4.a.1. Geology of Dar Jaïdet and Jebel Tekzim sections

The sections of Dar Jaïdet and Jebel Tekzim belong geologically to the Kharrouba Flysch mountain massifs of the eastern Jebilet, which extend from Sidi Bou-Othmane to the western flank of Jebel Smaha (region of El-Kelâa des Sraghna). Here, there is a disconcordance between the autochthonous terrains of the eastern Jebilet and the allochthonous nappe displaced during the major Hercynian orogeny movements, according to Huvelin (Reference Huvelin1967). These sliding bars are displaced over the olistostrome and the platform facies at the top of Jebel Tekzim.

The Kharrouba Formation is composed of at least 2000 m-thick sediments such as turbidites, bioclastic limestones, shales and sandstones. The outcrop at Dar Jaïdet represents one of the thickest sections in the Kharrouba Formation, on the southeast flank, where, according to Huvelin (Reference Huvelin1977), atop about a thousand metres of flysch, there are about fifty metres of very fossiliferous green shales at certain levels, well dated by Posidonia becheri and Goniatites crenistria. In the green schist at the base of the Kharrouba Formation, Hollard et al., (Reference Hollard, Huvelin and Mamet1977) found Goniatites crenistria and Posidonia becheri at point 2 (Figure 2). These are overlain by bedded flysch, then by the olistostrome, which extensively outcrops throughout the plain at the southern foot of Jebel Tekzim. This olistostrome formation is composed of reworked flysch and notably contains blocks of bioclastic limestones of varying sizes as well as blocks of calcareous sandstones, probably from flysch, embedded in a grey schistose cement or matrix (Huvelin, Reference Huvelin1977). Some microfold structures and surfaces with differently oriented striations are observed, likely reflecting gravity-driven sliding movements during the formation of the flysch. At Jebel Tekzim, the olistostrome is overlain by shales and green sandstones and sometimes calcschists containing crinoids and corals, capped by bedded, sometimes cross-bedded, bioclastic calcareous sandstones followed by calcareous sandstones (Huvelin, Reference Huvelin1977). The bioclastic limestones (sample Dj14) are sometimes sandy and bioclastic.

Figure 2.

Stratigraphic log of Dar Jaïdet-Jebel Tekzim (eastern Jebilet), combining the Dar Jaïdet section (samples Dj1 to Dj5), the Jebel Tekzim section (samples T2, T3, Dj6 to Dj14) and the three limestone bars of Jebel Tekzim (B1, B2 and B3); distribution of foraminifera, algae and algospongia.

Figure 2. Long description

The table presents the stratigraphic log of Dar Jaiet-Jebel Tekzim, combining the Dar Jaiet section (samples Dj1 to Dj5), the Jebel Tekzim section (samples T2, T3, Dj6 to Dj14), and the three limestone bars of Jebel Tekzim (B1, B2, and B3). It details the distribution of foraminifera, algae, and algospongia across different formations and zones. The table includes columns for system, stage, period, zones, formation, lithology, and samples. Notable formations include the Kharrouba Formation, Tekzim Formation, and Green Formation. The lithology column uses various patterns to represent different rock types, such as calceshist, green schists, blue limestone, greenschist, bioclastic limestone, limestone block olistostrome, grey shale, fine sandstone benches, and ooliths. The foraminifera column lists various species, while the algae and algospongia columns indicate the presence of specific types. The table provides a detailed view of the geological strata and biological distribution in the region.

The outcrops with T1 and T2 samples are located in platform facies at the base of the Kharrouba Fm from the Jebel Tekzim area, and the same is true for outcrops with Dj1–Dj5 samples from Dar Jaïdet. These samples from Dar Jaïdet are probably platform facies, like Koudiat Bourkis. The outcrops Dj6–Dj14 samples and B1, B2 and B3 samples in Jebel Tekzim, corresponding to the Tekzim Fm, are allochthonous in a gliding nappe above the olistostrome (Figure 3b).

Figure 3.

Photograph showing the olistostrome with bioclastic limestone blocks embedded in a micritic siliceous matrix on the northern slope of Jebel Tekzim (a) and schematic section north of Jebel Tekzim and Dar Jaïdet, after Andre (Reference Andre1989) (b).

Figure 3. Long description

The photograph shows a person standing on a rocky slope with bioclastic limestone blocks embedded in a micritic siliceous matrix. The blocks are labeled as ‘Bioclastic limestone block’ and ‘Block unit (olistostrome)’. The schematic section illustrates the geological structure north of Jebel Tekzim and Dar Jai. It includes labels such as ‘Jebel Tekzim’, ‘Bar N°2’, ‘Bar N°3’, ‘Limestone blocks’, ‘Olistostrome’, ‘Spotted schists and siltstones’, ‘Flysch of Kharrouba’, and ‘Anticline Dar Jai’. The section shows the spatial arrangement of these geological features, with elevations marked in meters.

