Int J Earth Sciences (Geol Rundsch) (2001) 90 : 393±411 DOI 10.1007/s005310000115
ORIGINAL PAPER
A. El Harfi ´ J. Lang ´ J. Salomon ´ E. H. Chellai
Cenozoic sedimentary dynamics of the Ouarzazate foreland basin (Central High Atlas Mountains, Morocco)
Received: 6 October 1999 / Accepted: 9 May 2000 / Published online: 6 September 2000 Springer-Verlag 2000
Abstract Cenozoic continental sedimentary deposits of the Southern Atlas named ªImerhane Groupº crop out (a) in the Ouarzazate foreland basin between the Precambrian basement of the Anti Atlas and the uplifted limestone dominated High Atlas, and (b) in the Aït Kandoula and Aït Seddrat nappes where Jurassic strata detached from the basement have been thrust southwards over the Ouarzazate Basin. New biostratigraphic and geochronological data constraining the final Eocene marine regression, the characterization of the new ªAït Ouglif Detrital Formationº presumed to be of Oligocene age, and the new stratigraphic division proposed for the Continental Imerhane Group clarify the major tectonogenetic alpidic movements of the Central High Atlas Range. Four continental formations are identified at regional scale. Their emplacement was governed principally by tectonic but also by eustatic controls. The Hadida and Aït Arbi formations (Upper Eocene) record the major Paleogene regression. They are composed of marginolittoral facies (coastal sabkhas and fluviatile systems) and reflect incipient erosion of the underlying strata and renewed fluvial drainage. The Aït Ouglif Formation (presumed Oligocene) had not been characterized before. It frequently overlies all earlier for-
A. El Harfi UniversitØ d'Agadir, FacultØ des Sciences, BP S/28, 80 000 Agadir, Morocco (e-mail:
[email protected], Fax: +212-8-220100) J. Lang ()) ´ J. Salomon UniversitØ de Bourgogne, Centre des Sciences de la Terre, UMR-CNRS 5561, 6, boulevard Gabriel, 21000 Dijon, France E-mail:
[email protected] Phone: +03-80-396366 Fax: +03-80-396387 E. H. Chellai UniversitØ Cadi Ayyad, FacultØ des Sciences Semlalia, BP S/15, 40 000, Marrakech, Morocco
mations with an angular unconformity. It includes siliciclastic alluvial deposits and is composed predominantly of numerous thin fining-upward cycles. The Aït Kandoula Formation (Miocene±Pliocene) is discordant, extensive, and represents a thick coarsening-upward megasequence. It is composed of palustro-lacustrine deposits in a context of alluvial plain with localized sabkhas, giving way to alluvial fans and fluviatile environments. The Upper Conglomeratic Formation (Quaternary) is the trace of a vast conglomeratic pediment, forming an alluvial plain and terraces. The second and third formations correspond to two megasequences engendered by the uplift of the Central High Atlas in two major compressive phases during late Oligocene and Miocene±Pliocene times. These two geodynamic events were separated by a tectonically calm phase, materialized by palustro-lacustrine sedimentation (Görler et al. 1988). Tectono-sedimentary analysis of the two megasequences shows that the basin structure and depositional processes were controlled by the compressive tectonic context generated by the collision of North Africa and Iberia in Tertiary times (Jacobshagen et al. 1988). The Quaternary Formation was apparently controlled by a tectonic continuum and by climatic variations. Keywords Ouarzazate Basin ´ Aït Kandoula Nappe ´ Aït Seddrat Nappe ´ Central High Atlas ´ Continental facies ´ Tectono-sedimentary ´ Compression ´ Cenozoic
Introduction The Ouarzazate Basin and the Southern Atlas Marginal Zone are between the intracontinental High Atlas range to the north and the Panafrican Craton of the Anti Atlas to the south. They attest to two major episodes of sedimentation: (a) late Cretaceous to middle Eocene, where diachronous marine deposits of a transgressive megacycle were controlled primarily by
394
Fig. 1 a Geology and structural units of the southern slopes of the Central High Atlas western part. b North±south cross section of the southern slopes of the Central High Atlas: (I) axial zone; (II) Subatlas Zone or southern Atlas Marginal Zone; (III) Ouarzazate Basin; (IV) Anti Atlas. (Modified after Laville et al. 1977, and Jossen and Filali 1988)
eustatic changes (Herbig 1986, 1991; Trappe 1991; Brede et al. 1992); and (b) late Eocene to Quaternary, during which a large basin separated and filled with thick continental series largely through uplift of the Central High Atlas (Gauthier 1960; Görler and Zucht 1986; Fraissinet et al. 1988; Görler et al. 1988). The southern slopes of the western part of the Central High Atlas Montains comprise the following structural units (Fig. 1; Bourcart and Roch 1942): 1. Axial zone: This is the mountainous zone of the High Atlas, composed of a Variscan basement and Mesozoic, mainly Liassic, limestone cover. Neogene deposits crop out in two basins which correspond to the Toundout (Laville 1975) or Aït Kandoula Nappe (Görler and Zucht 1986) to the west, and the Aït Seddrat Syncline or Nappe (Roch 1939; Gauthier 1960) to the east.
2. Subatlas Zone or Southern Atlas Marginal Zone: Compressional deformation of this zone, which is folded over a width of approximately 10 km, decreases from west to east and north to south (Zylka 1988). It includes very narrow and often asymmetrical anticlines and synclines oriented E±W and NE±SW. Deposits in this folded and thrusted zone are mostly Cretaceous and Tertiary. Locally the thrust sheet edge overrides Neogene and Quaternary sediments of the Ouarzazate Basin with a southward vergence. 3. Ouarzazate Basin: This is an asymmetrical synclinorium of structural origin approximately 150 km long and 40 km wide with Cenozoic continental formations locally up to 1200 m thick (Görler et al. 1988). 4. Anti Atlas: This is a stable domain of Precambrian basement with Paleozoic cover. Cenozoic continental sedimentation on the northern edge of the Ouarzazate Basin was repeatedly interrupted by tectonic and geodynamic events (e.g., buckling, folding, thrusting, erosion). These events are reflected in the sedimentary series by locally complex discontinuities related to overthrusting and the insertion
395
of klippen and other, commonly allochthonous structural units (Laville 1980; Errarhaoui 1998; Beauchamp 1999). This N±S compressive episode coincided with the convergence of the Iberian and North African plates (Jacobshagen et al. 1988; Brede et al. 1992; Giese and Jacobshagen 1992), and is thought to be at the origin of the warping and folding of the High Atlas. In this highly complex structural context of the Southern Atlas Marginal Zone, the difficulties in studying Tertiary continental detrital facies (where stratigraphic profiles and logs are never complete) are compounded by the scarcity of characteristic fossils and the absence of sedimentary marker beds. However, by comparing and contrasting a sedimentological survey of the Ouarzazate Basin and adjacent regions conducted since 1989 with the wealth of existing geological data [more recently of the German team: Görler and Zucht (1986); Geyer and Herbig (1988); Görler et al. (1988); Herbig (1991)], we have been able to clarify the spatio-temporal development of the Cenozoic continental sedimentary systems in the Ouarzazate Basin and the Southern Subatlas Zone. This development has to be viewed against the context of uplift of the Atlas Range during this period.
