Skipp (1970), in whichsome of the characteristic markers are Rugosoarchaediscus andEosigmoilina, respectively. Nevertheless, as Brenckle et al.(1977) demonstrated, they both occur at equivalent strati-graphic levels in the North American Realm. In England andScotland, Eosigmoilina was regarded as Arnsbergian (lateSerpukhovian) by Fewtrell et al. (1981) and Riley (1992).

In Algeria, according to Lys (1975, 1985), Eosigmoilina andBrenckleina are first recorded in the E1 Zone in the TindoufBasin and Bechar Basin whereas, other authors working inthe same basins, suggest they both first occur in the E2 Zone(Mamet et al., 1994; Sebbar, 1997; Sebbar et al., 2000). In thecentral Saharan basins only Eosigmoilina was documented inthe E2 Zone. In North America, however, Eosigmoilina/

FIGURE 3—Stratigraphic ranges of the selected microfossils in the Mouarhaz section.


Brenckleina first occur within the Menard Limestone in theupper part of the Chesterian (Brenckle et al., 1982; Brenckle,1990b), a limestone correlated with the Pendleian or E1 Zoneby Brenckle et al. (1977), Baxter and Brenckle (1982) andBrenckle (1990a), but considered as late Serpukhovian(Protvinskian) by Kulagina et al. (2008) (Fig. 14). In Scot-land, Cummings in Lumsden and Wilson (1961), documentedthe genus Eosigmoilina as Agathammina robertsoni from theBlae Pot Limestone in the Archerbeck Borehole5LittleLimestone of the Pennines area in northern England. Also,in England, in the Woodland Borehole, Eosigmoilina hasbeen recorded recently from the Rookhope Shell-BedsLimestone (Stephenson et al., 2010).

Other typical late Serpukhovian foraminifers recognizedare Eostaffellina ‘‘paraprotvae’’ (Fig. 13.4–13.6), Eostaffellina‘‘protvae’’ (Fig. 13.7, 13.8), Bradyina cribrostomata (Fig. 10.10),Loeblichia minima (Fig. 11.15, 11.16) and Plectostaffella(Fig. 13.9–13.13, 13.19, 13.20) (e.g., Conil et al., 1991).

Gibshman (2003), Brenckle (2005) and van Ginkel (2010)suggested E. protvae and E. paraprotvae as synonyms because inthe holotype of the former, the specimen is missing the last halfvolution, and thus, the wider form ratio was considered as anartifact of the poor orientation and preservation. Due to the onlyillustration of a single holotype in each species, this proposal isdifficult to demonstrate, and futher taxonomic studies will benecessary in the stratotypes. Certainly, more compressed formsare published in the literature as well as wider forms, and thus,both diagnoses seem to be found in the stratigraphical record,

although the validity of the names proposed by Rauser-Chernoussova (1948) can be questioned. Further studies shouldbe necessary to clarify the validity of both species and also, thevalidity of both species names. In the present study both specieswill be referred to in quotation marks.

Loeblichia minima was recorded in the early Serpukhovianin the Reggane and Ahnet-Mouydir basins (Algeria) by Lys(1975, 1985) but the illustrated specimens probably do notcorrespond to the Russian forms. The oldest record in theRussian Platform is from the Moscow Syncline, where it firstoccurs at the top of the Steshevskian Horizon, close to theearly/late Serpukhovian boundary (Fig. 14). Loeblichia mini-ma is recorded in the late Serpukhovian at Adarouch inIdmarrach 1 and 2 sections (Figs. 6, 7).

Bradyina cribrostomata has been documented from the earlySerpukhovian in Algeria (Lys, 1985; Sebbar et al., 2000) butthe specimens illustrated are considered to be closer to B.rotula. The earliest record of B. cribrostomata in the DonetzBasin is at the top of the Samarskian (Fig. 14) (Brazhnikovaand Vdovenko in Aizenverg et al., 1983), considered as theearly/late Serpukhovian boundary. Bradyina cribrostomata isrecorded in the late Serpukhovian at Adarouch in Idmarrach 2and Tirhela sections (Figs. 7, 8).

In the upper part of the Adarouch succession, E. post-mosquensis (Fig. 12.5, 12.6) first occurs in the late Serpukho-vian. A similar stratigraphic range is observed in the Urals(Kulagina et al., 2001, 2009) and in Alaska (Harriset al., 1997), whereas in the Donetz Basin it first occurs in the

FIGURE 4—Stratigraphic ranges of the selected microfossils in the Akerchi 1 section. Lithological legend as in Figure 3.


upper part of the early Serpukhovian (Brazhnikova andVdovenko in Aizenverg et al., 1983), and in the Bechar Basinin the Bashkirian (Lys, 1985).

Some of the specimens identified as Plectostaffella sp. are large,close to P. varvariensis, however, they are slightly oblique sectionsand do not permit a definite identification (Fig. 13.19, 13.20).

Bashkirian.—Seminovella (Fig. 13.14–13.16) was consideredby Conil et al. (1980, 1991) as a marker of the Bashkirian in

Western Europe and in North Africa (Lys, 1985). However, itis present from the latest Serpukhovian in England (Grind-stone Limestone, Stephenson et al., 2010). This could be alaterally equivalent level to the Zapaltyubinskian Horizon inthe Donetz Basin (Fig. 14), where it is the oldest record of thegenus (Brazhnikova and Vdovenko in Aisenverg et al., 1983).In general, in the Russian Platform it is Bashkirian in age(Vachard and Maslo, 1996). In Adarouch, Seminovella

FIGURE 5—Stratigraphic ranges of the selected foraminifers in the Akerchi 2 section. Lithological legend as in Figure 3.


elegantula occurs in the youngest limestone beds in Akerchi 2,Idmarrach 2, and Tirhela sections (Figs. 5, 7, 8). Also recordedbut rare in these beds are Novella? sp. (Fig. 13.17, 13.18),Globoomphalotis? (Fig. 10.11) and Globivalvulina bulloides (witha differentiation of the wall in the inner whorls; Fig. 10.9).