4.a.2. Description of the Dar Jaïdet section (Dj)

Our sampling route began on the northeast flank of the Dar Jaïdet anticline, just beside a water tributary below the hill, and continued up to the ridge summit towards the south. All the samples studied from this section were collected within the Flysch of the Kharrouba Formation, below the olistostrome. The stratigraphic sequence from bottom to top consists of about fifty metres of heavily weathered grey shales at the base of the hill (Figure 2). These shales cover the northern flank of the anticline and are sometimes characterized by nodules and cubic pyrite crystals. They are overlain by beds of friable calcschists. These strata are followed by reddish calcareous sandstones with thicknesses ranging from 10 to 40 centimetres. Above comes a series of yellowish, grey-fractured, bioclastic, sandy limestone beds interbedded with iron-rich, reddish calcareous sandstones. Sample Dj1 corresponds to a very fine micritic crystalline limestone, 60 cm thick, with a yellowish to light grey patina on the fracture (Figure 2). It is overlain by a sandstone-dominated alternation of sandstones and pelites, characterized by beds ranging from 20 to 50 centimetres thick and occasionally up to 90 centimetres. This alternation is followed by 4 metres of heavily weathered shales, then by bed Dj2, a finely crystalline light grey laminated limestone 50 centimetres thick, followed by 2 metres of shales. The next bed, Dj3, is a fine-grained limestone with a light grey patina, itself overlain by a metre of grey shales. Bed Dj4 consists of thin limestone lenses about 10 centimetres thick. This shale-lenticular limestone alternation (from 5 to 40 cm thick) repeats over a thickness of about 30 metres (Figure 2). Bed Dj5 is a finely crystalline limestone, 20 centimetres thick, which yielded Gnathodus pseudosemiglaber s.l. as well as Polygnathus glaber medius, Pseudopolygnathus cf. fusiformis and Palmatolepis sp. A. Dj5 is overlain by some beds of sandy limestones interbedded with shale or red sandstone beds, forming a small ridge at the summit of the well-known Dar Jaïdet hill, with a vertical dip corresponding to the hinge of the kilometre-long Dar Jaïdet anticline elongated east-west, which includes calcschist strata and some upper sandy limestone beds (Figure 2).

4.a.3. Description of the Jebel Tekzim section (T)

To the northwest and at the base of the Kharrouba Formation, within the calcshists, two fine lenticular limestone beds (about 15 cm) provide the two samples T2 and T3. Only T2 (N31°56′34.60″N, W7°47′12.81″), a highly recrystallized bioclastic limestone, yielded a few small foraminifera (Figure 2). Further above and to the southeast, a few metres from the house at the base of Jebel Tekzim, the strata outcrop continues from those of Dar Jaïdet (Dj6a, Dj6b and Dj6c) (Figure 2). About 90 metres south of the house, the olistostrome appears as fragments of large blocks of bioclastic limestone (Figure 3a), which can reach up to 2 metres in thickness within a greyish matrix (Dj6, Dj7). This flysch outcrops cover almost the entire hill of Dar Jaïdet and the base of Jebel Tekzim to the east. At the base of the outcrop, there are three metres of a sandstone-pelite sequence dominated by sandstones, characterized by sandstone beds ranging from 30 to 90 centimetres thick and alternating with calcarenites. After a 60-metre gap in observation, a few beds of calcschists and highly fractured sandstones appear (Figure 3b). The first sampled beds of the olistostrome (Dj6, Dj7), located just 100 metres from the Douar, consist of limestone containing fragments and pieces of limestone within an olistostrome cemented by sparite. This petrographic assemblage is complex, composed of siliciclastic materials and carbonate particles strongly mixed in a detrital matrix, reflecting a turbulent environment marked by slumps or slides. Dj6 and Dj7 belong to a limestone unit 5 to 6.5 metres thick, with a blue patina and grey fracture. Its general texture is an oolitic and bioclastic packstone that includes fragments of probable algal encrustations. Notably, Dj6 yielded reworked Devonian conodont specimens along with Viséan ones: Neopolygnathus communis communis, Polygnathus sp., Palmatolepis sp. A and Gnathodus pseudosemiglaber s.l., as well as foraminifers (Figure 2). Dj7 also yielded conodont taxa: Gnathodus pseudosemiglaber s.l. and Palmatolepis sp. B, and foraminifers (Figure 2). This unit is overlain by bed Dj9, one metre thick, showing a very bioclastic limestone with a sandy tendency, blue fracture and a still-yellowish patina. Towards the bars, the olistostrome (Figure 3a) thickens progressively. Above it, samples Dj10 and Dj11 are massive bioclastic limestone beds rich in crinoids, separated by a few very weathered limestone beds. These are overlain by beds Dj12 (40 cm thick) and Dj13 at the foot of Jebel Tekzim, which display a carbonate facies particularly rich in crinoids. Next comes bed Dj14, a hard limestone bed with blue patina and grey fracture, 30 centimetres thick, which yielded two conodont specimens: Gnathodus semiglaber and Gnathodus pseudosemiglaber s.l. These limestones are followed by three metres of grey shales, which separate them from the Jebel Tekzim bars. The first bar of calcareous sandstone is affected by folding and fracturing and is rich in foraminifers (Figure 2). This first bar (B.1) is overlain by 60 metres of flysch with intercalations of small calcschist beds about 20 centimetres thick and with some beds of fractured fine sandstone (Figure 3b). The second bar, more or less vertical and slightly dipping south, is about 60 metres thick and consists of very bioclastic blue limestone intercalated with highly fractured crystalline sandstone, calcarenites and bioclastic limestone lenses in places. The continuation of the succession consists of 200 metres of flysch with intercalations of some sandstone beds (10 to 30 cm thick) (Figure 2). At the summit of Jebel Tekzim, the third bar (B.3) is roughly horizontal (Figure 3b), 15 metres thick and composed of calcarenites with subcircular limestone blocks 30 to 120 cm in diameter containing ooids, bryozoans and corals. This third bar, forming the famous ridge of Jebel Tekzim at 1060 m altitude, corresponding to the bioclastic limestone lenses (h2) described by Huvelin (Reference Huvelin1977), yielded common foraminifers and algae (Figure 2).

