Biostratigraphy and palaeoecology of Lower Ordovician graptolites from the Fezouata Shale (Moroccan Anti-Atlas)

Palaeogeography, Palaeoclimatology, Palaeoecology 460 (2016) 35–49

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Biostratigraphy and palaeoecology of Lower Ordovician graptolites from the Fezouata Shale (Moroccan Anti-Atlas) Juan Carlos Gutiérrez-Marco a,b, Emmanuel L.O. Martin c,⁎ a b c

Instituto de Geociencias (CSIC, UCM), José Antonio Novais 12, E-28040 Madrid, Spain Departamento de Paleontología, Facultad de Ciencias Geológicas, José Antonio Novais 12, E-28040 Madrid, Spain Univ Lyon, Université Claude Bernard Lyon 1, ENS de Lyon, CNRS, UMR 5276 LGL-TPE, F-69622 Villeurbanne, France

a r t i c l e

i n f o

Article history: Received 30 October 2015 Received in revised form 4 July 2016 Accepted 20 July 2016 Available online 22 July 2016 Keywords: Graptolites Biostratigraphy Chronostratigraphy Palaeoecology Lower Ordovician Morocco Gondwana platform

a b s t r a c t The Fezouata Shale (=Fezouata Formation) has produced the most complete Lower Ordovician graptolite succession known from the African continent, which was studied from 32 sections located along the western, central, and eastern Moroccan Anti-Atlas. A composite biostratigraphic and chronostratigraphic scheme is presented for the entire formation that, in ascending order, comprises the Anisograptus matanensis–Rhabdinopora flabelliformis anglica zones (uppermost lower Tremadocian), “Adelograptus” tenellus and Aorograptus victoriae zones (middle Tremadocian), Araneograptus murrayi and Hunnegraptus copiosus zones (upper Tremadocian), ?Cymatograptus protobalticus Zone (lower Floian), ?Baltograptus jacksoni Zone (middle Floian), and the Baltograptus minutus Zone plus an “Azygograptus interval” (upper Floian). Most of these zones or biozones are recorded for the first time in Africa, together with important graptolite species such as Ancoragraptus bulmani (Spjeldnaes), ?Cym. protobalticus (Monsen), ?B. jacksoni Rushton, Clonograptus multiplex (Nicholson), B. minutus (Törnquist) and Azygograptus eivionicus Elles. A correlation with the graptolite sucession from the Algerian Sahara is also suggested, reinforced by the common record of the minute anisograptid Choristograptus louhai Legrand, providing its second world occurrence in the Tremadocian of Morocco. The prior late Tremadocian dating of the Fezouata Lagerstätte is here extended to the middle Floian as revealed by the graptolite biochronology. The repeated record along the lower and middle parts of the Fezouata Formation of deepwater mesopelagic species of the genera Araneograptus — with mass occurrences of conical colonies, together with large horizontal rhabdosomes of Paratemnograptus, Paradelograptus, Clonograptus, “Tetragraptus” and Holograptus/Schizograptus do not fit the sedimentological interpretation of deposition of these strata in much shallower inshore to mid-shelf environments. This inconsistency has implications when inferring the living conditions of the Fezouata soft-bodied assemblages. © 2016 Elsevier B.V. All rights reserved.

1. Introduction Ordovician graptolites are relatively rare fossils in the Anti-Atlas mountain range of southern Morocco, where identification of Tremadocian and Arenigian strata was mainly based on typical assemblages of trilobites and other shelly fossils (Choubert et al., 1955; Destombes, 1962a, 1967; Destombes in Destombes et al., 1985). Graptolites were first reported in this geological domain by Destombes and Willefert (1959) and Destombes (1960a, 1960b). They were discovered earlier in the Ordovician of the High Atlas (Roch, 1929; Termier and Termier, 1947; Du Dresnay and Willefert, 1960) and in the western Meseta (Yovanovitch, 1933; Gigout, 1946, 1948, 1951, 1956; Destombes and Jeannette, 1954; Delarue et al., 1956), ⁎ Corresponding author. E-mail addresses: [email protected] (J.C. Gutiérrez-Marco), [email protected] (E.L.O. Martin).

http://dx.doi.org/10.1016/j.palaeo.2016.07.026 0031-0182/© 2016 Elsevier B.V. All rights reserved.

with some specimens figured by Termier and Termier (1950) and Gigout (1951). Destombes and Willefert (1959) reported the occurrence of early Tremadocian rhabdinoporinids at the base of the Fezouata Shale (= Fezouata Formation) in the central Anti-Atlas, followed by the record of late Tremadocian adelograptids and Bryograptus at a few localities of the same formation from the central and eastern AntiAtlas (Destombes, 1960a, 1963) and also by some Arenig isograptids, tetragraptids and didymograptids, in the western Anti-Atlas (Destombes, 1960b). From these early records, the production of the Geological Map of Morocco at 1:200,000 scale, covering all the Palaeozoic rocks of the Anti-Atlas in ten sheets, led the French geologist Jacques Destombes to discover during the following twenty-four years about one hundred localities or horizons with Tremadocian and Arenigian graptolites in the Fezouata Formation (Destombes, 2000, 2006a, 2006b, 2006c, 2006d, 2006e, 2006f, 2006g, 2006h, 2006i, 2006j). These records demonstrate the existence of a regional

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diachronous and transgressive contact between the base of the Fezouata Formation and the different sandstone and shale units that comprise the middle–upper Cambrian Tabanite Group (Destombes, 1962b and Destombes in Destombes et al., 1985). Also, the southwestern equivalent of the Fezouata Formation unconformably overlies Archean rocks of the West African Craton, for example, the graptolite-bearing shales in the Zemmour region of northern Mauritania (Destombes et al., 1969). However, none of the Lower Ordovician graptolite records reported in these seminal papers and in the map field-notes from the Anti-Atlas were ever described, although some graptolites from fifteen localities around Zagora were illustrated by Aceñolaza et al. (1996) and Destombes (2006a). In contrast to this, Tremadocian graptolites and trilobites from the southwestern extension of the Anti-Atlas in Mauritania were described and illustrated by Sougy (1961 — with Araneograptus identified as a bryozoan) and Destombes et al. (1969). The recent discovery of the Fezouata Lagerstätte in the Zagora region renewed the interest in graptolites as the best means of accurate correlation of the soft-bodied metazoan-bearing beds. For this purpose, Lefebvre and Botting (2007) cited “dendroid” graptolites (= Araneograptus) and the late Tremadocian form Paradelograptus norvegicus from a locality approximately 20 km north of Zagora. From these and nearby outcrops, Van Roy et al. (2010, Figs. S2h–i), figured specimens of ?Clonograptus (= P. norvegicus) and putative tuboids, ranging from Tremadocian to early Floian in age. A detailed stratigraphic and palaeonvironmental study of the same strata (Martin et al., 2016) was accompanied by the identification of ten graptolite species within the range of the Fezouata Lagerstätte, and these species supported a correlation with the upper Tremadocian biozones of Araneograptus murrayi and Hunnegraptus copiosus. Nine planktonic species plus two benthic dendroids were figured in the same paper (Martin et al., 2016, Fig. 4A–P), and a comprehensive taxonomic list of the most recent finds was provided by Van Roy et al. (2015, Table 1). In the present paper, a general overview of the graptolite data from the Fezouata Formation is presented, focusing on the review of some important localities of Destombes and presenting new data that allow for a better reappraisal on the Lower Ordovician from a regional and international perspective. The precise position of most of the graptolite localities was indicated in the papers by Destombes and Willefert (1959) and Destombes (1960a, 1960b, 1963, 2000, 2006a, 2006b, 2006c, 2006d, 2006e, 2006f, 2006g, 2006h, 2006i, 2006j). Figured specimens belonging to Jacques Destombes' collection (prefixed JD) are housed in the Ministry of Energy, Mines, Water and Environment (Rabat). Additional material collected by the authors was deposited in the Faculty of Sciences and Technics of the Cadi-Ayyad University of Marrakesh (prefixed AA, material from Martin et al., 2016), and in the Department of Palaeontology of the Complutense University of Madrid (temporary deposit, prefixed DPM).