The genus Novella is only known in the Bashkirian(Vachard and Maslo, 1996; Maslo and Vachard, 1997),although a rather similar specimen was illustrated from theLisbourne Group in Alaska, also identified as Novella? sp., byHarris et al. (1997, fig. 7.23), about 16 m below theMississippian/Pennsylvanian boundary, a level that can beinterpreted as latest Serpukhovian. However, Baesemann et al.(1998), studying the same outcrops, only recorded specimensidentified as Novella sp. in the Bashkirian.

Typical species of Globoomphalotis are described from themiddle and late Visean, and thus, its stratigraphic range doesnot correspond to the Baskirian recorded in Adarouch.However, the granular aspect of the wall, as well as thetectoria differentiation, seem to be conspecific with a specimen

illustrated by Harris et al. (1997, fig. 8.8), as Endothyra sp., ameter below the Morrowan/Atokan boundary (Bashkirian) ofthe Lisburne Group of Alaska.

Globivalvulina bulloides usually first occurs in the lateSerpukhovian in Western Europe, where there was migrationto the midcontinent U.S.A., where it first occurs in theBashkirian (e.g., Brenckle et al., 1997a, 1997b). In between, inthe Arctic area, its first occurrence is situated a few metersbelow the base of the Bashkirian, and thus, in the uppermostlatest Serpukhovian (e.g., Harris et al., 1997; Baesemann et al.,1998). Its late occurrence in central Morocco is possibly relatedto facies control or an artifact due to the scarcity of specimens.

In Idmarrach 2, the conodont Declinognathodus noduliferusoccurs at sample 2355 (5 m below the top of the limestones)(Fig. 7). This conodont was used for defining the Mississippian/Pennsylvanian GSSP in Arrow Canyon (Brenckle et al., 1997a,1997b; Lane et al., 1999).

Comparison with other basins Western Europe.—WesternEurope is generally poor in Serpukhovian carbonates, except

FIGURE 6—Stratigraphic ranges of the selected foraminifers in the composite Idmarrach 3 and 1 sections (left column). Lithological legend as in Figure 3.


for those of deep-water setting in the Cantabrian Mountains,where apart from goniatites, only conodonts are biostrati-graphically useful (e.g., Nemyrovska, 2005). In consequence,the number of publications based on new data on theSerpukhovian foraminifers is limited to a restricted suite ofpapers (e.g., Laloux, 1988; Conil et al., 1991; Perret, 1993;Krainer and Vachard, 2002; Cozar, 2003; Poty et al., 2006; Pille,2008). In addition, the correlation of the E1 (5Pendleian)

and E2 (5Arnsbergian) ammonoid biozones with the early/lateSerpukhovian of the Moscow Basin is not well established yet,and different levels of correlation can be found in the literature(Fig. 14). Thus, correlation can be found with the E1/E2 zonalboundary equating with 1) the Steshevskian/Protvinskianboundary (e.g., Aizenverg et al., 1979a, 1979b; Vachard andTahiri, 1991; Hecker and Osipova, 2007; Cozar et al., 2008b;Nikolaeva et al., 2009b); 2) at a level within the middle part of

FIGURE 7—Stratigraphic ranges of the selected foraminifers in the Idmarrach 2 section. Lithological legend as in Figure 3.


FIGURE 8—Stratigraphic ranges of the selected foraminifers in the Tirhela section. Lithological legend as in Figure 3.


the Protvinskian (e.g., Vachard and Berkhli, 1992; Vdovenko,2001; Nikolaeva and Kullmann, 2001; Krainer and Vachard,2002; Alekseev et al., 2004); or 3) without any precise locationto the above-mentioned levels (e.g., Einor et al., 1979;Vdovenko et al., 1990).

In Austria, Krainer and Vachard (2002) only recognizedMississippian (late Serpukhovian) carbonates assigned to theE2 Zone. This attribution was supported by some species ofEostaffella, Eolasiodiscus dilatatus, and Bradyina concinna. Asimilar stratigraphy was described in southern France (inArdengost) and Belgium (Tramaka Encrinite), although there,exceptionally, some H to G and Westphalian A beds(Chokierian to Langsettian) were recorded (see Laloux, 1988).In the Montagne Noire and Mouthoumet Massif (southernFrance), early Serpukhovian outcrops (Roc de Murviel, LaSerre-vignoble, and col de Couise) have been described basedon the foraminiferal and algal assemblages (e.g., Vachardand Aretz, 2004; Pille, 2008), although they are not free ofcontroversy, because none of the listed taxa seem to beexclusively Serpukhovian, and they might be upper Brigantianrocks. The most reliable data come from the ArdengostLimestone in the Pyrenees, already established as E2 Zone(Perret and Vachard, 1977; Massa and Vachard, 1979; Perret,1993; Pille, 2008), as well as the Tramaka Encrinite in Belgium(Austin et al., 1974; Laloux, 1988). Late Serpukhovian markersin those outcrops are mostly: ‘‘Turrispiroides’’, Loeblichiaminima (the single illustrated specimen by Laloux, 1988, isquestioned here), Brenckleina, and Brownediscus (endemic), andhence the comparison with the rich assemblages of Morocco isunsustained. Conil et al. (1991) (and Poty et al., 2006, whomostly followed the same data) considered also Bradyina

cribrostomata as an E2 Zone marker, whereas apart from theArdengost section, the only record of the species in WesternEurope was documented by Laloux (1988) in the Bashkirian.Globivalvulina s.s. was considered as a Bashkirian marker, whileMonotaxinoides and Archaediscus at tenuis stage were firstrecorded in the latest Visean. We recognize the first occurrenceof Monotaxinoides in the latest Visean (see Cozar et al., 2005,figs 8.16, 8.17), but this is in an exceptional case, and noconvincing illustrated specimen is known by us in the literaturefrom Western Europe. On the other hand, true A. at tenuis stageillustrated from Europe, are all included in E2 Zone outcrops,except those recently published from Britain (e.g., Cozar andSomerville, 2004; Cozar et al., 2008b; Stephenson et al., 2010),but always in E1 Zone outcrops in the Great Limestone, andthus, they are exclusively considered as Serpukhovian.

