PALEVO 1631-0683 Elsevier S1631-0683(08)00050-X 10.1016/j.crpv.2008.04.001 Research article Systematic Palaeontology (Micropalaeontology) Paléontologie systématique / Systematic palaeontology (Micropaléontologie / Micropalaeontology) Pennsylvanian fusulinids and calcareous algae from Sonora (northwestern Mexico), and their biostratigraphic and palaeobiogeographic implications Fusulines et algues calcaires du Pennsylvanien de l’État de Sonora (Nord-Ouest du Mexique) ; implications biostratigraphiques et paléobiogéographiques Gomez-Espinosa Catalina a Vachard Daniel daniel.vachard@univ-lille1.fr b Buitrón-Sánchez Blanca c Almazán-Vazquez Emilio a b c Mendoza-Madera Cynthia a b c Universidad Autónoma de México, Instituto de Geología, Departamento de Paleontología, Ciudad Universitaria, 04510 México, D.F., Mexico Université de Lille-1, UFR Sciences de la Terre, UMR CNRS 8157, Géosystèmes, bâtiment SN5, 59655 Villeneuve-d’Ascq cedex, France Universidad de Sonora UniSon, Departamento de Geología, División de Ciencias Exactas y Naturales, Departamento de Geología, Blv. Luis Encinas y Rosales, CP 83000, Hermosillo (Sonora), Mexico 7 5 S1631-0683(08)X0005-3 259 268 © 2008 Académie des sciences. Published by Elsevier B.V. All rights reserved. 2008 Académie des sciences Full (PDF)

Pennsylvanian carbonates are widespread in Sonora (Mexico) and contain a diverse biota of foraminifers and calcareous algae. Detailed studies here are devoted to the outcrops of the Sierra Agua Verde and Cerro El Tule. The Late Atokan (early Late Moscovian part), Desmoinesian (= late Late Moscovian) and Missourian (= Kasimovian) stages are especially rich in fusulinids and algae. The principal zones of fusulinids of Wilde encountered are A3, DS1 and MC1–2. New data are given about the genera Fusulinella, Parawedekindellina, Zellerella, Komia and Paraepimastopora, in order to establish migrations or vicariances between Mexico and Palaeotethys.

Les carbonates du Pennsylvanien de l’État de Sonora (Mexique) sont riches en fusulines et algues calcaires dans la Sierra Agua Verde et le Cerro El Tule. L’Atokien supérieur et le Desmoinésien (tous deux équivalents du Moscovien supérieur) et le Missourien (=Kassimovien) sont les étages les mieux caractérisés, avec les biozones A3, DS1 et MC1–2 de l’échelle de fusulines de Wilde. Des informations complémentaires sur les genres Fusulinella, Parawedekindellina, Zellerella, Komia et Paraepimastopora permettent de discuter si ces peuplements résultent de migrations ou de vicariances.

 Foraminifers, Algae, Biostratigraphy, Palaeobiogeography, Pennsylvanian, Sonora, Mexico Foraminifères, Algues, Biostratigraphie, Paléobiogéographie, Pennsylvanien, Sonora, Mexique presented Presented by Jean Dercourt Version française abrégée

Les échantillons de calcaires recueillis en février 2003, 2004 et 2005, dans l’État de Sonora au Mexique, ont livré des microfaciès de wackestones et de packstones bioclastiques à fusulinidés, petits foraminifères et algues.

Les séries examinées les premières ont été celles de la Sierra Agua Verde, colline où le Mississippien (= Carbonifère inférieur) affleure [30], et où le Pennsylvanien comporte du Morrowien et de l’Atokien inférieur, que nous attribuons à la zone A2 de Wilde [36]. Au Cerro El Tule, seules quelques fusulines pennsylvaniennes avaient été mentionnées, sans être illustrées [7] ; Triticites ventricosus avait permis d’identifier le Virgilien [7].