Stratigraphic framework Cenozoic marine formations: Subatlas Group The transition from the Paleogene marine strata or Subatlas Group defined by Trappe (1989, 1991) and Herbig (1991) to the Upper Eocene continental beds is progressive and concordant (Gauthier 1960; Herbig
1986). The marine formations were laid down in an epicontinental sea on the northern edge of the Anti Atlas (Herbig 1991; Trappe 1991; Trappe 1992; Herbig and Trappe 1994). Paleogene sedimentation was controlled exclusively by global variations in sea level. No tectonic movement has been detected in the study region or in the Anti Atlas for this period (Herbig and Trappe 1994). The latest paleontological studies by Geyer and Herbig (1988) conclude that the oysters Ostrea todraensis and Ostrea sidialiensis, together with the algae Ovulites margaritula, are indicative of the end of a regression occurring ± at the earliest ± at the end of Lutetian times and ± at the latest ± at the end of the Bartonian. Stratigraphic attributions of the marine regression have been extensively discussed by Geyer and Herbig (1988), Herbig (1991), and Gheerbrant et al. (1993; Fig. 2). Cenozoic continental formations: Imerhane Group The Tertiary continental series of the southern margin of the Central High Atlas has been studied by Roch (1939), Choubert (1945), Gauthier (1960), Görler and Zucht (1986), Fraissinet et al. (1988), Görler et al. (1988), and Herbig (1991) who refer to it as the Imerhane Group (Fig. 3). Fig. 2 Synthesis of the litho- and biostratigraphic datings of the late Eocene marine regression (arrows) on the southern edge of the High Atlas. Ruled: minimum stratigraphic range of Subatlas Group, with maximum stratigraphic range of Subatlas Group
396
Fig. 3 Relationships between the Hadida and Aït Kandoula formations (1, 2, and 3), and possible interpretations after Herbig (1991; 4a and 4b). 4a The Hadida Formation and the ªalluvial conglomeratic base Memberº are different units. 4b The Hadida Formation and the ªalluvial conglomeratic Base Memberº are the same units
Görler and Zucht (1986) and Görler et al. (1988) distinguish two Cenozoic continental formations on the southern edge of the Central High Atlas: the Hadida Formation (named after a village in the NE of the Ouarzazate Basin; Fig. 1a), conformably overlying the marine formations defined in the north of the Ouarzazate Basin, and the Aït Kandoula Formation, after the basin of the same name (Fig. 1a); the latter comprises two alluvial conglomeratic members above and below an intermediate member of palustro-lacustrine limestones. The lack of datings for the conglomeratic strata and absence of a complete profile including both formations makes their horizontal and vertical relations imprecise, particularly in view of the complex tectonic context. These imprecisions make it difficult to establish correlations between sections of Ouarzazate, Aït Kandoula, and Aït Seddrat basins (Fig. 1a). To connect
the two formations, Herbig (1991) proposes inclusion of a conglomeratic Aït Arbi Member within the Hadida Formation (Fig. 3). All these works point to a problem of articulation between the continental Hadida and Aït Kandoula formations. Data from the literature (Fig. 4) ascribe the base of the continental series either to the Upper Eocene or to the Oligocene, which raises the question as to whether the latter is represented in the Ouarzazate Basin or not.
Stratigraphy and sedimentary evolution Hadida Formation (Upper Eocene) Hadida Formation (Figs. 5, 6, F1 South or F1S; Görler and Zucht 1986) is synonymous with the ªArgiles à gypse suprabartonien ou Éocne supØrieurº of Roch (1939), the ªGrs calcaires ou marnes à gypse de l'Éocne supØrieurº of Gauthier (1960), and the ªAmekchoud Red Gypsum Formationº of Fraissinet et al. (1988). It is the marls-silts lateral equivalent of the ªFormation conglomØratique des Aït Arbiº of Gauthier (1960; Fig. 6).
397
Fig. 4 Summary of the different stratigraphic divisions of the Tertiary in the Southern Atlas Marginal Zone from a section by Görler and Zucht (1986; modified from Zylka 1988) including the latest data
Lithofacies and sedimentological characteristics Hadida Formation with its typical red-purple color is invariably concordant with the underlying marine formations of the Subatlas Group. It is up to 600 m thick around Hadida (Görler and Zucht 1986; Görler et al. 1988; Zylka 1988) but averages not more than 300 m. It is made up of clay, silt, and fine sandstone facies with primary gypsum lenses at the base and terminates locally with sandstones and conglomeratic lenses. North of Aïfer village (Figs. 5, 7) the same formation is much finer-grained and rich in evaporites. Its consists of marls, clays, red siltstones, and sandy dolomites with varying extents of ªbirds-eyeº structures and cross-bedded sandstones. Locally, very friable, coarse sandstones exhibit highly irregular bluish marks probably related to mottling and soil formation processes. The base also displays interbedded symmetrical ripples with nearly straight crests. Towards the top of the formation, massive sandstones enclosing scarce conglomeratic lenses appear.
These rubefied facies continuously and progressively supercede the gray to light-green marine sediments (siltites, marls, and locally limestone with marine fauna) of the Subatlas Group. They are interpreted as coastal sabkha deposits (Kendall 1992) cut by eolian dune sediments (Görler and Zucht 1986; Görler et al. 1988; Zylka 1988; Swezey 1998). Rare deposits related to the final marine incursions are recognizable at the base, whereas alluvial plain deposits cut by channels of a distal braided fluvial system are toward the top. Above the Hadida Formation is a sandstone±conglomerate complex 60±100 m thick ascribed to the Oligocene by Gauthier (1960). It is composed of Liassic limestone pebbles of more than 30 cm in size. Herbig (1991) considers that these conglomerates are conformably interbedded within the top of the Hadida Formation and refers to them as the Aït Arbi Member (Figs. 3, 4, 5, 7). In this study we propose another interpretation of this sandstone±conglomerate unit (see Aït Ouglif Formation). The conglomerates are discordantly overlain by Mio-Pliocene sediments (Gauthier 1960). Near Amekchoud, 40 km west of the previous site (Figs. 3, 5, 7), outcrops are visible at the core of an anticline partly exposed by erosion revealing gypsum red beds. These display the same coastal sabkha and lagoonal facies as described earlier in the Aïfer area
398
Fig. 5 Geological sections of the Imerhane Continental Group (Ouarzazate Basin and Subatlas Zone) show the relationship between the different continental formations
and attributed to the Hadida Formation. However, the base of the continental series and the fossiliferous marine limestones do not occur at Amekchoud, which explains why the formation is not as thick. The resemblance in facies is particularly noticeable concerning the paleo-eolianite deposits, ripples, mottled sandstone facies related to pedogenetic transformations, rubefied clay-siltstones rich in primary gypsum, sandstone dolomites, and, above all, the occurrence at the top of a coarse sandstone complex; the latter is 150±200 m thick, conglomeratic at the base, and can be correlated with the Aïfer sandstone±conglomerate complex (Fig. 7). In conclusion, the gypsifer rubefied formation of Amekchoud, associated by Fraissinet et al. (1988) with the Aït Kandoula Formation (Figs. 3, 7, 8), apparently correlates with the gypsum marls of Aïfer and the Hadida Formation. It is thought to be of late Eocene age (proposition 4b of Herbig 1991; Fig. 3).