2. Geological setting Lower Ordovician rocks of the Moroccan Anti-Atlas are included in the Fezouata and Zini formations. They are overlain by the lower to middle Darriwilian Tachilla Formation in the External (or Outer) Feijas Group (Choubert, 1952; Destombes, 1962a, 1971; Destombes et al., 1985). The Fezouata Formation (= the lower half of the Outer Feijas Shales of Choubert and Termier, 1947) consists of blue-green to yellow-green sandy mudstones and siltstones that coarsen upwards, and they are up to 900 m thick. Due to the regionally transgressive character of the Ordovician sedimentation over Cambrian strata, some thin microconglomeratic and glauconitic horizons are frequently intercalated at or near the base of the unit, and are rare in the middle part of the formation, where a single glauconitic and ferruginous horizon was used traditionally as a boundary-marker to separate the “Lower” and “Upper” Fezouata “formations” on geological maps (Destombes, 2006a, 2006b, 2006c, 2006d, 2006e, 2006f, 2006g, 2006h, 2006i,

2006j), and later treated as a single formation named Fezouata Shale (Martin et al., 2016). According to Destombes et al. (1985) and Michard et al. (2008), Ordovician sedimentation began during the Tremadocian in an east-west trending sag-basin south of the Saghro-Ougnate high. Afterwards, a gently subsiding shallow-water shelf extended progressively over the entire area, gently deepening northwards and with a shoreline located some distance from the northern rim of the Reguibat Shield (West African Craton). In the absence of significant synsedimentary tectonics, the Tremadocian to lower Floian marine clays and silts unconformably overlie middle to upper Cambrian strata. The passive margin sedimentation of the Fezouata and Zini formations occurred in a wave-dominated and tide-modulated shallow-marine shelf within a general transgressive-regressive trend (Martin et al., 2016). The interpreted palaeoenvironments range from proximal offshore to foreshore (Vaucher and Pittet, 2014; Vaucher et al., 2015a, 2015b; Martin et al., 2016). Additional data derived from trilobite biofacies indicate a deepening trend reaching its climax in the middle part of the Fezouata Formation succeeded by a progressive shallowing (from upper offshore to shoreface environments) in its upper third (Martin et al., 2016–in this volume). The record of identifiable early Ordovician graptolites is so far limited to the Fezouata Formation, where a few graptolite horizons have been recognized in 32 sections along the western, central and eastern Anti-Atlas. Identifiable graptolites have not yet been recorded from the overlying Zini sandstone. Fig. 1 shows the examined localities in the Fezouata Formation, mainly discovered by Destombes (2000, 2006a, 2006b, 2006c, 2006d, 2006e, 2006f, 2006g, 2006h, 2006i, 2006j) and Martin et al. (2016). Graptolites occur generally in fine argillites and siltstones as flattened imprints preserving some organic material, often coated by iron oxides and, in some instances, by pressure-shadow minerals. In the limited interval with soft-bodied and slightly-sclerotised organisms, associated graptolites are usually preserved in partial to full relief, involving an early diagenetic pyritisation and subsequent weathering to reddish iron oxides. These are responsible for the strong contrast shown by many graptolites compared to the surrounding green, blue-grey, or yellow matrix. Some internal graptolite casts preserve delicate details such as thecal budding and fusellar rings. None of the specimens examined have traces of stolons or zooidal bodies within the thecae, although an exceptional case of preserved zooids has been claimed to occur in a benthic tuboid colony (Van Roy et al., 2010, Fig. S2i). Besides their common preservation in argillites, some graptolites are found in mediumgrained sandstones, micaceous siltstones and slightly carbonaceous lenses, where their preservation with some of their original relief may indicate an early diagenetic pyritisation, as well. 3. Graptolite biochronology Most of the graptolite localities occurring in the Fezouata Shale are isolated exposures, or occur in partial stratigraphic sections with one or a few graptolite horizons, but commonly within a single graptolite biozone. However, some sections include two to five graptolite zones. These sections are in a large region around the city of Zagora, west of Foum Zguid and east of N'kob (central Anti-Atlas) as in the Jbel Tazoult n'Ouzina (eastern Anti-Atlas). The sections near Zagora are located on the flanks of the Bou-Dehir anticline and in the graben of Zagora (sections 14 to 16, Fig. 1). A composite biostratigraphic scheme based on these sections and from single outcrops is presented for the entire formation (Fig. 2). The graptolite zones recognized are as follow. 3.1. Anisograptus matanensis and Rhabdinopora flabelliformis anglica zones This interval corresponds to the lowermost 6–70 m of the Fezouata Formation in the localities of Adrar n'Tassefat, Sidi Blal, N Zagora, Jbel Amergou, E Jbel Bou Dehir, E N'kob and Bou Ljir (numbers 9, 12, 14, 15, 16, 20 and 21 in Fig. 1, respectively). The assemblage is numerically

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Fig. 1. A–B, Location sketch-map of all known occurrences of Ordovician graptolites in the Lower Ordovician Fezouata Formation from the western (a), central (b) and eastern (c) Anti-Atlas. Numbers mostly refer to individual graptolite finds, instead of extensive graptolite-bearing sections. Many graptolite occurrences are adopted from the Explanatory booklets of the Geological Map of the Anti-Atlas at 1:200,000 scale (Destombes, 2000, 2006a, 2006b, 2006c, 2006d, 2006e, 2006f, 2006g, 2006h, 2006i, 2006j), and are partly reviewed herein. Schematic maps modified from Destombes (in Horný, 1997, Fig. 1). C, Idealised longitudinal section illustrating Lower Ordovician lithostratigraphy of the Moroccan Anti-Atlas. Numbers for sections correspond to the localities indicated on map B. Thicknesses of the Zini and Fezouata formations after Destombes (2006a, 2006b, 2006c, 2006d, 2006e, 2006f, 2006g, 2006h, 2006i, 2006j). a, Approximate position of the Tremadocian/Floian boundary; b, location of the stratigraphic contact between the former “lower” and “upper” Fezouata “formations” of Destombes et al. (1985); c, approximate stratigraphic range of the Fezouata Lagerstätte; d, basal unconformity of the Fezouata Formation over different formations of the Tabanite Sandstone Group (middle Cambrian to Furongian). Stratigraphic scheme based on Michard et al. (2008, Fig. 3.6). Key for localities: 1, Jbel El Khannfra; 2, Kheneg M'Karz (Aouin-Deliouine); 3, Taskala; 4, W Torkoz (Aouinet-Torkoz); 5, Timoulaye (SE Bou-Izakarn); 6, Tisgui Cheikh (NW Foum-el-Hassane); 7, Foum-Akka n'Tamia (W Akka); 8, Kheneg/Hassi Brahim (W Tata); 9, Adrar n'Tassefat (E Tata); 10, Assif n'Tafraout n'Bani (W Foum-Zguid); 11, Oued Lamhamid/Hdeb Mhdi (NW Foum-Zguid); 12, Zaouit/Sidi Blal (SE Tazenakht); 13, SW Ksar Igdaoun (=“Oulad Slimane“ or “Oulad-Atmane” locality of Fortey, 2009 and Moroccan trilobite dealers); 14, diverse sections 15–25 km N Zagora (“Bou Izargane”, Oued Tarhia n'Imrhaldene, Oued Ouaoufraou and others); 15, Jbel Amergou (W Zagora) and Jbel Adafane (E Zagora); 16, E Jbel Bou Dehir (NE Zagora); 17, Jbel Tibasksoutine (E Zagora); 18, N Timiderte (N Jbel Kissane); 19, N Jbel Taddrist; 20, Akka n'Ousdidene (E N'kob/Nekob); 21, Bou Ljir (NE Mlal/Mellal); 22, Isk n'Tafsast (N Tazzarine); 23, Isk Tamotjane (Amerdoul n'Oufsad); 24, Ikhf n'Ourarh (Arhenbou n'Dali); 25, Afrou n'Tarhoucht (S Tinejdad); 26, Tourza; 27, Tizi n'Taourakt (N Istlhou); 28, Jbel Bou Legroun (NW Rissani); 29, Jbel Signit (E M'cissi/Mecissi); 30, Jbel Tijekht; 31, E Jbel Tazoult-n'Ouzina (NW Ouzina); 32, N Jbel Zorg (SSE Tawz/Taouz).

dominated by Rhabdinopora flabelliformis flabelliformis (Eichwald) (Fig. 3A–C), with specimens often occurring as mass-accumulations on bedding planes. Other specimens represent the subspecies R. f. canadensis (Lapworth) (Fig. 3H) and R. f. socialis (Salter) (Fig. 3D– E), recorded from the lower beds of the zones, and R. f. anglica (Bulman) (Fig. 3F–G), which is restricted to the upper beds of the interval. The record of the latter subspecies (and its naming zone) is so far restricted to the localities of Sidi Blal and N Zagora, but may have a wider distribution in the Anti-Atlas basin than is presently known. The remaining localities bearing abundant R. f. flabelliformis are referred to the An. matanensis Zone by their association with other subspecies that occurs above the Last Appearance Datum (LAD) of R. f. parabola (Bulman) and below the First Appearance Datum (FAD) of R. f. anglica, according to the global biochronologic scheme for lower Tremadocian graptolites of Cooper et al. (1998) and Cooper (1999). The record of Anisograptus in the Anti-Atlas (Destombes et al., 1985) is still pending confirmation, so far limited to a single stipe fragment with well-preserved autothecae (not figured) tentatively attributed to this genus in a section located north of Zagora (lat. 30°33′44.8″N, long. 5°49′28.8″W). Previously, Destombes (1960a, 1962a, 2006b), and Destombes et al. (1985) cited Anisograptus cf. matanensis Ruedemann from an horizon placed 180 m above the base of the Fezouata Formation to the east of Jbel Bou Dehir (Fig. 1, loc. 16). However, it is supposedly associated with much younger graptolites such as “Bryograptus” and “Clonograptus tenellus”, which made that identification highly improbable.