L’assemblage de l’Atokien supérieur A3 de Sierra Agua Verde est identique à celui de la partie supérieure du calcaire de Marble Falls, dans le Texas central [10]. Il se compose d’Eugonophyllum ? sp., Kamaena ? sp., Zidella ( ?) sp., Komia abundans, Pachysphaerina pachysphaerica, Eotuberitina reitlingerae, Insolentitheca horrida, Endothyra ex gr. bowmani, Globivalvulina bulloides, Climacammina ex gr. moelleri, Deckerella sp., Mediocris breviscula, Eostaffella grozdilovae, Millerella sp., Pseudostaffella sp. (rare), Staffella powwowensis, Eoschubertella texana, Fusulinella llanoensis, F. aff. llanoensis, Zellerella sp. 1, Calcivertella sp., Baryshnikovia sp. et Syzrania sp. Les bancs à fusulines atokiennes sont interstratifiés dans des niveaux bioconstruits à Chaetetes [1], [2] and [30] ou bioaccumulés à crinoïdes [3] (Fig. 2).

L’association du Desmoinésien inférieur DS1 du Cerro El Tule comporte de rares Komia abundans, Endothyra sp., Bradyina spp., Polytaxis sp., Climacammina moelleri, Globivalvulina sp., Eoschubertella sp, Wedekindellina euthysepta, Beedeina leei, B. euryteines et B. cf. novamexicana.

Enfin, le Missourien du Cerro El Tule contient de très abondants Triticites canyonensis et de rares T. springvillensis, Paraepimastopora kansasensis, Bradyina sp., Polytaxis sp. et Globivalvulina bulloides. Triticites canyonensis date plutôt les biozones MC1 et MC 2 [37].

Les fusulines supramoscoviennes (Atokien–Desmoinésien), Fusulinella llanoensis, Beedeina leei, B. euryteines et Wedekindellina euthysepta, sont les formes habituelles du Sud des États-Unis [4], [7], [10], [23], [24] and [28]. En Sonora, de multiples transitions morphologiques, entre Fusulinella llanoensis et son écophène probable F. thompsoni, s’observent, ce qui confirme la synonymie proposée au Texas [10]. La découverte la plus importante est celle de Zellerella sp. 1 (Fig. 3.2), dont l’apparition dans l’Atokien supérieur du Sonora précède l’acmé desmoinésienne dans les Big Hatchet Mountains du Nouveau Mexique [37]. Le genre Zellerella, quoique décrit depuis peu [37], a une indéniable valeur paléobiogéographique et phylogénétique, car il apparaît très proche morphologiquement du genre Parawedekindelllina de l’Oural. Les vraies Wedekindellina des États-Unis d’Amérique, qui se développent à partir du Desmoinésien [36] and [37], sont peut-être à distinguer génériquement de leurs contemporaines de Russie. Par ailleurs, une autre espèce nord-américaine, Wedekindellina matura, est considérée par certains auteurs comme une Nipperella, autre genre voisin [37], tandis que des « Wedelindellina » assez similaires à celles du sud des États-Unis, comme « W. » pseudomatura [20] and [24] et « W » praematura [3] and [6], apparaissent aussi proches de Parawedekindellina que de Zellerella. On est donc conduit à penser que l’on pourrait préciser la limite biostratigraphique Atokien-Desmoinésien grâce à de possibles lignées, soit migrantes, soit vicariantes : (a) Zellerella-Wedekindellina sensu stricto ; (b) Nipperella-Wedekindellina sensu 2 ; (c) Parawedekindellina-Wedekindellina sensu 3.

Les fusulines missouriennes du Sonora appartiennent au groupe I de Wilde [36] décrit au Nouveau Mexique et partiellement connu dans d’autres états des États-Unis.

L’algue problématique Komia est assez représentative de l’Atokien de Sierra Agua Verde. La répartition de ce genre, dont l’attribution a oscillé entre algues rouges et microstromatoporoïdes, fait l’objet de controverses ; elle est particulièrement abondante dans le Desmoinésien des États-Unis [36], mais s’y observe dès l’Atokien [9]. Cela semble être l’inverse dans le Sonora. Par ailleurs, si Komia a été signalée dans le Bashkirien, et même dès le Viséen [16], c’est probablement à cause de confusions avec Foliophycus, Efluegelia ou Chuvashovia. Enfin, dans les populations de Komia que nous avons étudiées, les caractères de Pseudokomia se rencontrent chez plusieurs individus, ce qui nous incite à penser que ces deux taxons sont synonymes.