Aït Arbi Formation (Upper Eocene) The Aït Arbi Formation (F1 North or F1 N; Figs. 5, 6) was initially named ªCouches des Aït Arbiº by Gauthier (1960) near the villages of Aït Arbi and Aït Ouglif (Figs. 4, 5). It is synonymous with the ªConglomØrats de l'Éocne supØrieurº of Roch (1939), the ªCouches rouges de Boumalneº of Choubert (1945), the ªCouches des Aït Arbiº and the ªConglomØrats de Tafrent-Nordº of Gauthier (1960), the Red Aznag Formation and the NW Toundout Formation of Fraissinet et al. (1988), and the Aït Arbi conglomeratic member of Herbig (1991; see below). It is the coarse lateral equivalent of the Hadida Formation of Görler and Zucht (1986) and Görler et al. (1988; Fig. 6). Lithofacies and sedimentological characteristics Like the Hadida Formation, the Aït Arbi Formation conformably overlies the marine limestones and green marls of the Subatlas Group; however, it differs in its northerly location and the predominance of coarse facies (areno-rudites, light-pink conglomeratic sandstones, and orthoconglomerates with highly indurated, carbonate sandstone cement). Couplets of sandstone and conglomeratic facies correspond to the superposi-
399
Fig. 6 Stratigraphic attributions by the different investigators of equivalents to the Hadida and Aït Arbi Formations
tion of several longitudinal bars of a proximal braided fluviatile system. The formation reaches 600 m in thickness (Gauthier 1960) but the mean thickness is 400 m. The dark, detrital predominantly angular to subangular clasts (4- to 6-cm average diameters) become blunter upward. They are essentially of eruptive and volcanic origin (rhyolites, dacites, andesites, basalts, dolerites, granites, ignimbrites, quartzites) and rarely sedimentary (wine-red sandstones and Jurassic limestones; Roch 1939; Choubert 1945; Herbig 1986, 1991; Zylka 1988). It is important to emphasize the difference between the sandstone and orthoconglomeratic facies (dominance of Precambrian and Paleozoic material) of the Aït Arbi Formation (Fig. 5), and the coarse breccia and ortho- and paraconglomerates (dominance of jurassic material) of the overlying Aït Ouglif Formation. The Aït Arbi Formation is commonly overthrust by the southern edge of the Aït Kandoula or Aït Seddrat nappes (Fig. 5). Sedimentary dynamics of the Hadida and Aït Arbi Formations At the end of Lutetian times, at the latest toward the end of the Bartonian, the sea covering the region receded from the southern margin of the Central High Atlas. The regression was marked by an upward change in facies (Herbig 1986, 1991): (a) open, shallow
marine carbonate facies with diversified biota; (b) oolitic and bioclastic limestone sand bars (barrier deposits); (c) muddy lagoon deposits with oysters; and (d) evaporitic coastal sabkha and siliciclastic facies (Hadida and Aït Arbi formations, respectively). The important latest Middle Eocene sea-level drop of eustatic origin (Haq et al. 1987; Vail 1987) was largely responsible for the progradation of continental sediments (evaporitic coastal sabkha and siliciclastic facies) over marine facies (muddy, oyster-rich lagoons). Such regressive episodes are generally characterized by renewed fluvial drainage on dry land and an increase in detrital and siliciclastic input (Vail 1987; Shanley and McCabe 1994). The size and nature of the gravel and pebbles transported and the paleogeographic interpretation of the marine Paleogene (Herbig and Gregor 1990; Herbig 1991; Trappe 1991; Herbig and Trappe 1994) suggest that, on the edge of a margino-littoral (coastal sabkha) environment, fluviatile systems draining from the adjacent relief eroded the previous lithologies (locally the first Jurassic outcrops of the Central High Atlas). Among these paleoreliefs there must have been the ªmassif ancienº or ªSkoura moleº in the west and the ªSaghro Massifº in the east (Fig. 1), as well as the Anti Atlas to the south. Aït Ouglif Formation (presumed Oligocene; Fig. 5) Named by Fraissinet et al. (1988) in reference to the Aït Ouglif type locality (Fig. 9), the Aït Ouglif Formation (presumed Oligocene; Fig. 5, F2), a poorly dated azoic formation, is synonymous with the ªPartie
Fig. 7 Correlation between the schematic lithostratigraphic sections of the Aït Kandoula Nappe, the Subatlas Zone, and the Ouarzazate Basin (see Figs. 1b, 5)
400
401
basale brØchique et conglomØratique de la sØrie des Aït Ibrirneº of Gauthier (1960) and the ªConglomØrats des Aït Ibrirneº of Michard (1976). It is the eastern lateral equivalent of the ªConglomØrats de Tafrent-Sudº of Roch (1939), of the ªComplexe grØsoconglomØratique d'Aïferº (Fig. 7), of the ªBrche de Timadliouineº and the ªGrs rose avec lentilles de poudingues de la vallØe d'Aqqa n'Oussº of Gauthier (1960), of the Upper Eocene red alteritic series of Laville (1975), of the ªSØrie des Aït Ibrirneº (presumed Oligocene age) on the 1:200,000 geological map of Morocco, Jbel Saghro-Dads sheet of Choubert et al. (1980), of the Alluvial Base Member or conglomeratic lower member of the Aït Kandoula Formation of Görler and Zucht (1986) and Görler et al. (1988; Figs. 3, 7), of the Issil n'Ouzalad Formation of Fraissinet et al. (1988), of the Aït Arbi conglomeratic member interbedded at the top of the Hadida Formation of Herbig (1991; see also Aït Arbi Formation), and, finally, of the Amekchoud sandstone±conglomeratic complex defined in this study (Fig. 7). Lithofacies and sedimentological characteristics This detrital sandstone±conglomeratic facies grades laterally either into breccia and paraconglomerates with angular clasts of up to 1.20 m or into orthoconglomerates with rounded and blunted clasts, or into massive beds of coarse sandstones. The petrography of the material is very variable but above all rich in Jurassic and Paleogene limestone and dolomites. This formation lies with an angular unconformity over the Liassic limestone, Lower Cretaceous (sandstones and marls with dolomitic and conglomeratic lenses), the marine Lower and Middle Eocene, or the continental Upper Eocene deposits (Figs. 5, 7). It is overlain discordantly by other continental sediments (Mio-Pliocene palustro-lacustrine limestones of the Aït Kandoula Formation or by Quaternary deposits). Contrary to the representation of the geological map of Choubert et al. (1980) which confines it to the Aït Ibrirne and Hadida regions as a narrow E±W or ENE±SSW strip (ªSØrie des Aït Ibrirneº of presumed Oligocene age), this formation is also found in the centre of the Ouarzazate Basin and along its northern edge, in the Aït Kandoula and Aït Seddrat Nappes, and in the thrust zone between the two (Figs. 7, 9). Aït Seddrat Nappe. In the Aït Ibrirne region (Fig. 9), where the Aït Ouglif Formation was defined by Gauthier (1960) as the basal breccia of the Aït Ibrirne series, Aït Seddrat Nappe unconformably overlies the deformed and eroded Lower Cretaceous beds. The series may be up to 40 m thick and dips 25±35 NNW. It includes breccias and paraconglomerates, with clasts of up to 1.20 m composed of Liassic limestone, rhyolites, quartzites, sandstones, and schists.
