Structural and facies architecture of a diapir-related carbonate minibasin (lower and middle Jurassic,High Atlas,Morocco) |
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| Institution: | 1. Institute of Earth Sciences Jaume Almera, ICTJA-CSIC, Group of Dynamics of the Lithosphere, Spain;2. Joseph Fourier University, ISTerre, France;3. Tullow Oil, Norge AS, Norway;4. Montpellier 2 University, Géosciences Montpellier, France;1. Dipartimento di Scienze della Terra, Università degli Studi di Firenze, via La Pira 4, Firenze, Italy;2. CNR-Istituto di Geoscienze e Georisorse-Sede Secondaria Firenze, via La Pira 4, 50121 Firenze, Italy;1. Laboratory of Sedimentary Basins Dynamic and Geological Correlations, Department of Geology, Faculty of Sciences Ben M''sik, Hassan II University, B.P. 7955, Sidi Othman, Casablanca, Morocco;2. CONICET - INCITAP, Facultad de Ciencias Exactas y Naturales, Universidad Nacional de La Pampa, Av. Uruguay 151, 6300 Santa Rosa, La Pampa, Argentina;3. Laboratory of Stratigraphy of Oil and Gas Bearing Reservoirs, Department of Paleontology and Stratigraphy, Institute of Geology and Petroleum Technologies, Kazan (Volga Region) Federal University, Kremlyovskaya str. 18, 420008 Kazan, Russia;4. Toulouse III University, 13 Terrasses de la Figuière, 30140 Anduze, France;5. Laboratory of Geodynamic and Geomatic, Department of Geology, Faculty of Sciences, Chouaïb Doukkali University, B.P. 20, 24000 El Jadida, Morocco;6. Polish Geological Institute, ul. Rakowiecka 4, 00-975 Warszawa, Poland;7. Stowarzyszenie “Delta”, ul. Sandomierska 4, 27-400 Ostrowiec ?w., Poland;8. Moab Giants, 112W. SR 313, Moab, UT 84532, USA;9. Saurierwelt Paläontologisches Museum Alte Richt 7, D-92318 Neumarkt, Germany;10. Laboratory of Geosciences and Environment, Faculty of Sciences and Techniques, Cadi Ayyad University, Boulevard Abdelkrim El Khattabi, BP 549, 40000 Guéliz, Marrakesh, Morocco.;1. Department of Geological Sciences, The University of Texas at Austin, 2275 Speedway Stop C9000, Austin, TX 78712, USA;2. Ivan Rakovec Institute of Palaeontology ZRC SAZU, Novi trg 2, SI-1000 Ljubljana, Slovenia;3. GeoRessources, University of Lorraine, Faculty of Science and Technology, BP 70239, 54506 Vandoeuvre-lès-Nancy, CEDEX, France;4. Department of Geological Sciences, Faculty of Science and Techniques of Errachidia, University Moulay Ismail, BP 509, 52000 Boutalamine, Errachidia, Morocco;5. Department of Geoscience, Aarhus University, Høegh-Guldbergs Gade 2, 8000 Aarhus C, Denmark |
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| Abstract: | We report the structural geometry and facies architecture of a small diapir-related carbonate-dominated basin from the Jurassic rift of the Moroccan High Atlas. The Azag minibasin is a lozenge-shaped depocenter completely enclosed by tectonic boundaries that we interpret as welds after former salt anticlines or salt walls. The exposed ca. 3000 m-thick infill of the Azag minibasin is asymmetric; layers are tilted to the W defining a rollover geometry. Areally-restricted sedimentary discontinuities and wedges of growth strata near the basin margins indicate sedimentation contemporaneous with diapiric rise of a Triassic ductile layer. Facies evolution through the basin reflects local accommodation by salt withdrawal and regional events in the High Atlas rift. The early basin infill in the Sinemurian and Pliensbachian shows thickness variations indicative of low-amplitude halokinetic movements, with reduced exposed thicknesses compared to surrounding areas. The exposed Toarcian and Aalenian deposits are also reduced in thickness compared to areas outside the basin. Subsidence increased dramatically in the Bajocian-early Bathonian (?), the main phase of downbuilding, when over 2600 m of carbonates and shales accumulated at a rate > 0.5 mm/a in the depocentral area of the minibasin governed by W-directed salt expulsion. The stratigraphic units distinguished often show maximum thicknesses and deeper facies in the depocentral area, and rapidly change to shallower facies at the basin margins. The Bajocian carbonate facies assemblage of the minibasin include: reservoir facies as microbialite-coral reefs in the basin margins (formed during periods of strong diapir inflation and bathymetric relief), basin-expansive oolite bars (formed during episodes of subdued relief), and organic-rich, dark lime mudstones and shales that show source-rock characteristics. The Azag basin is a good analog for the exploration of salt-related carbonate plays in rifts and continental margins where source-rock and reservoir can form in a same minibasin. |
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| Keywords: | Salt tectonics Minibasin Carbonate facies Jurassic High Atlas Morocco |
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