A continuous Visean–Serpukhovian succession is recordedin Britain, even though, up to the Baskhirian there are onlyrare thin shallow-water carbonates, in predominantly silici-clastic-rich sequences. These include the Midland Valley ofScotland (Cozar et al., 2008b, 2010), and the Pennines innorthern England, with numerous natural sections andboreholes (e.g., Rookhope Borehole, Cozar and Somerville,2004; Woodland Borehole, Stephenson et al., 2010), as well asin the transitional areas (Archerbeck Borehole, Lumsdenand Wilson, 1961). There, Monotaxinoides and Archaediscusat tenuis stage occur from basal E1 Zone limestones,while Eostaffellina and Plectostaffella are recorded fromrocks attributed to the Arnsbergian (E2). The FAD ofEosigmoilina is in lower levels in E1 Zone, but it becomesabundant in E2 Zone levels. It is also noteworthy, that rarespecimens of Seminovella, which is common in the Bashkir-

FIGURE 9—Summary of the stratigraphic ranges of the selected foraminifers in the Adarouch area. Dashed line5rare occurrences, solid line5commonoccurrences. Stratigraphical stages and substages are situated in the left column. Bash.5Bashkirian.


ian, occur at the top of a limestone of E2 Zone (GrindstoneLimestone in the Woodland Borehole), as well as Plectos-taffella bogdanovkensis, a taxon which generally occurs inthe Bashkirian.

North American basins.—The establishment of the Missis-sippian/Pennsylvanian boundary at Arrow Canyon, Nevadaled to detailed studies in the region and surrounding areas.Although mostly based on conodonts, foraminifers were alsoanalyzed (Brenckle, 1973, 1990b; Brenckle et al., 1977, 1982,1997a, 1997b; Skipp et al., 1985; Groves et al., 1999). Toestablish the Visean/Serpukhovian boundary, American au-

thors used the recognition of Zone 17 of Mamet and Skipp(1970), in which the main marker is the rapid development ofAsteroarchaediscus baschkiricus, although as the authorsrecognized, some specimens can occur in older levels. Mametand Skipp (1970) assigned the Glen Dean Limestone of thetype Chesterian section (Kentucky, Mississippi Valley) toZone 17, and it was equated with the Ship Formation, situatedabove the Battleship Wash Formation in Nevada. However,Brenckle (1973) assigned the latter formation to Zone 17.Later, Baxter and Brenckle (1982) recognized the acme ofA. baschkiricus within the Beech Creek Limestone-Haney

FIGURE 10—1, Pseudocornuspira sp. 1, sample Pc3267, Mouarhaz, late Brigantian; 2, Pseudocornuspira sp. 2, sample Pc3278, Mouarhaz, lateBrigantian; 3, Pseudocornuspira sp. 3, sample Pc3366, Mouarhaz, late Brigantian; 4, Ammovertella sp., sample Pc3390, Idmarrach 3, early Serpukhovian;5, Calcivertella sp., sample Pc3195, Akerchi 2, late Serpukhovian; 6–7, Globivalvulina sp. 1: 6, sample Pc3391, Idmarrach 3, early Serpukhovian;7, sample Pc3299, Tirhela, late Serpukhovian; 8, Globivalvulina parva Chernysheva, 1948, sample Pc2317, Idmarrach 1, late Serpukhovian; 9,Globivalvulina bulloides (Brady, 1876), sample Pc3202, Akerchi 2, Bashkirian; 10, Bradyina cribrostomata Rauser-Chernoussova and Reitlinger inRauser-Chernoussova and Fursenko, 1937, sample Pc2325, Idmarrach 2, late Serpukhovian; 11, Globoomphalotis? sp., sample Pc3333, Tirhela, lateSerpukhovian; 12, Janischewskina delicata (Malakhova, 1956), sample Pc2325, Idmarrach 2, late Serpukhovian; 13, 14, Endothyranopsis planaBrazhnikova in Brazhnikova et al., 1967: 13, sample Pc3365, Tirhela, Bashkirian; 14, sample Pc3362, Tirhela, Bashkirian; 15, Insolentitheca horrida(Brazhnikova in Brazhnikova et al., 1967), sample Pc3393, Idmarrach 3, early Serpukhovian; 16, Monotaxinoides subplana (Brazhnikova and Yartseva,1956), sample Pc2338, Idmarrach 2, late Serpukhovian; 17, 22, ‘‘Turrispiroides’’ spp.: 17, sample Pc2303, Idmarrach 1, late Serpukhovian; 22, samplePc3341, Akerchi 1, late Serpukhovian; 18, Monotaxinoides priscus (Brazhnikova and Yartseva, 1956), juvenile, sample Pc2771, Akerchi 2, lateSerpukhovian; 19, 21, Monotaxinoides ex gr. subplana (Brazhnikova and Yartseva, 1956): 19, sample Pc3309, Tirhela, late Serpukhovian); 21, samplePc2356, Idmarrach 2, Bashkirian; 20, Monotaxinoides cf. gracilis (Dain in Reitlinger, 1956), sample Pc2306, Idmarrach 1, late Serpukhovian. Scalebar5100 microns.