This breccia continues westwards as far as Aqqa n'Ouss with interbedded pink sandstones (Fig. 9). We have also traced it as far as Aïfer where it overlies the gypsum marls of the Hadida Formation (Fig. 7). It is mapped as the Aït Ibrirne Series by Choubert et al. (1980). Further east in the Aït Ouglif region (Fig. 9), this formation overlies the Liassic limestone, overthrusting the top of the Aït Arbi Formation. It is approximately 60 m thick and made up of ortho- and paraconglomerate beds separated by coarse sandstone and silt±sandstone beds with, locally, carbonate nodules near the top. Average clast size is 30 cm with a maximum of 40 cm. This facies association, characterized by a succession of numerous elementary fining-upward cycles, is interpreted as deposits of the proximal part of a braided river system adjoining alluvial fans. The basal breccia was redefined by Fraissinet et al. (1988) under the name Aït Ouglif Formation as a unit overlying the Lower Cretaceous and unconformably overlain by the Aït Ibrirne Series. Our own observations show that this latter formation here contains only the palustrolacustrine limestones or upper part of the Aït Ibrirne Series of Gauthier (1960; Fig. 9). Aït Kandoula Nappe. Görler and Zucht (1986 and Görler et al. (1988) describe above the Aït Kandoula Nappe (Fig. 7) the outcrop of the conglomeratic Alluvial Base Member (Figs. 3, 10b), formed of paraconglomerates and coarse breccia with material floating in a sand±silt±clay matrix. These typical mudflow facies, with clasts of often more than 1 m, have interbeds of ortho- and paraconglomerates with clearly erosional bases related to torrential deposits. The association of such facies is characteristic of alluvial fan systems. Görler and Zucht (1986) report that the sedimentary structures and pebble imbrication indicate that the fans derived from the north, where the High Atlas was being uplifted. This member lies with an angular unconformity over the Jurassic strata (Fig. 10a), over the marine Paleogene, and over the Aït Arbi Formation (Fig. 10b). At Issil n'Ouzalad (Figs. 5, 7), it lies with an angular unconformity over the Lower Cretaceous. It has been described at the same locality by Fraissinet et al. (1988) as the Issil n'Ouzalad conglomeratic Formation. This conglomeratic formation is found to the south of the Aït Kandoula Nappe, south of Toundout as far as Amekchoud in the centre of the Ouarzazate Basin. There it becomes finer distally, and is reduced to a massive, continuous bed approximately 30 m thick with orthoconglomerates at the base and a sandstone complex at the top (Fig. 7). This detrital formation is therefore discordant at the north over the Lower Cretaceous and over the Aït Arbi Formation, and to the south over the fine gypsum facies of the Hadida Formation. In the Aït Kandoula Nappe, the conglomeratic lower Member grades conformably into the overlying
402
Fig. 8 Geological section in Ameckchoud Fold (see Fig. 5; after Görler and Zucht 1986). New interpretation differentiating the Aït Ouglif Formation sandstone±conglomerate complex
palustro-lacustrine Member (Görler and Zucht 1986; Görler et al. 1988). This normally unconformable boundary is more difficult to pinpoint because, unlike the zones along the active, faulted edges, the deeper and subsiding ones provide a poor record of deformation. However, the transverse schematic section of the Aït Kandoula regions (Fig. 10a; Görler and Zucht 1986; Görler et al. 1988) clearly shows the erosional truncation between the conglomeratic lower Member and the remainder of the Aït Kandoula Formation and shows a typical expression of a progressive and intraformational unconformity (Riba 1976) with a syntectonic character of sedimentation. Ouarzazate Basin. On the NE edge of the Ouarzazate Basin, the Aïfer and Hadida conglomeratic complex (Figs. 5, 7), unconformably overlying the fine silt-sand-
stone gypsum facies of the Hadida Formation, exhibits a stack of red-violet sandstone and orthoconglomerate beds. Mean clast size is 20±30 cm with a maximum of 50 cm. This complex corresponds to longitudinal bar deposits of a braided fluviatile system. In the Amekchoud fold at the centre of the basin (Figs. 5, 7, 8) a sandstone±conglomeratic unit can be attributed to this formation. The base is a massive unbroken bed of approximately 30 m of ortho- and paraconglomerates whose Paleozoic, Precambrian, and Liassic clasts are approximately 20 cm on average. These conglomerates are overlain by a sandstone complex approximately 150±200 m thick, forming a finingupward megasequence composed of a series of sequences from 1 to 10 m thick with a fining-upward trend. Each sequence typically begins with microconglomerates or coarse sandstones, commonly with channeltype bases, and continues with finer sandstone deposits. The sequence ends with rubefied deposits of fine sandstones, siltites, and marls, locally with gypsum and limestone. This sequence can be subdivided into three
Fig. 9 Chronostratigraphic interpretations by different workers of the "SØrie des Aït Ibrirne" defined by Gauthier (1960). See Figs. 1 and 5 for section locations 403
404
Fig. 10 a Cross-section across the Aït Kandoula Nappe (modified after Görler and Zucht 1986; Görler et al. 1988). b Cross section of the western end of the Aït Kandoula Nappe (modified after Laville 1980; Görler and Zucht 1986)
or four facies associations: at the base deposits of coarse channel bottoms, a central sandstone body corresponding to the ªsandflatsº complex of Cant and Walker (1978) including, among others, transverse bar deposits, migrating channel, and water-lain dunes. At
405
the top, mud deposits are locally associated with palustro-lacustrine carbonates. Similar elementary sequences are recognized by Steel and Thompson (1983) in braided fluviatile systems which belong to the distal part of a mixed-load braided system (Miall 1996). The Aït Ouglif Formation grades conformably into the thick palustro-lacustrine deposits of the Aït Kandoula Formation. Sedimentary dynamics Analysis of the different facies and deposits shows a system of alluvial fans to the north of the basin giving way southwards to one or more proximal fluvial systems flowing toward a more distal fluvial environment. The vertical and lateral facies arrangement of this fining-upward megasequence show that the coarse material derived mostly from the High Atlas. Dimension and petrography of the gravels suggest intense hydrodynamic activity and the proximity of a hinterland whose Jurassic, Cretaceous, and Paleogene cover supplied sediment. Sediment accumulated as alluvial fans including debris flows with angular to subangular material. The fans occur in the north, in the Aït Kandoula and Aït Seddrat nappes and in the Aït Ibrirne area. On the edge of the South Atlas and around Assermou, Aïfer, Hadida, and Aqqa n'Ouss (Fig. 5), the formation consists of proximal braided fluviatile system facies. In the more distal zones (Amekchoud fold), the megasequence is reduced to a sandstone complex with a continuous conglomeratic bed at the base. It includes the oldest Jurassic limestone material of the High Atlas which was transported to the centre of the Ouarzazate Basin and deposited on the fine gypsum red facies of the Hadida Formation. This sudden vertical change from calm sedimentation to coarse conglomeratic deposits is indicative of tectonic and geodynamic changes affecting the Atlas Range. Aït Kandoula Formation (Mio-Pliocene) The Aït Kandoula Formation (Mio-Pliocene; Fig. 5, F3) defined by Görler and Zucht (1986) and Görler et al. (1988) in the Aït Kandoula syncline (Fig. 1) initially comprised three Members (Fig. 3). The conglomeratic lower Member has been included in the new presumed Oligocene Aït Ouglif Formation (Figs. 8, 10a). The formation thus reduced to the Lacustrine Middle Member and Alluvial Top Member is masked in the northern part of Aït Seddrat Nappe by scree and the Quaternary conglomeratic pediment; however, it crops out extensively in the Aït Kandoula Nappe and the Ouarzazate Basin over a length of 140 km and a maximum width of 40 km. It varies considerably in thickness from the north where it reaches 700 m to