4.a.4. Biostratigraphic results

The first sample T2 from the base of the Kharrouba Formation (Figure 2) is at least middle Viséan (Cf5) due to the first occurrence of Nodosarchaediscus and Archaediscus at the concavus stage. In the middle part of the Kharrouba Formation, beneath the olistostrome, sample Dj5 yielded reworked Upper Devonian conodonts along with probable Viséan conodonts, notably Palmatolepis sp. A and Gnathodus pseudosemiglaber s. l. Within the olistostrome, sample Dj6 provided reworked Upper Devonian conodonts and a foraminiferal assemblage of the Archaediscus karreri group, first occurring from the base of the late Viséan but most commonly from the upper Asbian upwards in Morocco (Vachard and Tahiri, Reference Vachard and Tahiri1991; Cózar et al., Reference Cózar, Vachard and Somerville2023). The presence of Stacheoides tenuis, which first appears between biozones Cf6β and Cf6γ (early to late Asbian) (Vachard and Tahiri, Reference Vachard and Tahiri1991), suggests that sample Dj6 should be assigned to the late Asbian Cf6γ1 subzone. The reworking of Devonian conodonts, although absent from the autochthonous deposits of the eastern Jebilet, suggests the existence of a Famennian platform prior to the upper Viséan transgression. Sample Dj7, from the top of the olistostrome, contains a few rare specimens of primitive Neoarchaediscus, whose range extends from the late Asbian to the base of the early Brigantian (Cf6δ = V3c) (Cózar et al., Reference Cózar, Vachard and Somerville2023). However, these forms become dominant only from the Brigantian onwards, indicating that Dj7 likely belongs to the Gnathodus bilineatus bilineatus zone, i.e., the late Asbian. Thus, based on the foraminiferal fauna, the upper part of the olistostrome is dated to the latest Asbian (Cf6γ2). In the upper part of the section, the limestone bar of Tekzim, the first limestone bed (B.1) is dated to the early Asbian (Cf6β) based on the presence of foraminifers such as Archaediscus cf. karreri grandis, Pseudoendothyra sp., Endothyranopsis compressa and Stacheoides tenuis (see complete assemblage in Figure 2). These taxa are recorded in Morocco during the early Asbian (e.g., Vachard and Tahiri, Reference Vachard and Tahiri1991), whereas no marker of the late Asbian is recorded by us. Finally, the third limestone bed is assigned to a late Asbian age (Cf6γ1), as evidenced by the presence of Endothyranopsis cf. crassa, Neoarchaediscus? sp. and Ungdarella uralica? (Figure 2), typical taxa of the assigned biozone in Morocco (Vachard and Tahiri, Reference Vachard and Tahiri1991; Cózar et al., Reference Cózar, Vachard, Somerville, Berkhli, Medina Varea, Rodríguez and Said2008, Reference Cózar, Vachard, Izart and Coronado2020a, Reference Cózar, Vachard and Somerville2023; Izart et al., Reference Izart, Vachard and Berkhli2017; Becker et al., Reference Becker, Aboussalam, El Hassani, Cózar, Herbig and Ernst2021).

4.b.1. Description

The first bed consists of a finely crystalline grey-beige limestone (oo1), 46 cm thick, showing some sedimentary structures (Figure 4). It yielded conical forms of conodonts, Drepanodus sp. and Belodella resima. Sample oo2, located 25 metres higher across a wheat field, consists of a thick yellowish carbonate facies (1.5 m) with beige fracture surfaces, highly recrystallized with some iron oxide nodules. It is directly overlain by a dark grey centimetre-thick limestone, followed by lenticular bioclastic-rich beds interbedded with grey shales over five metres thick, from which sample oo3 was taken. Oo3 yielded the following conodont taxa: Gnathodus cuneiformis, Gnathodus pseudosemiglaber s.l., Gnathodus semiglaber, Gnathodus antetexanus, Gnathodus girtyi and Geniculatus glottoides, as well as foraminifers (Figure 4). Higher up, sample oo4 contains Palmatolepis delicatula delicatula, Gnathodus cuneiformis and Gnathodus pseudosemiglaber s.l. The whole sequence is overlain by a 1.5-metre-thick limestone layer (oo5), lenticular and highly fractured, rich in large bioclasts. Oo5 yielded Gnathodus cuneiformis, Gnathodus pseudosemiglaber s.l., Gnathodus girtyi meischneri, Gnathodus girtyi girtyi and Cavusgnathus unicornis, as well as foraminifers and algae/algospongia (Figure 4). Bed oo6 is characterized by a finely crystalline carbonate facies with blue patina and grey fracture, rich in crinoids, overlain by a crystalline crinoidal limestone with abundant detrital material and numerous foraminifers. After 1.5 metres of grey shales, oo7 shows a fine grey-to-black limestone with large crinoids and foraminifers. Oo7 yielded Palmatolepis glabra prima, Icriodus praealternatus praealternatus, Gnathodus cuneiformis, Gnathodus pseudosemiglaber s.l., Gnathodus semiglaber s.l., Gnathodus texanus, Gnathodus girtyi meischneri, Gnathodus girtyi girtyi, Geniculatus glottoides and Kladognathus complectens. After 3 metres of grey shales, beds oo8, oo9 and oo10 show thicknesses varying between 20 and 40 centimetres. They are interbedded with shales over a distance of 10 metres. Note that bed oo10 consists of a quartzitic limestone rich in foraminifers (Figure 4), with blue patina and grey fracture. One metre above, bed oo11 is characterized by a finely crystalline blue limestone, showing sedimentary structures (Figure 4). Bed oo12, located five m higher, is blue limestone which yielded Gnathodus cuneiformis, Gnathodus pseudosemiglaber s.l., Gnathodus girtyi girtyi, Hindeodella cristulus and foraminifers (Figure 4). It is followed by ten metres of non-deposition or an erosion period. The succession continues with a 15-metre-thick massive grey limestone with blue fracture where samples oo13 and oo14 were collected.