La dasycladale Paraepimastopora a été diversement définie [13] and [25]. Selon nos observations, elle se compose (a) d’une grande cellule centrale, entourée (b) d’un manchon calcaire percé de nombreux pores polygonaux à l’emplacement de latérales parallèles, prismatiques et aspondyles, et (c) d’intusannulations obliques bien développées [12] and [13] ; sa répartition stratigraphique s’étend du Viséen supérieur [5] au Permien [15].

Les associations d’algues et de fusulines du Sonora, similaires à celles du Sud des États-Unis (Tableau 2), les complètent par la découverte d’une espèce précoce de Zellerella. Il conviendrait de préciser efficacement ses différences morphologiques avec l’élément ouralien Parawedekindellina. Cette distinction est d’autant plus importante que des migrations de microfaunes sont prouvées dans le Permien mexicain et guatémaltèque [32]. En ce qui concerne la paléogéographie locale, les associations étant semblables dans les deux grands domaines géodynamiques du Sonora, le craton Nord-Américain et le « terrane » Caborca [8] and [27], ceux-ci ne sont donc pas encore individualisés au Carbonifère–Permien. Il y a aussi liaison des plates-formes continentales, entre le Sonora et le « terrane » Mixteco, au Missourien, à cause de la présence conjointe de certaines espèces de Triticites, malgré l’intercalation de bassins remplis de flyschs. Cette continuité s’étend à la bordure périgondwanienne de l’Amérique du Sud [1], [2] and [3] (Fig. 4).

 Introduction

The Sierra Agua Verde and Cerro El Tule in the Sonora State, northwestern Mexico (Fig. 1 and Fig. 2), were sampled by our team in February 2003, 2004 and 2005. The Pennsylvanian carbonates are composed of bioclastic wackestones and packstones with fusulinids, smaller foraminifers and calcareous algae. In the Sierra Agua Verde, the Mississippian (Early Carboniferous) and the Early Pennsylvanian (Morrowan = Early Bashkirian), as well as the Early Atokan (= Profusulinella zone = zone A2 of Wilde [36] = Late Bashkirian–Early Moscovian) were found (Table 1). In Cerro El Tule, only few Pennsylvanian fusulinids have been mentioned, but never illustrated [7]. Its Virgilian deposits were dated based on the occurrence of Triticites ventricosus [7].

The aim of this paper is to describe the Pennsylvanian fossil assemblages, with emphasis on the calcareous algae and foraminifers, and the carbonate depositional environments of the strata. Other goals are to confirm the palaeobiogeographical affinities with the southwestern United States, and document the possible migrations or vicariances from the Urals and Southeast Asia that have been previously proposed in Mexico (Patlanoaya) and Guatemala [32], [33] and [34].

 Previous work

The Pennsylvanian carbonates and their microfaunal and microfloral assemblages are rather poorly studied in Sonora [14], [19], [26] and [34]. Few fossiliferous outcrops are known. The Pennsylvanian of the other Mexican States is even more poorly known [34]. The Pennsylvanian limestones previously studied in Sonora and Chihuahua are parts of the Horquilla Formation, with outcrops located near the American border [31] in the Sierra de Palomas (Chihuahua) and Cerro El Tule (Sonora) [7]. The Sierra Agua Verde was also studied up to the Early Atokan [18] and [30]. In this locality, the Pennsylvanian section is denominated La Joya Formation [18], which is coeval to unit 4 of Sierra Santa Teresa [29]. The fusulinids are mentioned in a few publications [7], [14] and [19], but are very rarely illustrated [31] and [38]. In the USA, the Pennsylvanian subsystem is divided into five stages (Table 1): Morrowan, Atokan, Desmoinesian, Missourian, and Virgilian. The approximate correlations with global stages are as follows: Morrowan = Early Bashkirian, Atokan = Late Bashkirian to Early Late Moscovian (Podolskian); Desmoinesian = late Late Moscovian (Myachkovian); Missourian = Kasimovian; Virgilian = Gzhelian. Wilde [36] recognized 16 zones of fusulinids in the Permian Basin of the southwestern USA (Table 1). Pennsylvanian calcareous algae are poorly known in Mexico, but have been well studied further north in North America (e.g., [9] and [16]).