the south where the sediments thin out over the Anti Atlas Precambrian basement. Locally verticalized at the edges of the Subatlasic zone, it becomes nearly horizontal southwards. It lies unconformably over all the previous terrains (Hadida Formation, Aït Arbi and Aït Ouglif formations, marine Eocene, Cretaceous, Precambrian). At many points, as on the western (Aït Ben Haddou section; Fig. 5) and southern edges (Imassine section; Fig. 5) of the Ouarzazate Basin, deposits fill the topographic depression cut into Eocene, Senonian, Cenomanian±Turonian, and Precambrian strata (Choubert 1945; Gauthier 1960; Görler and Zucht 1986; Görler et al. 1988). Unlike the Aït Ouglif Formation, the Aït Kandoula Formation displays a coarsening- and thickening-upward trend. The basal palustro-lacustrine unit (Görler and Zucht 1986), which is up to 500 m thick in the Ouarzazate and Aït Kandoula basins, comprises limestones, travertines, marls, clay-siltstones, sapropelites, and primary gypsum. Ostracods, diatoms, molluscs (gastropods and bivalves), macrophytes, algae (charophytes, oncolites, stromatolites), and fish and mammal teeth and bones are observed. The earliest datings of lacustrine fauna of Ouarzazate and Aït Kandoula (Görler et al. 1988; Helmdach 1988) indicate a Langhian to early Seravallian age (Middle Miocene) with, in particular, one bed (Fig. 8, T12) containing the earliest ostracod fauna of the genus Cypris sp. A. and rodent teeth. The upper conglomeratic unit (Görler and Zucht 1986) contains sandstones and mainly conglomerates. No fossils have been found. However, in the Aït Kandoula Nappe, 65 m below the conglomeratic unit (in the palustro-lacustrine unit), a mammal tooth indicates a late Pliocene age. Latest Pliocene or even Pleistocene age is therefore possible (Görler et al. 1988; Helmdach 1988). Lithofacies and sedimentological characteristics On the northern edge of the basin (Figs. 5, 11) sedimentological analysis of the Aït Kandoula Formation shows prograding alluvial fans in the context of a palustro-lacustrine alluvial plain system (El Harfi 1994; El Harfi et al. 1996). Palustro-lacustrine alluvial plain system. The carbonate and siliciclastic deposits display two evolutionary trends from north to south: 1. Fining reflected by reduced conglomerate-to-sandstone and siliciclastic-to-carbonate ratios and decreasing maximum grain size 2. Increasingly marked organization of deposits and a gradual change in morphology of channels and fluviatile bars. More or less coarse material torn from the High Atlas was transported by rivers N±S and N±SW before reaching a braided system on the immediate margin of the basin, on playa environ-
406
Fig. 11 a Facies distribution of the palustro-lacustro-alluvial plain system in the Lower Member of the Aït Kandoula formation in the Ouarzazate Basin. b Alluvial fan facies prograding over the plaustro-lacustro-alluvial plain system in the Upper Member of the Aït Kandoula formation
ments to the southwest, in an extensive palustro-lacustrine environment in the centre, and finally on a floodplain to the south and southeast. Alluvial fan system. Unlike the first system, paraconglomerates (mean clast size varies from 10 cm at the base to 1.15 cm at the top) here represent more than 90% of all deposits with a majority of subangular to subrounded items. Their texture reflects mass transport (mud flows and debris flows) and turbulent fluviatile deposits with high bed loads. The preserved remains of these Mio-Pliocene alluvial fans stretch along the northern edge of the basin. Petrographic analysis, morphology, and distribution of these conglomerate deposits show that the coarse facies concentrate as alluvial fans around outlets on the northern edge of the basin, whereas the fine sediments were carried by distributary streams towards the basin centre. On the southern edge of the basin (Figs. 5, 11b) where petrographic analysis of clasts in the conglomer-
ates shows that they originated from the Anti Atlas, no alluvial fans have been observed; however, fluviatile deposits do occur, which are coarser than the fine underlying floodplain sediments. These coarse deposits prograde from south to north and interpenetrate the uppermost deposits of the Mio-Pliocene infilling. The coarsening-upward trend is at least partly coeval with that of the northern edge of the basin. Sedimentary dynamics The presence of palustrine and lacustrine limestones in the basin centre and of playa evaporites especially to the west is indicative of an endoreic closed basin. Although evaporites occur in the western part of the basin, the sheer extent of the palustro-lacustrine limestones and the fossils found indicate a wide continental lake, covering the Aït Kandoula, Aït Seddrat, and Ouarzazate basins from Middle Miocene to Pliocene times (Görler et al. 1988). This palustro-lacustrine alluvial plain system gave way northwards to an alluvial fan system derived from the High Atlas and southwards to fluviatile deposits from the Anti Atlas (Fig. 11). The vertical and lateral transition from a lacustrine alluvial plain system to alluvial fans, although progressive, is quite distinct. It is reflected by a rapid increase in carbonate-to-siliciclastic and
407
sandstone-to-conglomerate ratios, but above all by a clear coarsening-upward trend. The arrangement of sedimentary bodies indicates north-to-south progradation of a coarser proximal system to finer distal deposits. Depocentre migration occurred by the advance of sedimentary systems towards the passive margin of the Anti Atlas (El Harfi 1994). Quaternary Formation The relatively constant thickness of Quaternary Formation (Fig. 5, F4) of approximately 30 m increases slightly to the north. Described by Choubert (1945), Gauthier (1960), and Couvreur (1988), it corresponds to the Quaternary Upper Conglomeratic Formation of Görler et al. (1988), the Aït Seddrat Formation and probably also to the Boumalne Formation of Fraissinet et al. (1988). The Quaternary Formation lies with an angular unconformity over the Mio-Pliocene deposits in the Aït Kandoula and Aït Seddrat basins (Fig. 5). In the Ouarzazate Basin it is represented by a conglomeratic pediment which is clearly differentiated from the underlying deposits and forms an excellent marker level. These highly consolidated and very heterometric conglomerates are coarser than the MioPliocene ones (except at the northern edge of the basin). They are indicative of constant rejuvenation of relief. Six conglomeratic pediment with bajada and alluvial terraces strata have been identified (Choubert 1965). Their geomorphological evolution is essentially related to Quaternary climatic variations including alternating phases of erosion and accumulation of sediment (Couvreur 1988; Möller et al. 1988; Schmidt 1992).