Limestone interval, underlying the Glen Dean Limestone(Fig. 14). For other authors, the top of the Glen DeanLimestone (the Tar Springs Sandstones) was correlated withthe Visean/Namurian boundary (Baxter et al. [1975] based onforaminifers and Collinson et al. [1971] on conodonts).Foraminiferal markers in the Tar Springs Sandstones for theE1 Zone included the Archaediscus at tenuis stage by Baxter etal. (1975), which were equated with the Archaediscus of thePennington Formation of Tennessee (also with Eosigmoilina;see Hewitt and Conil, 1969). This archaediscid assemblage, inturn, was compared with the Tramaka Encrinite of Belgium,which is currently assigned to the E2 Zone. The firstappearance of ‘‘Millerella’’ tortula/designata was locatedwithin the Glen Dean Formation. Nevertheless, Brenckle(1990a) correlated the first occurrence of those species with the

first occurrence of Janischewskina in the Franco-Belgianbasins, in the V3c or Brigantian. The Menard Limestonewas correlated with the base of the Pendleian, due to the FADof Eosigmoilina and Brenckleina, whereas no latest Chesterianmarkers were distinguished. Only in the upper part of theuppermost Chesterian, are the earliest Globivalvulina (possiblyG. moderata) and ‘‘Turrispiroides’’ recognized. Monotaxinoidesand evolved Millerella (M. pressa and M. marblensis) werealready recognized in the Pennsylvanian, and not necessarilyfrom the basal beds (Skipp et al., 1985). Recently, Kulagina etal. (2008) has correlated the occurrence of ‘‘Millerella’’ withthose from the basal Serpukhovian in the Zabory Quarry, andconsidered the Beech Creek Limestone as the base of theSerpukhovian, whereas the Menard Limestone was situtatedin levels equivalent to the late Serpukhovian. If the occurrence

FIGURE 11—1, Kasachstanodiscus sp., sample Pc3367, Tirhela, Bashkirian; 2, 4–6, Archaediscus spp. at tenuis stage: 2, P sample c3366, Tirhela,Bashkirian; 4, sample Pc2775, Akerchi 2, late Serpukhovian; 5, sample Pc2774, Akerchi 2, late Serpukhovian; 6, sample Pc2376, Akerchi 1, earlySerpukhovian; 3, Archaediscus aff. velguriensis Grozdilova and Lebedeva, 1954, sample Pc3343, Tirhela, late Serpukhovian; 7, 8, Brenckleina rugosa(Brazhnikhova, 1964): 7, sample Pc3338, Akerchi 1, late Serpukhovian; 8, sample Pc2774, Akerchi 2, late Serpukhovian; 9, Neoarchaediscus postrugosus(Reitlinger, 1949), sample 2369, Akerchi 1, late Brigantian; 10, 11, Eosigmoilina sp.: 10, sample Pc3338, Akerchi 1, late Serpukhovian; 11, sample Pc2304,Idmarrach 1, late Serpukhovian; 12–14, Euxinita pendleiensis Cozar et al., 2008b: 12, sample Pc3367, Tirhela, Bashkirian; 13, sample Pc3340, Akerchi 1,late Serpukhovian; 14, sample Pc2358, Idmarrach 2, late Serpukhovian; 15, 16, Loeblichia minima Brazhnikhova, 1962: 15, sample Pc2313, Idmarrach 1,late Serpukhovian; 16, sample Pc2347, Idmarrach 2, late Serpukhovian; 17–20, Loeblichia ukrainica Brazhnikhova, 1956: 17, 19, sample Pc2337,Idmarrach 2, late Serpukhovian; 18, sample Pc2335, Idmarrach 2, late Serpukhovian; 20, sample Pc3392, Idmarrach 3, early Serpukhovian; 21–25,Endostaffella? sp. 2: 21, sample Pc3337, Akerchi 1, late Serpukhovian; 22, sample Pc3375, Tirhela, Bashkirian; 23, sample Pc2774, Akerchi 2, lateSerpukhovian; 24, sample Pc3347, Akerchi 1, late Serpukhovian; 25, sample Pc3338, Akerchi 1, late Serpukhovian. Scale bar5100 microns.


of Eosigmoilina is the key marker for the recognition of Zone19 of Mamet, this implies that in the midcontinent, it would berepresented during the late Serpukhovian, contrary to theearly suggestion by Brenckle et al. (1977), in which, zones 17to 19 would correspond to the early Serpukhovian. Incontrast, despite numerous published correlations of Mamet’szonal scheme, assigning Zones 17 and 18 to the earlySerpukhovian and Zone 19 to the late Serpukhovian, or Zone17 to the early Serpukhovian and Zones 18–19 to the lateSerpukhovian (e.g., in Perret, 1993, fig. 129), the three zones(17–19) correspond with the early Serpukhovian in the Tethys,

and no new zone exists for the late Serpukhovian.At the baseof the Bashkirian no diagnostic foraminifers exist in the so-called ‘‘No Man’s Land’’ in Alaska as described by Mametand Batz (1989). Reitlinger (1980) observed a similar intervallacking age diagnostic foraminifers in Europe. The Zone 20 isthe first Bashkirian zone, approximately equivalent to theBogdanovskian/Siuranskian horizons, which is characterizedby the incoming of the first Globivalvulina bulloides and largeMillerella in the Midcontinent (Skipp et al., 1985).

The fauna is distinct in the Arctic American basins/Taimyr-Alaska Realm (e.g., Armstrong and Mamet, 1977). It occurs in

FIGURE 12—1, Eostaffella angusta Kireeva, 1949, sample Pc3304, Tirhela, late Serpukhovian; 2, 3, Eostaffella pseudostruvei Rauser-Chernoussova andReitlinger in Rauser-Chernoussova et al., 1936: 2, sample Pc2314, Idmarrach 1, late Serpukhovian; 3, sample Pc2347, Idmarrach 2, late Serpukhovian; 4,Eostaffella acutiformis Kireeva in Rauser-Chernoussova et al., 1951, sample Pc3331, Tirhela, late Serpukhovian; 5, 6, Eostaffella postmosquensis Kireevain Rauser-Chernoussova et al., 1951; 5, sample Pc3202, Akerchi 2, Bashkirian; 6, sample Pc2311, Idmarrach 1, late Serpukhovian; 7, Eostaffella aff.postmosquensis Kireeva in Rauser-Chernoussova et al., 1951, sample Pc3390, Idmarrach 3, early Serpukhovian; 8, Eostaffella sp., sample Pc3311,Tirhela, late Serpukhovian; 9, 10, Eostaffella cf. exilis Grozdilova and Lebedeva, 1950, Tirhela, late Serpukhovian: 9, sample Pc 3313; 10, sample Pc3318; 11, ‘‘Millerella’’? sp., sample Pc2304, Idmarrach 1, late Serpukhovian; 12, 13, Endostaffella? sp. 1: 12, sample Pc3300, Tirhela, late Serpukhovian;13, sample Pc3302, Tirhela, late Serpukhovian; 14, 15, Endostaffella? discoidea (Girty, 1915): 14, sample Pc3346, Akerchi 1, late Serpukhovian; 15,sample Pc3198, Akerchi 2, late Serpukhovian; 16, ‘‘Millerella’’ sp., sample Pc3329, Tirhela, late Serpukhovian; 17, 18, ‘‘Millerella’’? sp. or Eostaffella?sp., Tirhela, late Serpukhovian: 17, sample Pc3300; 18, sample Pc3326; 19, 20, ‘‘Millerella’’ aff. tortula (Zeller, 1953), sample Pc2375, Akerchi 1, earlySerpukhovian. Scale bar5100 microns.