 Biostratigraphy

Late Atokan (A3) assemblages of the Sierra Agua Verde (location of the section in [17]) are similar to those of the upper part of the Marble Falls Limestone [10] of central Texas. They contain: Eugonophyllum? sp., Kamaena? sp., Zidella? sp., Komia abundans, Pachysphaerina pachysphaerica, Eotuberitina reitlingerae, Insolentitheca horrida, Endothyra ex gr. bowmani, Globivalvulina bulloides, Climacammina ex gr. moelleri, Deckerella sp., Mediocris breviscula, Eostaffella grozdilovae, Millerella sp., Pseudostaffella sp. (rare), Staffella powwowensis, Eoschubertella texana, Fusulinella llanoensis, F. aff. llanoensis, Zellerella sp. 1, Calcivertella sp, Baryshnikovia sp., and Syzrania sp. Beds with Atokan fusulinids are intercalated with bioconstructions of Chaetetes, which have been previously cited from this outcrop [30], and are being re-investigated by our team [1] and [2].

The Early Desmoinesian (DS1) limestone from Cerro El Tule contains rare Komia abundans, Endothyra sp., Bradyina spp., Polytaxis sp., Climacammina moelleri, Globivalvulina sp., Eoschubertella sp, Wedekindellina euthysepta, Beedeina leei, B. euryteines, and B. cf. novamexicana.

The Missourian of Cerro El Tule is very rich in representatives of Triticites canyonensis, but the associated biota is poorly diversified, consisting of only Triticites springvillensis, Bradyina sp., Polytaxis sp., Globivalvulina bulloides, and Paraepimastopora kansasensis. This Missourian assemblage corresponds probably to biozone MC 1 or MC 2 [36], characterized by two out of the seven species of group I of Wilde, 2006 [37].

 Micropaleontology

Generally, the Pennsylvanian fusulinids of Sonora are well-known species of the southern USA: e.g., Fusulinella llanoensis, Beedeina leei, B. euryteines and Wedekindellina euthysepta (e.g., [4], [6], [10], [23], [24] and [28]). The most notable difference in the Mexican fauna is the presence of the recently described genus Zellerella [37] in the Late Atokan of Sonora (Fig. 3.2); i.e., prior to its appearance in the Desmoinesian of New Mexico. That confirms the opinion of Wilde [37] that Zellerella is the ancestor of the Desmoinesian Wedekindellina euthysepta. However, some atypical Wedekindellina of the USA, such as W. praematura [6] and W. pseudomatura [24] probably belong to Zellerella, and W. matura itself has been assigned by some authors to the genus Nipperella. In northern Urals, two genera are quoted: Parawedekindellina and Wedekindellina [22]. Consequently, in order to characterize more accurately the Atokan–Desmoinesian (i.e. the Podolskian–Myachkovian) boundary in North America and the northern Urals, the following hypothetical generic phylogeny might be used: (a) Zellerella-typical Wedekindellina; (b) Nipperella-atypical North American Wedekindellina; (c) Parawedekindellina-atypical Russian ‘Wedekindellina’ If we have only two genera, Wedekindellina and its ancestor, migrations are necessary. In case of three lineages, vicariances are the explanation.

It should also be noted that transitional stages in our material confirm, as previously suggested in Texas [10], that Fusulinella llanoensis is synonym of F. thompsoni (Fig. 3.1, 3.3 and 3.4).

The Late Atokan smaller foraminifers of the Sierra Agua Verde correspond exactly to the assemblages of Marble Falls, Texas [11]. Two calcareous algae have a particular importance. First, the dasyclad Paraepimastopora, which has been diversely defined [13] and [25], but is distinguished by a large axial cell, parallel prismatic aspondyl laterals, and oblique intusannulations [12] and [13] (Fig. 3.15–16). Its stratigraphical distribution is from the Late Visean [5] to the Permian [15]. Second, the alga incertae sedis Komia, which has been assigned to the red algae or the microstromatoporoidean, is uncommon in the Atokan of the USA, and is generally considered as Desmoinesian in age [36], but, in Sonora, it is more common in the Atokan [9]. Previous citations of Komia in the Early Bashkirian, and even the Visean [13], are probably due to confusions with Foliophycus, Efluegelia or Chuvashovia. Finally, we illustrate here (Fig. 3.6) some specimens of Komia that look like Pseudokomia by the irregularity of the central skeleton, and we suggest that the genera are synonyms.

