Ithe Lower and Middle Devonian at El Khraouia (Southern Tafilalt)

International Field Symposium“The Devonian and Lower Carboniferous of northern Gondwana” – Morocco 2013 70THE LOWER AND MIDDLE DEVONIAN AT EL KHRAOUIA (SOUTHERN TAFILALT) BECKER, R.T.1, ABOUSSALAM, Z.S.1, , BAIDER, L.2, EL HASSANI, A.3 & STICHLING, S.1 1 Institut für Geologie und Paläontologie, WWU, Corrensstr. 24, D-48149, Münster, Germany, rbecker@uni-muenster.de Departement de Géologie, Faculté des Sciences, Université Hassan II, Casablanca 20100, B.P. 5366 Maarif, Casablanca, Morocco, lbaidder@gmail.com 3 Institut Scientifique, Université Mohammed V- Agdal, 10106 Rabat, Morocco, ahmed.elhassani@gmail.com 2 1. INTRODUCTION El Khraouia lies in the southern Tafilalt on the topographic sheet Taouz-Ouest (NH-30-XIV-4), just north of the sharp bend at the eastern end of the northern limb of the Amessoui Syncline, ca. 11 km NNW of Taouz and 4 km E of the abandoned El Atrous settlement (Fig. 1). It has been included in a cross-section by WENDT et al. (1984: fig. 8), who noted its palaeogeographical position at the transition from the southern Tafilalt Platform to the eastern Tafilalt Basin. A succession ca. 2-3 km to the N has been named in WENDT & BELKA (1991) and KLUG (2002) as Rich Tamirant. KRÖGER (2008) described the Lower Devonian stratigraphy and nautiloid faunas at Filoun Douze at the southern limb of the Amessoui Syncline, 4 km to the south. The Devonian sequence dips with ca. 40-50° to the NE. The GPS position for Bed 9b is W 4° 4´ 20´´, N 31° 0´ 24´´. The Lower Devonian is dominated by thick, poorly fossiliferous shale/marl, interrupted by fossiliferous marker limestones (Pl. 1, Fig. 1). The Middle Devonian (Pl. 1, Fig. 8) consists of limestone with pelagic to neritic fauna (up to middle ramp facies). The Eifelian forms a high ridge. From the Taghanic Event level on, basinal shales return. The visited succession has several advantages: 1. Its large outcrop size, 2. Due to its relative remoteness it has been less collected than easy accessible sections, 3. Due to its basinal setting it is complete and most units are relatively thick, 4. It has recently been logged during the revised geological mapping of the Taouz region. However, research is still at an initial stage. Fig. 1. Geographic position of the El Khraouia ridge E of El Atrous, N of the Jebel Ouaoufilal (= Aoufital), W of the Oued Ziiz, and NNW of Taouz, topographic sheet Taouz-Ouest (the main piste Rissani-Taouz is marked). 31 International Field Symposium“The Devonian and Lower Carboniferous of northern Gondwana” – Morocco 2013 2. LOWER/MIDDLE DEVONIAN SUCCESSION A. Scyphocrinites Limestone Two 12 and 20 cm thick beds of solid, bluish, coarse crinoidal limestone (Beds 1 and 3a) are separated by ca. 4-5 m deeply weathered marl (Bed 2). Bed 1 yields abundant scyphocrinitids, including crowns and plate lobolites (Pl. 1, Fig. 2). The latter are known to be associated with the genera Camarocrinus and Marhoumacrinus (HAUDE & WALLISER 1999). A third crinoidal limestone (Bed 3c) follows ca. 1.7 m above Bed 3a, a fourth (Bed 4b) yet 1.2 m higher up. Bed 4b (Pl. 2, Fig. 1) is a representative crinoid rudstone with a recrystallized lobolite of 33 mm diameter, and a dark, organic-rich, slightly peloidal micrite matrix. The widespread disarticulation of the crinoids in Unit A suggests that they were hit by occasional storms. Age: So far there is a very poor local conodont record; a sample from Bed 1 was barren. According to HOLLARD (1977) and HAUDE & WALLISER (1998), Unit A spans the Silurian-Devonian boundary. So far, we have only obtained basal Lochkovian conodonts, including Caudicriodus woschmidti (see its revised range in CARLS et al. 2008), from the lower part of the unit at other sections. This agrees with data in BELKA et al. (1999). Bed 4 yielded a juvenile Caud. alcolae (Pl. 3, Fig. 1) and acodiniform elements (Acodina, Distacodina). Based on data in GARCÍA-LOPEZ et al. (2002) and CORRADINI & CORRIGA (2012), Caud. alcolae suggest a middle Lochkovian age. However, relatives were already observed high in the lower Lochkovian (higher transiens Zone) of Cantabria. The top part of Unit A ranges in any case at least into the upper part of the lower Lochkovian, based on Caud. transiens from Jebel el Mrier, 13 km to the SW. B. Lochkovian Shale A subsequent ca. 200 m wide plain covers poorly exposed shales, which may be 70-100 m thick (Bed 5). They indicate a major late lower/middle Lochkovian deepening episode. Near the top (Bed 6a), there is a laminated, silty mudstone with foraminifers and rare dacryoconarids in a dark, pyrite- and organic-rich micrite matrix (Pl. 2, Fig. 2). It grades upwards into a layer of silty ostracod-crinoid wacke-packstone with some orthocones, probably a rare distal storm layer. Even 1.5 to 2 m higher there is a level of siderite platelets (Bed 6c), which indicate a sedimentary break during hypoxic conditions. Age: Bed 6a yielded no conodonts, only rare ostracods and foraminifers (Thurammina, Psammosphaera, Tolypammina). According to HOLLARD (1977) the middle to upper parts of Unit B contain Monograptus praehercynicus and Neomonograptus hercynicus of the middle/early upper Lochkovian. C. Jovellania Limestone (sensu KRÖGER 2008) Ca. 80 cm thick grey, nodular limestone with abundant orthocones (Bed 7), lying in the plain. Age: HOLLARD (1977) reported from this level of the Taouz area the early upper Lochkovian Homoctenowakia bohemia. KRÖGER (2008) added Paranowakia 32 intermedia, the index of the next higher nowakiid zone. However, a neighboring locality yielded the middle Lochkovian (CORRADINI & CORRIGA 2012) Ancyrodelloides transitans. This contradiction is deepened by an association of Homoct. bohemia and Ancyrodell. cf. transitans in HOLLARD (1977). International Field Symposium“The Devonian and Lower Carboniferous of northern Gondwana” – Morocco 2013 Fig. 2. Upper Pragian to lower Emsian lithology, and conodont biostratigraphy at El Khraouia. D. Pragian Marl and Shale Two intervals of deeply weathered marl/shale (Beds 8a and 9a, ca. 8.5-9 m thick), interrupted by a thin nodular limestone (Bed 8b), which is a strongly bioturbated dacryoconarid-crinoid packstone with many fragmented trilobites, mollusk debris, ostracods, some extraclasts, and Bryozoa (Pl. 2, Fig. 3). The micrite matrix is rich in very fine pyrite. The many neritic faunal elements indicate a regressive trend but the benthic environment remained dysoxic. The crinoidal Beds 9b and 9d in the upper part of Unit D support the regressive trend. Bed 9b is a bioturbated bioclastic wacke-packstone with crinoid, trilobite and mollusk debris, dacryoconarids and ostracods. Some sparite fenestrae may represent microbial mats. Age: HOLLARD (1977), ALBERTI (1981), and KRÖGER (2008) place the base of the Pragian at a color change just above the Jovellania Limestone. ALBERTI (1998) reported in agreement with this view Now. (Turkestanella) acuaria cf. prisca from the basal Unit D of the central Tafilalt, followed higher by the typical subspecies. Sample MA RTB 2a from Bed 9b yielded a flood of Belodella and a few Caud. cf. curvicauda (Pl. 3, Fig. 2). This suggests an upper Pragian age (SLAVIK 2004; regional curvicauda Zone). E. Pragian Limestone Unit E begins with a low, ca. 1 m thick ridge of solid, thin- to medium-bedded, light grey limestone (Beds 11a-g). Bed 11d is a nodular, bioturbated bioclastic packstone with abundant crinoid, dacryoconarid, mollusk, and trilobite debris, and ostracods. It represents a storm-influenced, deeper neritic, lower carbonate ramp. Reddish, hematite-rich, diagenetically overprinted seams represent condensation intervals between depositional events. The higher part of