a transitional zone between the prolific Tethyan and theimpoverished sub-Arctic North American basins. This areacontains numerous taxa never or rarely encountered furthersouth (Harris et al., 1997), and conversely, explains the routeof migration and dispersion of typical North American taxa inthe Tethys. Despite this cosmopolitan distribution of bio-stratigraphically useful taxa, they usually first occur in youngerrocks than in their respective realms, with a variable degree ofdiachroneity (Harris et al., 1997; Baesemann et al., 1998).

Moscow Basin.—This is one of the best known basins due tothe fact that the Serpukhovian Stage was defined by Nikitin(1890) in the southern outcrops of the Moscow Basin.Unfortunately, the base of the Serpukhovian exposed inZabory Quarry contains a non-sequence and the uppermostSerpukhovian is poorly developed in the basin due to theerosion and non-deposition of the Pestovo ‘Series’ (Fig. 14),in which foraminifers have been rarely studied (Fomina,

1977). Gibshman (2001) has proposed the subdivision of theTarusskian-Steshevskian-Protvinskian interval in four fora-miniferal zones for the basin: Neoarchaediscus postrugosus,Pseudoendothyra globosa, Eostaffellina decurta, and Eostaf-fellina ‘‘protvae’’ Zones. The basal zonal taxon, N. post-rugosus shows different stratigraphic ranges elsewhere: e.g.,in the Algerian basins and Kazakhstan, Bashkirian or lateSerpukhovian (Lys, 1985; Brenckle and Milkina, 2003);latest Brigantian in Morocco (Cozar et al., 2008a), Britain(Cozar et al., 2008b), Ireland (Cozar et al., 2005), and theUrals (Kossovaya et al., 2001). P. globosa is restricted bystrong facies control (Vdovenko, 2001), and it is relativelyrare or absent at equivalent stratigraphic levels outside ofthe Moscow Basin. Eostaffellina is recognized as a morecosmopolitan genus, being recorded in the entire Paleo-tethys, and at more or less equivalent levels. In Morocco,more compressed Eostaffellina occur in older beds than E.

FIGURE 13—1–4, Eostaffellina sp.: 1, 2 sample Pc2769, Akerchi 2, early Serpukhovian; 3, sample Pc3364, Tirhela, Bashkirian; 4, sample Pc3230,Akerchi 1, early Serpukhovian; 5–6, Eostaffellina ‘‘paraprotvae’’ Rauser-Chernoussova, 1948: 5, sample Pc3201, Akerchi 2, late Serpukhovian; 6, samplePc3338, Akerchi 1, late Serpukhovian; 7, 8, Eostaffellina ‘‘protvae’’ Rauser-Chernoussova, 1948: 7, sample Pc3341, Akerchi 1, late Serpukhovian; 8,sample Pc3364, Tirhela, Bashkirian; 9, 10, Plectostaffella varvariensiformis tenuissima Brazhnikhova and Vdovenko in Aizenverg et al., 1983: 9, samplePc3311, Tirhela, late Serpukhovian; 10, sample Pc2345, Idmarrach 2, late Serpukhovian; 11–13, Plectostaffella varvariensiformis Brazhnikhova andVdovenko in Aizenverg et al., 1983: 11, 12, sample Pc3300, Tirhela, late Serpukhovian; 13, sample Pc3364, Tirhela, Bashkirian; 14, Seminovella aff.elegantula Rauser-Chernoussova in Rauser-Chernoussova et al., 1951, sample Pc2356, Idmarrach 2, Bashkirian; 15, 16, Seminovella elegantula Rauser-Chernoussova in Rauser-Chernoussova et al., 1951: 15, sample Pc2776, Akerchi 2, Bashkirian; 16, sample Pc3377, Tirhela, Bashkirian; 17, 18, Novella?sp., sample Pc 3365, Tirhela, Bashkirian; 19, 20, Plectostaffella sp.: 19, sample Pc2331, Idmarrach 2, late Serpukhovian; 20, sample Pc3311, Tirhela, lateSerpukhovian. Scale bar5100 microns.


‘‘paraprotvae’’ or E. ‘‘protvae’’. Aisenverg et al. (1979a)mentioned Eostaffellina in the Tarusskian Horizon, but nospecies were determined. Reitlinger et al. in Einor (1996)also acknowledged this record but they attributed it to‘‘rounded eostaffellids.’’