In addition to the recognized subspecies of R. f. flabelliformis, Destombes and Willefert (1959) and Destombes (2006d) mentioned the occurrence of R. f. norvegica (Kjerulf) and R. f. multithecatum (Bulman) from Akka n'Ousdidene (Fig. 1, loc. 20), but this was not confirmed in our review of the locality. The first subspecies was surely mistaken with mineralised remains of R. f. canadensis or even of R. f. flabelliformis, that in some beds show a thick, dark-mineral coating that affected both the stipes and dissepiments, reminiscent of the extensive cortical thickening characteristic of this form. R. f. norvegica was also cited by Destombes (2006b) from the section lying east of the Jbel Bou Dehir (Fig. 1, loc. 16), occurring about 410 m above the base of the formation, at a level placed in the upper Tremadocian. Due to its association with ?paradelograptids and ?kiaerograptids, the specimens were probably confused with some kind of benthic dendroid graptolite. 3.1. “Adelograptus” tenellus Zone The species “Ad.” tenellus was reported in the Anti-Atlas by Destombes (1971, 2006b, 2006e) and Destombes et al. (1985) but, at present, the most convincing specimens closely similar to “Ad.” tenellus (Linnarsson) (Fig. 3I) are from a section NW of Ouzina (eastern AntiAtlas: Fig. 1, loc. 31). However, this occurrence is in a horizon relatively high in the Fezouata Formation that is in an unusually high stratigraphic position relative to the graptolite zones recorded there. The claimed occurrence of “Ad.” tenellus in the Zagora region (Destombes, 2006b)

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J.C. Gutiérrez-Marco, E.L.O. Martin / Palaeogeography, Palaeoclimatology, Palaeoecology 460 (2016) 35–49

Fig. 2. Stratigraphic distribution of selected graptolite taxa from the Fezouata Formation in the generalised section of the Zagora region (central Anti-Atlas). The occurrence of “Adelograptus” tenellus and Ancoragraptus bulmani are based on their records in two localities of the eastern Anti-Atlas (Jbel Tijekht and E Jbel Tazoult-n'Ouzina, respectively). Numbers below correspond to the approximate location of the following graptolite zones: 1, Anisograptus matanensis; 2, Rhabdinopora flabelliformis anglica; 3, “Adelograptus” tenellus; 4, Aorograptus victoriae; 5, Araneograptus murrayi; 6, Hunnegraptus copiosus; 7, Tetragraptus phyllograptoides (tentative placement in a barren interval); 8, ?Cymatograptus protobalticus; ?Baltograptus jacksoni; 9, Baltograptus minutus; 10, “Azygograptus interval”.

comes from a bed 180 m above the base of the Fezouata Formation in the Jbel Bou Dehir-east section (Fig. 1, loc. 16). This occurrence is also out of place biostratigraphically, and the specimens are probably misidentified. 3.2. Aorograptus victoriae Zone Among the numerous specimens of “Adelograptus” in the J. Destombes collection, it was impossible to recognize any specimen with the primary robust stipes and the pendent to reclined rhabdosome, with regular dichotomous branching, characteristic of Ao. victoriae (T.S. Hall). In spite of its well-known worldwide distribution, the species is so far apparently absent from Morocco. Another widespread genus like Bryograptus, commonly recognized elsewhere in the lower part of the Ao. victoriae Zone (Maletz et al.,

2010), or just below it, is rare in Africa. Its only known occurrences are in Algeria, in the Saharan subsurface (Blain, 1963; Legrand, 1973) and it may also occur in the Ougarta Range (Gomes Silva et al., 1963), but the specimens need examination. Bryograptus has been listed from the Moroccan Anti-Atlas (Destombes, 1971a, 1971b, 1971c, 1971d, 1971e, 1971f; Destombes et al., 1985) but the specimens may be misidentified. Such is the case with the reports of “Bryograptus kjerulfi cumbrensis Elles”, “B. lapworthi Ruedemann” and “B. gr. divergens Elles and Wood”, three forms excluded from Bryograptus (see Zalasiewicz et al., 2009 and Maletz et al., 2010). However, in the review of one of the localities with Bryograptus at the Jbel Tijekht (eastern Anti-Atlas; Fig. 1, loc. 30), the original specimens correspond not to this genus, but to minute rhabdosomes of Ancoragraptus bulmani (Spjeldnaes) (Fig. 3O–Q). This species has also been recorded from north of Zagora (Fig. 1, loc. 14; Fig. 3N) and is reported here for the first time in Africa. Ancoragraptus bulmani is a widespread

Fig. 3. Tremadocian graptolites from the Fezouata Formation, southern Morocco. A–C, Rhabdinopora flabelliformis flabelliformis (Eichwald): A, fragment of large rhabdosome, JD1147a, loc. 15 (Jbel Amergou, Zagora); B, proximal part of a colony showing intervals of stipe bifurcations and authothecae in lateral views, DPM-8120, loc. 14 (N Zagora); C, detail of meshwork in a mesial part of rhabdosome, JD1147b, loc 15. D–E, R. f. socialis (Salter) from loc. 20 (E N'kob): D, large rhabdosomes with typically close stipe spacing, DPM-8121; E, detail of pyritised stipes with undulating thecae and stipes, DPM-8122. F–G, R. f. anglica (Bulman): F, fragments of conical rhabdosomes, DPM-8123, loc. 14; G, detail of characteristic meshwork with widely spaced stipes and dissepiments, DPM-8124, loc. 14. H, R. f. canadensis (Lapworth), detail of meshwork showing thin and irregularly spaced dissepiments, commonly paired and some of them obliquely placed, DPM-8125, loc 20. I, “Adelograptus” tenellus (Linnarsson), two partially superimposed rhabdosomes, JD359a, loc. 31 (NW Ouzina). J–M, Choristograptus louhai Legrand from locality 14 (N Zagora): J, proximal fragment showing complete sicula and nema, as well as declined first thecae, DPM-8126; K, stipe fragment with long and isolated autothecae, DPM-8127; L–M, diverse fragments of stipes and dichotomies, DPM-8128 and 8129. N–Q, Ancoragraptus bulmani (Spjeldnaes), proximal ends showing the isograptid development type, isolated lower part of metasicula and prominent sicular bitheca (arrowed in Q): N, DPM-8130, loc. 14 (N Zagora); O–P (part and counterpart), JD1194a1-a2, loc. 30 (Jbel Tijekht); Q, JD1194b, loc. 30. R–U, Paradelograptus norvegicus (Monsen), proximal part of diverse rhabdosomes (dorsal views) with characteristic branching and cortical overgrowth, all from locality 14 (N. Zagora): R, DPM-8131; S, with stipes darker that the peridermal cover, DPM-8132; T, rhabdosome showing thin and recurved lateral stipes, possibly a sign of regeneration, DPM-8133; U, small rhabdosome with thick cortex cover and comparatively thin stipes, in process of ?regeneration, DPM-8134. Scale bars: A–D, F–G, I and R–U, =5 mm; E, H, J–M and N–Q, =2 mm.

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graptolite occurring in the Kiaerograptus kiaeri plus K. stoermeri (=Aorograptus victoriae) zones of Scandinavia, Canada, Argentina and China (Spjeldnaes, 1963; Maletz and Egenhoff, 2001; Jackson and Lenz,

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2003; Jackson and Norford, 2004; Zeballo et al., 2008; Wang et al., 2013a). A slightly older species of the same genus is known from the “Ad.” tenellus Zone of Korea (Cho et al., 2009).

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A second novelty among the Tremadocian graptolite record of the Anti-Atlas is the identification north of Zagora (Fig. 1, loc. 14) of fragmentary specimens of Choristograptus louhai Legrand (Fig. 3J–M). This

represents the first occurrence in surface outcrops of a very rare genus, so far only known from a deep borehole in the Algerian Sahara (Legrand, 1963). Choristograptus louhai was recognized from two