Discussion on the age of the Cenozoic continental formations Hadida and Aït Arbi Formations We have already stated that continental sedimentation of the Imerhane Group began at the earliest by the end of the Middle Eocene and at the latest at the end of the Bartonian. For most workers (Fig. 2), the base of continental sedimentation includes the Priabonian (Upper and uppermost Eocene). For lack of evidence that continental sedimentation continued until the Oligocene, we hypothesize that the Hadida and Aït Arbi formations, which conformably overlie the marine Eocene, were laid down in late Eocene times. Aït Kandoula Formation In the Aït Seddrat Nappe (Aït Ibrirne locality) the palustro-lacustrine limestones have yielded gastropods, which, according to the latest revised biostratigraphic
data of Görler and Zucht (1986), are identical to the earliest palustro-lacustrine fauna of the Aït Kandoula Nappe. Moreover, the datings of Görler and Zucht (1986), Helmdach (1988), and Görler et al. (1988) in the Ouarzazate and Aït Kandoula limestones (Benammi et al. 1996) show that palustro-lacustrine sedimentation began at the latest in the middle Miocene and continued uninterrupted until the early Pliocene, giving way progressively to increasingly coarse detrital sedimentation during the late Pliocene. However, west of Amekchoud in the Ouarzazate Basin, Görler et al. (1988) have reported that below sample A 97 (Fig. 8), which is of middle Miocene age, are another 400 m of palustro-lacustrine fossil-bearing sediments which have not yielded biostratigraphic fossils. Calculating from the rate of lacustrine sedimentation, estimated by Görler et al. (1988) at 0.05 mm per year, this indicates that an early Miocene age for the base of the 400 m of remaining limestone cannot be ruled out. The MioPliocene stratigraphic attribution to the Aït Kandoula Formation which includes the lower palustro-lacustrine and upper conglomeratic units is therefore vindicated. Aït Ouglif Formation The underlying Hadida and Aït Arbi formations are reportedly of late Eocene age, and the overlying Aït Kandoula Formation spans the middle Miocene to Pliocene. From these datings, a range from the Oligocene to the early Miocene could fit the Aït Ouglif Formation. However, in the Amekchoud section, the most subsiding part of the Ouarzazate Basin, estimates calculated from the rate of palustro-lacustrine sedimentation indicate an early Miocene age for the earliest limestones of the southern side of the Central High Atlas. As these limestones are restricted to the Aït Kandoula Formation, the Aït Ouglif Formation could be restricted to the Oligocene. Furthermore, the wide spread clastic input of Aït Ouglif Detrital Formation, the major sedimentological, paleogeographic, structural, and geodynamic changes accompanying their emplacement, should be correlated with the most important global marine regression event of that period: major Late Oligocene regression (global sea-level curve of Haq et al. 1987). From these data and despite the absence of fossils from this period, a late Oligocene age may be assumed for the Aït Ouglif Formation. We propose the following stratigraphic attributions: 1. Hadida and Aït Arbi formations: late Eocene; early Oligocene (?) 2. Aït Ouglif Formation: presumed late Oligocene 3. Aït Kandoula Formation: Mio-Pliocene
408
Geodynamic and tectonic evolution of the Central High Atlas during the Cenozoic Tectonism appears to have been the main control on sedimentary dynamics at megasequence scale and on engendering discontinuities between the different formations of the Ouarzazate Basin. This is confirmed by the intensely deformed deposits of the Southern Atlas Marginal Zone (reversed faults, folding, overthrusting, nappes, cover decollements, and tectonic slabs; Errarhaoui 1998; Beauchamp 1999) and by the distribution of debris flows along the northern but not the southern edges of the basin (Fig. 11b). Finally, the advance and retreat of alluvial fan systems, which can be traced immediately below and above the palustro-lacustrine deposits, are more closely related to tectonic movements than to climatic changes (Görler et al. 1988). This N±S compressive tectonism of the Central High Atlas is associated with Tertiary convergence between the North African and Iberian plates (Jacobshagen et al. 1988; Brede et al. 1992; Giese and Jacobshagen 1992). In the absence of any transitional data between the Hadida and Aït Kandoula formations, Görler and Zucht (1986) and Görler et al. (1988) used the first appearance of Mesozoic and Cenozoic limestone material to date the uplift of the High Atlas, and from that the inversion of the Atlasic system. The lower conglomeratic unit (Aït Ouglif Formation) clearly reflects the first change in the petrography of deposits. Based on the old datings of Helmdach (1986) and Görler and Zucht (1986), the first major phase of uplift was attributed to the early Miocene by reference to the underlying Hadida Formation which was dated Oligocene±early Miocene(?) (Figs. 2, 8). New biostratigraphic and geochronological data about the final marine regression, the characterization of the new Aït Ouglif Detrital Formation presumed to be of Oligocene age, and the new stratigraphic division proposed for the Imerhane Continental Group clarify the major phases of Atlasic movements (Fig. 12). The transition from the Lutetian (or Bartonian) marine beds (Herbig and Trappe 1994) to the Upper Eocene to early Oligocene (?) continental red beds (Hadida and Aït Arbi formations) is progressive and concordant. The petrography of the microconglomeratic material shows almost exclusive involvement of a Paleozoic and Precambrian foreland and hinterland with local evidence of outcropping of the High Atlas Mesozoic limestone. It can be accepted therefore that initial and local uplift of the Atlas range commenced during the late Eocene. The final regression of the Subatlas Sea from central Morocco (south of the Rif Mountains) had been in the latest Middle Eocene (Brede et al. 1992). During this period, local conglomerate clastic strata reworked Jurassic limestones of High Atlas were deposited at the southern rim of the central High Atlas (Aït Arbi Formation).
The initial movement of the Jurassic Aït Kandoula and Aït Seddrat nappes dates probably from the end of this period (latest Eocene, early Oligocene). The coarse Aït Arbi Formation is confined to the north and is often overridden by the southern front of the nappes with the earliest sediment overlying them corresponding to the Aït Ouglif Formation. The presumed Oligocene (Aït Ouglif Formation) is characterized by extensive, azoic, coarse detrital facies. These form a mappable megasequence of terrigenous, fining-upward deposits lying unconformably over the continental and lagoonal deposits of the late Eocene, the early Cretaceous, and over the Jurassic nappes. The occurrence of large amounts of Mesozoic and Cenozoic rock debris, often of large dimensions, mainly composed of Jurassic and Paleogene limestones, suggests the exposure and erosion of Central High Atlas series. These major changes in sedimentology and paleogeography reflect structural and geodynamic changes in the Atlas range. They indicate uplift and erosion of reliefs during formation, a phenomenon that can consequently be considered indicative of the first phase of uplift and inversion of the Central High Atlas. During this phase the large anticlines and synclines of the Subatlasic zone formed (Choubert 1945; Gauthier 1960). In the Aït Ibrirne region, the rubefied and upturned Lower Cretaceous beds on which the presumed late Oligocene series rest are evidence of the amplitude of this phase. In the Middle Atlas coarse conglomerates (Jbel Hayane Formation) occur in a comparable lithostratiographic position south of the northern Middle Atlas Fault (Herbig 1993). Although biostratigraphically undated, they are presumably also of Oligocene age (Dresnay 1969; Martin 1981; Brede et al. 1992). The deposition of these predominantly clastic Oligocene formations (Jbel Hayane and Aït Ouglif formations) succeeding on a regionally documented unconformity, was related to a major compressive phase all across the Atlas System, and might be connected with Oligocene nappe emplacement in the Alboran block (Brede et al. 1992). The Mio-Pliocene deposits (Aït Kandoula Formation) extend largely beyond the zones occupied by the presumed Oligocene, particularly to the south and west. They cover surfaces that were previously folded and eroded and correspond to the installation of a vast, constantly subsiding foreland basin in the centre of which a more or less permanent lake formed with predominant carbonate deposits (Görler et al. 1988). Later (Pliocene), the progressive emplacement of a system of alluvial fans covered the palustro-lacustrine fluviatile sediments of the alluvial plain. The progradation of facies over the two flanks of the basin (Fig. 12) testifies to reliefs being uplifted and marks the onset of a second phase of tectonic uplift of the Atlasic range (Görler and Zucht 1986; Görler et al. 1988; Jacobshagen et al. 1988; Brede et al. 1992; Giese
409
periods (Couvreur 1988; Möller et al. 1988; Schmidt 1992).