Other taxa that first occur in the Tarusskian Horizon arePseudocornuspira (Cepekia auct.) and Planoendothyra aljuto-vica (Gibshman, 2001). The former genus is well-known inthe Brigantian in the Ukraine (Vdovenko, 2001), whereas thelatter taxon is commonly attributed to the latest Serpukho-vian or Bashkirian (Brazhnikova and Vdovenko in Aizenverget al., 1983; Kulagina et al., 2001). In Morocco, Pseudocor-nuspira is commonly observed in thin-section from the lateBrigantian (Cozar et al., 2008a) and Rectocornuspira (cf.Vdovenko, 2001) are rarely recognized in the late Serpukho-vian of Idmarrach (only recorded as 3D cast samplesprocessed for conodonts). Gibshman (2001) identified Cepe-kia from the Steshevskian Horizon. Although unrecorded bythe previous author, Aisenverg et al. (1979a) consideredLoeblichia ukrainica to be from the Tarusskian Horizon in theMoscow Basin. Other taxa recorded from the SteshevskianHorizon in the Moscow Basin by Gibshman (2001) areLoeblichia minima, Eostaffellina paraprotvae, ‘‘Millerella’’tortula, and Millerella pressa. The latter species, is generallyused as a marker of the Bashkirian in the sub-Arctic North

American basins, in concert with other large species ofMillerella (e.g., Brenckle, 1990b), even its rarity in ArcticNorth American basins prevents its use as a potential marker(Harris et al., 1997).

For the Protvinskian Horizon, the key taxa include the well-rounded Eostaffellina protvae and Eostaffellina shartimensis,as well as Brenckleina. Eosigmoilina does not occur in theMoscow Basin.

In Aisenverg et al. (1979a), Bradyina cribrostomata is alsorecognized from the Protvinskian Horizon. Fomina (1977) isthe only study of the Pestovo foraminifers, an interval whichwas characterized by the occurrence of new species of the generaEostaffella, Eostaffellina, and Pseudoendothyra. It is surprisingthat while Howchinia occurs up to the Protvinskian, thecommon Monotaxinoides species of the Donetz Basin and theUrals have not been documented in the Moscow Basin.

Urals.—Eostaffella pseudostruvei is rarely recorded at thetop of the Visean, but is common in the Serpukhovian(Reitlinger et al. in Einor, 1996). As mentioned previously,Neoarchaediscus postrugosus first occurs in some outcropsfrom the late Brigantian (Kossovaya et al., 2001), although inother sections of the Urals, it first occurs in the lowerSerpukhovian Kosogorskian Horizon (Nikolaeva et al., 2001,2009a; Fig. 14). Other taxa that have been documented in thishorizon are Globivalvulina minima and G. parva (Kossovaya

FIGURE 14—Correlation of the Serpukhovian stage and substages between North America, Western Europe, Moscow Basin, Urals, and DonetzBasin. Correlation with Western Europe and North America is still controversial; source for the correlation is exposed and discussed in the text.Correlation between Moscow, Urals, and Donetz basins are mostly based on Aizenverg et al. (1979a, 1979b), Nikolaeva et al. (2009a), Vdovenko (2001),and Einor (1996). Mamet’s foraminiferal zones 17–20 shown in the midcontinent U.S.A. column, where the type Chesterian limestones in southernIllinois are based on Brenckle et al. (2005) and its correlation based in Kulagina et al. (2008).


et al., 2001; Reitlinger et al. in Einor, 1996), Monotaxinoides?sp. (Nikolaeva et al., 2009a) and Eostaffellina subsphaerica(Reitlinger et al. in Einor, 1996).

The Khudolozovian Horizon is correlated with the upperpart of the Steshevskian and the entire Protvinskian horizonsof the Moscow Basin (Fig. 14), and thus, the early/lateSerpukhovian boundary interval is included within the middlepart of this horizon (see Nikolaeva et al., 2009a). Taxa thatfirst occur in the Khudolozovian Horizon are numerous:Monotaxinoides priscus, M. subplana, M. transitorius, Eostaf-fellina decurta, E. paraprotvae, E. protvae, Eostaffella mirifica,Plectostaffella varvariensis, as well as other primitive Plectos-taffella, and Eosigmoilina. No major differences are observedbetween the lower and upper part of this horizon, and thus,the boundary between the early and late Serpukhovian cannotbe precisely correlated with the Moscow Basin.

The youngest horizon in the Urals is the Chernyshevian,which is laterally equivalent to the Pestovo beds (Fig. 14). Thisis characterized by numerous species of Monotaxinoidesunrecorded in lower levels, including M. gracilis and M.planus (Nikolaeva et al., 2009a), Globivalvulina bulloides(Groves, 1988; Groves et. al., 1999), Eostaffella postmosquen-sis, Planoendothyra aljutovica, Globivalvulina kamaensis (Ku-lagina et al., 2001), and Bradyina cribrostomata (Groves, 1988;Kulagina et al., 2001).

Several new species of Eostaffella, Plectostaffella, Millerella,and Plectomillerella are first recorded in the basal BashkirianBogdanovskian Horizon in the type section in Bashkiria, southUrals (Reitlinger, 1980; Groves, 1988; Kulagina et al., 2001).

Donetz Basin.—Four Serpukhovian substages are consid-ered in the Donetz Basin, the Samarskian (equivalent to theTarusskian and Steshevskian horizons combined), the Pro-khorovskian (lower part of the Protvinskian), Novolyubovs-kian (upper part of the Protvinskian) and Zapaltyubinskian(5Pestovo Beds) (Fig. 14).

In the Samarskian and older rocks of the Visean,Brazhnikova and Vdovenko in Aizenverg et al. (1983),Poletaev et al. (1991) and Vdovenko (2001) recorded the firstRectocornuspira, Loeblichia ukrainica, Eostaffella ex gr.pseudostruvei, and Monotaxinoides (M. subplana, M. subco-nica, M. priscus, M. declivis; considered as Howchinia byVdovenko, 2001, except for M. priscus). In the top limestonebed of this horizon (C4), Bradyina cribrostomata, Eostaffellapostmosquensis, E. pseudostruvei s.s., and Endothyranopsisplana are recorded (Brazhnikova and Vdovenko in Aizenverget al., 1983). Brenckleina is also listed from the C4–C5 lime-stones. However, as well as Eosigmoilina, only specimens fromthe D3 Limestone or younger horizon (Zapatulyubinskian)were illustrated. Poletaev et al. (1991) and Vdovenko (2001)revised and reillustrated a specimen of Eosigmoilina, consid-ered here as valid, from the C5 Limestone. In contrast to olderpublications, the C5 Limestone was considered as the basalpart of the Prokhorovskian Horizon, and as the base of thelate Serpukhovian by Vdovenko (2001). Other markers of theProkhorovskian Horizon are Eostaffellina protvae, E. para-protvae, and Eostaffella mirifica.