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horizons 100 m over the base of the Fezouata Formation, directly above the beds yielding Anc. bulmani in the Oued Tarhia n'Imrhaldene section. Legrand (1985) described Ch. louhai in the “γIIb” graptolite assemblage of the Algerian Sahara, which places it in the upper part of the stratigraphic range of “Ad.” tenellus. The close occurrence of Anc. bulmani and Ch. louhai in the lower part of the Fezouata Formation provides indirect evidence for the Ao. victoriae Zone in the Anti-Atlas. Although considered barren of graptolites, the overlying 200–250 m of the sections around Zagora should be explored for Ao. victoriae and the many other species that characterize the Aorograptus victoriae Zone plus the “kiaerograptid interval” in Scandinavia. In any case, the apparent absence of the genera Bryograptus and Aorograptus in the Moroccan successions is rather puzzling and is probably related to the intensity of collecting, which has been rather low in these beds, where graptolites are confined to thin laminae within thick unfossilifeous mudstones. This could also be the case for beds located near the Tremadocian-Floian boundary (upper part of the H. copiosus Zone and the T. phyllograptoides – sensu stricto – Zone). Alternatively, the absence of Bryograptus and Aorograptus in North Africa could also be explained in terms of palaeolatitudes, because neither of these two genera has so far been recorded in other places of the “cold” periGondwanan shelves of southwestern Europe (Gutiérrez-Marco et al., 2015a). 3.3. Araneograptus murrayi Zone Above a large stratigraphic interval (up to 250 m thick) with rare fragments of unidentifiable graptolites, the Araneograptus murrayi Zone begins with mass-occurrences of the nominal form, first forming monospecific assemblages and gradually incorporating other biramous to multiramous taxa. Higher in the zone, Ar. murrayi is less common, occurring as single rhabdosomes and small fragments on bedding planes that are dominated by long stipes of big forms such as Paratemnograptus and Clonograptus. The identification and vertical range of graptolite species recognized within this biozone have been illustrated in a partial composite section presented by Martin et al. (2016, Fig. 4). It resulted from a bed-by-bed exploration of the Fezouata Lagerstätte through more than 80 m of strata. The zonal assemblage is composed of Ar. murrayi (Hall) (Fig. 4A–F), “Kiaerograptus” supremus Lindholm, Paratemnograptus magnificus (Pritchard) (Fig. 4G), Paradelograptus norvegicus (Monsen) (Fig. 3R–U), P. tenuis Lindholm, Paradelograptus sp., “Didymograptus sp. 1” sensu Lindholm (1991), Clonograptus rigidus (Hall) and “Tetragraptus” bulmani Thomas (= T. longus Lindholm according to Maletz and Egenhoff, 2001), to which we add a recently found 3-stiped tetragraptid possibly related to T. krapperupensis Lindholm. Besides the record of this graptolite biozone in the Zagora area (Fig. 1, loc. 14–16), mass-occurrences of Ar. murrayi were cited by Destombes (2006g) from the northwest of Foum-Zguid (Fig. 1, loc. 11). The first African report of the species was by Sougy (1961), who described it as “Nissenia zemmourensis” (a primitive bryozoan) found in the Zemmour region of northern Mauritania. The specimens were recognized as graptolites by Destombes et al. (1969), who identified them as “Dictyonema gr. murrayi”. The name “Dictyonema murrayi

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zemmourensis” was used in a report in the Algerian Sahara (Legrand, 1985), before Gutiérrez-Marco and Aceñolaza (1987) placed this African taxon in synonymy with Ar. murrayi. Regarding the precise taxonomic affiliation of Ar. murrayi, the type species of the upper Tremadocian genus Araneograptus Erdtmann and VandenBerg (1985), Dictyonema macgillivrayi T.S. Hall has recently been transferred to the genus Sagenograptus Obut and Sobolevskaya by Maletz et al. (2016, Fig. 3.8). This reassignment could mean that the remaining species of Araneograptus, including Ar. murrayi, also will eventually be included in that genus. However, the original material of the type species of Sagenograptus, S. gagarini Obut and Sobolevskaya (1962, pl. 1, Fig. 5, 5a), consists of a distal fragment of the mesh lacking taxonomically relevant details at the generic level, although the genus was differentiated by Bulman (1970, p. V39) as having a coarse irregular network relative to “Dictyonema” sensu lato (including both benthonic and planktonic species). In spite of the fact that we are dealing with a single fragmentary specimen, S. gagarini is rather similar to the umbrella-shaped colonies of Ar. macgillivrayi. The absence of details of the sicula and proximal branching of the former (clearly free-siculated and with two instead of three or four primary stipes in Ar. macgillivrayi) shows that the identity (and generic priority) of Sagenograptus over Araneograptus cannot be established at present. This is even more obvious for different species such as Ar. murrayi, which shows a different mesh configuration from those of both Ar. macgillivrayi and S. gagarini. The Russian species seems to be restricted to a single “lower Arenig” (probably upper Tremadocian) locality in Taymir, where the species is accompanied by “Temnograptus aff. noveboracensis Ruedemann” (Obut and Sobolevskaya, 1962, pl. 3, Fig. 3), which however probably belongs to Paratemnograptus sp. 3.4. Hunnegraptus copiosus Zone This zone was identified based on the occurrence of H. copiosus Lindholm in the section north of Zagora (Martin et al., 2016). Only the lower part of the zone is so far recognized, and the graptolite assemblage includes several taxa that extend upwards from the underlying chronozone. These include Paratemnograptus magnificus, P. norvegicus, C. rigidus, and “Didymograptus sp. 1”. Poorly preserved specimens of “Kiaerograptus” cf. supremus were recorded about 45 m above the FAD of H. copiosus, and probably also range into the zone. Based on the discovery of a lower occurrence of H. copiosus, the base of the chronozone is here placed ca. 5 m lower in the section than that reported by Martin et al. (2016, Fig. 4). Also recently discovered is a possible new species similar to Clonograptus multiplex (Nicholson) but with long first-order stipes. 3.5. ?Cymatograptus protobalticus Zone This zone was introduced by Egenhoff and Maletz (2007) and Maletz and Ahlberg (2011) for the upper interval of the T. phyllograptoides Zone in Scandinavia, being defined by the lowest occurrence of Cymatograptus protobalticus (Monsen). Its possible identification in Morocco is limited to a single section north of Zagora (Fig. 1, loc 14), where a poorly-preserved rhabdosome (Fig. 4J) is very similar to British specimens of Cym. protobalticus from the Lake District (Rushton

Fig. 4. Tremadocian (A–G) and Floian (H–Q) graptolites from the Fezouata Formation, southern Morocco. A–F, Araneograptus murrayi (Hall) from locality 14 (N Zagora): A, three colonies, the left one shows a nematularium, AA-OFTa-OI-23; B, laterally preserved stipe (arrows) showing thecal profiles, DPM-8135; C, fragment of rhabdosome showing pyritised thecae in ventral view, DPM-8136; D, early mature rhabdosomes, with one preserved oblique to bedding and partially sectioned (center), DPM-8137; E, detail of meshwork showing wide dissepiments, DPM-8138; dissepiments forming pouch-like “balconies” due to their oblique orientation to the stipes, DPM-8139. G, Paratemnograptus magnificus (Pritchard), latex cast from the external mould of a pyritised stipe showing plaited thecal structure, counterpart of AA-BZG-OI-13 from loc. 14. H–I, unidentified horizontal to slightly declined biramous dichograptids, DPM-8140 and 8141, from loc. 14. Specimen in H is similar to Cymatograptus demissus (Törnquist) but with a different proximal structure; the second is slightly declined proximally and shows a rather steady stipe expansion as in Expansograptus nitidus (Hall). J, Cymatograptus cf. protobalticus (Monsen), DPM-8142 from loc. 14. K–L, Baltograptus deflexus (Elles and Wood), DPM-8143 and 8144 from Jbel Tibasksoutine (loc. 17). M, Tetragraptus sp. (reclined form), DPM-8145 from Jbel Zorg (loc. 32). N, Baltograptus minutus (Törnquist), latex cast of relief specimen in reverse view, DPM-8146 from loc. 17. O, Baltograptus cf. jacksoni Rushton, two partially superimposed rabdosomes, DPM-8147 from Jbel Bou Legroun (loc. 28). P, Azygograptus eivionicus Elles, poorly preserved rhabdosomes, DPM-8148 from locality 14 (Jbel Adafane, E Zagora). Q, Clonograptus multiplex (Nicholson) showing a “trichotomy” (i.e. two consecutive dichotomies) originated early from one of the second order stipes, JD1047a from Ikhf n'Ourarh (loc. 24). Scale bars: A and D–F, =10 mm; B–C, O and Q, =5 mm; G–N and P, =2 mm.

