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Earth Science Frontiers, Vol. 17, Special Issue, Aug. 2010 ISSN 1005-2321 Key words: Callovian; GSSP; Ostracods; Bio- stratigraphy References: Bate R.H. Middle Jurassic (Aalenian – Bathonian). In: Whittaker J.E., Hart M.B. (ed). Ostracods in British Stratigraphy. London: The Micropalaeon- tological Society, Special Publications, 2009: 199- 223, fig. 3, 4 pl. Bodergat A.M. Les ostracodes marins du Jurassique Europeen – utilisation stratigraphique. In: Groupe Française d’étude du Jurassique (1997): Biostrati- graphie du Jurassique Ouest-Européen et Méditer- ranéen. Bulletin du centre des recherches Elf Exploration-Production, Mémoires, 1997,17: 197- 223. Brand E., Mönnig E. Litho- und Biostratigraphie des Mittel-Jura (Dogger) in Bohrungen Norddeut- schlands.Schriftenreihe der Deutschen Gesell- schaft für Geowissenschaften, Stuttgart, 2009, 54: 5-73, fig. 24, tab. 1, enclose 6. Buck E., Hahn W., Schädel K. Zur Stratigraphie des Bajociums und Bathoniums (Dogger delta – 50 epsilon) der Schwäbischen Alb. Jahreshefte des Geologischen Landesamts Baden-Württemberg, 1966, 8: 23-46, fig. 5-6, pl. 4-9; Freiburg i. Br. Callomon J.H., Dietl G. Proposed definition of the Callovian Stage. Field Symposium in Swabia, Stuttgart/Albstadt (16-21 September, 1990). ISJS, Callovian Working Group, MS: XI + 20 p, 1990: (unpublished). Callomon J.H., Dietl G. On the proposed Basal Boundary Stratotype (GSSP) of the Middle Jurassic Callovian Stage. GeoResearch Forum, 2000, 6: 41-54, figs. 4. Franz M, Tesakova E., Beher E. Documentation and revision of the index ostracods from the Lower and Middle Jurassic in SW Germany according to BUCK (1954). Palaeodiversity, Stuttgart, 2009, 2: 119-167, fig. 3, tab. 5, pl. 6. Wilkinson I.P., Whatley R.C. Upper Jurassic (Cal- lovian – Portlandian). In: Whittaker J.E., Hart M.B. (ed). Ostracods in British Stratigraphy. The Micro- palaeontological Society, Special Publications, London, 2009, 241-287, fig. 7, pl.11.
Earth Science Frontiers, Vol. 17, Special Issue, Aug. 2010 ISSN 1005-2321 Moroccan Jurassic System: An Overview E.H. Chellai Cadi Ayyad University, Faculty of Sciences Semlalia, Geology Department, P.O. Box 2390, Marrakech, Morocco (E-mail: chell@ucam.ac.ma) Jurassic Paleogeography of Morocco Jurassic sedimentation is marked by a strong differentiation in the Atlas domain with a distinct development of two main regions: Western area corresponding to a newly created basin open to the Atlantic but closed in the east along the length of the ancient mountain massif. This repre- sents the coastal region (Essaouira, Agadir Basins). Central and eastern part consisting of the intra- continental basins of the central High Atlas and Eastern or Sahara Atlas, separated by the Tamlelt sill. These basins together with the Middle Atlas Basin to the north constitute the western prolongation of the Tethys Ocean. Atlas domain The distribution of facies during the Jurassic is controlled by the structural framework inherited from the Hercynian orogeny, in particular by faults N60-70, N30-40 and E-W at N120. Episodes of rifting and expansion of the Tethys occurred during this period, and sedimentation became subjected to both eustatic and tectonic control. In the Atlas region, Laville (1985) noted the following A transgression in the early Lias, originating from the east and linked to the Tethys, reaching its maximum in the Pliensbarchian. A regression in the Toarcian. A new transgression towards the end of the late Toarcian, which reached its peak in the Aalenian- Bajocian, when significant subsidence occurred. Basin infilling and regression in the Bajocian- Bathonian with widespread development of carbonate reefs, dolomite and deltaic facies. In the Callovian-Oxfordian, the regressive mega- sequence, which started in the previous cycle, kept on accumulating. Deltaic, coarse-grained, quartz domi- nated sediments were deposited within small subsiding basins. In the Kimmeridgian-Portlandian, this cycle regi- sters the ongoing emergence of the High Atlas with the withdrawal of the Tethys to the east in the Sahara Basin. Figures summarize the evolution of Jurassic deposits in the Atlas region, especially for the central Atlas. Du Dresnay (1979) identified: Early Lias: thin carbonate deposits on platforms with relatively rare reefs. Middle Lias: widespread development of reefs. Basinal facies are rich in ammonites. Carbonates be- come more marly towards the top. Late Lias and middle Jurassic (Toarcian to Bajocian/Bathonian) with intercalations of calcareous horizons within the marly facies rich in ammonites in the center of the basin. On the platform, the Toarcian is transgressive and the Bajocian/Bathonian is characterized by the development of carbonate ramps. End of middle Jurassic, marked by basin infilling and development of red beds containing the well known Moroccan dinosaur Cétiosaurus Moghrébiensis newly renamed Atlasaurus Imlaki. Structural characteristics of Jurassic basins In the Atlas region (High and Middle Atlas), the overall geometry of basins is characterized by two types of surrounding structures: 1-depocenters: forming large subsiding basins with clear “S”- or lozange-shape. This geometry is often prominently delineated by the contacts between individual Jurassic formations and by the sigmoid appearance of their cartographic axis. 2-furrows: consisting of narrow, synsedimentary anticlines, which are marked by thinning along their flanks with progressive discordance, intraformational breaks, gravitational structures and even local angular unconformities. 3-subvolcanic intrusions: In the center and a long the axis of basins, they are located in the central part of some furrows. They form a group of small subvolcanic massifs associated with dykes, sills, flows. Their mineralogical characteristics exhibit an alkaline affinity. Laville (1985) noted in the Amouguer intrusions the presence of: doleritic dykes (d1), trocholitic pluton (tc) recut by monzodiorites (mz), four networks of microfractures.To these intrusions(dyke and pluton) are associated concentric and radial joints, which recut previous formations. Genesis model of Atlas basins An examination of the geometry of Jurassic depocenters allows the following characters to be recognized: the Atlas basin consists of small basins that are more or less fitted together; their limits correspond to very narrow anticlinal furrows, which follow three directions related to late Hercynian events (N50-N60; N80-N90 et N120); these basins have an “S” or lozange-shape. In the center and along the axis of these basins, subvolcanic intrusions occupy the central part of some furrows. The overall characters of Atlas basins suggest an origin linked to displacements. With the aim to better understand the importance of these displacements, we shall briefly describe the 51
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