The Desmoinesian and Missourian fusulinids of Sonora are well-known endemic North-American taxa (Table 2).

 Palaeobiogeography

The Sonoran Pennsylvanian fusulinids, algae, smaller foraminifers and chaetetids have clean palaeobiogeographical affinities with biota from Arizona, New Mexico, Texas, and California, similar to the Permian ([20] and [21]; see also [11] and [35]) (Table 2). An exception should be the lineage Zellerella–Wedekindellina compared with that of Parawedekindellina–Russian Wedekindellina. A possible connection between Mexico and the Urals and/or Palaeo-Tethys was previously observed by our team [32], [33] and [34], but it remains difficult to explain geodynamically.

The regional geodynamic problem in Sonora is simpler, because the assemblages are similar in the two domains of Sonora: Craton and Caborca Terranes [8] and [27]. These two domains apparently were not separated during the Carboniferous–Permian. The continuity with the Mixteco Terrane during Missourian times is evidenced by the presence of Triticites of group I, although the two domains were separated by basins filled by flysch deposits (Fig. 4).

These data confirm the previous palaeobiogeographical reconstructions of our team [32], [33] and [34]. The North American Craton is separated from the Gondwana of South America by a remnant of the Rheic Ocean, where there are some separated tectonostratigraphic terranes with carbonate platforms, such as Mixteco and Oaxaquia, while many basins with flysch are developed in the intermediary parts of Mexico [1], [2] and [3] (Fig. 4).

 Conclusions

Pennsylvanian carbonates from Sonora (Mexico) in Sierra Agua Verde and Cerro El Tule contain different assemblages of carbonate microfossils.

The Wilde zones A3, DS1 and MC1–2 of Wilde are well developed.

The Late Atokan Fusulinella belong to F. llanoensis and correlate the outcrops to Texas.

A newly encountered form in Mexico and in the Atokan in general, Zellerella sp. 1, is phylogenetically and palaeobiogeographically interesting. They seem to be morphologically similar to the Russian genus Parawedekindellina. The interpretation of this discovery is difficult, either a migration or a vicariance; i.e. the presence or absence of a palaeobiogeographic connection with the Uralian Province.

Desmoinesian fusulinids are represented by three species of the genus Beedeina and a species of Wedekindellina. They are all well-known species in the USA, but are essentially unknown in the Tethys.

The calcareous alga Komia is abundant in the Atokan of Sonora, unlike in the USA, where its acme is Desmoinesian in age.

Paraepimastopora kansasensis is reported from Sonora at Cerro El Tule, for the first time.

The Mexican Pennsylvanian palaeogeography is composed of only one domain in Sonora, more or less related to the Oaxaquia and Mixteco terranes.

Acknowledgements

This study was financed by the programs ECOS/ANUIES (ECOS M 00 U06) and PAPIIT 2003. Thanks to Sébastien Clausen, Thérèse Vachard and Lucie Pille for the technical help. The reviewers E. Villa (Oviedo), B. Granier (Brest), and two anonymous referees are thanked for their constructive criticisms.

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Les fusulines du Mexique, une revue biostratigraphique et paléogéographique Geobios 33 6 2000 655–679 R.R. West, Chaetetes (Demospongiae): its occurrence and biostratigraphic utility, in: P.K. Sutherland, W.L. Manger (Eds.), Recent advances in Middle Carboniferous biostratigraphy – A symposium, Okla. Geol. Surv., Circ. 94 (1992) 163–169. Wilde G.L. Practical Fusulinid zonation: the species concept, with Permian Basin emphasis West Tex. Geol. Soc. Bull. 29 7 1990 5-15 & 28-34 Wilde G.L. Pennsylvanian-Permian fusulinaceans of the Big Hatchet Mountains, New Mexico New Mex. Mus. Nat. Hist. Sci. 38 2006 1–311 J.L. Wilson, A. Madrid-Solis, R. Malpica-Cruz, Microfacies of Pennsylvanian and Wolfcampian strata in southwestern U.S.A. and Chihuahua, Mexico, in: D.A. Córdoba, S.A. Wengerd, J. Shomaker (Eds.), Guidebook of the border region, New Mexico Geological Society, Twentieth Field Conference, 1969, pp. 80-90.