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in Cooper et al., 2004, Fig. 9q). Besides this rare occurrence of Cymatograptus, the strata assigned to this biozone record the incoming of a large clonograptid with highly irregular branching, identified as Clonograptus multiplex (Nicholson) (Fig. 4Q). The species is very abundant throughout the Anti-Atlas and ranges up into the lower beds of the next zone. It was confused either with “Temnograptus” sp., Schizograptus sp., or Holograptus sp. in earlier papers by Destombes (2006b, 2006e, 2006i, 2006j). 3.6. ?Baltograptus jacksoni Zone This chronozone is tentatively identified by the occurrence of poorly preserved specimens of Baltograptus cf. jacksoni Rushton (Fig. 4O) in the section of Jbel Bou Legroun (Fig. 1, loc. 28). It is possibly more widespread and is represented by deflexed didymograptids from a few localities in the central and eastern Anti-Atlas (Fig. 1, locs. 14, 19, 29). Strata attributed to this zone may extend 50–150 m below the FAD of typical upper Floian forms such as Baltograptus minutus (Törnquist) or B. deflexus (Elles and Wood) that characterize the next zone. Graptolite diversity from beds provisionally correlated with the B. jacksoni Zone is surprisingly low when compared with other graptolite sequences worldwide. Only C. multiplex occurs in Morocco towards its lower part, whereas higher beds contain rare specimens of Expansograptus? spp., unknown elsewhere (Figs. 4H, I), and stipe fragments of dichograptoids, which have been identified with problematic forms such as Expansograptus patulus (Hall), E. pennatulus (Hall), E. nitidus (Hall), E. sparsus (Hopkinson), E. extensus (Hall), Acrograptus nicholsoni (Lapworth), or A. nicholsoni planus (Elles and Wood) in previous literature (e.g. Destombes, 2006b, 2006c, 2006e, 2006i; Destombes et al., 1985). Nevertheless, the review of some of the original samples in the J. Destombes collection reveals that they are misidentifications based on broken stipes, and the specimens could even be multiramous forms. Sometimes the graptolite assemblage occurring below the B. minutus Zone is composed almost exclusively of tetraramous forms, as in the sections of El Khannfra, Taskala, Timidert, Akka n'Oubsidene and Jbel Zorg (Fig. 1, locs. 1, 3, 18, 20 and 32, respectively). Most of the original material corresponds to horizontal tetragraptids close to Tetragraptus quadribrachiatus (Hall) sensu lato, in part confused with proximal parts of ?multiramous forms. But others are true reclined tetragraptids (Fig. 4M) among which the long-ranging species Tetragraptus amii (Elles and Wood) and T. reclinatus Elles and Wood ssp. indet. have been identified. It is likely that “Isograptus caduceus var. gracilis Rued., I. caduceus var. armatus Rued.”, and “I. furcula Rued.” from the Taskala locality (Willefert in Destombes, 1960b; Fig. 1, loc. 3) are misidentifications based on deformed specimens of one or more species of Tetragraptus, showing sicula and highly reclined rhabdosome, with two first-order stipes in the median plane (the socalled “1–2 preservation”), but lacking the “isograptid symmetry” and the proximal arch so characteristic of the genus Isograptus. Tetragraptus approximatus Nicholson has been also listed from the El Khannfra section (Fig. 1, loc 1), but the original specimen corresponds to an obliquely-flattened, slightly reclined Tetragraptus preserved in quadribrachiate mode. The lowest occurrence of true T. approximatus internationally defines the base of the Floian, and it is restricted to lower stratigraphic horizons and deeper-water palaeoenvironments that were represented by the Fezouata Formation. 3.7. Baltograptus minutus Zone The base of this widespread chronozone is established by the FAD of B. minutus (Törnquist). In the Moroccan sucessions, B. minutus (Fig. 4N) occurs at different horizons in an interval 118–167 m below the base of the Zini Formation in the Zagora region (Fig. 1, locs. 14–15), and is associated with B. deflexus (Elles and Wood) (Figs. 4K–L) at the horizon of 112 m below the Zini Formation. In Scandinavian sucessions, B. deflexus is restricted to the uppermost part of the B. minutus Zone

(Maletz and Ahlberg, 2011). Therefore, the co-occurrence of both species in the lower part of the Moroccan B. minutus Biozone in Zagora may indicate that a major part of this biozone essentially corresponds to the upper part of the B. minutus Zone on peri-Gondwana and Baltica. Baltograptus minutus was cited in the previous Moroccan literature as “Didymograptus cf. – or “gr.” – indentus Hall” (Destombes et al., 1985; Destombes, 2006a, 2006b, 2006c, 2006d, 2006e). It also occurs in some collections with B. deflexus as recognized in the illustrations by Destombes (2006a, pl. 12, Fig. 1) for Jbel Tibasksoutine material (Fig. 1, loc. 17). In a different section from the eastern Anti-Atlas (Destombes, 2006f; Fig. 1, loc. 30), B. minutus is associated with a declined didymograptid, originally identified as “Didymograptus nicholsoni Lapw.”, which is reminiscent of Baltograptus kurcki (Törnquist), a species common in the B. jacksoni and B. minutus zones elsewhere. The reports of multiramous dichograptoids like Schizograptus or Holograptus/Trochograptus from numerous sections in the Anti-Atlas are only confirmed on the unpublished J. Destombes' localities 612 (=864, “to the east of Erfoud”) and 540 (Taskala). In the sample from the first locality, B. minutus (labelled either as “D. nanus” or “D. indentus”) co-occurs with fragments of a large dichograptoid identified as “Temnograptus multiplex” but with lateral division of “secondary” stipes instead of dichotomous branching. The same kind of dichograptoid was found in the second sample, labelled as “Schizograptus sp. or Temnograptus sp.” Finally, a stipe fragment with a laterally arranged dichotomy was also collected by us at Jbel Tibasksoutine, where it occurs with B. minutus, but the absence of complete rhabdosomes preserving the proximal part prevents their precise identification. 3.8. “Azygograptus interval” The highest graptolites recorded in the Fezouata Formation, from beds 5–63 m below the top of the formation in the eastern Anti-Atlas (Destombes, 2006e; Fig. 1, locs. 26 and 29), are forms similar to B. deflexus and to the specimens of “A. nicholsoni” reported from the western Anti-Atlas (Destombes, 2006h; Fig. 1, loc. 9). However, in two different sections of the central Anti-Atlas, monospecific assemblages of Azygograptus have been discovered 15–49 m below the base of the Zini Formation (Fig. 1, locs. 15 and 17). Drawings of nice rhabdosomes of Azygograptus sp. provided by Destombes (2006a, pl. 12, Fig. 9) are not adequate for specific identification, and the original material has not been located. However, probably the same horizon with abundant specimens of Azygograptus eivionicus Elles has been recorded at the Jbel Adafane section in the surroundings of Zagora (Fig. 4P). This species ranges from the middle Floian to the lower Dapingian (Fortey and Owens, 1987; Beckly and Maletz, 1991; Zalasiewicz et al., 2009), but is here correlated with the upper Floian because of the laterally-coeval strata with B. deflexus and its occurence above the B. minutus Zone in the central Anti-Atlas. In some Gondwanan shelves of South America showing affinities with the Baltic succession, the B. minutus Zone is succeeded by a biozone dominated by azygograptids. This is the case in southern Bolivia (Egenhoff et al., 2004) and northern Argentina (Monteros et al., 1996; Martínez et al., 1999), where the corresponding strata could be referred to the Floian stage. Of special interest is an unresolved question regarding the precise taxonomic affiliation of graptolites illustrated by Destombes (2006a, pl. 11, Fig. 8) as “Acrograptus cf. nicholsoni” from Jbel Tibasksoutine (Fig. 1, loc. 17). They were collected from a horizon “sandwiched” below the last local occurrence of B. minutus and the first record of Azygograptus, about 73 m below the base of the Zini Formation (Destombes, 2006a, 2006b: sample 431). Although the original material has yet to be found, the figured specimens show a strong resemblance to representatives of the genus Cymatograptus from the lower Floian T. phyllograptoides Zone. Thus, many of the illustrations (published without scales) are small declined didymograptids with a long straight sicula and have a morphology very similar to Cymatograptus rigoletto

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(Maletz, Rushton and Lindholm). Some specimens of the assemblage also exhibit a variable development of prothecal folds like those of Cym. undulatus (Törnquist), but not so pronounced as those of Cym. bidextro Toro and Maletz. Definitively they are biostratigraphically too high to be referred to Cymatograptus, unless this genus persisted in the south-polar Gondwana shelf until the late Floian as is the case for Cym. bidextro, which in the Gondwana margin of South America occurs as high as the middle Floian Baltograptus jacksoni Zone (=B. cf. deflexus Biozone of Toro and Maletz, 2008). A poorly preserved specimen in the J. Destombes collection, occurring 344 m above the last record of Rhabdinopora in a section east of Tata (Fig. 1, loc. 9) and identified as A. nicholsoni (Destombes, 2006h, sample 286), also morphologically and dimensionally resembles Cym. rigoletto, but its proximal part does not show the details required for a precise identification. 4. Global and regional correlation The chronostratigraphic terminology based on the historical type areas of the British Ordovician has traditionally been followed in Morocco, where the “Tremadocian” and the “Arenigian” – or “Skiddawian” – (sic) were used as informal stages of a “lower Ordovician” series. General problems of correlation with the British stratotypes, which yield highly endemic benthic faunas, led Spjeldnaes (1967) to propose a regional chronostratigraphic scale for the Mediterranean Ordovician. He introduced the series name “Zagorian” – after the Zagora region of the Anti-Atlas – for all strata so far assigned to the Tremadoc-Arenig series in Morocco and southeastern France. Previous to this, Legrand and Nabos (1962) had already proposed a regional scale for the Ordovician of the Algerian Sahara, after finding the same correlation difficulties with the British scheme. The regional stage “n1” (roughly equivalent to the Tremadocian to lower Arenigian interval) was introduced in Algeria and subdivided into substages (“n1a, n1b, n1c”) according to the biostratigraphic data provided by the allegedly endemic graptolite faunas (Legrand, 1985; Fig. 5).