Figure 4.

Stratigraphic log and distribution of foraminifera, algae and algospongia of the Ouled Omar section.

Figure 4. Long description

The table presents the stratigraphic log and distribution of foraminifera, algae, and algospongia in the Ouled Omar section. It includes columns for system, stage, period, zones, lithology, samples, foraminifera, algae, and algospongia. The lithology column describes different types of limestone and shale, while the foraminifera, algae, and algospongia columns list various species found at different stages. The table spans from the Middle Devonian to the upper Visan period, detailing the presence of specific species at each stage. Notable trends include the distribution of different species across various stages and the types of lithology present.

4.b.2. Biostratigraphic results

The first bed, oo1, yielded Drepanodus sp. and Belodella resima. Although the latter taxon is known from the Lower Devonian to the Famennian (Druce, Reference Druce1976), it is of Middle Devonian age here because it belongs to the Devonian limestones of Koudiat Mbijia from the Eastern Jebilet nappe, dated as Middle Devonian by Huvelin (Reference Huvelin1977). Bed oo2 belongs to a nappe unit overthrusting the Devonian limestones of Koudiat Mbijia. It is barren of conodonts but is most probably of Devonian age. The contact between this bed and those overlying it is manifested by a paraconformity. Samples oo3 to oo7 contain the foraminifers, algae and algospongia of early n-Asbian age (Cf6α-β). Regarding the algae, the presence of Stacheoides tenuis and Cabrieropora also suggests an Asbian age (Vachard and Tahiri, Reference Vachard and Tahiri1991; Cózar et al., Reference Cózar, Vachard and Somerville2023) (Figure 4). From bed oo10 upwards, the succession is assigned to the late Asbian (Cf6γ) due to the occurrence of Archaediscus karreri grandis and Ungdarella uralica (Vachard and Tahiri, Reference Vachard and Tahiri1991; Cózar et al., 2020) (Figure 4).

Reworked conodonts, mostly broken, eroded and often too incomplete for generic identification, are found in samples oo3, oo4 and oo7. These contain a mix of pelagic taxa ranging from the Famennian to the middle Tournaisian. Sample oo4 yielded Palmatolepis delicatula delicatula (Famennian, Upper Devonian). The sample oo7 yielded Icriodus praealternatus praealternatus, Palmatolepis glabra prima (Famennian, upper Devonian) and Geniculatus glottoides (upper Tournaisian to lower mid-Viséan). These reworked conodonts indicate that a pelagic platform likely existed formerly in the source region of this Ouled Omar section, from which top Frasnian to Famennian and middle Tournaisian-middle Viséan limestones were eroded and redeposited in the limestones resulting from the upper Viséan transgression.

4.c.1. Description

The outcrop of this section is located near Sidi Bou Othmane, a few metres from Douar Lamkhalif, near the Marabout, where we collected three samples (Sb17–Sb19) (Figure 1; Table 1). Sample Sb18 contains poorer microbiota assemblages than Sb17 (Figure 5). In addition, Sb17 provided conodont specimens, such as Gnathodus pseudosemiglaber s.l., Gnathodus semiglaber and Gnathodus praebilineatus. These two beds constitute a very gritty limestone rich in bioclasts, especially crinoids. Near the track south of Douar Tolba (south of Douar Oulad Brahim), beds are cropping out (Sb19), 50 centimetres thick, with a very dark blue patina. It is a bioclastic limestone isolated within shales, poor in globular and elongated foraminifers (Figure 5). It yielded the conodont Gnathodus bilineatus bilineatus.

Figure 5.

Stratigraphic log and distribution of foraminifera, algae and algospongia of the Lamkhalif section.