Fig. 12 Chronostratigraphic diagram shows the vertical and lateral changes in the different lithostratigraphic units. Hadida Formation: Upper Eocene, F1 South; Aït Arbi Formation: Upper Eocene, F1 North; Aït Ouglif Formation: Oligocene, F2; Aït Kandoula Formation: Mio-Pliocene, F3; Quaternary Formation: F4 (cf. Fig. 5)
Conclusion
and Jacobshagen 1992). This geodynamic evolution must be related to intensified, compressive tectonics which coincided both with a major uplift of the Central High Atlas and with the rejuvenation of the central Anti Atlas relief. The uplift of the Anti Atlas can be correlated both with the Neogene continental infilling of the paleovalleys south of Ouarzazate (Jacobshagen et al. 1988; El Harfi 1990) and with the last volcanic activity of Jbel Siroua and Jbel Saghro at the close of Tertiary times (Stäblein 1988; Berrahma and Delaloye 1989; Ibhi 2000). Movements related to compression continued during the Quaternary and were evidenced by the final volcanic flows in the east of the basin (Foum El Kouss) and the inflow of hydrothermal and mineralized water (Tasbelbat) in the south of the basin (Fig. 5). These tectonic effects were compounded by climatic fluctuations controlling geomorphological change with the formation of pediments and bajadas in wet periods and their dissection and incision in arid
The sedimentological study of the Cenozoic continental series of the Southern Atlas (Imerhane Group) has revealed a succession of four formations, each the product of a specific tectono-sedimentary context: 1. Hadida and Aït Arbi formations (Upper Eocene, Lower Oligocene ?) of margino-littoral facies (sabkha and fluviatile systems) controlled mainly by eustatic factors related to the general late Eocene regression and to local uplift of the Atlas range. 2. Aït Ouglif Formation (presumed Upper Oligocene). Due to missing fossils of that age all across the High Atlas realm and due to the complex tectonic setting, this formation was often confused with other detrital formations (Aït Arbi), included within the upper part of Hadida Formation or into the lower part of Aït Kandoula Formation. It had not been characterized before and is only cited in one locality in the Aït Seddrat Nappe, firstly by Gauthier (1960) then by Fraissinet et al. (1988). This alluvial and siliciclastic formation is also found
410
in the centre of the Ouarzazate Basin and along its northern edge, in the Aït Kandoula Nappe and in the thrust zone between the two. 3. Aït Kandoula Formation (Mio-Pliocene), unconformable, thick, and extensive, basal palustro-lacustrine alluvial plain system giving way vertically to prograding alluvial fans. 4. Quaternary Formation, unconformable, vast conglomeratic pediment with bajada and alluvial terraces. This study has clarified the pattern of uplift of the Central High Atlas. The onset was often dated to the end of the Cretaceous (Laville et al. 1977; Stets and Wurster 1981) but those movements, once described as ªembryonic and precocious phasesº of Atlasic tectonics (Choubert 1945; Gauthier 1960; Michard 1976), probably originated at the margins of rotating blocks and do not reflect regional compression (Jacobshagen et al. 1988). These movements are interpreted to have been block-tipping events (Monbaron 1982), local upheaval (Jacobshagen et al. 1988), or oblique strikeslip faulting (Herbig 1991). The idea of generalized inversion of the Atlasic range in Cretaceous times has therefore been abandoned (Brede et al. 1992; Giese and Jacobshagen 1992). The present study indicates that the first phase of deformation began in the late Eocene, peaking in the late Oligocene (Aït Ouglif Formation). It seems to have been followed by relaxation of tectonic stress during the Mio-Pliocene when a vast, more or less permanent lake basin formed. The second phase apparently began at the end of the Neogene (Görler et al. 1988) with the progressive emplacement of the present-day structures which was not completed until Quaternary times. Acknowledgements This study was carried out under the Dijon±Marrakech convention supported by the Burgundy Regional Council and under Theme 3 ªEnregistrement des phØnomnes biologiques et sØdimentairesº of UMR 5561 of the CNRS. We are grateful to the Delegate of the Ministry of Energy and Mines of Ouarzazate for his support and interest in this work, to ONAREP of Morococo, and particularly to Mr. Bouchta, Mr. Boudda, and Mr. Zizi. The manuscript benefitted from critical comments by two anonymous reviewers.
References Beauchamp W, Allmendinger RW, Baranzagi M, Demnati A, El Alji M, Dahmani M (1999) Inversion tectonics and the evolution of the High Atlas Mountains, Morocco, based on a geological-geophysical transect. Tectonics 18:163±185 Benammi M, Calvo M, Prevot M, Jaeger JJ (1996) Magnetostratigraphy and paleontology of Aït Kandoula basin (High Atlas, Morocco) and the African±European Late Miocene terrestrial fauna exchanges. Earth Planet Sci Lett 145:15±29 Berrahma M, Delaloye M (1989) DonnØes gØochronologiques nouvelles sur le massif volcanique de Siroua (Anti-Atlas, Maroc). J African Earth Sci 9:651±656 Bourcart J, Roch E (1942) Carte gØologique provisoire des rØgions d'Ouaouizarht et de Dads (notice explicative). Notes MØm Serv GØol Maroc 54:1±37
Brede R, Hauptmann M, Herbig H (1992) Plate tectonics and intracratonic mountain ranges in Morocco. The Mesozoic± Cenozoic development of the Central High Atlas and the Middle Atlas. Geol Rundsch 81:127±141 Cant DJ, Walker RG (1978) Fluvial processes and facies sequences in the sandy braided South Saskatchewan River. Can Sedimentol 25:625±648 Choubert G (1945) Note prØliminaire sur le Pontien au Maroc. Essai de synthse orogØnique du Maroc atlasique. Notes MØm Serv GØol Maroc 65:1±87 Choubert G (1965) Évolution de la connaissance du Quaternaire au Maroc. Notes MØm Serv GØol Maroc 185:9±27 Choubert G, Destombe J, Gauthier H, Hindermeyer J (1980) Carte gØologique du Maroc, feuille jbel Saghro-Dads (HautAtlas central, sillon Sud-atlasique et Anti-Atlas oriental) au 1/200,000 Couvreur G (1988) Essai sur l'Øvolution du Haut-Atlas central calcaire (Maroc). Notes MØm Serv GØol Maroc 318:1±391 Depape G, Gauthier H (1953) Sur le genre Pistia et sa prØsence dans la flore Øocne de la vallØe de l'Oued Mgoun (Maroc mØridional). Ann Univ Lyon (Sci Nat Sect C):25±30 Dresnay R (1969) Discussions stratigraphiques sur les conditions de gisements de bois fossiles mØsozoïques du Maroc. Notes MØm Serv GØol Maroc 318:1±391 El Harfi A (1990) Les formations continentales nØognes, dØtritiques et encroßtØes du «bassin» d'Anzal (Anti-Atlas central, Maroc) DEA, Dijon, pp 1±50 El Harfi A (1994) Dynamique sØdimentaire des sØries continentales tertiaires au Sud du Haut-Atlas central (bassins de Ouarzazate et Anzal, Maroc). Facis et milieux de dØpôts. Evolution diagØnØtique et pØdogØnØtique. Thse, Univ Bourgogne, Dijon, pp 1±314 El Harfi A, Lang J, Salomon J (1996) Le remplissage continental cØnozoïque du bassin d'avant-pays de Ouarzazate. Implications sur l'Øvolution gØodynamique du Haut-Atlas central (Maroc). CR Acad Sci Paris 323:623±630 Errarhaoui K (1998) Structure du Haut-Atlas: plis et chevauchements du socle et de couverture (interprØtation des donnØes gØophysiques et gØologiques). Thse de Doctorat, Univ Paris XI Orsay, pp 1±328 Fechner GG (1988) Selected palynomorphs from the Lower to Middle Eocene of the South Atlas border zone (Morocco) and the environmental significance. Paleogeogr Palaeoclimatol Palaeoecol 3:73±79 Fechner GG, Mohr G (1986) Zur tertiaren Dinoflagellatten-gattung Carpatella GRIGORVICH, 1969 (Gonyaulacystaceñ). Paläontol Z 60:181±188 Fraissinet C, Zouine EM, Morel JL, Poisson A, Andrieux J, Faure-Muret A (1988) Structural evolution of the southern and northern Central High Atlas in Paleogene and Miopliocene times. Lecture Notes Earth Sci 15:273±291 Gauthier H (1960) Contribution à l'Øtude gØologique des formations post-liasiques des bassins du Dads et du HautTodra (Maroc mØridional). Notes Mm Serv GØol Maroc 119:1±212 Geyer G, Herbig HG (1988) New Eocene oysters and the final regression at the southern rim of the Central High Atlas (Morocco). Geobios 21:663±691 Gheerbrant E, Cappetta H, Feist M, Jaeger JJ, Sudre J, VianeyLiaud M, Sige B (1993) La succession des faunes de vertØbrØs d'âge palØocne supØrieur et Øocne infØrieur dans le bassin de Ouarzazate, Maroc. Contexte gØologique, portØe biostratigraphique et palØogØographique. Newslett Stratigr 28:33±58 Giese P, Jacobshagen V (1992) Inversion tectonics of intracontinental ranges: High and Middle Atlas, Morocco. Geol Rundsch 81:249±259 Görler K, Zucht M (1986) Stratigraphie und Tektonik des kontinentalen Neogens im Süden des Zentralen Hohen Atlas, Provinz Ouarzazate (Marokko). Berliner Geowiss Abh 66:471±494
411 Görler K, Helmdach FF, Gaemers P, Heissig K, Hinsch W, Mädler K, Shwarzhans W, Zucht M (1988) The uplift of the central High Atlas as deduced from Neogene continental sediments of the Ouarzazate province, Morocco. Lecture Notes Earth Sci 15:363±404 Haq BU, Hardenbol J, Vail PL (1987) Chronology of fluctuating sea levels since the Triassic. Science 235:1156±1167 Helmdach FF (1986) Zur Alterseinstufung des höchsten marinen Tertiärs im Bereich der Südatlas-Randzone (Provinz Ouarzazat, Marrokko). Berlin geowiss Abh 66:495±502 Helmdach FF (1988) The ostracods fauna of the Aït-Kandoula region, systematic description, Lecture Notes Earth Sci 15:405±423 Herbig HG (1986) Lithostratigraphisch-fazielle Untersuchungen im marinen Alttertiär südlich des zentralen Hohen Atlas (Marokko). Berliner Geowiss Abh 66:343±380 Herbig HG (1987) The Paleogene of the Atlas System (Morocco): facies control by eustacy and synsedimentary tectonics. In: Matheis and Schandelmeier (eds) Current research in African earth sciences. Rotterdam, pp 253±256 Herbig HG (1991) Das Paläogen am Südrand des zentralen Hohen Atlas und im Mittleren Atlas Marokkos. Stratigraphie, Fazies, Paläogeographie und Paläotectonik. Berliner Geowiss Abh135:1±289 Herbig HG (1993) Stratigraphy, facies, and synsedimentary tectonics of the post-Middle Eocene Tertiary, Middle Atlas West of Boulemane (Morocco). N Jahrb Geol Paläontol Abh 188:1±50 Herbig HG, Gregor HG (1990) The mangrove-forming palm Nypa from the early Paleogene of southern Morocco: paleoenvironment and paleoclimate. GØol MØditerrannØe 27:123±137 Herbig HG, Trappe J (1994) Stratigraphy of the Subatlas Group (Maastrichtian±Middle Eocene, Morocco). Newslett Stratigr 30:125±165 Ibhi A (2000) Le volcanisme Plio-quaternaire de Saghro (AntiAtlas central, Maroc) et les enclaves basiques et ultrabasiques associØes. Thse de Doctorat d'État, Univ Agadir, pp 1±359 Jacobshagen V, Görler K, Giese P (1988) Geodynamic evolution of the Atlas system (Morocco) in post-Palaezoic times. Lecture Notes Earth Sci 15:481±499 Jossen JA, Filali J (1988) Le bassin de Ouarzazate, synthse stratigraphique et structurale. Contribution à l'Øtude des aquifres profonds. Progr Nations Unies DØvelop, Dep Coop Techn, DØvelop Projet MOR 86/004, pp 1±36 Kendall A (1992) Evaporites (continental and supradital-sebkhaevaporits). In: Walker RG (ed) Facies models. Geoscience Canada, Reprints Series Laville E (1975) Tectonique et microtectonique d'une partie du versant sud du Haut-Atlas marocain (Boutonnire de Skoura, Nappe de Toundout). Thse de Doctorat Laville E (1980) Tectonique et microtectonique d'une partie du versant sud du Haut-Atlas marocain (Boutonnire de Skoura, Nappe de Toundout). Notes MØm Serv GØol Maroc 285:81±183
Laville E, Lesage JC, Seguret M (1977) GØomØtrie, cinØmatique de la tectonique atlasique sur le versant sud du Haut-Atlas marocain. Aperçu sur les tectoniques hercyniennes et tardihercyniennes. Bull Soc GØol France (VII) 19/3:527±539 Martin J (1981) Le Moyen-Atlas central. Etude gØomorphologique. Notes MØm Serv GØol Maroc 258:1±446 Miall A D (1996) The geology of fluvial deposits. Sedimentary facies, basin analysis, and petroleum geology. Springer, Berlin Heidelberg New York Michard A (1976) ElØments de gØologie marocaine. Notes MØm Serv GØol Maroc 252:1±408 Möller K, Stäblein G, Wagner P, Zillbach K (1988) Georelief, Abtragung und Gefügemuster an einem aktiven Kontinentalrand. Erde 114:41±54 Monbaron M (1982) PrØcisions sur la chronologie de la tectogense atlasique: exemple du domaine atlasique mØsogØen du Maroc. C R Acad Sci Paris 294:883±886 Riba O (1976) Tectogense et sØdimentation: deux modles de discordances syntectoniques pyrØnØennes. Bull BRGM (2) I/4:383±401 Roch E (1939) Histoire stratigraphique du Maroc. Notes MØm Serv GØol Maroc 51:1±483 Schmidt KH (1992) The tectonic history of the Pre-Saharan depression (Morocco). A geomorphological interpretation. Geol Rundsch 81:211±219 Shanley KW, McCabe (1994) Perspectives on the Sequence Stratigraphy of continental strata. AAPG Bulletin 78 (4): 544±568. Stäblein G (1988) Geomorphological aspects of the Quaternary evolution of the Ouarzazate basin, southern Morocco. Lecture Notes Earth Sci 15:433±443 Steel RJ, Thompson DB (1983) Structures and textures in Triassic braided stream conglomerates (Bunter pebble bed's in the Sherwood sandstone group, North Staffordshire, England). Sedimentology 30:341±367 Stets J, Wurster P (1981) Zur Strukturgeschichte des Hohen Atlas in Marokko. Geol Rundsch 70:801±841 Swezey C (1998) The identification of Eolian Sands and Sandstones. C R Acad Sci Paris 323:513±518 Trappe J (1989) Das marine Alttertiär im Westlichen Hohen Atlas: Mikrofazies, Paläogeographie, Phosphoritgenese. Thesis, Bonn pp 1±219 Trappe J (1991) Stratigraphy, facies distribution and paleogeography of the Marine Paleogene from the western High Atlas, Morocco. N Jahrb Geol Paläontol Abh 180:279±321 Trappe J (1992) Microfacies zonation and spatial evolution of a carbonate ramp: marginal Moroccan phosphate sea during the Paleogene. Geol Rundsch 81:105±126 Vail PR (1987) Seismic stratigraphy interpretaton using sequence stratigraphy. Am Assoc Petrol Geol Stud Geol 27:1±10 Zylka R (1988) Der Südrand des Hohen Atlas zwischen Toundout und Goulmima (Marokko). Eine photogeologische und strukturelle Analyse. Berliner Geowiss Abh 96:1±129