In the Novolyubovskian, only a few new taxa occur, such asM. transitorius, Globivalvulina ex gr. pulchra, and G. ex gr.eogranulosa (Brazhnikova and Vdovenko in Aizenverg et al.,1983).

The Zapaltyubinskian Horizon can be characterized bythe first appearances of Loeblichia minima, Planoendothyraspirillinoides, Globivalvulina moderata, Plectostaffella varvar-iensis, P. bogdanovkensis (with other species and subspecies ofthe genus), rare Millerella, Seminovella ex gr. elegantula, and

some new species of Eostaffellina (Brazhnikova and Vdovenkoin Aizenverg et al., 1983). Most Millerella and Seminovellaspecies do not occur up to the Bashkirian (VoznesenskianHorizon) (Fig. 14).

Saharan basins and Tunisia.—Three main areas of Carbon-iferous sedimentation can be distinguished in this region ofnorthern Africa (Fig. 1A): central Saharan basins (e.g.,Reggane and Ahnet-Mouydir, southern Algeria), westernSaharan basins (e.g., Bechar and Tindouf, northwesternAlgeria/southern Morocco), and Tunisia. Taxa described andused as markers in the Sahara have little in common withAdarouch. These faunal differences could be attributed toseveral factors: 1) inconsistent stratigraphic ranges for the taxain the same basin; 2) an incomplete foraminiferal database,because in many publications, no location of the samples wereprovided, only stratigraphic summaries of the species lists,split by stages or substages (e.g., Lys, 1975, 1985; Sebbar,1997; Mamet et al., 1994; Sebbar et al., 2000); 3) the number ofillustrated specimens is scarce, or poorly illustrated specimensof key taxa such as Bradyina cribrostomata, Loeblichia minima,and Eostaffella mirifica, or even non-existent illustrations ofLoeblichia ukrainica; 4) lack of a close calibration betweenammonoid and foraminiferal zonal schemes that might behelpful in validating the stratigraphic ranges of the foramin-ifers in the Sahara; and 5) strongly marked paleobiogeo-graphic contrast north and south of the Atlas TransformFault.

Analysis of the foraminiferal taxa in the Saharian basinsand Tunisia suggest that some species may have arisen inAlgeria and hence are older than in the western Basins ofRussia, including: 1) Bradyina cribrostomata from the basal E1Zone (Tindouf and Bechar, Lys, 1985; Sebbar, 1998; Mametet al., 1994; Sebbar et al., 2000), including the B. ex gr.cribrostomata from the Visean (Lys, 1985); 2) Eosigmoilinafrom the base of E1 Zone in Tindouf, Tunisia and Bechar(Lys, 1975, 1985, 1988; Sebbar, 1998); 3) Eostaffella mirificafrom the basal E1 Zone in Tindouf and Reggane/Ahnet-Mouydir (Lys, 1975, 1985; Sebbar, 1998; Sebbar et al., 2000);4) Globivalvulina moderata from the basal E1 Zone in Tindouf,Reggane/Ahnet-Mouydir, Tunisia (Lys, 1975, 1985, 1988;Sebbar and Lys, 1989; Sebbar, 1998); 5) Loeblichia minimaalso from the base of the E1 Zone in Bechar and Reggane/Ahnet-Mouydir (Lys, 1975, 1985; Sebbar and Lys, 1989); and6) Eostaffellina paraprotvae in the basal E1 Zone (Lys, 1985).In addition, the use of the two zonal schemes (Mamet’sforaminiferal zones and the classical Eumorphoceras ammonoidZone) also contributed more confusion to the data, because, aswas described in the North America sections, all the markersdefined for Mamet’s Zones 17, 18 and 19 are recorded in the E1Zone, but in some publications the Zone 18 and/or 19 areindistinctly used as equivalent to the E2 Zone in the Sahara(e.g., Mamet et al., 1994; Sebbar, 1998; Sebbar et al., 2000). Thisproblem is actually even more acute, because the E1 and E2zones and Mamet’s zones are not precisely calibrated with theSerpukhovian substages of the Russian Platform (Fig. 14).

PERSPECTIVES FOR BIOMARKERS OF THE

VISEAN/SERPUKHOVIAN AND SERPUKHOVIAN/

BASHKIRIAN BOUNDARIES

Globivalvulina parva and other species such as G. minima orG. moderata that in some works are considered as synonyms(e.g., Sebbar et al., 2000) can have only limited use as potentialmarkers for recognizing the Visean/Serpukhovian (V/S)boundary because primitive species of the genus first occurfrom the late Brigantian, and even in older rocks. Other more


evolved species with a clear light diaphanotheca occur muchlater, close to the Serpukhovian/Bashkirian (S/B) boundary(e.g., Globivalvulina bulloides). The new species G. sp. 1 with agranular wall, seems to be endemic to Morocco, and has arange from late Brigantian to Serpukhovian.

Neoarchaediscus postrugosus and Monotaxinoides speciescan be potentially useful for recognizing the V/S and early/lateSerpukhovian boundaries respectively, but have differentstratigraphic ranges elsewhere.

In the case of ‘‘Millerella’’, although mostly a NorthAmerican genus, it seems to have a worldwide distribution,but the Moroccan, European and Chinese species are difficultto compare with the species recognized in the U.S.A. orCanada.

In the case of the genus Loeblichia, some species first appearin the Brigantian (e.g., L. paraammonoides, L. ukrainica). InAdarouch L. ukrainica first appears later, in the earlySerpukhovian while L. minima occurs much later, aroundthe early/late Serpukhovian boundary (Fig. 9).