Figure 5. Long description

The table presents the stratigraphic log and distribution of foraminifera, algae, and algospongia of the Lamkhalif section. It includes columns for system, stage, period, zones, formation, lithology, samples, foraminifera, algae, and algospongia. The table has multiple rows detailing specific data points for each category. For instance, the lithology column includes bioclastic limestone, limestone, grey metamorphic, grey schist, and greenish lutite. The foraminifera column lists various species such as Archaeiscus at angulatus stage, Endothyra sp., Omphalotis minima, and Valvulinella sp. The algae column includes species like Koninckopora tenuiramosa and Fasciella kizilia. The algospongia column lists species such as Kamaenella sp. and Palaeoberesella lahuseni. The table also includes a legend explaining the symbols used for different types of microfossils. The data provides insights into the biostratigraphy and chronological constraints of the eastern Jebilet successions during the Variscan orogeny.

4.c.2. Biostratigraphic results

Sb18 and Sb19 contain markers at least of the early Asbian (Cf6α-β). Whereas Sb 17 corresponds to the upper Asbian (Cf6γ1), due to the occurrence of Archaediscus karreri grandis and Endothyranopsis crassa and Ungdarella uralica (Cózar et al., Reference Cózar, Vachard, Somerville, Berkhli, Medina Varea, Rodríguez and Said2008, 2020; Vachard and Cózar, Reference Vachard and Cózar2010) (Figure 5), the foraminiferal assemblages, algae and algospongia may include reworked specimens.

4.d.1. Description

The Marabout section is located at the western end of the eastern Jebilet (Figure 1; Table 1), ten kilometres east of the village of Sidi Bou Othmane, behind the Marabout (Figure 6a). Sampling began from the northwest slope, where an isolated nappe unit crops out within recent sediments, following an almost northeast direction. After crossing a few metres of grey shales, the first bed (Mr13) appears, composed of very massive, hard crinoid limestone. It is overlain by about ten metres of massive bioclastic limestones. Samples Mr11 and Mr10 correspond to a carbonate facies with a blue patina, while Mr9 and Mr8 are oolitic limestones with a light blue patina, rich in bioclasts. Sample Mr8 contains foraminifers (Figure 6b). Strata Mr7 to Mr5 form hard blue-patina limestone beds rich in bioclasts, overlain by bed Mr4, a well-preserved carbonate facies showing great richness in bioclasts and rare microbiota (Figure 6b). Above is a seven-metre-thick succession of bioclastic limestone beds. Mr3 directly followed by Mr2, showing a 1.5-metre-thick limestone containing fish scales and foraminifers (Figure 6b). The last bed, Mr1, is heavily weathered, with a grey patina and rich in crinoids.

Figure 6.

View of the outcrop of the allochthonous unit (Marabout section) of the eastern Jebilet nappe, showing massive bioclastic limestones (a) and stratigraphic log and distribution of foraminifera, algae and algospongia of the studied Marabout section (b).

Figure 6. Long description

The image presents a view of the outcrop of the allochthonous unit of the eastern Jebilet nappe, displaying massive bioclastic limestones. The stratigraphic log in the lower part of the image details the distribution of foraminifera, algae, and algospongia in the studied Marabout section. The log includes columns for system, stage, period, zones, formation, lithology, samples, foraminifera, algae, and algospongia. The lithology column shows different types of limestone and grey shale, while the other columns list specific fossils and organisms found in each sample. The legend at the bottom explains the symbols used in the log.

4.d.2. Biostratigraphic results

From Mr13 to Mr8, the microbiota corresponds to the early Asbian (Cf6α-β) owing to the occurrence of Archaediscus at the angulatus stage, whereas the occurrence of Neoarchaediscus in Mr4 suggests that the upper part of the section corresponds to the late Asbian (Cf6γ1-2) (Figure 6b).

4.e.1. Description

The Koudiat El Menjel section is located in the middle of the eastern Jebilet, south of Douar Oulad Brahim and southeast of Douar Jaïdet (Figure 1; Table 1). It forms a series composed of a succession of centimetre-thick beds of bioclastic limestones rich in crinoids. The gritty limestone facies of Koudiat El Menjel shows a strong affinity with that of Ouled Omar to the north, in terms of richness in large crinoids. The first sample, Mj1, about 50 centimetres thick, showing a dark blue patina and grey fracture, is overlain by a very hard and finely crystalline limestone bed, Mj2 (60 cm), which is rich in crinoid ossicles and rare foraminifers and algae (Figure 7). Bed Mj3, a lenticular carbonate facies, is overlain by three metres of limestone beds (Mj4 and Mj5), which are massive and crinoidal with a dark blue patina and microbiota (Figure 7). The sequence continues with some limestone lenses (Mj5a), more or less altered, rich in crinoid ossicles and trace fossils. This set is topped by a very hard, gritty limestone bed Mj6 (50 cm), with microbiota (Figure 7).

Figure 7.

Stratigraphic log and distribution of foraminifera, algae and algospongia of the Koudiat El Menjel section.

Figure 7. Long description

The table presents the lithology and distribution of foraminifera, algae, and algospongia in the Koudiat El Menjel section. It includes columns for system, period, stage, zone, formation, lithology, samples, foraminifera, algae, and algospongia. The lithology column features various types of limestone and shale, with a legend indicating bioclastic limestone, griotte limestone, blue limestone, greenish/greyish lutites, and grey shale. The foraminifera column lists different species such as Pseudoammodiscus sp., Plectogyranopsis ampla, and Archaediscus at stage angulatus. The algae column includes species like Koninkopora tenuiramosa, Windsoporella tulavae, and Konickopora inflata. The algospongia column lists species such as Palaeoberesella lahuseni, Roquesettia uralica, and Kamaenella denbighi. The table spans multiple rows and columns, providing a detailed stratigraphic log of the section.