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The conceptual value of the “Zagorian” series was questioned by Destombes (1971), who pointed out the imprecise definition of its boundaries and the better possibilities of correlation with the Bohemian Ordovician, so that this Moroccan-derived regional series was never used again. A more accurate Mediterranean (or south-Gondwanan) chronostratigraphic scheme was later developed in Bohemia (Havlíček and Marek, 1973) and modified in Iberia (Gutiérrez-Marco et al., 1995, 2002, 2008, 2015b). The resulting regional scale combined the former Tremadoc and Arenig series – turning them into stages – for the Lower Ordovician, followed by the several Bohemo-Iberian regional stages established for the remaining Middle to Upper Ordovician strata. The validity of the British stages for the Lower and basal Middle Ordovician in the south-Gondwanan regional scheme has been justified thus far by the shared palaeobiogeographical links prior to the complete splitting of Avalonia from southern Gondwana by late Arenigian times (=Dapingian to early Darriwilian; Murphy et al., 2006). Regarding the global subdivision of the Ordovician system, all the Ordovician GSSPs for the new series and stages (just like the as-yetinformal “stage slices”) are developed in deeper-water facies within continuous and fossiliferous sections (Bergström et al., 2009; Harper, 2011; Cooper et al., 2012b). In North Africa, as well as in other periGondwanan areas lying in high palaeolatitudes close to the Ordovician South Pole, the general scarcity of graptolites and conodonts for the Lower and Middle Ordovician imposes serious difficulties for correlating the regional successions with the new global chronostratigraphy. Due to this, the sequence of graptolite faunas here described from the Fezouata Formation of Morocco constitutes a first step to advance a more accurate global correlation for the Lower Ordovician (Fig. 5). The regional chitinozoan zonation (Paris, 1990) is useful for dating Ordovician strata, but its correlation with the global scale is highly speculative, recording continuous changes even by their proposing authors, as was demonstrated for the upper Floian, Dapingian and lower Darriwilian chitinozoan biozones (Gutiérrez-Marco et al., 2014). Similarly, the taxon-range biozones so far considered as indicators of the

Fig. 5. Correlation of Lower Ordovician graptolite zones (for details see text), after revising the British “D. varicosus” Zone into the new B. jacksoni Zone (Rushton, 2011).

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lower–middle Tremadocian (Lagenochitina destombesi) and lower Floian (Euconochitina symmetrica), and equated by Webby et al. (2004) with their “time slices” 1a–1b and 2a, respectively, occur in part within the range of the upper Tremadocian Araneograptus murrayi graptolite Biozone in peri-Gondwanan, mid-latitude areas of south China (Wang et al., 2013b). Paradoxically, these and other Lower Ordovician chitinozoan biozones of the regional scale have their stratotypes defined by their occurrences in the Moroccan Anti-Atlas or in the Algerian Sahara (Elaouad-Debbaj, 1984, 1988; Paris, 1990), but with little stratigraphic or biochronological control provided by graptolites. Even in the “modern” left-hand columns correlating the main Ordovician succesions from North Africa (e.g. Videt et al., 2010, Fig. 2), both chitinozoan and graptolite zonations need a deep review, together with their equivalence with the global stages and “substages” of the Lower Ordovician series (for comparison, see Fig. 5). The Moroccan graptolite zonal scheme achieved here shows good possibilities for detailed correlation with other Lower Ordovician biochronozones around the world (summarized by Loydell, 2012). However, the Moroccan scheme reaches its maximum precision on its correlation potential with the recently reviewed bio- and chronostratigraphic schemes for Southern Scandinavia, South America and Avalonia (Maletz and Egenhoff, 2001; Maletz and Ahlberg, 2011 and references therein), summarized in our Fig. 5. 4.1. Early Tremadocian Although the oldest graptolite material from the Fezouata Formation did not usually include complete rhabdosomes of rhabdinoporids, the regularity of the mesh on all specimens is more suggestive of a subspecies close to Rhabdinopora flabelliformis flabelliformis (Eichwald) rather than R. f. parabola (Bulman) or R. f. canadensis (Lapworth), that have less regular mesh. The age of these first graptolites, in the absence of older Staurograptus or good specimens of Anisograptus, is likely to be close of that of “Assemblage 2” of Cooper et al. (1998, Fig. 3), which is early – but not earliest – Tremadocian. Thus, the lower boundary of the Fezouata Formation does not coincide with the base of the Tremadocian, despite earlier studies reporting a Cambrian-Ordovician boundary age (Destombes, 1971). The Moroccan graptolite assemblages here assigned to the Anisograptus matanensis and Rhabdinopora flabelliformis anglica zones are correlatable with the local R. flabelliformis Biozone recorded from the subsurface of the Algerian Sahara (Blain, 1963) and from an outcrop in the Ougarta Range (Legrand, 1966). This was subdivided into four sub-biozones by Legrand (1973) based on the appearance of several endemic subspecies of R. f. socialis that were somewhat allied, in ascending stratigraphical order, with the R. f. socialis, R. f. flabelliformis, and R. f. anglica “groups”, plus that of “Bryograptus patens Matthew”. The latter is probably based on a species of Radiograptus or discoidally preserved specimens of R. f. anglica (see Erdtmann, 1982b and Cooper et al., 1998). The taxonomic status of the Algerian subspecies “Dictyonema sociale nilii, D. s. mehaïgueni (sic), D. sociale praeafricanum, D. s. incommodus”, as well as the transitional form “D. s. mehaigueni–D. s. praeafricanum”, is rather obscure. However, some of them show the clear quadriradiate development (Legrand, 1973, 1974) characteristic of the genus Rhabdinopora, and can be synonymized with other currently accepted subspecies of R. flabelliformis. According to Cooper et al. (1998); Cooper (1999), and Goldman et al. (2013), lower and middle Tremadocian graptolite chronozones can be used on a worldwide scale because of the absence of provincialism. The existence of these Saharan endemics has not been confirmed in the adjacent Moroccan Anti-Atlas, although some Gondwanan endemics seem to occur for example in northern Argentina, where R. f. acenolazai constitutes a mimic of the old subspecies R. f. parabola (Gutiérrez-Marco and Esteban, 2005) being recorded as high as the An. matanensis Zone. Other than the records mentioned above from North Africa, early Tremadocian (Tr1) graptolites are scarce within the South Polar region

of Gondwana, occurring in scattered localities of Sardinia (Pillola and Gutiérrez-Marco, 1988; Pillola et al., 2008), southeastern France (Aceñolaza and Gutiérrez-Marco, 1995), northern Turkey (Yalçinlar, 1963; Göncüoğlu et al., 2014) and northeastern Iran (Jahangir et al., 2015). 4.2. Middle Tremadocian Representatives of the early biradiate graptolite development have rarely been recognized in the “Adelograptus” tenellus and Aorograptus victoriae zones of the Fezouata Formation. Previous citations of the distinct pendent triradiate genus Bryograptus have been revised and its presence has been so far disregarded for the Anti-Atlas. An atypical Aorograptus victoriae Zone fauna was solely identified on the basis of minute branched rhabdosomes of Ancoragraptus bulmani and fragmentary specimens of Choristograptus louhai occurring in distant localities, under the generalised absence of Ao. victoriae. Middle Tremadocian graptolites are, however, best represented in the El Gassi Formation of the northwestern and central Algerian Sahara. The diachronic base of the unit closely resembles that of the Fezouata Formation, emphasizing the influence of basement tectonics on Ordovician sedimentation (Legrand, 1985). In the northwestern Algerian desert, the local R. flabelliformis Biozone grades up into the first occurrence datum of Bryograptus (Blain, 1963, Fig. 3B), a genus also cited in the Ougarta Range (Gomes Silva et al., 1963). To the southeast the beginning of Tremadocian sedimentation is slightly younger, and the El Gassi Formation includes successive graptolite assemblages within an Adelograptus Zone dominated by endemic forms such as Adelograptus bagueli, Ad. messaoudin and Choristograptus louhai (Legrand, 1963, 1964). The common record of “Adelograptus” tenellus (see Legrand, 1960) in the γIIa and γIIb graptolite assemblages of Legrand (1985, Table 3) supported their correlation with the “Ad.” tenellus graptolite Zone of Morocco and elsewhere (Fig. 5). Of special interest is the occurrence of the endemic African genus Choristograptus in the γIIb assemblage of the Algerian Sahara, corresponding to the upper part of the stratigraphic range of “Ad.” tenellus, as well as from slightly younger beds in Morocco (see above). The Algerian equivalent of the Aorograptus victoriae Zone may begin within this γIIb assemblage and be essentially represented by the γIIIa graptolite assemblage of Legrand (1985), which includes the record of adelograptids, ?clonograptids, and thick biramose forms. Chitinozoan biostratigraphy from the El Gassi Formation also indicates that this “Hassi-Messaud adelograptid fauna” might be younger than the early Tremadocian (Paris, 1990, p. 188). Videt et al. (2010) placed it in the Lagenochitina destombesi Biozone, assimilating it to the range of the former “Amphorachitina conifundus Biozone” of Paris (1990, 1999). The remaining strata assigned to the middle Tremadocian substage are mostly barren of graptolites in the south-polar peri-Gondwanan areas, as exemplified by the Fezouata Formation, with the exception of the sections of northern Zagora, Jbel Tijekht, and NW Ouzina. Two poorly preserved graptolite assemblages occurring below the Ar. murrayi Zone were recorded from northern Mauritania (Destombes et al., 1969). They include some “Ad.” tenellus-like specimens and remains of branched adelograptids of dubious biostratigraphic assignation, pending more complete and better-preserved material. 4.3. Late Tremadocian In contrast with the few graptolite records from those older Tremadocian strata, late Tremadocian (Tr3) beds of the Fezouata Formation yielded rather abundant graptolites of the Araneograptus murrayi plus Hunnegraptus copiosus zones, as already stated by Martin et al. (2016). A local diversity peak of more than 10 planktonic species occurs within the Ar. murrayi Zone in the central Anti-Atlas, with some species ranging up into the following biozone, defined by the FAD of H. copiosus.