Location maps of the studied outcrops in Sonora State (northwestern Mexico).

Fig. 1. Cartes de localisation des affleurements étudiés dans l’État de Sonora (Nord-Ouest du Mexique).

Scheme of the lithostratigraphic section. 0, 50, 100 = thickness (in metres).

Fig. 2. Coupe lithostratigraphique synthétique. 0, 50, 100 = épaisseur (en mètres).

Fusulinids and algae from the Pennsylvanian of Sonora. (1, 3–4) Fusulinella llanoensis (Thomas) (= F. thompsoni Skinner and Wilde). Three axial sections. Atokan A3, Sierra Agua Verde. 1. Sample SAV 1, ×20. 3. Sample SAV 6 (1), ×25. 4. Sample SAV 7. ×20. (2) Zellerella sp. 1. Axial section, Atokan As3, Sierra Agua Verde, ×25. (5) Fusulinella aff. llanoensis (Thomas). Axial section, sample SAV 6 (1), Atokan A3, Sierra Agua Verde, ×12.5. (6) Komia abundans Korde. Longitudinal section relatively similar to a Pseudokomia, because of the irregular central part, sample SAV 7, Atokan A3, Sierra Agua Verde, ×25. (7) Phylloid alga Eugonophyllum ? sp. Longitudinal section, sample M.SAV.03.4, Atokan A3, Sierra Agua Verde, ×8. (8, 9) Beedeina leei (Skinner). Two axial sections, sample ST 1, Desmoinesian DS1, Cerro El Tule, ×20. (10) Wedekindellina euthysepta (Henbest). Axial section, sample ST 2 (2), Desmoinesian DS1, Cerro El Tule, ×20. (11) Beedeina cf. novamexicana (Needham), subaxial section, sample ST 2, Desmoinesian DS1, Cerro El Tule, ×25. (12) Beedeina euryteines (Thompson), axial section, sample ST 2, Desmoinesian DS1. Cerro El Tule, × 16. (13–14, 17–18) Triticites canyonensis Wilde. 13. Subaxial section, sample ST 4, Missourian MC1–2, Cerro El Tule, × 16. 14. Axial section, sample ST 5 (2), Missourian MC1–2, Cerro El Tule, × 16. 17. Subaxial section, sample ST 5 (2), Missourian MC1–2, Cerro El Tule, × 16. 18. Subtransverse section, sample ST 4, Missourian MC1–2, Cerro El Tule, × 16. (15–16) Paraepimastopora kansasensis (Johnson). 15. Longitudinal section, sample ST 5, Missourian MC1–2, Cerro El Tule, × 25. 16. Transverse section, sample ST 5 (2), Missourian MC1–2, Cerro El Tule, ×16.