4.e.2. Biostratigraphic results

No conodonts were recovered from the samples of the Koudiat El Menjel section. However, all the foraminifers found in the residue from washing and those identified from thin sections indicate a late Asbian age (Cf6γ1-2), including the occurrence of Neoarchaedicus and Ungdarella uralica (Figure 7).

4.f.1. Description

The Douar Tolba section is located in the centre of the eastern Jebilet, about one kilometre southwest of the Douar and seven kilometres south-southwest of Douar Ouled Brahim, near a small watercourse. It is characterized by small hills ranging from 100 to 200 m in altitude, with various orientations and slopes, separated by a network of wadis and tributaries. The hill of the Douar Tolba section (Figure 1; Table 1) forms a small mound about 50 metres high, composed of a series of carbonate strata with intercalations of folded grey shales, cut by networks of faults. This section is also one of the best exposures in the eastern Jebilet, showing clearly the direct contact between the pre-Viséan (Middle Devonian) and the Viséan. The Devonian, with a thickness of 40 metres, consists of siliceous shales and sandstone beds. Its top is made up of ‘griottes’ limestones containing tentaculites. These Devonian limestones are overlain by Viséan bioclastic limestones (Figure 8a). This pre-Viséan nappe unit is identical in appearance and facies to that of the Ouled Omar section. The outcrop is formed by a hill rising to 106 metres in altitude, representing a north–south elongated nappe unit. The first bed (Dt1) is a finely arenaceous, well-preserved limestone with a dark yellow patina, with a grey fracture surface and a thickness of 50 centimetres. It is directly overlain in normal contact by a bioclastic limestone bed (Dt2), 60 cm, with a dark blue patina and grey fracture surface (Figure 8b). This unit is followed by four metres of schist strata with intercalated limestone lenses, which are in turn overlain by another bioclastic arenaceous limestone (Dt3), rich in crinoids, elongate foraminifera and other bioclastic fragments. The following interval consists of about ten metres of highly weathered grey shale containing centimetre-scale bioclastic limestone lenses rich in crinoids. Bed Dt5 shows a crinoid-bearing carbonate facies. The succession continues with nine metres of shale, overlain by a massive, very hard and well-preserved reefal limestone bed (8 m). The washed residue from Dt6 is rich in elongated foraminifera, some rare crinoids, a few ostracods and numerous reefal organisms. Beds Dt7 and Dt8, separated by 12 metres of grey shale, are fine limestones with a few crinoids, showing a bluish patina. At the top of the section, four metres of shale are capped by a massive limestone bed (Dt8) rich in crinoids and ostracods, with a few traces of algae (Figure 8c).

Figure 8.

View of the Douar Tolba section showing the Devonian outcrops at the base, overlain by the Viséan limestones toward the top (a), detail of the normal contact between the Viséan deposits and the Devonian red nodular limestones, separated by an unconformity (b) and stratigraphic log and distribution of foraminifera of the Douar Tolba section (c).

Figure 8. Long description

The image consists of three parts. Part a shows a view of the Douar Tolba section with Devonian outcrops at the base and Viséan limestones toward the top. Part b provides a detailed view of the normal contact between the Viséan deposits and the Devonian red nodular limestones, separated by an unconformity. Part c presents a stratigraphic log and the distribution of foraminifera of the Douar Tolba section. The stratigraphic log includes columns for system, period, stage, zone, lithology, samples, and foraminifera. The lithology column shows different types of limestone and grey schist. The foraminifera column lists various species of foraminifera found in the samples.

4.f.2. Biostratigraphic results

The sample taken from the Devonian was barren of conodonts. The samples Dt5 to Dt7 do not provide precise biostratigraphic information. Many of the foraminiferal specimens present in thin sections appear from the early Viséan onwards, but the first Endostaffella occurs in the mid-Viséan. Furthermore, the rare Archaediscus specimens are still in the involute stage, suggesting a rather primitive assemblage, indicative of the mid-Viséan (Figure 8c).