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The Ar. murrayi Biozone is widespread in south-polar periGondwanan areas such as southern France (Thoral, 1935), southwestern Spain (Robardet and Gutiérrez-Marco, 2004), Sardinia (Pillola et al., 2008), Thuringia (Heuse et al., 1994), northern Mauritania (Destombes et al., 1969), and the Algerian Sahara (Legrand, 1985). In contrast, the H. copiosus Biozone has so far been rarely identified in SW Spain (Robardet and Gutiérrez-Marco, 2004; Gutiérrez-Marco et al., 2015a) and in the central Taurides, Turkey (Sachanski et al., 2006). From the Pontides area of the latter, Göncüoğlu et al. (2014) add the record of Paradelograptus cf. antiquus (T.S. Hall), which is a characteristic graptolite for the upper Tremadocian (Jackson and Lenz, 2000) but may range into the basal Floian (Maletz and Egenhoff, 2001). 4.4. Lower and middle Floian Despite showing a very low diversity when compared with other records in mid to low Ordovician latitudes, the Floian graptolite assemblages from the Fezouata Formation are of some value for biostratigraphical subdivision and correlation, thanks to the probable record of the Cymatograptus protobalticus and Baltograptus jacksoni zones. Although the range of Cym. protobalticus has been equated with the T. phyllograptoides Zone in Great Britain (Cooper et al., 2004; Zalasiewicz et al., 2009), its correlation with Baltica led Egenhoff and Maletz (2007) and Maletz and Ahlberg (2011) to restrict the FAD of the species to the upper range of T. approximatus (Cooper and Lindholm, 1990), postdating the LAD of T. phyllograptoides, which is followed in the present paper. A striking biostratigraphic fact regarding the Floian graptolite zones in Morocco is the generalised absence of direct correlation with the Bohemian Lower Ordovician zonation (Bouček, 1973; Kraft and Kraft, 1995, 1999). Work in progress both in Spain and southwestern France also points to the same differences with Bohemia. They may be related with environmental factors favouring the development of endemic faunas in a deeper shelf and more temperate environment. It may also indicate the need for a careful review of some of the Bohemian species, which are closely allied and may eventually be synonymized with certain cosmopolitan or provincial forms. 4.5. Late Floian The upper graptolite assemblages recorded from the Fezouata Formation are also of low diversity by comparison with late Floian occurrences around the world, in particular with the lack of isograptids, pseudophyllograptids, pendent species of Tetragraptus and Didymograptellus, etc. Instead of them, minute pendent, deflexed, and declined baltograptids plus fragments of large horizontal dichograptoids predominate in the B. minutus Zone (see above). The latter is followed by monospecific assemblages of Azygograptus assigned to an “Azygograptus interval”, which strongly resemble similar horizons occurring in the same stratigraphic position in other Gondwanan successions of southern Bolivia and northern Argentina (Fig. 5). 5. Palaeoecological remarks Sedimentological and palaeobiogeographical evidence indicates that the Lower Ordovician Fezouata Formation of the Moroccan Anti-Atlas was deposited on the Gondwanan shelf at a high palaeolatitudinal context close to the Ordovician South Pole (Martin et al., 2016). The corresponding cool-water environments link directly the recorded graptolite assemblages with the “Atlantic Province” faunas, which in Morocco show a minimal diversity compared to many other Ordovician regions around the world. Graptolite provincialism began in the late Tremadocian with some genera restricted to the shallow-water shelf of high-latitude regions, such as the genera Kiaerograptus (Goldman et al., 2013), and Choristograptus, the latter being endemic to the North African platform.

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Another genus biogeographically restricted to high palaeolatitudes is Bryograptus (Maletz et al., 2010), as shown by its Algerian records. By the early and middle Floian, faunal endemism includes T. phyllograptoides (recognized in Spain, but still absent from North Africa) and primitive two-stiped dichograptids such as Cymatograptus and Baltograptus, both related with high-latitude regions (Goldman et al., 2013). In the late Floian, endemicity in faunas of similar palaeolatitudes is represented by members of the genus Azygograptus, which usually occur in monospecific shallow-water, bedding-plane assemblages (Beckly and Maletz, 1991). The horizontal didymograptids Expansograptus nitidus (Hall) and E. pennatulus (Hall), although frequently cited in the old geological literature from North Africa (e.g., Roch, 1939; Gigout, 1951, 1956; Destombes, 1960b; Legrand and Nabos, 1962; Destombes and Jeannette, 1966 and Beuf et al., 1968), have not been recorded in our present study. Both are warm-water species commonly occurring from the mid Floian Pendeograptus fruticosus Biozone upwards, and restricted to palaeotropical localities (Williams and Stevens, 1988; Goldman et al., 2013). Apart from the graptolite taxa typical of high-palaeolatitudes, many pandemic taxa are well represented in the Fezouata Formation. The early Tremadocian (Tr1) graptolite assemblages are of low-diversity and include cosmopolitan Rhabdinopora flabelliformis and its ecological subspecies R. f. socialis and R. f. anglica, adapted to outer or mid-shelf environments (Cooper, 1999). The extreme rarity of multiramous horizontal Anisograptus (such as the zonal index An. matanensis) may be related to the deep-water or oceanic preference of this genus, in certain degree similar to Staurograptus, which was restricted to deep biotopes in continental slope deposits (Cooper et al., 1998; Cooper, 1999; Goldman et al., 2013). Regarding the palaeocological constraints of Ordovician graptolites, Cooper et al. (1991) recognized an inshore graptolite biotope (the “didymograptid biofacies”) that contained shelf-restricted species and cosmopolitan epipelagic taxa. The latter are normally found in two other biotopes following a depth-stratification model: a deeper, mesopelagic biotope (the “isograptid biofacies”) composed of species restricted to deep-water environments, and a shallow, epipelagic biotope with species found in all biofacies. Although Cooper and Sadler (2010) provided further evidence of depth-stratified biotopes for graptolite assemblages occurring within deep-water sediments, Egenhoff and Maletz (2007) noted that the majority of the mesopelagic taxa listed by Cooper et al. (1991) and Cooper (1999) are instead part of an epipelagic biofacies. The competing model of Finney and Berry (1997) admitted that depth stratification and lateral differentiation of faunas did occur, but only within the narrow outer-shelf to proximal-slope environment, and that inner-shelf waters were only occasionally inhabited by a few opportunistic species. However, it seems clear that both depth biotope-stratification (mesopelagic/epipelagic) and surface-water temperature (inshore epipelagic endemics-offshore epipelagic pandemics) play an important role in biogeographical differentiation of Ordovician planktonic graptolites (Cooper et al., 2012a; Goldman et al., 2013). The graptolite record of the Fezouata Formation strongly contrasts in palaeoecological terms with the rather shallow epicontinental sedimentation argued by the sedimentological studies (Vaucher and Pittet, 2014; Vaucher et al., 2015a, 2015b, 2016–in this volume; Martin et al., 2016). Their interpreted palaeoenvironments range from proximal offshore to foreshore, although palaeoecological data derived from trilobites restricted the occurrence of truly inshore trilobite genera (the Neseuretus biofacies) to the upper third of the formation (Vidal, 1998). This matches the graptolite data, coinciding with the shoreward development indicated by Azygograptus in the highest beds of the formation. Graptolite occurrences within the “Ad.” tenellus, Ar. murrayi and H. copiosus zones are particularly significant, because these Tremadocian assemblages are largely dominated by genera unambiguously considered elsewhere as representative of the deep-water graptolite biotope,