Fig. 3. Fusulines et algues du Pennsylvanien de Sonora. (1, 3–4) Fusulinella llanoensis (Thomas) (= Fusulinella thompsoni Skinner et Wilde). Trois sections axiales. Atokien A3, Sierra Agua Verde. 1. Échantillon SAV 1, ×20. 3. Échantillon SAV 6 (1), ×25. 4. Echantillon SAV 7, Atokien A3, Sierra Agua Verde, ×20. (2) Zellerella sp. 1. Section axiale, échantillon SAV 2 (2), Atokien A3, Sierra Agua Verde, ×25. (5) Fusulinella aff. llanoensis (Thomas). Section axiale, échantillon SAV 6 (1), Atokien A3, Sierra Agua Verde, ×12,5. (6) Komia abundans Korde. Section longitudinale atypique évoquant une Pseudokomia, à cause de sa partie centrale irrégulière, échantillon SAV 7, Atokien A3, Sierra Agua Verde, ×25. (7) Algue phylloïde Eugonophyllum ? sp. Section longitudinale, échantillon M.SAV.03.4, Atokien A3, Sierra Agua Verde, ×8. (8, 9) Beedeina leei (Skinner). Deux sections axiales, échantillon ST 1, Desmoinésien DS1, Cerro El Tule, ×20. (10) Wedekindellina euthysepta (Henbest). Section axiale, échantillon ST 2 (2), Desmoinésien DS1, Cerro El Tule, ×20. (11) Beedeina cf. novamexicana (Needham), section subaxiale, échantillon ST 2, Desmoinésien DS1, Cerro El Tule, ×25. (12) Beedeina euryteines (Thompson), section axiale, échantillon ST 2, Desmoinésien DS1, Cerro El Tule, ×16. (13–14, 17–18) Triticites canyonensis Wilde. 13. Section subaxiale, échantillon ST 4, Missourien MC1–2, Cerro El Tule, ×16. 14. Section axiale, échantillon ST 5 (2), Missourien MC1–2, Cerro El Tule, ×16. 17. Section subaxiale, échantillon ST 5 (2), Missourien MC1–2, Cerro El Tule, ×16. 18. Section subtransverse, échantillon ST 4, Missourien MC1–2, Cerro El Tule, ×16. (15–16) Paraepimastopora kansasensis (Johnson). 15. Section longitudinale, échantillon ST 5, Missourien MC1–2, Cerro El Tule, ×25. 16. Section transverse, échantillon ST 5 (2), Missourien MC1–2, Cerro El Tule, ×16.

Palaeogeographic reconstruction showing the connections between Sonora, the North American Craton (Arizona, Texas) and the Perigondwanan South American Domain, via several Mexican terranes: Coahuila, Maya, Oaxaquia and Mixteco. 1 = carbonate platforms; 2 = flysch basins; 3 = mainlands and islands (after [1], [2] and [3]).

Fig. 4. Reconstitution paléogéographique indiquant une possible connexion entre le Sonora, le craton Nord-Américain (Arizona, Texas) et le domaine périgondwanien Sud-Américain via différents « terranes » mexicains : Coahuila, Maya, Oaxaquia, and Mixteco. 1 = plates-formes carbonatées ; 2 = bassins à flyschs ; 3 = îles et continents (d’après [1], [2] and [3]).

Chronostratigraphic and biostratigraphic (fusulinids) scales of the Pennsylvanian, and biozones identified in Sonora (Mexico)

Tableau 1 Échelles chronostratigraphiques and biostratigraphiques (fusulines) du Pennsylvanien et biozones identifiées dans l’État de Sonora (Mexique)

International stages North American stages Zones of fusulinids of Wilde (1990) Zones discovered in Sonora PENNSYLVANIAN GZHELIAN VIRGILIAN VC 3 VC 2 VC1 KASIMOVIAN MISSOURIAN MC 4 MC 3 MC 2 MC 1/2 MC 1 LATE MOSCOVIAN (Myachkovian) DESMOINESIAN DS 5 DS 4 DS 3 DS 2 DS 1 DS 1 LATE MOSCOVIAN (Podolskian) LATE ATOKAN A 4 A 3 A 3 EARLY MOSCOVIAN EARLY ATOKAN A 2 LATE BASHKIRIAN A 1 EARLY BASHKIRIAN MORROWAN M 2 M 1

Geographical distribution in the USA of the fusulinids and algae identified in Sonora (Mexico)

Tableau 2 Répartition géographique aux États-Unis des fusulines et algues identifiées en Sonora (Mexique)

SONORA TEXAS NEW MEXICO ARIZONA MID CONTINENT Fusulinella llanoensis ● ● Zellerella sp. ● ● Wedekindellina euthysepta ● ● ● ● ● Beedeina leei ● ● ● ● ● Beedeina novamexicana ● ● ● ● ● Beedeina euryteines ● ● ● ● ● Komia abundans ● ● ● ● Paraepimastopora kansasensis ● ● ●