4.g.1. Description

The Douar Fokra outcrop corresponds to the platform facies at the top of the Kharrouba flysch close to the Koudiat Bourkis mapped by Huvelin (Reference Huvelin1977) as Sarhlef limestone. The Douar Fokra section is located near the small Douar Fokra, in the central part of the eastern Jebilet, south of Douar Lakakla, approximately 35 kilometres northeast of Marrakech and 17 kilometres east of Sidi Bou Othmane (Figure 1; Table 1). This area, along with that of Douar Ouled Ben Tounsi, has been the subject of numerous studies (Huvelin, Reference Huvelin1977; Oukemeni, Reference Oukemeni1987; Essamani, 1988). It forms a series of small hills that become more pronounced eastward, reaching elevations of 300 to 400 metres. These hills are composed of bioclastic, or ‘griotte’, limestones alternating with psammitic shales. The sampling of this section began with an isolated bed, showing a well-preserved lenticular crinoidal limestone (D1) with a thickness of 60 centimetres, brown patina and a blue fracture, which is rich in bioclasts. It is followed by several metres of grey shales, deformed, altered and folded; notably, at the level of the water stream, we crossed to reach a small segment where four sandy carbonate beds crop out. D2 is a limestone with a yellowish patina (30 cm), while D3, D4 and D5 are lenticular beds of yellowish colour with beige fractures, highly recrystallized, with thicknesses ranging from 20 to 40 centimetres within the shales. Sample D3 contains foraminifers (Figure 9). The sequence continues with a massive bed, five to ten metres thick, from which we collected samples D6 to D9, consisting of an alternation of grey crystalline limestone rich in crinoids and bioclasts. Only sample D7 contains foraminifers (Figure 9). In the middle of this massive bed lies bed D10, which is a crystalline limestone lithologically similar to the previous beds and which contains many crinoids, ostracods, some gastropods and corals. This bed is rich in foraminifers, algae and algospongia (Figure 9). The beds D11 and D12, forming a finely crystalline limestone, are overlain by seven metres of shale, within which two carbonate beds (D13 and D14) are intercalated with thicknesses of 40 and 60 centimetres, respectively, showing a beige-coloured carbonate facies with a grey fracture. D15 directly overlies these grey shales. It is a massive (5 m) bed whose base consists of finely crystalline limestone rich in foraminifers and abundant crinoids, with some ostracods and reef organisms. In the middle of this massive bed, we collected sample D16, showing a highly recrystallized facies, while at the top of the layer lies bed D17 characterized by well-preserved limestone with a beige patina and grey fractures, rich in crinoids. The whole sequence is topped by very altered grey shales, about one metre thick, overlain by a huge limestone bar (7 m). At its base, sample D18 was collected, showing a beige-to-yellow carbonate facies containing crinoids and rare foraminifers. Samples from D19 to D23, 20 to 60 centimetres thick, are characterized by massive beige limestone with grey fractures, rich in crinoids. Beds D20, D25 and D26 display a carbonate facies rich in crinoids and some foraminifera, algae and algospongia (Figure 9). The continuation of the section is located 130 metres NNE from the previous beds, crossing the Viséan flysch of the Kharrouba Formation, and is generally folded and locally deformed, showing some probable epizonal metamorphic minerals. Beds D27 and D28 correspond to limestone beds similar to the previous ones, reflecting a beige-coloured limestone with grey fractures, more or less altered. The second subsector, located 700 metres to the east, consists of four distinct samples (D30 to D33) collected at the northeast base of Koudiat Bourkis, corresponding to the h2 unit of Huvelin (Reference Huvelin1977) and dated as Viséan-Namurian, mainly composed of bioclastic limestones.

Figure 9.

Stratigraphic log and distribution of foraminifera, algae and algospongia of the Douar Fokra section.

Figure 9. Long description

The table presents the stratigraphic log and distribution of foraminifera, algae, and algospongia in the Douar Fokra section. It includes columns for system, period, stage, zones, formation, lithology, samples, foraminifera, algae, and algospongia. The lithology column features bioclastic limestone, griotte limestone, and grey schist. The foraminifera column lists various species such as Archaeiscus at angulatus stage, Pseudoendothyra similis, Endothyra sp., and others. The algae column includes species like Koninckopora inflata, Saccamminopsis sp., and others. The algospongia column lists species like Fasciella kizilia, Pseudotachydiscus loomis, and others. The table spans multiple rows and columns, detailing the presence of these species across different stratigraphic levels.

4.g.2. Biostratigraphic results

The foraminifera recovered from sample D10 of the Douar Fokra section correspond to the latest Asbian age (Cf6γ1-2), mostly due to the occurrence of Neoarchaediscus, Saccamminopsis and Zidella. So, we attributed the lower part of the section to early Asbian (Cf6α-β) (Figure 9).

4.h.1. Description

The El Gargabat section is located in the centre of the eastern Jebilet, one kilometre south of Douar Oulad Ben Tounsi and three kilometres NNE of Douar Fokra (Figure 1; Table 1). The zone is characterized by small low-altitude mounds generally ranging from 100 to 200 metres high, with varying directions and slopes formed by sandstone or sometimes schistose hills. This section is one of the best studied in the eastern Jebilet by Huvelin (Reference Huvelin1977), where the transition from the Devonian to the Viséan can be observed, showing the reworking of some Devonian limestone pebbles within the Viséan limestones (Figures 10a, b). It is mainly composed of a succession of limestone beds intercalated with greenish-black to dark grey shales. The sampling direction is from northeast to southwest, with the first sample located near the northern bank of a watercourse, where the beds are vertical. Sampling began from the top of the series with closely spaced samples taken from centimetre-thick beds of Viséan sandy limestones or, sometimes, bioclastic limestones (Huvelin, Reference Huvelin1977). The section shows a concordant transition from the pre-Viséan, generally represented by a facies of more or less altered griotte limestones rich in large orthoceras, from sample Gr23 to Gr21. These griotte limestones are in contact with Viséan bioclastic limestones corresponding to beds Gr10 to Gr1 (Figure 10a). The entire sequence belongs to the nappe of the eastern Jebilet.

Figure 10.

Field photo showing the contact between the Devonian and the Viséan within the El Gargabat outcrop (a) and field image of the boundary between the Devonian and the Viséan, showing the reworked Devonian blocks within the Viséan limestones (b).