the Pragian Limestone is more nodular and less condensed (Beds 12a-13b, ca. 4 m). The microfacies of Bed 13b (Pl. 2, Fig. 4), a crinoidmollusk packstone, resembles Bed 11d. Gastropods, small brachiopods and nautiloids add to the deep neritic setting. Age: The base and top of the unit (Beds 11a, 13b) are dominated by Belodella (Pl. 3, Fig. 3), which supports a neritic setting, but there are some associated Caud. celtibericus (Pl. 3, Fig. 4). This regional celtibericus Zone appears to correlate with the lower Emsian Conodont Step 17 of CARLS & VALENZUELA-RÍOS 2002, the level of the first Eolinguipolygnathus excavatus Morphotype 114, the proposed future basal Emsian index taxon. However, the direct association of Eoctenopolygnathus pireneae and Caud. celtibericus in the allochthonous Devonian of the Tinerhir area (RYTINA et al. this volume) proves an upper Pragian range of Caud. celtibericus, as suggested for the Bohemian type region (SLAVIK 2004). The Pragian Limestone probably falls in the lower Emsian of its current (Zinzilban) GSSP definition but the future, revised Emsian base will lie somewhere in its middle/upper part. Such an interpretation is in accord with nowakiid data from other Tafilalt sections (ALBERTI 1981, 1998: last acme of Now. (Turkestanella) acuaria acuaria and first peak of Guerichina africana). F. Devonobactrites Shale Ca. 9-10 m thick marl with many limestone nodules and a rich neritic fauna in the lower part, including trilobites (phacopids, scutelluids), small, smooth brachiopods, crinoids, and tabulate corals (Thamnopora and others). The upper half is less fossiliferous (some orthocones) and rich in weathered pyrite. This indicates a deepening upwards. Age: In the adjacent Amessoui Syncline, for example at El Atrous North (= Takkat ou el Heyene) and Jebel Ouaoufilal (KLUG et al. 2008), there is a diverse fauna, including the oldest bactritids, which define the basal Emsian cephalopod zone LD III-A. ALBERTI (1998) recorded from the base of Unit F of the central Tafilalt the last Now. (Turk.) anteacuaria and Guerichina. Therefore, the base of the unit may correlate with the transgressive basal Emsian atopus Shale of Bohemia (SLAVIK 2004), slightly below the Lower Zlichov Event level sensu CHLUPÁČ & KUKAL (1986). G. Deiroceras Limestone Ca. 2 m massive, solid, grey limestones (Beds 15af), forming a small, prominent cliff. The base (Bed 15a) is a bioturbated bioclastic packstone with many styliolinids, crinoid ossicles, ostracods and mollusk debris. Bed 15f is very similar (Pl. 2, Fig. 5) but also includes gastropods. The microfacies is typical for a shallow hemipelagic carbonate platform. The base reflects a sharp regression and probably a sequence boundary, followed by a LST. Age: The very rich conodont fauna from the base (Sample MA RTB 3) is, again, dominated by Belodella. But there are also frequent Criteriognathus miae (Pl. 3, Fig. 7) and icriodids, including Caud. celtibericus, Caud. sigmoidalis (Pl. 3, Fig. 5), and Latericriodus bilatericrescens multicostatus (Pl. 3, Fig. 6). The latter characterizes the basal Emsian bilatericrescens Zone. A single Eol. excavatus Morphotype 114 (Pl. 3, Figs. 8-9) confirms the basal Emsian age. Bed 15f is dominated by the three subspecies of Lat. bilatericrescens, in association with Crit. miae, Caud. sigmoidalis, Eol. excavatus (s.str. and Morphotype 114), and rare Eol. n. sp. aff. pannonicus (sensu BECKER & ABOUSSALAM 2011, Pl. 3, Fig. 10). This assemblage, especially the last species, is regionally typical for the top part of the excavatus M114 Zone. ALBERTI (1981) found in the central Tafilalt Now. (Now.) zlichovensis maghrebiana and Now. (Now.) praesulcata in Unit G and just above. H. Metabactrites Shale 1.7 m of poorly fossiliferous shale/marl (Bed 16), which represent a significant deepening episode 33 International Field Symposium“The