The archaediscids are still of great significance, not only forthe subdivision of the Visean, but possibly also for theSerpukhovian. For recognizing the V/S boundary species ofNeoarchaediscus, particularly N. postrugosus, may be impor-tant in North African basins, despite the fact that it is recordedin uppermost Brigantian rocks in Europe. In Adarouch it firstoccurs only a few meters below the V/S boundary. Thesignificance of Asteroarchaediscus baschkiricus in Zone 17, asdefined in Mamet’s zones, is minimized, because its FAD isrecognized earlier in Zone 16, a fact frequently demonstratedin many Paleotethyan and North American basins. Neverthe-less, the A. baschkiricus group is still important, because of itsworldwide distribution, and hence has several advantages.Firstly, within the group, can be recognized 1) severalmorphotypes/species; 2) different stages of evolution; 3)different number of whorls; and 4) different development ofthe microgranular layer, from A. pustulus to A. baschkiricuss.s., and even other larger specimens with a reducedmicrogranular layer (unnamed and usually included in A.baschkiricus). These features also coincide with the reductionof the number of pores in the fibrous layer, characteristic ofthe Archaediscus at tenuis stage and also in the species ofAsteroarchaediscus and Neoarchaediscus (e.g., Hewitt andConil, 1969, pl. 2, figs. 31–33).

In addition, within the archaediscids there is another group,the Archaediscus at tenuis stage. The use of this group in theBrigantian by Conil et al. (1980) is confusing, because theydescribed ‘‘transitional forms to the Archaediscus at tenuisstage’’, and later (Conil et al., 1991) they used those taxa as keymarkers for the Cf7 Zone (Namurian). The only publication inwhich various Archaediscus at tenuis stage were illustrated inWestern Europe is in Austin et al. (1974), from the TramakaEncrinite, and subsequently in Perret (1993) from the Arden-gost Limestone, and always from the E2 Zone. The smallprimitive specimens generally occurring at the base of theSerpukhovian, and with uniform wall thickness from the innerwhorls seems to be derived from Archaediscus stilus, with sometenuis final whorls that are already present in the Brigantian.

Furthermore, among the archaediscids, Eosigmoilina is alsoan excellent marker as it has a worldwide distribution and isrelatively common, but its FAD is situated in the earlySerpukhovian in some basins, whereas in the majority it can beused as marker for the early/late Serpukhovian boundary.

A similar case to Eosigmoilina seems to be Endothyranopsisplana, occurring in younger beds than the current position ofthe V/S boundary. However, it must be admitted that the

stratigraphic range and geographic distribution of this speciesis not well established yet.

The FAD and species determination of the primitiveEostaffellina is not well established in the literature. It wouldbe necessary to establish precisely if this FAD can be locatedat the base of the Serpukhovian or in slightly younger beds, asin the case of Eosigmoilina, which is not clear enough in thepublished data.

In Western European basins, Endostaffella? sp. 2 is alsopotentially an excellent marker for the base of the Serpukho-vian, but this needs to be confirmed in other basins, especiallyin Eastern Europe.

CONCLUSIONS

A continuous uppermost Visean to Bashkirian sequence isrecorded in the Adarouch area of central Morocco. It is apredominantly limestone and shale sequence passing up at thetop into red bed siliciclastic rocks.

The Adarouch sequence is one of the few successions inMorocco where limestones have yielded a rich suite of lateBrigantian and Serpukhovian foraminifers, algae, corals andconodonts.

The Visean/Serpukhovian boundary at Adarouch is markedby the first appearance of Eostaffellina sp., Eostaffellapseudostruvei, and Archaediscus at tenuis stage. It is alsocharacterized by unusual and rare taxa such as ‘‘Millerella’’,Endostaffella? sp. 1, Endostaffella? sp. 2, Insolentitheca horrida,and Loeblichia ukrainica, which might have more localregional significance. In slightly higher beds in the earlySerpukhovian, Endothyranopsis plana first occurs.

An early/late Serpukhovian boundary is recognized atAdarouch, based on the first appearance of Brenckleina,Eosigmoilina, Loeblichia minima, Bradyina cribrostomata,Plectostaffella spp., Eostaffellina ‘‘paraprotvae’’, E. ‘‘protvae’’,‘‘Turrispiroides’’, and locally by Monotaxinoides spp. Higherin the late Serpukhovian is recorded Eostaffella postmosquensisand Globoomphalotis?. Also recorded in this E2 zonal interval isthe zonal conodont Gnathodus bilineatus bollandensis.

The Serpukhovian/Bashkirian (Mississippian/Pennsylvanian)boundary at Adarouch is marked by the first occurrence of rareSeminovella elegantula and Novella? The base of the Bashkirian ismarked by the zonal conodont Declinognathodus noduliferus.

Comparisons are made between the Adarouch area and otherPaleotethyan regions containing Serpukhovian-Bashkirian sec-tions, including the Sahara, Donets Basin, Moscow Basin andthe Urals, as well as North America.

A significant aspect of the Adarouch succession is that it iscomposed of thick limestone intervals, unlike many otherMississippian sequences in the western Paleotethys, which areusually characterized by cyclothems dominated by siliciclasticrocks, in which limestones form only a minor component.Hence, it is much more likely to be able to trace evolutionarylineages in foraminifers in Adarouch.

The Adarouch succession represents a late Mississippian–Pennsylvanian sequence from the northern margin of Gond-wanaland, but yet shows all the characteristic taxa of westernPaleotethyan basins, and even shows some affinities with NorthAmerican successions, particularly in the Serpukhovian.

ACKNOWLEDGMENTS

The authors would like to thank the collaboration of theDepartment of Mine Development of the Ministere de l’Energieet des Mines of Morocco, who kindly gave us permission tocarry out field work. Also, thanks to M. Howe (Chief Curator,Palaeontological Unit, Keyworth) and M. Dean (Palaeonto-


logical Unit, Edinburgh) of the British Geological Survey whokindly allowed the examination of the material from theWoodland and Archerbeck boreholes. This research wassupported by the projects CGL2006-03085 and CGL2009-10340 of the Spanish Ministry of Research and Innovation. Wethank the two reviewers D. Altiner and J. Groves for theirhelpful comments which significantly improved this paper.

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