Figure 10. Long description

A person stands on a rocky outcrop, with labels indicating the geological periods Viséan and Devonian. The image includes markers for sampling direction, a boundary line, and specific points labeled Gr10 and Gr11. Below, a close-up shows reworked Devonian blocks within Viséan limestones, with a hammer for scale and labels indicating normal contact between the Devonian and Viséan layers.

At the base of the section, 15 m of Silurian graptolite shales are overlain by bed Gr23, a well-preserved limestone bed, about 50 cm thick, containing agglutinating foraminifera belonging to the genus Hyperammina. Gr23 is overlain by three thin limestone beds interbedded within grey shales, followed by a pseudonodular griotte limestone bed overlain by bed Gr22. The latter is a nodular limestone with a grey-greenish patina, rich in orthocones. This is followed by a series of griotte limestone beds (2 m), topped by Gr21, a small nodular limestone bed (10 cm) rich in tentaculitoids. After 20 cm of fine limestone and massive limestone (2 m) interspersed with grey schist comes Gr20, a finely crystalline limestone (80 cm). This is followed by two metres of griotte limestone (Gr18 and Gr19) rich in orthocones and tentaculitoids, particularly nowakiids. The next layer (Gr17) is a finely marly limestone, followed by 1.2 m of massive limestone (Gr15–16), rich in crinoids. Then a massive bed (Gr13–14), 1.5 m thick, of gritty limestone at the base, with horizontal laminations. Note that Gr14 is rich in tentaculitoides. Next comes Gr12, a greyish micritic nodular limestone (45 cm) containing the foraminifer Lagenammina sphaerica, bivalves, crinoid stems and ossicles and ostracods. Gr11 shows a grey-to-reddish pseudonodular limestone, 40 cm thick, containing orthocone shells and some goniatites and which yielded the foraminifera Saccammina sp., Tolypammina irregularis and Tolypammina sp. 2 (Figure 11). The first Viséan bed corresponds to Gr10, a limestone (50 cm) with a blue patina and rich in iron oxide. This is directly overlain by a massive (1.5 m) bed (Gr7–Gr9) of dark, gritty limestone. Note that Gr8 contains an individual of Lagenammina sphaerica, while Gr9 yielded unidentifiable Viséan foraminifera. Gr6 is a 40 cm thick, blackish, gritty limestone rich in iron, whose washed residue contains fish scales. The following bed is metric in thickness (Gr5) with a very fine dolomitic limestone facies containing pyrite crystals. Meanwhile, Gr4 shows a highly recrystallized carbonate facies (50 cm) and yields a foraminiferal assemblage, algae and algospongia. Beds Gr3 and Gr2 constitute a very marly and highly altered carbonate facies, 80 cm and 40 cm thick, respectively. They contain some fish scales. At the top of the section, Gr1 is a gritty limestone with a grey patina, 50 cm thick and rich in microbiota (Figure 11).

Figure 11.

Stratigraphic log and distribution of foraminifera, algae and algospongia of the El Gargabat section.

Figure 11. Long description

The table presents the stratigraphic log and distribution of foraminifera, algae, and algospongia of the El Gargabat section. It includes columns for system, stage, period, zone, lithology, samples, foraminifera, algae, algospongia, and graptolites. The lithology column features various types of limestone and schist, with specific beds labeled from Gr1 to Gr23. The foraminifera column lists different species found in each bed, while the algae and algospongia columns indicate the presence of specific types. The table also includes a legend explaining the symbols used for different fossils. Notable trends include the presence of specific foraminifera species in certain beds and the interbedding of different types of limestone and schist.

4.h.2. Biostratigraphic results

Two lithostratigraphic formations (Smaha Fm and Jaidet Fm), whose ages have been determined using conodonts, ammonites and microfacies, were identified in the allochthonous Devonian of the eastern Jebilet by Becker et al., (Reference Becker, Aboussalam, El Hassani, Cózar, Herbig and Ernst2021). Based on lithological correlation, the black shales and nodular limestones at the base of the El Gargabat section correspond to the Smaha Fm, dated from the Silurian to the Lochkovian–Praguian. The griotte limestones (Gr23 to Gr18), rich in orthocones and tentaculitoids, correspond to the lower and middle members of the Jaidet Fm and are of Praguian age (Becker et al., Reference Becker, Aboussalam, El Hassani, Cózar, Herbig and Ernst2021). The overlying layers (Gr17 to Gr13) correspond to the upper member of the Jaidet Fm, dated early Emsian (Becker et al., Reference Becker, Aboussalam, El Hassani, Cózar, Herbig and Ernst2021). The griotte limestones interbedded with nodular shales (Gr11 and Gr12) containing some goniatites likely represent the upper part of the upper member of the Jaidet Fm and are assigned to the upper Emsian (Becker et al., Reference Becker, Aboussalam, El Hassani, Cózar, Herbig and Ernst2021). Due to the presence of rare specimens of primitive Neoarchaediscus, Endothyranopsis crassa and Fascifolium pantherinium (this latter taxon is rare and mostly restricted to Morocco; Vachard and Cózar, Reference Vachard and Cózar2010), the samples Gr1, Gr4 and Gr10 are assigned to the latest Asbian age (Cf6γ2) (Figure 11).