Devonian and Lower Carboniferous of northern Gondwana” – Morocco 2013 (TST/HST, Chebbi Event sensu BECKER & ABOUSSALAM 2011). Unit H is in the Amessoui Syncline generally much less fossiliferous than Unit F (KLUG et al. 2008 and own data). Age: In the central and eastern Tafilalt the rich oldest ammonoids (Metabactrites, Chebbites, Erbenoceras, etc.) of Unit H define the lower Emsian zone LD III-B (see KLUG 2001 and KLUG et al. 2008). I. Anetoceras Limestone At the base there are ca. 50 cm solid limestone with poor macrofauna (Bed 17), followed by 24 cm marl (Bed 18a), another solid limestone with few goniatites (Bed 18b), and ca. 85 cm platy limestone (Bed 19) with some phacopids (Fig. 2). The base marks a sharp regression, turning into condensed LST (Bed 17) and subsequent TST deposits. Age: Erb. solitarium (Pl. 1, Fig. 5) indicates the midlower Emsian Anetoceras obliquecostatum Zone (LD III-C). A conodont sample from Bed 17c was unexpectedly barren. At Jebel el Mrier to the south, and elsewhere in the Tafilalt, Crit. steinhornensis is typical for Unit I but polygnatids are always rare at this level. In the central Tafilalt, the base of Unit I has Now. (Now.) praesulcata and Now. (Now.) tafilaltana, followed by Now. (Now.) praecursor and, near the top, Now. (Now.) barrandei (ALBERTI 1981, 1998). J. Mimagoniatites Limestone Above ca. 80 cm deeply weathered marl (Bed 20, ?late TST), Unit J consist of ca. 4.7 m middle grey nodular limestone, which is bioclastic and somewhat darker than the Anetoceras Limestone in the lower part (Bed 21, with goniatites) but light-grey at the top (top Bed 22). The top of Unit J is a slightly bioturbated dacryoconarid packstone, with cone-incone stacking of nowakiids and styliolinids, abundant shell debris, some fragmentary crinoids, and an upwards decreasing pyrite content of the fine micrite matrix. This suggests an improved oxygenation and circulation upwards despite a slight deepening, as indicated from the influx of deeper-water conodonts. Age: Mimagoniatites cf. fecundus from Bed 21 is the index of the top lower Emsian zone LD III-D. The conodont fauna from the top of Bed 22 is rich in Belodella and Neopanderodus but also includes Linguipolygnathus laticostatus (Pl. 3, Figs. 11-12), Ling. vigierei, Ling. inversus (Pl. 3, Fig. 13), and Caud. ultimus. This association is typical for the laticostatus Zone at the top of the lower Emsian. In the central Tafilalt, Now. (Now.) elegans enters low in Unit J and Now. (Now.) cancellata (unrevised) at its top (ALBERTI 1981). K. Daleje Shale Equivalents 100–120 m silty, greenish-grey, poorly fossiliferous shales (“Bed” 23), which are only well exposed in small, steep gullies (Pl. 1, Figs. 1, 6). The (main) transgressive Daleje Event occurred at the base, above a minor discontinuity surface. 34 Age: In the central and eastern Tafilalt, Unit K carries rich goethitic (originally pyritic) ammonoid faunas of the early upper Emsian LD IV-A to IV-C (BECKER & HOUSE 1994, KLUG 2002, WEBSTER et al. 2005). There are no conodonts. L. Anarcestes Limestone Several meters of yellowish weathering, light-grey, marly nodular limestone (“Bed” 24), with abundant goniatites (Sellanarcestes, Anarcestes, Achguigites), and phacopid trilobites. Outcrops are heavily covered by debris from the Eifelian cliff above. Unit L represents a HST. Age: The goniatites are typical for the higher upper Emsian Anarcestes Zone (LD IV-D), which correlates with the serotinus to patulus Zones (e.g., BELKA et al. 1999, KLUG 2002). Polygnathids, however, are rare in the Anarcestes Limestone. The Emsian/Eifelian boundary lies elsewhere in the Tafilalt (e.g., BECKER & ABOUSSALAM this vol.) near its top. M. Lower/Middle Eifelian Limestone At the base there is a ca. 1.4 m thick interval of dark-grey, solid limestone (Bed 25a) with common goniatites, including Fidelites, Werneroceras, and (loose) early Subanarcestes (Pl. 1, Fig. 7), as well as bivalves (Pterochaenia) that are typical for pelagic low-oxygen facies. The transgressive and eutrophic Chotec Event is expected in this interval but styliolinites have not yet been seen, perhaps due to the restricted outcrop (wide cover by debris from above). Above, there is a more massive, ca. 80 cm thick Subanarcestes Marker Limestone (Bed 25b), which occurs widely on the Tafilalt Platform (e.g., BULTYNCK 1985, BECKER & HOUSE 1994, KLUG 2002). It represents a short regressive interval (late HST) and yielded Pinacites sp., Suban. sphaeroides, and Fidelites. It is overlain by ca. 4.5 m nodular limestone with Subanarcestes, other goniatites, orthocones, brevicones, and Panenka sp. (Beds 25c26). 1.3 m below the top thin and fine distal turbidites commence. The top of Bed 26 is a bioturbated bioclastic packstone with many styliolinids, crinoids, and mollusk debris, indicative of a shallow pelagic carbonate platform/ramp. Age: Bed 25a falls in the basal Eifelian Fidelites or Foordites Zone (MD I-B), which correlates with the partitus Zone (BULTYNCK 1985, BECKER & ABOUSSALAM, this vol.). Bed 25b can be placed in the higher part of the Pin. jugleri Zone (MD I-C), which equals the basal part of the costatus Zone (BULTYNCK 1985, BECKER & HOUSE 1994, KLUG 2002). The minor subsequent deepening of the lower costatus Zone seems to have high correlation potential in North Africa. Ling. linguiformis, Ling. pinguis, Icriodus regularicrescens (Pl. 3, Fig. 15), and Polygnathus angusticostatus (Pl. 3, Fig. 14) from the last nodular level of Bed 26 fall in the upper part of the costatus Zone. International Field Symposium“The Devonian and Lower Carboniferous of northern Gondwana” – Morocco 2013 N. Upper Eifelian Turbidites Ca. 3 m dark-grey, solid, laminated turbiditic limestones forming the cliff top, sometimes with convolute bedding. The top of Bed 27 is a representative laminated and recrystallized (microsparitic) limestone with grading from dacryoconarid wackestone with some trilobite and mollusk debris into silty mudstone (Pl. 2, Fig. 7). The identical turbidites of the adjacent eastern slope (Bed Fig. 3. Middle/Upper Givetian lithostratigraphy at El Khraouia across the Upper Pumilio and Taghanic Events (Middle and Upper Givetian). 28, ca. 3 m) show large Zoophycos but other macrofauna is rare. Downslope, vertically bedded, ca. 10 m alternating dark-grey marls and thin turbidites follow (see Pl. 1, Fig. 8), which end with two more solid turbidite beds (Beds 29d and 29d). The turbiditic interval reflects both a deepening and steepening of the slope, which suggests a regional tectonic trigger. However, the rough correlation of its base with the Bakoven Event sensu DE SANTIS & BRETT (2011) may be more than a coincidence. Bed 30 (ca. 60 cm) is defined by a return to light-grey marls and nodular goniatite limestone with Holzapfeloceras and Agoniatites. The main Kačák Event Interval may be (partly) represented by an overlying marl unit (Bed 31, ca. 4 m). Its coincidence with the end of wide-spread turbidite shedding, which is also true for the NW (Ottara), E (Hassi Nebech) and SW (Jebel el Mrier), is remarkable. Age: The top of Bed 27 produced a rich conodont fauna with Tortodus kockelianus kockelianus (Pl. 3, Fig. 16), Po. angusticostatus, Po. robusticostatus, Po. pseudofoliatus, Po. angustipennatus, Ling. linguiformis Morphotypes γ1-2, and I. anterodepressus. This is a typical assemblage of the (main) kockelianus Zone (compare BELKA et al. 1997). Bed 30b contains the index species of the latest Eifelian Holz. circumflexiferum Zone (KLUG 2002a, MD I-F2 of BECKER & HOUSE 1994), which characterizes the Kačák Event Interval. O. Lower/Middle Givetian Limestone At the base there is an alternation of thin-bedded grey limestone and marl with some phacopid remains (Bed 32). These are overlain by a ca. 1 m high cliff composed of more solid limestone beds (Bed 33). At the base is a fining upwards bioturbated bioclastic limestone with many dacryoconarids, some ostracods and mollusk debris. This microfacies is characteristic of a calm, hemipelagic carbonate ramp. On the main eastern slope there is a still poorly studied, more than 15 m thick alternation of thin- to thick-bedded solid limestone and deeply weathered marl with some rugose and tabulate corals. They indicate a shallower, neritic mid-ramp setting. Bed 43 is a laminated, dark-grey limestone, which sandwiches a mass occurrence of minute brachiopods (Ense). The thin section of this Lower Pumilio Event bed (LOTTMANN 1990) shows a strongly recrystallized brachiopod-dacryoconarid-ostracod packstone, which is interpreted to be the result of a sudden eutrophication event. It is followed by a ca. 10 m thick, almost vertical succession of bioclastic limestones (up to 50 cm thick) and marls. Bed 45 is the Upper Pumilio Event level and consists of two brachiopod coquinas. The thin-shelled brachiopods are strongly recrystallized, imbricated and associated with some dacryoconarids (Pl. 2, Fig. 8). The marls just below (Bed 44) mark the base of the transgressive 35 International Field Symposium“The Devonian and Lower Carboniferous of northern Gondwana” – Morocco 2013 Depophase If-UPum sensu BECKER & ABOUSSALAM (2011). Further downslope there are more, mostly thin-bedded bioclastic limestones alternating with marls. The 3 m thick Bed 47 and the 4.65 m thick Bed 9 (Fig. 3) are tentatively correlated with phases of the Maenioceras Marl (BECKER & ABOUSSALAM 2011, Depophase If-Win). A sequence of solid limestones forms Bed 51, which includes a 41 cm thick marker unit (Beds 51e-f) and a bundle of three thin limestones (Beds 51g-i) at the top. Age: The base of Bed 33 yielded Po. varcus (Pl. 3, Fig. 17), Ling. linguiformis, I. difficilis (Pl. 3, Fig. 18), and others. Therefore, it falls already in the basal Middle Givetian. Consequently, there is a strong condensation of the Lower Givetian, in large contrast to the Middle Givetian to Frasnian. The Upper Pumilio Event layer yielded Po. ansatus (Pl. 3, Fig. 19), Po. varcus, Po. xylus, I. brevis brevis, and others, indicative of the basal ansatus Zone, as at Bou Tchrafine (BULTYNCK 1985). There is also the sudden influx of Latericriodus (Pl. 3, Fig. 20), as at Oued Ferkla (WARD et al this vol.), which suggests an immigration pulse from eastern North America. The apparent breakdown of a palaeobiogeographic barrier by the Upper Pumilio Event is currently not understood at all. Bed 50i yielded a diverse conodont association, including Ling. weddigei, Ling. mucronatus, Po. ansatus, Po. varcus), Tortodus caelatus (Pl. 3, Fig. 1), T. aff. weddigei, I. brevis brevis, and others. T. aff weddigei indicates the upper part of the ansatus Zone, probably within the Taghanic Event Interval. Therefore, the massive limestone within Bed 50 is correlated with the regionally widespread Upper Sellagoniatites Limestone (ABOUSSALAM 2003, ABOUSSALAM & BECKER 2011). The marly Bed 51f is thought to mark the base of Depophase IIa-Tagh but more detailed data are required. crinoid ossicles, and gastropods) and pyritic pelagic fauna (tornoceratids, Pharciceras, Stenopharciceras, and two species of Pseudoprobeloceras, Fig. 5). This sharp break reflects the significant basal Upper Givetian eustatic rise (Geneseo Transgression, base of Depophase IIa-Gen of ABOUSSALAM & BECKER 2011). Bed 51b is a 18 cm nodular limestone (bioturbated mudstone with rare styliolinids and ostracods) with some small brachiopods and increasing fine siliciclastic detritus at the top. It is separated by ca. 90 cm marl (Bed 52a) from a vertical, laterally variably thick prominent marl unit (Bed 52b). Fig. 5. Pseudoprobeloceras cf. praecox (left, 17 mm diameter) and Ps. pernai (right, 21 mm dm) from the Upper Givetian marl (Bed 51a). Age: The goniatites from Bed 51a correlate straight away with the famous Pharciceras Fauna of Hassi Nebech to the east (BENSAID 1974, BOCKWINKEL et al. 2013). Since this assemblage comes mostly from the middle part of the Upper Givetian (MD III-D), its lower part must be represented by the lower part of the thick marl. Locally, there is no evidence for the regional Lower Marker Bed (sensu BECKER & HOUSE 1994, 2000; see ABOUSSALAM 2003), which is normally a rather massive goniatite limestone. However, Bed 51b can be correlated with the regional Upper Marker Limestone (dengleri dengleri Subzone, = upper part of previous Upper disparilis Zone, ABOUSSALAM & BECKER 2007), based on the presence of Po. dengleri dengleri (Pl. 3, Fig. 22), Po. ordinatus, Po. tafilensis (Pl. 3, Fig. 23), Po. paradecorosus, and Schmidtognathus peracutus. The observed shallowing upwards is rather characteristic for the unit. The Givetian/Frasnian boundary lies close to Bed 52b or within the subsequent wide plain. 3. REFERENCES Fig. 4. Phillipsastrea, partly overgrown by an alveolitid, Bed. 51a, basal upper Givetian (ca. x 0.9). P. Upper Givetian Marl and Limestone The termination of the Middle Givetian neritic limestone succession is abrupt. The subsequent, ca. 11 m thick, deeply weathered marls contain a mixture of neritic (colonial Phillipsastrea, Fig. 4, tabulate corals, 36 ABOUSSALAM, Z.S. 2003. Das “Taghanic-Event” im höheren Mittel-Devon von West-Europa und Marokko. – Münstersche Forschungen zur Geologie und Paläontologie, 97: 332 pp. ABOUSSALAM, Z.S. & BECKER, R.T. 2007. New upper Givetian to basal Frasnian conodont faunas from the Tafilalt (Anti-Atlas, Southern Morocco). – Geological Quarterly, 51 (4): 345-374. ABOUSSALAM, Z.S. & BECKER, R.T. 2011. 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Lower Devonian (Emsian) – Middle Devonian (Eifelian and lowermost Givetian) conodont successions from the Ma´der and the Tafilalt, southern Morocco. – Courier Forschungsinstitut Senckenberg, 75: 261-286. CARLS, P. & VALENZUELA-RÍOS, J.I. 2002. Early Emsian Conodonts and associated shelly faunas of the Mariposas Fm (Iberian Chains, Araon, Spain). – Cuadernos del Museo Geominero, 1: 315-333. CARLS, P., SLAVÍK, L. & VALENZUELA-RÍOS, J.I. 2008. Comments on the GSSP for the basal Emsian stage boundary: the need for its redefinition. – Bulletin of Geosciences, 83 (4): 383-390. CHLUPÁČ, I. & KUKAL, Z. 1986. Reflection of possible global Devonian events in the Barrandian area, C.S.S.R. – Lecture Notes on Earth Sciences, 8: 171-179. CORRADNI, C. & CORRIGA, M.G. 2012. A Prídoli-Lochkovian conodont zonation in Sardinia and the Carnic Alps: implications for a global zonation scheme. – Bulletin of Geosciences, 87 (4): 635-650. DE BAETS, K., KLUG, C. & MONNET, C. 2013. Intraspecific variability through ontogeny in early ammonoids. – Paleobiology, 39 (1): 75-94. DESANTIS, M.K. & BRETT, C.E. 2011. Late Eifelian (Middle Devonian) biocrisis: Timing and signature of the preKačák Bakoven and Stony Hollow Events in eastern North America. - Palaeogeography, Palaeoclimatology, Palaeoecology, 304: 113-135. GARCÍA-LÓPEZ, S., JAHNKE, H. & SANZ-LÓPEZ, J. 2002. Uppermost Pridoli to Upper Emsian stratigraphy of the Alto Carrión Unit, Palentine Domain (Northwest Spain). – Cuadernos del Museo Geominero, 1: 229-257. HAUDE, R. & WALLISER, O.H. 1998. Conodont-based Upper Silurian-Lower Devonian range of scyphocrinoids in SE Morocco. – In: GUTIERREZ-MARCO & J.C., RABANO, I. (Eds.), Proceedings of the Sixth International Graptolithe Conference of the GWG (IPA) and the SW Iberia Field Meeting in 1998 of the International Subcommission on Silurian Stratigraphy (ICS-IUGS), pp. 94-96, Madrid (Instituta Tecnologico Geominero de España). HOLLARD, H. 1977. Le domaine de