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which starts at a depth of 150–200 m (Cooper et al., 1991, 2012a). It is the case of the pandemic species “Adelograptus” tenellus, Hunnegraptus copiosus, Paradelograptus norvegicus, “Tetragraptus” bulmani (= T. longus), and Paratemnograptus magnificus (see Egenhoff and Maletz, 2007). Goldman et al. (2013) suggest that the distribution of “Kiaerograptus” supremus, which they believed to be a two-stiped dichograptid, appears to indicate a deep-water preference for this species as well. Within the Ar. murrayi Zone north of Zagora, up to six mass-accumulation horizons of its naming species were sucessively recorded in the “Bou Izargane” partial section. They range from 10 to 35 cm in individual thickness and the thicker beds may reach several tens of meters of lateral continuity. Also in the same zone, some bedding planes are covered by monospecific assemblages formed either by large specimens of “T.” bulmani found complete and without current orientation in their inferred life orientation (e.g., with the thecal apertures directed downward during settling in the sediment), or by large concentrations of stipes and broken rhabdosomes of P. magnificus, indicating current action and associated fragmentation. Interestingly, graptolites are often preserved partially pyritised and their dense accumulations are closely associated with the record of the soft-bodied metazoans of the Fezouata Lagerstätte. These are either represented on the same beds, or mesopelagic graptolites occur in close stratigraphic vicinity to the most prolific horizons of the latter. The mass occurrences of Ar. murrayi may also represent the onset of repeated toxic events in the water column, that rapidly kill hundreds of thousand to millions of colonies in all their astogenetic stages. This phenomenon apparently is unknown in modern times, but this speculative idea is regarded by Erdtmann (1982a) as congruent with the life models for graptolites (either on stratified or laterally differentiated biotopes). The Moroccan mass occurrences of the species do not constitute single horizons, but rather true “graptolitic lenses” tens of meters wide and up to 80 cm thick, repeated several times in the same section and extending from northern Mauritania to the western and central AntiAtlas. As stated by Gutiérrez-Marco and Aceñolaza (1987) and Aceñolaza et al. (1996), similar en masse concentrations of Ar. murrayi occur in other Gondwanan sections of Argentina and Spain. Just a single Moroccan “graptolite lense” of Ar. murrayi measuring 30 m long by ?20 m wide and 50 cm thick, yielding ca. 60 adult rhabdosomes per square meter, or 300 m3 of graptolite sediment (with an average of five flattened colonies per 10 mm in thickness). This gives a conservative estimation of ca 4,500,000 colonies in just a single “graptolite lense” of moderate size. The resulting “graptolite rain” at the time of sedimentation suddenly entombed complete trilobites and other organisms of the Fezouata Lagerstätte on the sea-floor, and consequently these graptolite beds are being intensively quarried by fossil collectors. Araneograptus murrayi is a common pandemic species in deeper-shelf to slope environments (Egenhoff and Maletz, 2007). The propulsion and buoyancy of its large conical rhabdosome (reaching up to 25–30 cm long) were mainly possible by the coordinated movements developed of the zooids. Dissepiments lie obliquely to the dorso-ventral plane of the stipes (Fig. 4F) and show cortical overgrowths, organizing the water circulation through the rhabdosome for feeding and stabilization purposes (Gutiérrez-Marco and Aceñolaza, 1987; Aceñolaza et al., 1996). Rotational movements of the young colonies were also favoured by the development of elaborated nemal structures (Fig. 4A). Egenhoff and Maletz (2007) interpreted monospecific massoccurrences of deep-water graptolites as indicators of maximum flooding surfaces in monotonous shelf successions, normally associated with condensation during sea-level rise and representing single to amalgamated flooding events during a general transgressive phase. But such mass-occurrences seem at odds with the sequencial development deduced for the Fezouata Formation (Martin et al., 2016; Vaucher et al., 2016–in this volume), where an especially rapid sedimentation is suggested instead. Fairly similar mass-occurrences of Lower Ordovician graptolites has been explained in a number of ways, either in relation with water-mass specifity of some populations that

die after dissipation of its influx when carried by currents into the shallow shelf, or either as graptolites caught in a “death-trap” by sudden upwelling of anoxic water-masses (Erdtmann, 1982a). The second possibility seems untenable for the extensive epicontinental shelf of very little gradient where the sedimentation of the Fezouata Formation took place. The Moroccan assemblages recorded from Floian strata also show an unbalanced graptolite record when compared with other sequences around the world. Besides the rare representatives of the genera Cymatograptus, Baltograptus and Azygograptus, classified by Egenhoff and Maletz (2007: supplementary information) as common inshore endemics in Atlantic faunas, large specimens of multiramous dichograptids, usually well-preserved and rather complete, are abundant in many of the studied sections. This is the case of Clonograptus multiplex, a rare graptolite in shallow-water environments, that is strongly dominant in several horizons within the ?Cym. protobalticus and lower ?B. jacksoni zones, and resembles its common occurrence in deep-water strata elsewhere. Some other pandemic multiramous dichograptids, such as Holograptus and Schizograptus, have been frequently mentioned for the Fezouata Formation, and are now interpreted as possibly mesopelagic faunal elements (Egenhoff and Maletz, 2007). The puzzling presence of many deep-water graptolites in the presumed shallow-water sucession of the Fezouata Formation adds to the apparent absence of graptolites clearly indicative of the isograptid biofacies. These were reinterpreted as belonging to the epipelagic biotope because of their flourishing on the medial to distal shelf areas of the Scandinavian platform (Egenhoff and Maletz, 2007), far from a truly deep-marine environment. 6. Conclusions The first complete chronostratigraphic scheme for the Fezouata Formation based on graptolites is achieved and correlated with previous findings of Lower Ordovician graptolites in northern Mauritania (Destombes et al., 1969), the subsurface of the Algerian Sahara (Blain, 1963; Legrand, 1960, 1963, 1964, 1973, 1974) and the Ougarta Range (Gomes Silva et al., 1963; Legrand, 1966). Many of the identified graptolites, especially those of Tremadocian, have a cosmopolitan or periGondwanan distribution and have been widely used for global correlations. They occur in Scandinavia (Lindholm, 1991; Maletz and Ahlberg, 2011), Great Britain (Cooper et al., 2004; Zalasiewicz et al., 2009), North America (Williams and Stevens, 1988, 1991; Maletz, 1997; Jackson and Lenz, 2003), South America (Maletz and Egenhoff, 2001; Ortega and Albanesi, 2005; Albanesi et al., 2008; Zeballo et al., 2008), China (Feng et al., 2009; Li et al., 2010) and southwestern Europe (Aceñolaza et al., 1996; Pillola et al., 2008). The Fezouata Lagerstätte-bearing beds were initially estimated as ranging from upper Tremadocian to upper Floian (Van Roy et al., 2010) and later restricted to the upper Tremadocian (Martin et al., 2016). The new graptolite data presented herein extend its record to the ?Cymatograptus protobalticus and ?Baltograptus jacksoni zones of the lower and middle Floian, respectively. However, the maximum diversity, and abundance of the exceptionally-preserved soft-bodied biota clearly occurs within the late Tremadocian Araneograptus murrayi and Hunnegraptus copiosus zones. According to sedimentological studies (Martin et al., 2016; Vaucher et al., 2016–in this volume), the benthic communities of the Fezouata biota lived in an open-marine environment, in a relatively shallow setting (upper offshore to lower shoreface) above storm wave base. However, graptolite assemblages recorded in the KonservatLagerstätte are dominated by deep-water planktonic forms that are assumed to have lived in mesopelagic niches (Egenhoff and Maletz, 2007; Goldman et al., 2013). This is the case of the giant conical colonies of Araneograptus murrayi (often reflecting toxic events which generated mass-occurrences), and the large horizontal rhabdosomes of multiramous to pauciramous genera like Paratemnograptus,

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Paradelograptus, Clonograptus, “Tetragraptus” and Holograptus/ Schizograptus. The latter group was adapted to living in quiet waters clearly below the storm wave base, where their large colonies could achieve a passive buoyancy, increased by frictional drag in dense, cool water-masses. Maybe some of the monospecific bedding-plane occurrences of such large graptolites were connected with short episodes of onshore transport by currents of mesopelagic graptolites into the shelf, but their repeated occurrence throughout the Fezouata Formation and the taphonomic evidence from its preservation indicate that many other occurrences are linked to the normal record of truly deep-water pandemic graptolite assemblages, as far as presently known from graptolite palaeoecology.

Acknowledgements The authors are indebted to Julio Martín (Madrid, Spain), Artur A. Sá (Vila Real, Portugal) and Saturnino Lorenzo (Almadén, Spain) for the help during fieldwork on the Moroccan outcrops, Jacques Destombes (Pessac, France) and Philippe Legrand (Gradignan, France) for providing support information on the Saharan localities and graptolites. The authors cordially thank Jörg Maletz (Berlin) for his help with some graptolite identifications, as well as Jan Zalasiewicz (Leicester, UK), Petr Kraft (Prague, Czech Republic) and Nikolay Sennikov (Novosibirsk) for their very helpful comments and suggestions, Diego García-Bellido (Adelaide, Australia), Stan Finney (Long Beach, California, USA) and Heyo Van Iten (Hanover, Indiana, USA) for their linguistic work on the manuscript, and Ismail Said (Rabat, Morocco) for facilitating the search of graptolite samples in the J. Destombes collection, housed in the Ministry of Energy, Mines, Water and Environment (Rabat). Carlos Alonso (Universidad Complutense de Madrid, Spain) photographed the graptolite specimens. This paper was financed by the project CGL2012-39471 of the Spanish Ministry of Economic Affairs and Competitivity, and is also a contribution to the projects RALI 197 of the French ANR and IGCP 591 and 653 (IUGS-UNESCO). The present study is dedicated to the French geologists J. Destombes, Ph. Legrand and Solange Willefert, pioneers in the modern research on Ordovician graptolites in the African continent.

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