l´Anti-Atlas au Maroc. – In: MARTINSSON, A. (Ed.), The Silurian-Devonian Boundary, International Union of Geological Sciences, Series A, 5: 168-194, Stuttgart (Schweizerbart). KLUG, C. 2001. Early Emsian ammonoids from the eastern Anti-Atlas (Morocco) and their succession. – Paläontologische Zeitschrift, 74 (4): 479-515. KLUG, C. 2002. Quantitative stratigraphy and taxonomy of late Emsian and Eifelian ammonoids of the eastern AntiAtlas (Morocco). – Courier Forschungsinstitut Senckenberg, 238: 1-109. KLUG, C., KRÖGER, B., RÜCKLIN, M., KORN, D., SCHEMMGREGORY, M., DE BAETS, K. & MAPES, R.H. 2008. Ecological change during the early Emsian (Devonian) in the Tafilalt (Morocco), the origin of the Ammonoidea, and the first African pyrgocystid edrioasteroids, machaerids, and phyllocarids. – Palaeontographica, Abteilung A, 283: 83-176. KRÖGER, B. 2008. Nautiloids before and during the origin of ammonoids in a Siluro-Devonian section in the Tafilalt, Anti-Atlas, Morocco. – Special Papers in Palaeontology, 79: 110 pp. LOTTMANN, J. 1990. Die pumilio-Events (Mittel-Devon). – Göttinger Arbeiten zur Geologie und Paläontologie, 44: 98 pp. SLAVÍK, L. 2004. The Pragian-Emsian conodont successions of the Barrandian area: search of an alternative to the GSSP polygnathid-based correlation concept. – Geobios, 37: 454-470. WEBSTER, G., BECKER, R. T. & MAPLES, C. G. 2005. Biostratigraphy, paleoecology, and taxonomy of Devonian (Emsian and Famennian) crinoids from southeastern Morocco. – Journal of Paleontology, 79 (6): 1052-1071. WENDT, J. & BELKA Z. 1991. Age and Depositional Environment of Upper Devonian (Early Frasnian to Early Famennian) Black Shales and Limestones (Kellwasser Facies) in the Eastern Anti-Atlas, Morocco. – Facies, 25: 51-90. WENDT, J., AIGNER, T. & NEUGEBAUER, J. 1984. Cephalopod limestone deposition on a shallow pelagic ridge: the Tafilalt Platform (upper Devonian, eastern Anti-Atlas, Morocco). – Sedimentology, 31: 604-625. Acknowledgements T. FÄHRENKEMPER produced the section logs, E. KUROPKA processed most of the conodont samples. S. HARTENFELS and T. FISCHER joined the field team in spring 2012. Field work was part of the revised geological mapping in the SE Anti-Atlas, sheets Marzouga, Irara, Al Atrous, Mfis, and Tawz (Run No 14/2009). We thank A. FEKKAK, Université Chouaïb Doukkali, El Jadida, for his good cooperation. 37 International Field Symposium“The Devonian and Lower Carboniferous of northern Gondwana” – Morocco 2013 38 International Field Symposium“The Devonian and Lower Carboniferous of northern Gondwana” – Morocco 2013 Plate 2 Fig. 1. Bed 4b, top of Scyphocrinites Limestone. Fig. 2. Bed 6a, within upper Lochkovian Shale. Fig. 3. Bed 8b, within Pragian Marl/Shale . Fig. 4. Bed 13b, top of Pragian Limestone. Fig. 5. Bed 15f, top of Deiroceras Limestone. Fig. 6. top Bed 22, top of Mimagoniatites Limestone. Fig. 7. Top of Bed 27, upper Eifelian turbidite. Fig. 8. Upper pumilio Bed (Bed 45). 39 International Field Symposium“The Devonian and Lower Carboniferous of northern Gondwana” – Morocco 2013 Pl. 3. Lower/Middle Devonian conodonts from El Khraouia. 1. Caud. alkolae juv., oblique view of poorly preserved specimen, Bed 4, 2. Caud. cf. curvicauda, Bed 9b, 3. Belo. triangularis, Bed 9b, 4. Caud. celtibericus, Bed 11a, 5. Caud. sigmoidalis, Bed. 15a, 6. Lat. bilatericrescens multicostatus, Bed 15a, 7. Crit. miae, Bed 15a, 8-9. Eol. excavatus Morphotype 114, Bed 15a, 10. Eol. n. sp. aff. pannonicus, Bed 15f, 11-12. Ling. laticostatus, Bed 22top, 13. Ling. inversus, Bed 22top, 14. Po. angusticostatus, top Bed 26, 15. I. regularicrescens, Bed 26, 16. T. kockelianus kockelianus, top Bed 27, 17. Po. varcus, Bed 33, 18. I. difficilis, Bed 33, 19 Po. ansatus, Bed 45, 20. Lat. latericrescens latericrescens, Bed 45, 21. T. caelatus, Bed 50i, 22. Po. dengleri dengleri, Bed 52, 23. Po. tafilensis, Bed 52. 40